Physiology of Flowering in Perennial Fruit Crops

Physiology of Flowering in Perennial Fruit Crops

Hkkd`vuqi ICAR

SD

SH

NABARD

National Horticulture Board

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NCPAH

The Society for Development of Subtropical Horticulture (SDSH)

Central Institute for Subtropical Horticulture (ICAR) Rehmankhera, Lucknow - 226 101, Uttar Pradesh Website:www.cish.lko.org Email:[email protected]

Souvenir National Seminar-cum-Workshop on Physiology of Flowering in Perennial Fruit Crops

Edited by : H. Ravishankar V.K. Singh A.K. Misra Manish Mishra

Hkkd`vuqi ICAR

SD

SH

NABARD

National Horticulture Board

jk"Vªh; ckxokuh cksMZ

NCPAH

The Society for Development of Subtropical Horticulture (SDSH)

Central Institute for Subtropical Horticulture (ICAR) Rehmankhera, Lucknow - 226 101, Uttar Pradesh Website:www.cish.lko.org Email:[email protected]

© Central Institute for Subtropical Horticulture (ICAR), Lucknow Address Central Institute for Subtropical Horticulture (ICAR) Rehmankhera, P.O. Kakori, Lucknow-226 101 (U.P.) Phone-0522-2841022, 24 Fax: 0522-2841025 Web: www.cish.lko.org Email: [email protected] The Society for Development of Subtropical Horticulture (SDSH) (Regd. No. 1196-2005-06) Citation Souvenir, National Seminar-cum-Workshop on Physiology of Flowering in Perennial Fruit Crops, 2014 Eds. H. Ravishankar, V. K. Singh, A. K. Misra and Manish Mishra Edited by H. Ravishankar V. K. Singh A. K. Misra Manish Mishra Assisted by Manoj Kumar Soni and Neeraj Kumar Shukla Disclaimer All rights are reserved. No part of this book shall be reproduced by transmitting in any form, print, microlm, or any other means without prior permission of Central Institute for Subtropical Horticulture, Lucknow. The opinion expressed in the book is of the authors, not of the publishers. Sponsored by ICAR, New Delhi NHB, Gurgaon NABARD, Mumbai NCPAH, New Delhi Published by President, SDSH & Director, CISH Central Institute for Subtropical Horticulture (ICAR), Lucknow Rehmankhera, P.O. Kakori, Lucknow - 226 101, U.P., India

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GOVERNMENT OF INDIA DEPARTMENT OF AGRICULTURAL RESEARCH & EDUCATION AND INDIAN COUNCIL OF AGRICULTURAL RESEARCH MINISTRY OF AGRICULTURE, KRISHI BHAVAN, NEW DELHI-110 001 Tel. : 23382629; 23386711 Fax : 91-11-23384773 E-mail : [email protected]

Mk- ,l- v¸;Iiu lfpo ,oa egkfuns'kd Dr. S. AYYAPPAN SECRETARY & DIRECTOR GENERAL

Message

I am happy to learn that a National Seminar-cum-Workshop on "Physiology of Flowering in Perennial Fruit Crops" is being organized by the Society for Development of Subtropical Horticulture (SDSH), Lucknow under Central Institute for Subtropical Horticulture (CISH), Lucknow from 24-26 May, 2014 at its Rehmankhera campus in collaboration with ICAR, NABARD, NHB and NCAAP. Wide range of fruits from tropical, subtropical, temperate, and arid and fruits of the cold deserts though are being grown across diverse agro-ecologies, with considerable success but prevailing wide gaps in their productivity as compared to that of other producing countries offer challenges to the scientists. Apparently, these gaps largely prevail due to variations in owering phenology on one hand and pollination and fruit set events occurring across different agro ecologies that need to be addressed. Flowering since, is the major phenological event that exerts direct inuence on the fruit production tendencies, it has direct impacts on the livelihood of orchardists and the family nutritional basket. However, in fruit crops, there is lack of information on natural variations in gene expression, and even less is known about the functional signicance of the existing gene expression variations in relation to owering which are crucial to accomplish meaningful genetic introgression. Understanding of specic genes involved in the regulation of owering, and climate resilience are thus crucial for deciphering the functional signicance of gene expression to pave way for traitspecic climate smart varieties. It is hoped that the National Seminar will provide an interactive platform to different stakeholders to deliberate in the context of physiological basis of this complex phenological variations in perennial fruit crops having considerable impacts on protability of fruit crops based farming system. I wish the seminar all success.

Dated the 17th May, 2014 New Delhi

(S. Ayyappan)

Òkjrh¸k d`fÔvuqla/kku ifjÔn d`fÔvuqla/kku ÒouµII iwlk] uÃ fnYyh 110 012 Hkkd`vuqi ICAR

INDIAN COUNCIL OF AGRICULTURAL RESEARCH KRISHI ANUSANDHAN BHAWAN-II PUSA, NEW DELHI-110 012

Mk- ,u- ds- d`"Æ dqekj mi egkfunsÓd ¼ckxokuh½ Dr. N.K. Krishna Kumar Deputy Director General (Horticulture)

Message

I am happy to learn that the National Seminar-cum-Workshop on Physiology of Flowering in Perennial Fruit Crops is being organized by the Society for Development of Subtropical Horticulture (SDSH) in collaboration with Central Institute for Subtropical Horticulture (CISH) during 24-26 May, 2014 at Lucknow. The importance of fruits and vegetables in human diet has gained increased importance in the recent past with increased income, urbanization and literacy. An orchard has always been looked upon as one of the potential options for crop diversication for ensuring sustainability and efcient land used patterns. Sustainability has meaning only when bud initiation, owering, fertigation and fruit set are in balance and harmony. However, a great variation in owering and fruit set is being observed in the recent years across different agro-ecological regions which is impacting the productivity of fruit crops. This complex biological phenomenon is less understood in perennial tropical and subtropical fruit crops. Further, the physiological basis of phenological variations especially the root signals, carbon partitioning, assimilation and transformation, hormonal interpolations etc. in regulating owering phenology need elucidation to ensure productivity. The impact of climate change on this syndrome is even less understood. An interdisciplinary meeting of minds encompassing canopy management, crop regulation, C-N ratio, impact of abiotic stress, light interception and hormonal regulation is needed so that everybody can share their strength as well leave their weakness. In the light of above it has become imperative to hold this national seminar in order to deliberate upon the important issues concerning owering and empower orchardists with horticultural innovations and tools to manage owering in perennial fruit crops. I compliment the Society and the Institute for oganizing such an interactive event and wish a grand success.

(N.K. Krishna Kumar) Phone : (Off.) 91-11-2584 2068(M) : 91-8447284636, Fax : +91-11-2584 1976; e-mail: [email protected];[email protected]

F-1, NASC Complex, Todapur, New Delhi-110 012

(Padma Shri) Dr. K.L. Chadha Ex-Deputy Director General (Horticulture), ICAR and President The Horticultural Society of India

Message India, acclaimed for its rich genetic diversity of mango, has also assembled a reasonably good amount of genetic variability of other perennial fruit crops viz., citrus, grape, guava, banana, aonla, bael, litchi, jamun, besides many temperate and underutilized fruit crops. While a large number of seedling selections have been made and are now clonally propagated, some trait-specic varieties have also been developed in these crops which are gradually entering into the production system in suitable regions of the country. Fruits, besides being sources of nutritional-cum-nutraceutical principles, now nd a prominent place in the family food basket from health perspectives besides providing ample opportunities for protable fruit culture in the sub-continent. Diversied fruit culture is being pursued in different parts of the country with productivity gaps prevailing. Low productivity in different crops is often attributed to variations in owering phenology. Knowledge gaps in this regard also exist which need to be proled and challenges especially in the context of emerging climate scenario need to be addressed. I am happy to note that a National Seminar-cum-Workshop on “Physiology of Flowering in Perennial Fruit Crops” is being organized by the Society for Development of Subtropical Horticulture (SDSH), Lucknow under the Central Institute for Subtropical Horticulture (CISH), Lucknow from 24-26 May, 2014 at its Rehmankhera campus to take stock of the situation and strategize the path ahead.. I congratulate Dr. H. Ravishankar, Director, the Central Institute for Subtropical Horticulture (CISH), Lucknow for providing distinguished leadership in providing an interactive forum to deliberate on such vital issues like owering phenomenon in perennial fruit crops. I am sure brainstorming on this subject shall lead to development of a road map for management of issues related to owering and improving productivity and protability of commercial fruit culture in the subcontinent. I congratulate the organizers and wish the seminar all success.

Date: 15.05.2014 New Delhi

(K.L. Chadha)

dsUnzh; miks".k ckxokuh laLFkku jgeku[ksM+k] Mkd?kj dkdksjh] y[kuÅ&226 101 CENTRAL INSTITUTE FOR SUBTROPICAL HORTICULTURE Hkkd`vuqi ICAR

Mk- ,p- jfo'kadj funsÓd Dr. H. Ravishankar

Rehmankhera, PO Kakori, Lucknow- 226 101

Preface

DIRECTOR

Orchard systems evolving are characterized by intensive planting strategies aimed at efcient use of different factors of production primarily dominated by solar use efciency. This disposition harnessing carbon capture and its conversion to photosynthate, envisage a wide canvas of sink-source relationships that entail carbon gradients in the plant system ultimately setting in chain, a plethora of metabolic events under the regulatory control of genes being up or down regulated or silenced contributing to productivity. Different physiological events under the impacts of environmental cues that contribute to perennial fruit crops productivity though have been researched upon for quite some time, the different processes associated with 'owering phenology' themselves appear not only complex but also defy in many cases, practical approaches to manage the owering and fruit set events for translating them to augmented tree productivity outcomes. A number of studies have pointed out in this regard to the issues of carbon acquisition, its translocation and transformation in plant systems impacting tree yields considerably that could be signicantly inuenced by genetics, rootstocks, training and pruning practices, use of growth regulators and other orchard management practices. In order to harness the potential benets of the above, it is crucial to understand the 'whole tree physiology' of perennial fruit crops. Useful leads in this regard, though are available in a good number of temperate perennial fruit crops culminating in problem resolution; they are yet to be unraveled in tropical, subtropical, fruits of the cold arid and of the deserts for developing management strategies. This largely appears to be due to over emphasizing issues of shoot morphogenesis at the expense of rhizosphere events especially the 'root signals' in regulation of shoots behaviour establishing intelligent shoots-roots communication eventually resulting in reproductive phenophases. Evidently, knowledge generation in this regard is constrained by the difculties involved in non-destructive studies on root dynamism in perennial fruit crops. The present seminar envisaged, aims to consolidate the knowledge available in these crops, identify gaps and develop road map for futuristic research. I am grateful to Dr. N.K. Krishna Kumar, Deputy Director General (Horticultural Science) for entrusting the responsibility of organizing this national seminar to Central Institute for Subtropical Horticulture, Lucknow. I am also thankful to all my colleagues at the institute especially, Dr .V. K. Singh Principal Scientist (Plant Physiology) and Organizing Secretary of the seminar for ably coordinating different activities and Dr. A .K. Misra who took all the pains to edit the papers received leading to bringing out this publication in its present form on time. I am sure the deliberations of the seminar will prove intellectually stimulating to unfold the path ahead for planning basic and strategic research towards enhanced understanding of this complex phenological event leading to problem solving and improved protability of perennial fruit crops production systems. Dated 19 May, 2014 CISH, Lucknow

(H. Ravishankar)

Contents Messages Preface Current Status of Flowering Control: Will it Provide Options for Chemical Regulation of Flowering? Parvathi M. Sreekumar, Mahesh Salimath, Ramu S. V. and M. Udayakumar

1

Assimilate Partitioning and Transformations in Some Perennial Fruit Crops with due Focus on Mango (Mangifera Indica L.): Dynamics of Shoot-Root Communication in Reproductive Phenology-An Appraisal H. Ravishankar

3

Induction of Flowering in Fruit Crops - Physiological and Plant Architectural Implications Y.N. Reddy and A. Bhagwan

24

Physiology of Flowering in Perennial Temperate Fruit Crops Nazeer Ahmed, Dinesh Kumar, Javid Iqbal Mir and A.A. Pal

48

Physiological Signals, Environmental Cues and their Interactions for Induction of Flowering in Perennials – Lessons for Mango V. Ravindra

59

Citrus Flowering and Fruiting - Recent Research Advances A.D. Huchche and M. S. Ladaniya

74

Physiology of Flowering of Grapevine S. D. Ramteke

89

Environment Determines Success of Natural and Induced Off-Season Flowering in Mango Shailendra Rajan, V.K. Singh, Y.T.N. Reddy, K.K. Upreti1, M.M. Burondkar, A. Bhagwan, R. Kennedy, Pooja Saxena, Sakkthi Subramaniyam and S.R. Shivu Prasad

99

Physiology of Flowering, Fruit and Nut Development in Cashew P.L. Saroj, M.G. Nayak and R.K. Meena

105

Differential Scope of Traditional/ Molecular Breeding for Regularity in Bearing Habit of Fruit Crops M.R. Dinesh and K.V. Ravishankar

115

Molecular Aspects of Flowering Behaviour in Perennial Fruit Crops K.V. Ravishankar, Kanupriya and M.R. Dinesh

134

Molecular Insights into Flowering Pathway Genes in Mango Anju Bajpai, M. Muthukumar, V.K. Singh and S. Rajan

143

Engineering Crop Improvement Through RNAi Sangeeta Saxena

155

Molecular Events during Flower Induction in Mango Manish Srivastav, S. K. Singh and A. K. Singh

158

Regulatory Roles of Phytohormones and Carbohydrates of Flowering in Mango K.K. Upreti, S.R. Shivu Prasad and G. Bindu

164

Physiology of Flowering in Litchi in Relation to Shoot Maturity Vishal Nath and Sanjay Kumar Singh

173

Canopy Management and Effects of Pruning on Flowering Tendencies in Fruit Trees W.S. Dhillon and Anirudh Thakur

182

Pruning in Guava (Psidium Guajava L.) and Appraisal of Consequent Flowering Phenology using Modied Bbch Scale : Source-Sink Relationships V.K. Singh, H. Ravishankar, Anurag Singh and Manoj Kumar Soni

202

Synergestic Effects of Plant Growth Regulators and Fruit Set Improving Chemicals on Flowering, Fruit Set and Yield of Mango cv Banganpalli A. Bhagwan, Vijaya Krishna and M. Rajkumar

210

Induction of Mango Off-Season Flowering through Chemical and Canopy Management in Peninsular India T. N. Balamohan and A. Nithya Devi

229

Chemical Induction of Flowering in Mango Y.T.N. Reddy, V. Srilatha, and S.R. Shivu Prasad

235

Mango Flowering Physiology in Response to Paclobutrazol Application V. Srilatha, Y.T.N.Reddy and S.R. Shivu Prasad

241

Unlocking Mystery of Phase Change and Flowering in Litchi (Litchi chinensis Sonn.) Cultivars Rajesh Kumar

250

Response of Pruning and Canopy Management on Flowering, Fruiting and Yield of Guava (Psidium guajava L.) Rajneesh Mishra, R. B. Ram, Gorakh Singh, Rubee Lata, D. H. Dwivedi and M.L. Meena

257

Interventions by Bio-Regulators on Phenlogical Events of Flowering in Acid Lime S.K. Sarkar, N. Gurung, H. L. Devi and T.K.S. Irenaeus

260

Diagnostic Approaches for Identication of Nutrient Imbalance Inuencing Flowering and Yield in Mango H.B. Raghupathi and Y.T.N. Reddy

266

Effect of Climatic Variation on Flowering and Fruit Development of Mango Under Konkan Agroclimatic Conditions of Maharashtra P.M. Haldankar, Y.R. Parulekar, S.B. Thorat and K.E. Lawande

270

Flowering and Fruiting Behavior of Mango Cultivars in Relation to Weather Parameters R.K. Yadav, D.K. Sarolia, Virendra Singh and R.A. Kaushik

275

Off Season Flowering and Fruiting in Mango under Andaman Conditions T. Damodaran and S. Rajan

279

Fusarium mangiferae Induced Stress Ethylene Causes Floral Malformation of Mango : A Scanning Electron Microscopic Study Varsha Rani, Archana Singh, Mohammad Wahid Ansari, Alok Shukla, Ramesh Chandra Pant and Gurdeep Bains

282

Surveillance of Pollinators and their Behaviour in Mango Flowers D. Anitha Kumari, Jyothirmayee Madhavi, A. Bhagwan, M. Raj Kumar

285

Physiology of Flowering in Banana M.M.Mustaffa and I. Ravi

289

PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS

CURRENT STATUS OF FLOWERING CONTROL: WILL IT PROVIDE OPTIONS FOR CHEMICAL REGULATION OF FLOWERING? Parvathi M. Sreekumar, Mahesh Salimath, Ramu S. V. and M. Udayakumar Department of Crop Physiology, UAS, GKVK, Bangalore-65, Karnataka [email protected]

Plants integrate environmental cues for their growth and more specifically for flowering phenomena. In the flowering process, the most important phenomena that is regulated by environmental factors is the floral transition. Infact, the differentiation of vegetative primordia to reproductive primordia is the crucial first step for the reproductive phase which determines the blossom intensity and yield capacity. From this context, floral transition is the key factor that determines the productivity especially in perennial fruit crops. The perennial fruit crops are constantly exposed to annual climate variability and climate change and hence, assumes greater significance in determining productivity. It is now evident that the different environmental signals influence the flowering time/flowering control such as photoperiod, light quality, vernalisation and other environmental factors like ambient temperature besides nutrient status and moisture stress. The molecular mechanisms regulated by these environmental cues are well elucidated, though predominantly in model systems. Interestingly, all the upstream molecular mechanisms are triggered by diverse environmental factors converged at the so called “floral integrators”- a small set of genes where all flowering time pathways come together. The consensus is that the Flowering locus T (FT), Suppressor of CO (SOC1) and Leafy (LFY) are regarded as floral integrator genes. These inturn regulate genes associated with floral meristem identity like

AP1, CAL, FUL and finally the signal percolates to floral homeotic genes AP2, AG, AP3, and PI, to complete the process. Identification of the mechanisms of perception of the environmental cues and signalling pathways (both positive and negative) leading to the regulation of floral integrators has been the major outcome of the recent discoveries in this area. The developments in the genomics have provided leads in structurally characterising these genes/proteins. Further, the phenomenal developments in functional genomics area added new insights in validating the relevance and function of these regulatory genes. The significance of many regulatory genes in flowering process like FLC, FVE, FT, CO, SOC1, PIF4, etc. has been shown. The outcome of these studies has infact provided an option to regulate the flowering time and intensity in crop plants. Unlike in annuals, the mechanisms regulating the floral transition is more complex in perennial fruit crops, wherein they are constantly exposed to environmental cues. Still, the basic factors controlling the juvenility are yet to be elucidated. Besides, the crucial environmental factor that brings about floral transition and development of flushes is yet to be clearly elucidated in many fruit crops including mango. In tropical and subtropical fruit crops like mango, besides photoperiod, the major environmental factors that regulating floral transition and flowering initiation are day and night temperatures,

NATIONAL SEMINAR-CUM-WORKSHOP, 24-26 MAY, 2014

1

PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS moisture and nutrient status and finally the factors that govern maturity of flushing branches. Lower day and night temperatures during the flower evocation period are emerging as the major environmental cue for floral differentiation. It has further significance in the global climate change scenario. The cooler temperature being the major factor in crops like mango, the predictive sequence of events leading to floral transition has been suggested in recent reports by Davenport, Nunez-Elisea and Whiley. The mature leaves perceive the optimum cooler temperature and synthesises a flowering promoter which is claimed to be subsequently transported to the apical meristem for vegetative to floral transition. Significant genotypic variation in response regarding the threshold cooler temperature for floral induction exists. However, systematic studies correlating temperature variations with respect to flowering phenomena is not available even in mega varieties which are widely cultivated in India. Even at a similar latitude across the country, a considerable variation exists in day and night temperatures during flower evocation period. It is crucial and necessary to study floral transition response in diverse locations in a similar latitude. Further, the information on molecular mechanisms, mainly differential expression of genes involved in flowering process is very limited. Therefore, the crucial aspect is to generate temperature versus flowering response in different latitudes. In addition, it is time that we adopt the genomic tools and develop basic

2

information about the genes regulating flowering process as influenced by environmental cues in perennial fruit crops. In the view of the importance of ambient temperature fluctuations in regulating flowering, the upstream genes/molecular mechanisms involved in regulating floral integrators have been well studied in model systems like Arabidopsis thaliana. Similar basic studies may provide greater insight in flowering behaviour of perennial crops. What is the relevance in understanding the structure and function of floral regulatory genes and their environmental control? The strategic and basic approach would be to genetically modify them which would be difficult. From this context, the new emerging trend is to take clues from chemical drug science to identify molecules for alteration of the target proteins/transcripts. Recent developments on the role of miRNAs in regulating flowering substantiates this concept. In a recent study it was shown that the chemical PARP (Poly-ADP-Ribose Polymerase) inhibition has substantially enhanced growth of Arabidopsis. Chemical/drug science has provided convincing evidences of the possibilities of regulating the function of a target protein. Genomics and the developments in delivery mechanisms along with bioinformatic tools will provide further options to design molecules for chemical regulation of plant processes, which of-course, is just emerging.



ASSIMILATE PARTITIONING AND TRANSFORMATIONS IN SOME PERENNIAL FRUIT CROPS WITH DUE FOCUS ON MANGO (MANGIFERA INDICA L.): DYNAMICS OF SHOOT-ROOT COMMUNICATION IN REPRODUCTIVE PHENOLOGY-AN APPRAISAL H. Ravishankar Central Institute for Subtropical Horticulture Rehmankhera, P.O. Kakori, Lucknow-226 101, U.P. E-mail: [email protected]

INTRODUCTION Resource allocation between tissues has been demonstrated to be a fundamental process in growth and development of all multicellular organisms. In higher plants, leaves function as the principle site of resource acquisition by utilizing the free energy captured in photosynthesis for the reductive assimilation of oxidized forms of carbon and nitrogen into carbohydrates and amino acids, respectively. Studies have shown that these photosynthate are subsequently partitioned to the many heterotrophic tissues of the plant with as much as 80 per cent of the carbon acquired in photosynthesis is transported in the plant’s vascular system to the importdependent organs. Sucrose is the principal metabolite in this scheme of resource allocation as it is the major end product of photosynthetic carbon metabolism and, in majority plants; it is the predominant form of carbon transported to the heterotrophic tissues. This systemic distribution of photosynthate is known as ‘assimilate partitioning,’ a crucial process associated with plant growth and productivity (Tzyy-Jen Chou and Bush, 1998). Geiger and Servaites, 1991 observed that assimilate partitioning is a crucial event as the pattern of resource allocation between different organs is responsive to both developmental processes and environmental factors depending upon the needs of plant. Michel Genard et al., (2008)

indicated that carbon allocation within plants depends upon complex rules linking source organs (mainly shoots) and sink organs (mainly roots and fruits). They further remarked that the complexity of these rules arises from regulations and interactions between various plant processes involving carbon. The existence of a sucrose-sensing pathway that modulates transport activity as a function of changing sucrose concentrations in the leaf signaling pathway controlling assimilate partitioning at the level of phloem translocation has been demonstrated (TzyyJen Chou and Bush, 1998). Their study suggested that this sucrose-dependent transduction pathway is an important regulatory step in resource allocation. It was further hypothesized by them that high sucrose levels in the vascular tissue, resulting from decreased ‘sink’ demand, down-regulates symporter activity. Because of decreased phloem loading, carbon will back up in the surrounding mesophyll. Carbohydrate accumulation in the mesophyll results in a concomitant down-regulation of photosynthetic activity. In contrast, elevated ‘sink’ demand would decrease sucrose levels in the phloem. This would up-regulate transport activity and, thus, increase the capacity for phloem loading. Enhanced phloem loading would draw down the sucrose levels in the mesophyll, perhaps


3

PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS stimulating photosynthetic activity and also increasing the percentage of recently fixed carbon directed to sucrose synthesis versus starch accumulation.

Flowering genes in some tropical and subtropical fruit crops a) Mango (Mangifera indica L.) Recent advances in molecular biology of flowering in the facultative, long-day, model herbaceous plant, Arabidopsis thaliana, [reviewed in Zeevaart (2006) and Aksenova et al. (2006)] has provided new insights into the nature of the floral stimulus. Activation of the CONSTANS (CO) gene encodes a protein, which in turn induces expression of the FLOWERING LOCUS T (FT) gene localized in phloem tissue in vascular veins of leaves. The protein product of FT acts as the florigenic component that is translocated to Arabidopsis buds (Corbusier et al., 2007). This conclusion is supported by translocation from leaves to buds of an analogous protein encoded by Hd3a, a rice ortholog of FT, which appears to be the florigen operating in that crop (Tamaki et al., 2007), and the aspen ortholog, PtFT1, which along with CONSTANS was demonstrated to regulate the timing of flowering and growth cessation of Populus trichocarpa (Bohlenius et al., 2006). Once translocated to buds, the protein product of FT is thought to combine with the bZIP transcription factor (FD) protein to activate transcription of floral identity genes, such as APETALA1(AP1) to begin floral expression (Abe et al., 2005; Wigge et al., 2005). Similar mechanisms may be active in mango but with greatly altered dynamics of gene expression. Zhang et al. (2005) and Davenport et al. (2006) isolated a CONSTANS-like gene (MiCOL) from mango leaf DNA by a combination of genomic walking and PCR methods. CONSTANS is a circadian expression gene interacting with the 4

photoperiodic pathway in Arabidopsis (Putterill et al., 2004). This gene is central to activation of the FT gene in Arabidopsis during long days, but because mango is nonphotoperiodic, the role of this gene in mango flowering systems remains unclear. The mango ortholog has 79 per cent, 76 per cent, and 62 per cent homology with two apple CONSTANS genes, MdCOL2 and MdCOL1, and the Arabidopsis CONSTANS gene (AtCO), respectively. Efforts to isolate the FT or homologous gene responsible for synthesis of the protein, FP, however, have, thus far, been unsuccessful (Davenport, 2006 and 2007) . b) Citrus In Satsuma mandarin (Citrus unshiu T.) , FT ortholog mRNA levels increased with the time spent under florally inductive conditions (Nishikawa et al. 2007). In sweet orange, LFY and AP1 ortholog RNA levels increased during and after florally inductive cool temperatures while RNA of the TFL ortholog was absent (Pillitteri et al. 2004a). In transgenic hybrid citrus, Citrus sinensis L. Osbeck x Poncitrus trifoliata L. Raf., over-expression of LFY and AP1 ortholog substantially reduced the juvenile phase, but flowering still appeared to be under both environmental and endogenous control because it occurred only once a year in the spring (Pena et al. 2001). Shalom et al., 2012 studied in citrus CiFT [35], CsAP1, CsLFY [37] and SOC1 [34] genes .Three CiFT genes were analyzed. Originally, the expression of three transcripts of CiFT were characterized, viz., CiFT1, CiFT2 and CiFT3, based on the EST database. However, when comparing the sequences of these three ESTs to the full genome sequence of citrus (http:// www.phytozome.org/), it became evident that CiFT1 and CiFT2 are most likely encoded by a single gene (Clementine0.9_023420), while CiFT3 is encoded by a different one


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Long days

Vernalization

Photoreceptors FRI CO

GA

Autonomous: several genes acting additively

FLC SOC1

FT Floral meristem identity genes Flowering

Fig.1a. Floral initiation in Arabidopsis occurs through the photoperiodic, vernalization, GA or the autonomous pathways. Pointed arrows represent positive regulation, ‘T’ arrows represent negative regulation, and both pointed and ‘T’ arrows represent positive and negative regulation. Under long days, photoreceptors stabilize CO allowing up-regulation of FT, the FT protein is transported from the leaf to the meristem, where it interacts with floral meristem identity genes, leading to flowering. Vernalization suppresses the floral repressor FLC both in the meristem and the leaf, the autonomous pathway also suppresses FLC through several genes that act additively. GA promotes flowering by up-regulating SOC1, and also appears to speed flowering though interactions with the other pathways. (Source: Wilkie, 2009)

(Clementine0.9_033594)[48]. In addition to these two genes, another gene, highly homologous to FT, was found in the genome sequence (Clementine0.9_023363) with no representative in the EST database. In their work, the transcript of Clementine0.9_023420 is denoted CiFT1, that of Clementine 0.9_033594 is denoted CiFT2 and that of Clementine0.9_023363 is denoted CiFT3. The mRNA levels of CiFT1 were significantly induced in ‘ON’ and ‘OFF’ buds from May to July, which decreased towards September, and remained relatively low during the flower induction period until January. During May and July , ‘ON’ buds

displayed higher transcript levels than in the ‘OFF’ buds. The mRNA levels of CiFT2 in buds of ‘OFF’ trees showed a gradual increase of 35-fold overall from September to January. Although gene expression of CiFT2 in buds of ‘ON’ trees showed a similar pattern, it was significantly lower than in ‘OFF’ buds during this period. The expression of CiFT3 in ‘OFF’ buds was relatively low and did not change during the tested period. However, in ‘ON’ buds, it was induced about 10-fold from July to September, and then decreased to levels similar to those of “OFF’ buds from November until January. In view the foregoing based on the studies of Shalom et al., 2012, it is therefore possible that CiFT1 and CiFT3 are involved in the control of vegetative rather than reproductive growth. There are three vegetative flushes in citrus: spring flush (February–March), summer flush (June–July) and fall flush (October–November). In light of the fact that, ‘ON’ trees displayed suppressed vegetative growth, the authors suggested that CiFT1 and CiFT3 either played a role in the suppression of vegetative flush development, or helped to determine ‘ON’ bud fate toward vegetative growth the following spring. If the latter indeed is the case, the early induction of CiFT1and CiFT3 should generate a signal that persists for a long time. If such a signal is indeed generated, then it was opined that it should also be considered to be reversible, as the defruiting of ‘ON’ trees induced flowering the following spring. Obviously, expression patterns provide only coincidental evidence for the involvement of the above genes in phase transitions. Their study underscored the requirement of more direct evidence, such as that provided to establish the involvement of FT, LFY and AP1 in the juvenile-to adult phase transition. However, one reasonable scenario (among others) according to them is that CiFT2, AP1 and LFY are induced in ‘OFF’ buds and leaves in response to flowering-


5

PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS permissive environmental and endogenous signals. In ‘ON’ organs, high fruit load prevents or reduces their induction by generating a ‘negative AB signal’. The nature of the endogenous signal affected by fruit load, is it nutritional status of the tree, hormonal or some other signal(s), Shalom et al., 2012 surmised, is yet to be precisely unraveled. (i) Photosynthesis Some studies in Citrus have provided evidence of genes belonging to the three components of photosynthesis-light reaction, Calvin cycle and photorespiration being induced in OFF buds (Shalom et al., 2012) . In addition, SEA of expression showed that processes involved in the detection of light stimulus (including red/far red light) and photo transduction are also induced in OFF buds . It also pointed out that bud morphology does not allow efficient photosynthesis and like the fruit, it provides a sink organ for photoassimilates. In ON trees, however the bud was found competing with the developing fruit for resources, while no such competition occurred in OFF trees, loaded with photoassimilates and storage molecules. Based on the nutritional theory, it may be reasonable to deduce that photoassimilates availability could play a regulatory role in flower induction. The study highlighted, among genes induced in OFF-crop trees was one homologous to SQUAMOSA PROMOTER BINDING-LIKE (SPL), which controls juvenile-to-adult and annual phase transitions, regulated by miR156. The expression pattern of SPL-like, miR156 and other flowering control genes suggested that fruit load affects bud fate, and therefore development and metabolism, a relatively long time before the flowering induction period. Their results shed light on some of the metabolic and regulatory processes that are altered in ON and OFF buds.

6

(ii) Trehalose metabolism The work of Shalom et al., (2012) indicated that ON buds showed increased expression of the two genes of trehalose metabolism, TPS and TPP. Trehalose, a minor carbohydrate which is a disaccharide, serving as an alternative sugar to sucrose in a variety of bacterial and fungal species. In resurrection plants, where it serves as an osmoprotectant, trehalose is present at high levels, but usually in higher plants it is below detection levels. Changes in the trehalose biosynthetic genes and/or enzymes, and not necessarily trehalose levels themselves, were postulated to play a signaling or regulatory role in stressresponse pathways. Moreover, Arabidopsis plants mutated in TPS show arrested-growth phenotypes, remaining in the vegetative growth phases, suggesting that the gene is required for proper embryo development. These results demonstrated the importance of the trehalose biosynthetic pathway for normal vegetative growth and transition to the flowering phase. An increase in the expression of TPS and TPP along with unchanged expression in trehalase, which catabolizes trehalose, suggested that trehalose level and / or pathway is induced in ON buds in May in citrus. They explained their results in two ways. First, as a result of the high investments in developing fruits, ON trees are commonly under stress, which might directly affect the bud. Increased production of trehalose might play a role in mitigating the effects of these stresses. Second, the significant differences in TPS and TPP expression in buds, but not in LS, in May suggested a possible role for trehalose and/or its biosynthetic pathway in citrus flowering induction and in the regulation of AB itself, via an unknown mechanism.


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS (iii) Flavanoid biosynthesis

Source–Sink relationships

Shalom et al., (2012) reported that they could induce in OFF buds, genes of a few pathways of secondary metabolism, including flavonoids, phenylpropanoids, alkaloids and lignin. Induction of five flavonoids biosynthesis genes was validated by nCounter technology, and metabolomics analysis confirmed that the pathway might indeed be induced in OFF buds of citrus in May. The induction of specific flavonoids was relatively marginal; however, the identification was limited by the standards used, and other flavonoids might also be induced. In any case, it seemed that not only the central pathway was induced, but also the side reactions. They hypothesized their synthesis to occur under conditions of excess photoassimilates, particularly sucrose; sucrose feeding of Arabidopsis plants has been shown to result in increased expression of Flavanoid biosynthetic genes, especially those encoding anthocyanin. In light of these findings, the researchers suggested that flavonoids in the bud serve as ‘‘sink’’ molecules for excess photoassimilates and other carbon molecules accumulating in the tree in OFF years. Their results highlighted the possibility that a relatively long time before the flowering induction period in citrus, fruit load affected many regulatory and metabolic processes in the bud. They however pointed out that year to year environmental and other external variations might affect the results, and therefore the conclusions. It was expressed that the nature of the AB signal, and whether it is produced that early, raises questions. Even if produced in May, or earlier, the signal must be reversible, as fruit thinning or complete removal from ON trees reversed the AB state. Though their study provided indications of involvement of trehalose metabolism in vegetative and reproductive growth, its precise role in AB control warrants further study.

Using the supply – demand terminology, some researchers visualize two situations: A] SUPPLY > DEMAND Under such conditions each sink should receive its share according to its potential growth rate. Growth of sink organs is not limited by the availability of photosynthates, but by other resources or genetic potential. Excess carbohydrates may exert a feedback inhibition and, according to the hypothesis of Neales & Incoll (1968) reduce the photosynthetic activity of source leaves. Photosynthesis is reduced indeed in girdled, fruitless branches (Bustan, 1996). This feedback control is not easily determined with whole trees under field conditions as there may be alternate sinks, roots in particular. There is, nevertheless convincing evidence that this feedback control exists (Lakso et al., 1999) and some fruit tree models have incorporated it into their models (Lescourret et al., 1998). Correspondingly, the tree may compensate for source limitation by increasing its photosynthetic rates (Layne and Flore, 1992).

B] SUPPLY < DEMAND Under such conditions [source limitation] the plant must ‘decide’ how to partition the available photosynthates among its sinks. The situation is comparable to economic problems of resource allocation and is known as the ‘partitioning priorities’ problem. All the modelers of plant productivity face this problem (Marcelis et al., 1998) but selection of the priority scheme is generally based on theoretical assumptions and only seldom on experimental evidence. Two kinds of partitioning modes thus may be envisaged:


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS 1]

A ‘hierarchical’ mode, assuming predetermined organ priorities (Gutierrez et al., 1985).

2]

A ‘proportional’ mode, in which every organ gets a fixed portion of the photosynthates supply, according to its relative ‘sink’ strength.

Carbon supply and consumption budget Goldschmidt and Samach (2004) explained the option for provision of an overall, quantitative description of fruit trees’ annual productivity is through equations of C supply and consumption: Pn+ Sto = Sr + Rr +Dr + Fn.w.r + Pr + Sto where, Pn- photosynthates production; Stononstructural C reserves ; Sr-current year’s shoot mass [including leaves and stem], multiplied by a respiratory quotient; Rr-current year’s root mass, multiplied by a respiratory quotient; Dr-current year’s drop of flowers and fruit lets, multiplied by a respiratory quotient; Fn.w.r -fruit number, multiplied by w, fruit weight, multiplied by a respiratory quotient; Pr- perennial organ mass, multiplied by a respiratory quotient The C supply consists of current year’s photosynthesis + some C reserves, which might be mobilized to support current year’s growth activity, primarily in the spring, although they might be available also later, particularly under stress conditions. The reserves appear also in the right wing of the equation, since reserves are replenished during the year. The vegetative organs (shoots and roots) appear separately with their specific respiratory quotient. The dropped reproductive structures are treated separately. The yield expression contains fruit numbers and unit weight, since both are of significance 8

in fruit tree crops. The bioenergetics cost of production of varying organs needs to be included to convert from fixed CO2 to dry matter and compare demands of different organs on the same energetic basis (Walton and DeJong, 1990 ; Bustan and Goldschmidt, 1998). This expression of bioenergetics costs is important for comparing species that are more carbohydrate based like most fruit trees (apples, citrus, peach) to crops that produce large amounts of energetically-expensive dry matter like lipids and proteins, for example avocado (Wolstenholme, 1986) or pistachio (Stevenson and Shackel, 1998). A central feature of crop models is the estimation of tree photosynthesis that provides the energy and carbon skeletons for biological productivity. There are a variety of approaches, primarily borrowed from earlier crop modeling, such as modifications of the annual crop growth model, SUCROS’86 (Grossman and DeJong, 1994). The light interception problem has also been addressed by separation of the total leaf area into sunlit and shaded components (Lescourret et al., 1998). Lloyd et al. (1995) showed that whole tree gas exchange rates of macadamia and litchi trees could be accurately simulated by treating the tree surface as a hemisphere and calculating gas exchange characteristics separately for sunlit and shaded portions of the tree. This model has also been adopted for citrus (Syvertsen and Lloyd, 1994; Bustan et al., 1999). Allen et al. (1974) reported that a common approach to evaluate tree photosynthesis is to estimate light penetration into the canopy from canopy structure leaf area and the Beer’s law extinction function. The light intensity gradient is estimated, and then photosynthesis is calculated by leaf area at given levels of light. This is usually done at time intervals of minutes or hours and summed


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS for daily totals. Due to the movement of the sun, radiation geometry and canopy form must be included in the calculations. For orchards with rows of discontinuous canopies and consequently significant lateral radiation fluxes, the role of diffuse light on canopy photosynthesis should be taken into account. This based on their studies opined, is especially true with thin vertical canopies typical of vineyards and some orchards where an entire side of the canopy may receive only diffuse radiation. This may be an important consideration in humid climates. Charles-Edwards (1982) outlined another simpler approach which uses a “big leaf” model that estimates canopy photosynthesis as a daily canopy light response to daily intercepted radiation that is based on incident radiation, fractional interception as estimated by Beer’s law, and exposed leaf photosynthesis. This approach ignores the gradients of light and photosynthesis of differing leaf populations and varying radiation geometry over time, but is much simpler. Both approaches require photosynthesis data and canopy extinction coefficients, but the daily big leaf model uses only daily radiation data. Additionally, daily fractional light interception from direct measurements can be entered to further simplify the model. This approach has been used in a simplified apple dry matter production model (Lakso and Johnson, 1990; Lakso et al., 2001) and the values simulated were quite well validated with field canopy gas exchange measurements.

Root dynamism and root-shoot correlations The perennial crops system present extreme difficulties in carrying out real time studies on toot growth, replenishment, sink activities including assimilate

transformations and other aspects of root dynamics non-destructively. Although in recent years, rhizotron studies have significantly enhanced our knowledge on root functions more focused studies on root-shoot communication in regulation of shoot morphogenesis contributing to productivity of perennial fruit crops are flagged in order to understand the efficiency of genotypes based on dynamic root systems. This appears to be particularly significant in view of the fact that in mango tap root had the highest DMC (53.4%) with starch grains being predominantly located in xylem parenchyma with longitudinal gradient established in tap root coarse roots, stump and branches (Dam our and Normand, 2003 and Normand et al., 2003). Further studies however are needed to understand the phenological relationships with starch content and whether the longitudinal gradient is constant during phenological cycle? It is also imperative to study these aspects in alternate and regular bearing genotypes in order pyramid the genes governing for articulating crop improvement initiatives accordingly. Teskey et al., (1987) opined that net carbon gain of a tree can be considered a function of the rate of photosynthesis per unit area of foliage, the respiration rate of the photosynthetic tissue, leaf area, and the surface area and respiration rate of nonphotosynthetic tissue (e.g., root, stem, branch). These components according to them can be related by the formula:

where, Li is the leaf area of an age class of foliage, Ai and Ri are the photosynthetic rate and respiration rate of that age class, respectively, B, is the surface area of nonphotosynthetic tissue of type x (e.g., root, stem,


9

PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS and branch) and R, is the respiration rate of that tissue. Their study pointed out though water and temperature are important factors regulating the productivity, they alone did not control productivity. They surmised that, productive potential of a tree or forest is defined by a combination of factors and interactions, including water, temperature, nutrients, light, disease, insects, as well as less understood factors such as allelopathic and root growth patterns. Goldschmidt and Samach, (2004) observed that most models have adopted some kind of hierarchical, sink ranking approach. Maintenance respiration is generally assumed to have the highest priority and reserves are believed to have the lowest priority. In their peach model, Grossman and DeJong (1994) assumed that having satisfied the top priority needs of maintenance respiration, then fruits, leaves, stems and branches have the same priority rank, followed by the trunk and finally the roots. Lakso et al., (2001) used in their apple model, the priority ranking: shoots >> fruits > roots = structure. During the spring flush of vegetative growth, bloom and fruit set there seemed to be a competition between the different, actively growing sink organs. In apple, early in the season, shoots appear to have higher priority

than the reproductive organs under carbonlimiting low light conditions (Bepete and Lakso, 1998). Later, as shoots terminated growth, the partitioning shifts to fruits and other organs (Lakso et al., 2001). The problem has been addressed experimentally by Bustan & Goldschmidt (1999) who examined fruit / root partitioning ratios using potted citrus trees and a simulation model. Young fruits [7d after petal fall] were found inferior to roots in competition for photosynthate, whereas older fruits [30d after petal fall] proved to be strong, dominating sinks. The varying patterns of fruit development suggested that the fruit sink demands vary with different stages of development. The similarity of the results with citrus described above and observations on apple development suggested that young fruits in general may have lower sink strength. This could be a mechanism to induce the large abscission needed to avoid excessive cropping in any year and the resultant erratic cropping over many years. Additionally, if fruits inhibited root and shoot growth as often reported, too much fruiting may be detrimental to survival in resource limiting conditions where root or shoot growth is needed to obtain the limited resource (e.g. water, nutrients or light). The results of Bustan and Goldschmidt (1999) indicated that although the

Table 1. Distribution of starch and soluble sugars in ‘On’ and ‘Off’ trees in Murcott trees Organ

Fruit Leaves Twigs : diam< 1 cm Branches : diam – 1-3 cm Branches : diam – 3-5 cm Branches : diam > 5 cm Trunk above graft union Trunk beneath graft union and main root Major roots Roots : diam > 0.5 cm Minor roots: diam < 0.5 cm

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Starch (mg g-1 dry matter) "Off" "On" "Off/On" 38.2 122.6 33.8 3.6 97.0 25.7 3.8 73.9 20.4 3.6 78.3 17.0 4.6 76.6 19.0 4.0 80.2 38.4 2.1 96.1 46.7 2.0 124.6 17.5 7.1 163.2 9.4 17.4 179.8 19.2 9.4

Soluble sugar (mg g-1 dry matter) "Off" "On" "Off/On" 407.0 178.2 121.6 1.5 102.6 83.6 1.2 70.4 47.0 1.5 55.8 40.2 1.4 70.06 47.8 1.5 50.4 43.2 1.2 47.2 58.4 0.8 56.0 47.8 1.2 77.2 40.0 1.9 67.8 52.0 1.3



After the structural use of photosynthates , soluble carbohydrates make up a pool that may be distributed among sinks and redistributed. Alternate bearing trees (On and Off) are a good comparison to understand this distribution as to how crop load alters distribution and perhaps accounted for alternate bearing (Smith, 1976). Total dry matter was found nearly equal, but distribution different. Starch and soluble sugars were found to make much larger pools in Off tree. Surprising reduction is in the major root dry matter (root loss?) Mango trees put forth growth in a discontinuous manner of course depending upon the variety and ‘On’ and ‘Off’ phases of the tree; the tree size increments accrue from the dynamics of vegetative flushes production that arise periodically . The vegetative growth restriction precludes flowering, since fruit bud differentiation event unless and otherwise it is not adversely impacted by factors viz., unseasonal rainfall (both in tropics and subtropics) and disturbances to cold (in subtropics); incidence of frost and hailstorms determine the fate of a particular meristem in favour of flowering. Temperatures between 20 to 30°C favor vegetative shoot development while temperatures between 6 to 18°C incentive the initiation of the inflorescence development. The development of the terminal inflorescence occurs after a cold period associated to a degree of drought stress. In locations where winter is not cold enough for an adequate flowering induction (minimum daily T° above 15°C), it is common to produce this induction by exposing trees to soil moisture deficiencies (drought stress) before flowering.

PER CENT STARCH (BY DRY WT.)

proportional mode of partitioning might be valid under certain circumstances, hierarchical partitioning mechanisms are felt necessary for the emergence and development of new plant organs.

JUN

AUG

OCT

DEC

FEB

Starch levels in different plant parts of Murcott trees with and without crop compared to Valencia, a mild alternate bearing cultivar. No fruit (empty) in Murcott trees are broken lines with open circles (Smith,1976)


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Table 2. Total dry matter, starch and soluble sugars of organs in ‘Off’ and ‘On’ trees organs in Murcott trees Organ

Fruitz Leaves Twigs : diam< 1 cm Branches : diam = 1-3 cm Branches : diam = 3-5 cm Branches : diam > 5 cm Trunk above graft union Trunk beneath graft union and main root Major rootsy Roots : diam > 0.5 cmy Minor roots: diam < 0.5 cm y Total per tree (kg)

Dry matter (kg) 10.58 6.49 21.21 24.44 23.22 14.37 7.20 15.04 20.43 1.06 144.04

A number of instances where the occurrence of these factors has even caused reversal of the already determined meristem fate of floral status in to vegetative growth instead of reproductive organs developing have been recorded. Further in mango there existed growth correlations between vegetative growth, flowering intensity and the crop load (Bruce Scaffer et al., 1994 , Davenport, 2007 and Wilkie, 2009).

Floral induction Tropical trees are generally induced to flower through environmental cues, whereas floral initiation of temperate deciduous trees is often autonomous. In the tropical evergreen tree mango, Mangifera indica L., cool temperature is the only factor known to induce flowering, but does not ensure floral initiation will occur because there are important interactions with vegetative growth (Davenport, 2007; Wilkie, 2009). The temperate deciduous tree apple, Malus domestica Borkh., flowered autonomously, with floral initiation dependant on aspects of vegetative development in the growing season

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"Off " tree "On" tree Starch Soluble Dry Starch Soluble (g) sugar (g) matter (g) sugar (kg) (g) 25.80 986.0 10499.0 1298.0 1885.5 7.72 261.0 938.4 629.0 665.8 6.78 174.0 567.0 1568.0 1493.3 20.98 428.0 986.2 1912.0 1363.8 24.60 419.0 989.0 1778.0 1639.3 29.14 553.0 1393.0 1152.0 724.3 14.08 541.0 608.1 691.0 399.7 6.82 319.0 398.5 1874.0 842.3 7.40 130.0 353.5 3334.0 1577.2 12.24 115.0 489.4 191.0 72.1 0.60 11.5 31.1 13.26 10.66 156.16 3.94 17.25

before anthesis, although the environment exerted some control. Floral initiation includes all of the developments necessary for the irreversible commitment by the meristem to produce an inflorescence (Kinet, 1993). Control of floral initiation is not restricted to the developing meristem, but may involve signals from other areas of the plant. Autonomous flowering is where internal developmental cues lead to floral initiation. Floral induction is where an environmental stimulus, most commonly photoperiod or temperature, leads to floral initiation. Often, interactions between environmental stimuli and endogenous developmental cues exerted some control over floral initiation. Some aspects of flowering in trees make them especially challenging for physiologists, breeders and growers; first, the juvenile phase, which lasts for several years during which time no flowering or fruiting occurs; second, interactions between vegetative growth, flowers and fruit of the previous year on floral initiation in the current year, affect growers through phenomena such as biennial bearing, and make interpretation


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS of research data difficult for scientists (Wilkie, 2009). Mango flowering involves hormonal regulation of shoot initiation and induction events resulting in reproductive shoot formation. A balance or ratio of endogenously regulated phytohormones, thought to be auxins from leaves and cytokinins from roots, appears to govern the initiation cycle independently from inductive influences. Induction of reproductive or vegetative shoots is thought to be governed by the ratio of a temperature-regulated florigenic promoter and an age regulated vegetative promoter at the time of shoot initiation. Management of off-season flowering in mango trees is being accomplished in the tropics by successfully synchronizing shoot initiation through tip pruning and use of nitrate sprays coupled

with management of the stem age to induce flowering such that it can be accomplished during any desired week of the year (Davenport, 2007).

Assimilate partitioning priorities Ravishankar (1987) studied the pattern of 14C-Sucrose translocation and assimilation in distinctly alternate (‘Alphonso’) and regular (‘Totapuri’) bearing mango varieties during pre, FBD and post-FBD stages. Based on 14CSucrose translocation, assimilation and metabolic labeling pattern, he provided evidence on the possible nature of interrelationships between the shoot apex and other parts of the mango tree viz., stem portion and leaves and the presumptive role of root system in the regulation of translocation and assimilation in flowering of mango (Fig. 2-6).

Mango Flowering Model

Fig.1. Conceptual flowering model of mango. The model summarizes the proposed roles for various phytohormones in initiation of shoot growth and in defining the vegetative or reproductive outcome of the growth (induction). Single lines in the scheme are promotive and double lines are inhibitory. (Source: Davenport, 2007)


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Fig.2. Autoradiograph of fruited shoot of alternate bearing ‘Alphonso’ at FBD stage . The arrow mark indicates the position of 14C-Sucrose fed leaf (‘candidate leaf’). Note the predominant acropetal 14 C-Sucrose translocation (Ravishankar, 1987)

Pattern of 14C-Sucrose translocation in alternate bearing 'Alphonso’ fruited shoot at fruit bud differentiation (FBD) stage from the candidate leaf (fed leaf) to other parts of shoot (Values in parentheses are the14C activities expressed as percentage of total translocated dpm. g. dry weight-1) (Ravishankar, 1987)

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Fig.3. Autoradiograph of unfruited shoot of alternate bearing ‘Alphonso’ at FBD stage. The arrow mark indicates the position of 14C-Sucrose fed leaf (‘candidate leaf’). Note the predominant acropetal 14C-Sucrose translocation (Ravishankar, 1987)

Pattern of 14C-Sucrose translocation in alternate bearing 'Totapuri’ fruited shoot at fruit bud differentiation (FBD) stage from the candidate leaf (fed leaf) to other parts of shoot (Values in parentheses are the 14C activities expressed as percentage of total translocated dpm. g. dry weight-1) (Ravishankar, 1987)


15


Fig.4. Autoradiograph of fruited shoot of regular bearing ‘Totapuri’ at FBD stage. The arrow mark indicates the position of 14C-Sucrose fed leaf (‘candidate leaf’). Note both acropetal as well as basipetal 14C- Sucrose translocation (Ravishankar, 1987)

Pattern of 14C-Sucrose translocation in regular bearing 'Totapuri’ fruited shoot at fruit bud differentiation (FBD) stage from the candidate leaf (fed leaf) to other parts of shoot (Values in parentheses are the 14C activities expressed as percentage of total translocated dpm. g. dry weight-1) (Ravishankar, 1987)

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Fig. 5. Autoradiograph of unfruited fruited shoot of regular bearing ‘Totapuri’ at FBD stage. The arrow mark indicates the position of 14C-Sucrose fed leaf (‘candidate leaf’). Note predominant 14 C-Sucrose translocation (Ravishankar, 1987)

Pattern of 14C-Sucrose translocation in regular bearing 'Totapuri’ unfruited shoot at fruit bud differentiation (FBD) stage from the candidate leaf (fed leaf) to other parts of shoot (Values in parentheses are the 14C activities expressed as percentage of total translocated dpm. g. dry weight-1) (Ravishankar, 1987)


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Fig.6. Autoradiograph of unfruited fruited shoot of regular bearing ‘Totapuri’ at panicle emergence stage . The arrow mark indicates the position of 14C-Sucrose fed leaf (‘candidate leaf’). Note both acropetal as well as basipetal 14C-Sucrose translocation (Ravishankar, 1987)

Pattern of 14C-Sucrose translocation in regular bearing 'Totapuri’ unfruited shoot at panicie emergence stage from the candidate leaf (fed leaf) to other parts of shoot

His studies indicating higher 14CSucrose translocation and SLI in the terminal bud of ‘Totapuri’ as compared to that of ‘Alphonso’ in fruited shoot at peak FBD indicated higher efficiency of former in attracting metabolites that signifies high ‘sink’ strength. The study also provided indirect

18

evidence that the terminal bud of ‘Totapuri’ is metabolically more active and when this is coupled with energy transducing mechanism , an integral part of flower initiation, conferring the potential to differentiate fruit buds even during ‘OFF ‘years. Further his study also provided indications of assimilate


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS partitioning priorities in the above varieties during FBD stages. Higher ratio of acropetal: basipetal 14C-Sucrose translocation in the fruited shoots of ‘Alphonso’ indicated an overall disturbed metabolism (Fig. 2), probably was gibberellins-directed (Chacko et al.,1972) and perhaps more so in the root system as compared to that of ‘Totapuri’ (Fig. 4) where, almost balanced acropetal: basipetal 14CSucrose translocation was observed. This appears significant in light of the scheme where the root system has been assigned pivotal role in the assimilation of NH4+ by the di- and tricarboxylic acid cycles and the circulation of substances (Kursanov, 1984). Indications of his study highlighting disturbed distribution of metabolites in ‘Alphonso’ during ‘OFF ‘years appears to cause metabolic block leading to sustenance of alternate bearing tendency in this variety. This is further supported by the predominant acropetal: basipetal 14C-Sucrose translocation even in the unfruited shoot of ‘Alphonso’ (Fig. 3) in contrast to that of ‘Totapuri’ probably indicated depressing effect on the general growth and functioning of root system thus affecting assimilate transport arising from root-shoot communication gaps so crucial in circulation of metabolites. The possible role of cytokinins in the scheme of things cannot be ruled out which needs detailed investigations. The balanced distribution of assimilates as indicated by acropetal: basipetal 14C-Sucrose translocation in both fruited (Fig. 4) at FBD as well as in unfruited (Fig. 5) shoots of ‘Totapuri’ and even in the panicle emergence stage (Fig. 6) together with 14C-Sucrose assimilation data (unpublished) is indicative of efficient organization of assimilate transport and circulation of substances under the influence of root dynamism. His studies pointed out to the strong possibilities of regular bearing feature of ‘Totapuri’ attributable to higher metabolic turnover, energy transducing

system under up/down regulation of genes at specific stages of fruit bud differentiation in response to environmental cues via hormonal route since paclobutrazol mediated flower induction in mango have been widely and successfully practiced globally.

Vegetative growth and floral initiation A wealth of information outlining interrelationships phenology of perennial fruit crops is available in literature of which, a few are cited here. An exhaustive review in this regard has been made by Willkie et al. 2009. Fruit tree species vary both in the types of shoots that produce flowers and where on these shoots the flowers are borne. The location of the flowers and the timing of floral initiation influence how flowering and vegetative growth interact. Mango and other several subtropical species, including litchi, tend to produce inflorescences from terminal buds; others, such as avocado, from both terminal as well as axillary buds; and still others, like macadamia, from axillary buds. Similar to apple, several other temperate deciduous species, such as pear, Pyrus communis L. (Faust, 1989), and sweet cherry, Prunus avium L. (Webster and Shepard, 1984), initiate flowers on specialized spur structures as well as on current season’s growth. On the other hand, peach, Prunus persica L. Batsch (Dorsey, 1935), and apricot, Prunus armeniaca L., (Jackson, 1969), initiate flowers in lateral buds of the current season’s growth. In the subtropical trees litchi , avocado, and possibly macadamia, flowering is dependent upon bud release during cool floral inductive temperatures (Olsen, 2005). This is largely regulated by maturity of the most recent flush but the likelihood of bud release and flowering can also be affected by characteristics of the shoot, as for macadamia (Willkie et al., 2009). In temperate deciduous species, however, the release of pre-existing floral or vegetative buds


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS in the spring after winter dormancy is dependent upon satisfying the chilling requirements (Rohde and Bhalerao, 2007). Vegetative growth in litchi is through recurrent flushing, with the interval between successive flushes dependent on the prevailing weather conditions (Olsen et al., 2002). There is only a small part of this cycle when the new shoots are receptive to floral induction, that being around the time of early flush development when the expanding buds are no more than a few millimeters in length (Batten and McConchie, 1995). Therefore, vegetative shoots that are not mature by late autumn often do not flower, because the cyclic nature of flush development means they will initiate new growth only after cool florally inductive winter conditions have passed. Macadamia is similar except that the cycle of flush development generally affects the flowering behaviour of mature shoots at a distance from the most recent apical flush instead of the flowering behaviour of the most recent apical flush itself (Olsen, 2005). Avocado is also similar, and intermediate to litchi and macadamia in its flowering behaviour (Olsen, 2005).

bud initiation in apple and some other temperate fruit trees (Faust, 1989; Forshey and Elving, 1989; Luckwill, 1974). Consistent with this, dwarfing rootstocks increase early flowering of apple (Luckwill, 1974); growth retardants such as daminozide can increase flower bud initiation of apple (McLaughlin and Greene, 1984); and for sweet cherry, as regrowth in response to pruning increases, floral initiation decreases (Guimond and Andrews, 1998). However, treatments that increase vigour do not always decrease floral initiation; greater shoot growth due to increasing temperatures (200C compared with 13 0C) during the growing season also increased flower bud initiation of apple (Zhu et al., 1997). These inconsistencies may be due to effects of the treatments that are independent of vigour, for example, dwarfing rootstocks may induce early flowering independent of their effect on vegetative growth; or high temperature during the growing season may promote flowering independently of vegetative growth.

The timing of vegetative growth also affects floral initiation in some temperate deciduous tree crops, where floral initiation occurs in the growing season before anthesis. In grapevine, the undifferentiated primordia have the potential to produce inflorescences or tendrils depending upon their location and climatic conditions; inflorescences tend to be formed in developing latent buds and tendrils in growing shoots (Boss et al., 2003). Floral initiation in peach is also reliant on, but not inhibited by, vegetative growth; floral initiation occurs in buds of the current seasons’ growth and begins when the buds are approximately four nodes back from the growing tip (Dorsey, 1935). Excessive vegetative growth has often been cited as being antagonistic to flower

The literature on the role of GA in the floral initiation of woody perennials though is vast but inconsistent. However, there is evidence to suggest that endogenous GA can inhibit floral initiation and that GA can also inhibit floral initiation through effects on shoot growth, as reported for mango (Chacko et al.,1972). For example, applied GA inhibits floral initiation in avocado (Salazar-Garcia and Lovatt, 1998), citrus (Lord and Eckard, 1987), sweet cherry (Lenahan etal., 2006), and peach (Garcia-Pallas and Blanco, 2001); reduced levels of endogenous Gas have been correlated with floral initiation in citrus (Koshita et al. 1999), and litchi (Chen, 1990); and GA biosynthesis inhibitors have improved flowering in mango (Winston, 1992), litchi (Menzel and Simpson, 1990), and

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Role of plant growth regulators


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS macadamia (Nagao et al., 1999). Floral initiation in grapevine occurs in uncommitted primordia of developing latent buds destined for dormancy and subsequent release in the following spring (Srinivasan and Mullins, 1980). The uncommitted primordia have the potential to produce tendrils as well as inflorescences, but tendrils tend to be produced only when uncommitted primordia initiate growth in the same season in which they were produced, that is, without undergoing winter dormancy (Boss et al., 2003). However, in a dwarf, GA-insensitive mutant of grapevine, only inflorescences and no tendrils were produced from uncommitted primordia of the expanding shoots (Boss and Thomas, 2002). Thus endogenous GA appears to inhibit floral initiation in grapevine. GA applications in citrus that inhibit flowering reduce the number of buds that are released in spring but not the proportion of buds that produce floral shoots (Garcia-Luis et al., 1986). Thus the effect seems to be on shoot growth rather than floral initiation. Applied GA also affects shoot growth in apple by reducing the rate of node development, lessening the chances of the buds reaching the critical appendage number (Bertelsen et al., 2002). The presence of fruit inhibits floral initiation in several species including the pome fruits (Weinbaum et al., 2001) and citrus (Garcia-Luis et al., 1986). Large crops can lead to poor floral initiation in the following year and induce a cycle of biennial bearing. GA exported from the seeds of pome fruits (Chan and Cain, 1967) and some part of citrus fruit to the buds (Garcia-Luis et al., 1986) is thought to be involved in the inhibition. Cytokinins may also be involved in floral initiation. Endogenous cytokinin levels in buds of litchi increase at the onset of floral initiation and differentiation, and exogenous applications increase floral initiation (Chen, 1991), although there is no evidence that cytokinins

can replace the floral inductive stimulus. Application of the growth retardant maleic hydrazide to ‘Japanese pear’, Pyrus pyrifolia Nakai, increased both endogenous cytokinin levels and floral initiation (Ito et al., 2001). Ethylene has long been used to promote flowering commercially in pineapple (Ananas comosus (L.) Merr.) (Turnbull et al., 1999); there are also indications that it promotes flowering in apple (Bukovac et al. 2006). More comprehensive accounts on the role PGRs in floral initiation of several horticultural trees are available, including apple (Buban and Faust, 1982; Dennis and Neilsen, 1999), mango (Davenport and Nunez-Elisea, 1997), and citrus (Davenport, 1990).

CONCLUSIONS There exist considerable knowledge gap in different fruit tree crop models especially with regard to the limited and incomplete database of good quantitative data on carbon acquisition, photo assimilates production, transformations in response to a range of environmental cues. Some researchers have prominently flagged for consolidation of important data and knowledge bases viz., phenology; leaf photosynthesis (light and temperature responses) ; shoot growth and leaf area development and fruit growth and respiration patterns. Among the perennial fruit crops, despite the best data being available in apple and citrus, variations do prevail while, tropical and subtropical fruits suffer from the dearth of critical knowledge perhaps due to low number scientists pursuing this line of work. Based on the information available so far, major gaps in perennial fruit crops appear to be root growth patterns, respiration, root turnover rates and their implications; respiration rates especially, responses to temperature fluxes on long-term;


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS seasonal demands for carbon of different tree organs, and crop load relations. Participation of genetic engineers, physiologists and horticulturists symphonically is highlighted. Need to engineer efficient, resilient and metabolically dynamic root systems and harmonize shoot-root communication are underscored.

FURTHER READING Aksenova, N.P., Milyaeva EL, Romanov G.A. 2006. Florigen goes molecular: seventy years of the hormonal theory of flowering regulation. Russ. J. Plant Physiol., 53:401-406 Bruce Schaffer, Whiley, A.W., and Crane J.H. 1994. Mango. Chapter 8. In : Hand Book of Environmental Physiology of Fruit Crops . Volume Ii. Subtropical and Tropical Crops (Eds. Bruce Schaffer and P.C. Anderson). CRC Press. Inc. Boca Raton, Florida, USA. Pp.165-196 Chacho, E.K., Singh, R.N. and Kachru, R.B. 1972. Studies on the physiology of flowering and fruit growth in mango (Mangifera indica L.) . VII. Naturally occurring auxins and inhibitors in the shoots of flowering (‘On’) and vegetative (‘Off’) mango trees. Indian J. Hortic., 29: 115-125 Corbesier, L., Vincent, C., Jang, S., Fornara, F., Fan Q, Searle I, Giakountis A, Farrona S, Gissot L, Turnbull C.G.N, and G . Coupland . 2007. FT protein movement contributes to long-distance signaling in floral induction of Arabidopsis. Science, 316:1030-1033 Damour, G. and Norrmand, F. 2003. Distribution and variability of dry matter in mango tree cv. Cogshall . Cirad-Flhor , Reunion Island, France, ISHS ppt Davenport, T.L. 2003. Management of flowering in three tropical and subtropical fruit tree species. Hort. Science, 38, 1331-1335. Davenport, T.L. and Nunez-Elisea .1997. Reproductive physiology. In: (ed. R.E. Litz , The Mango: botany, production and uses. Wallingford: CAB International, 69-146.

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Davenport, T.L., Ying, Z.T, Kulkarni, V, and T.L.White. 2006 Evidence for a translocatable florigenic promoter in mango. Scientia Horticulturae, 110: 150-159. Davenport, T.L., Ying, Z., Kulkarni, V., and White T.L. 2006. Evidence for a translocatable florigenic promoter in mango. Sci. Hort., 110:150-159 Davenport, T.L 2007. Reproductive physiology of mango. Braz. J. Plant Physiol., 19(4):363376. Garcia-Luis, A., Almela, V., Monerri, C., Agusti, M, and Guardiola, J.L. 1986. Inhibition of flowering in vivo by existing fruits and applied growth regulators in Citrus unshiu. Physiologia Plantarum 66, 515-520 Geiger, D. R. and Servaites, J. C. 1991 In: Response of Plants to Multiple Stresses, (eds. H. A. Mooney, W. E. Winner & E. J. Pell ) (Academic, San Diego), pp. 103–127 Goldschmidt, E.E. and Golomb, A. 1982. The carbohydrate balance of alternate-bearing citrus trees and the significance of reserves for flowering and fruiting. J. Amer. Soc. Hort. Sci., 107:206-208 Goldschimdt, E.E., and Samach, A. 2004. Aspects of flowering in fruit trees . Proc. 9th IS on Plant Bioregulators. Acta Hort., 653: 23-27. Kursanov, A.L. 1984 . Assimilate Transport in Plants. Elsevier, Amsterdam–New YorkOxford,pp. 463-509 Michel Genard, Jean Dauzat, Nicholas Frank, Francois Les courret, Nicolas Moitrier, Philippe Vast and Gilles Vercamore. 2008. Carbon allocation in fruit trees: from theory to modeling. Trees., 22: 269-282 Normand, F. Lagier, S., Escoutes, J., Verdiel, J.L., and I. Millet-Serra. 2003. Starch localization in mango tree : Histological observations . Cirad-Flhor, Reunion Island, France, and Cirad-Amis Montpellier, France , ISHS ppt Putterill, J., Laurie, R., and R. Mac Knight 2004. It’s time to flower: the genetic control of flowering time. Bioassays, 26:363-373 Ravishankar, H. 1987. Studies on physiological


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS and biochemical aspects in to the causes and control of alternate bearing in mango (Mangifera indica L.) . PhD Thesis, University of Agricultural Sciences, Dharwad, India p.310

Physiology and genetics of tree growth response to moisture and temperature stress: an examination of the characteristics of loblolly pine (Pinus taeda L.) Tree Physiology, 3: 41-61

Sanz, A., Martinez Cortina, C. and Guardiolla, J.L. 1987. The effect of the fruit and exogenous hormones on leaf expansion and composition of citrus. J. Expt. Bot., 38:20332042

Tzyy-Jen Chou and Bush, D.R. 1998. Sucrose is a signal molecule in assimilate partitioning. Proc. Natl. Acad. Sci. USA, 95, 4784–4788, April 1998 Plant Biology

Shalom, L., Samuels, S., Zur, N., Shlizerman, L., Zemach, H., et al., 2012. Alternate Bearing in Citrus: Changes in the expression of flowering control genes and in global gene expression in ON- versus OFF-Crop Trees. PLoS ONE 7(10): e46930. doi:10.1371/ journal.pone.0046930 Smith, P.F. 1976. Collapse of ‘Murcott’ tangerine trees. J. Amer. Soc. Hort. Sci., 101:23-25.

Whiley, A.W. 1993. Environmental effects on phenology and physiology of mango-a review. Acta Horticulturae, 168-176. Whiley, A.W., Rasmussen T.S., Saranah J.B., and Wolstenholme, B.N. 1989. Effect of temperature on growth, dry matter production and starch accumulation in ten mango (Mangifera indica L.) cultivars. Journal of Horticultural Science, 64, 753-765

Tamaki S, Matsuo S, Wong HL, Yokoi S, and K. Shimamoto . 2007. Hd3a protein is a mobile flowering signal in rice. Science, 316:10331036.

Wilkie, J.D. 2009. Interactions between the vegetative flush, flowering and yield of macadamia (Macadamia integrifolia, M.integrifolia x M. tetraphylla) in a canopy management context. PhD Thesis, Univ New England.

Teskey, R.O. Bongarten, B.C. Cregg, B.M. Dougherty, P.M. and Hennessey, T.C. 1987.

Zeevaart, J.A.D. 2006. Florigen coming of age after 70 years. Plant Cell, 18:1783-1789.


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INDUCTION OF FLOWERING IN FRUIT CROPS - PHYSIOLOGICAL AND PLANT ARCHITECTURAL IMPLICATIONS Y.N. Reddy and A. Bhagwan1 ANGRAU, Rajendra Nagar, Hyderabad and 1Fruit Research Station, Sangareddy.

INTRODUCTION Flowering, the first step of sexual reproduction is of paramount importance in agriculture, horticulture and plant breeding. The change from the vegetative state to the reproductive state is one of the most dramatic events in the ontogeny of a plant. Flowering leads to an exciting succession of events like anthesis, fruit set, fruit development, maturation and ripening. It provides for the propagation of the species and assists in crop improvement through genetic recombination. Many plants grow vegetatively for periods ranging from weeks to years and then flower autonomously, apparently without identiûable environmental control. Flowering of 25–30 year-old bamboo is one such example: no environmental cue is known for this species. Perhaps it has its own built-in developmental clock which determines flowering time as in some annuals which flower autonomously. In contrast, other species may flower late due to inappropriate cultural or environmental treatments. In this instance, flowering may not occur irrespective of whether the juvenile phase has ended. In some species, flowering occurs after the apex has produced a particular number of leaves. This apparent leaf counting may reflect interplay between older leaves and the roots. In banana and pineapple which are propagated vegetative through rhizomes and sucker, leaf number and leaf area or both were found to be constant at the time of floral initiation.

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Prolonged juvenility of woody species is a problem for growers and breeders of tree and vine crops. However, there are so many uncontrolled variables in the ûeld that it can be difficult to identify the inductive factors. Yields can be severely depressed by inappropriate timing of practices such as pruning, irrigation and fertilization. Furthermore, inductive conditions may be required for several months. One solution for mango, litchi, olive and citrus has involved the use of controlled environments and drawf plants. These showed that cool temperatures were required for induction, a response similar to Pimelea and many other ornamental and woody species. For some species, microscopic examination of shoot meristems has augmented our ability to make decisions on practical management of flowering. For example, in kiwifruit (Actinidia) and stone fruits (Prunus spp.) floral induction occurs in the previous growing season, whereas in many subtropical species no initiation takes place until winter. In the case of kiwifruit, it was discovered that late summer pruning was removing many of the floral apices. Clearly, knowledge of environmental effects on flowering has been essential for development of orchard crops. Particularly for ûeld crops, breeders have selected for dayneutral responses. For glasshouse crops, genotype and environment have often been altered. The future offers many opportunities for applying our knowledge of day length and photothermal responses.


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS In general, fruit crops pass through a juvenile stage during which flowering does not naturally occur. Once flowering capacity is attained, the plant may respond to environmental cues such as light (especially relative lengths of light and dark periods), temperature and nutrition. Flowering has been found to be chemically controlled. Leaves are sites of control substance synthesis: apices are receptor sites. It has been suggested that this control may take the form of: (a) a single flowering factor (florigen), (b) a group of flower promoting substances. (c) one or more flower inhibiting substances, or (d) interaction between flowering promoters and inhibitors. Canopy architecture is a natural expression of the genetic makeup of the tree. The visible morphological expression of genetic blueprint of a tree at any one time is referred to as its architecture. Architectural model of a tree refer to its plan of growth and many species may have the same models. The architecture models and bearing habits have their relevance to pruning in relation to tree size control and flowering. The branches of a tree form the skeletal system in which tree form is directly dependent. The tree productivity is related to only final one or two orders of branches, other lower order branches have only supporting role. Branching system apart from determining the size and shape of crown and crop load have the most important role to harvest the maximum and better ventilation. There should be judicious removal of unproductive shoots in order to increase the number of bearing laterals.

FLOWER INDUCTION Environmental factors In large number of plant species, it is the day length (photoperiod), which influences

initiation of flowering. Whereas, it is the temperature, especially low temperature, which affects flower induction in some other plant species. There are, however, strong interactions between these three factors i.e., genotype. photoperiod and temperature, which interactively controls flowering. In the sub-tropics, during winter months when the day lengths are shorter than 12 h. it appears that short days may promote flowering, whereas it is inhibited by long days in mango. However, Nunez-Elisea and Davenport (1995) observed that cool temperature (18°C day/ 10°C night) rather than a short photoperiod caused floral induction, whereas warm temperatures (30°C day/25°C night) rather than a long photoperiod inhibited flowering. Citrus is probably day-neutral (Moss, 1969) with flowering occurring at 8-15 h photoperiod. Although floral initiation is well studied in different citrus species, very little is known about the photoperiodic influence on these events in citrus. Citrus species are usually considered as auto-inductive plants as no single indispensable stimulates for induction has been identified. Low temperatures, like in mango, are promotive, although no investigations examined the threshold temperatures necessary to induce flowering (Davenport, 1993). In papaya also, it appears that both photoperiod (Nakasone and Storey 1955) and temperature have no effect on the induction of flowering. Sex expression, however, seems to be altered by environmental, PGRs and other factors. Similarly, flowering of smooth Cayenne group of pineapple occurs at any time of the year in Hawaii and in other pineapple growing regions regardless of the prevailing day length and temperature (Bartholomew and Kadzimin, 1977). However, interaction of these two factors has altered the flowering behavior. Increasing and


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS decreasing the photoperiod delayed flowering over natural day length (11-13h) in pomegranate. But the influence of light is considered to be caused by differences in the accumulation of metabolites (Roy and Bose, 1969). Whereas in case of litchi, low temperature coupled with low soil moisture is required during pre-flowering period to provide the physiological changes required for flower bud initiation/induction (Menzel, 1983). Rainless cool winter months are favourable for successful flowering in litchi. Similarly, in many of the perennial fruit crops temperature rather than photoperiod plays an important role in flower induction. Kozlowski et al. (1991) also reported that flowering in most woody perennials does not appear to be under photoperiodic control. Thus, the interaction effect of temperature and photoperiod on perennial fruit crops is less. However, this needs to be investigated further in detail. For example in Satsuma mandarin there was modulation of photoperiod requirement by the prevailing temperature. Likewise, studies are required in various fruit crops to assess the interaction of photoperiod and temperature in controlling the flowering.

Theories of endogenous control Three major theories attempt to explain the chemical control of the transition to flowering. 1.

Florigen concept

2. 3.

Nutrient diversion hypothesis The model of multi-factorial control

The florigen/anti-florigen concept In the 1930s, Chailakhyan postulated the existence of universal flowering hormone ‘florigen’ a hypothetical substrate, which is yet to be isolatea and characterized. He proposed that florigen consists of two

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components, gibberellin and anthesin, both of which are presumed to be required for flowering. Anthesin is again a hypothetical substance. According to this hypothesis, gibberellins are required for flowering of LDP’s and anthesin for flowering of SDP’s. The basic evidence for the existence of one or several transmissible leaf-generated promoters and inhibitors, ‘florigen’ and ‘antiflorigen’ comes essentially from grafting experiments. The florigen/antiflorigen concept proposes that the floral promoter and inhibitor are simple, specific and universal hormone that remain to be isolated and identified (Bernier. 1988). Studies in mango also indicated the existence of a floral stimulus (florigen), which is continuously synthesized in mango leaves during exposure to cool inductive temperature (Singh, 1959, 1961; Nunez-Elisea and Davenport, 1989; Davenport and NunezElisea, 1990; Davenport et al., 1995). Further, it is shown that the stimulus is graft transmissible (Singh, 1959; Kulkarni, 1991). Based on similar results concerning the inhibitor(s) from grafting experiments, Lang (1980) suggested that anti-florigen might also be identical in all photoperiodic plant types. Moment of these compounds is generally in the phloem along with assimilates (Bernier et al., 1981a) and their action often believed to be at the meristem. In plants shown to produce both florigen and anti-florigen, floral evocation would be caused when the balance of these two factors at the meristem is shifted in favour of florigen. In mango, simultaneous occurrence of flowering and non-flowering branches on the same tree and adjacent to each other and inability of immature shoots to flower along with the mature shoots, can be attributed to the balance between the promoter from the


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS mature leaves and inhibitor from the immature shoots. This explanation gains further strength from the finding that the inhibitory action can be removed by timely pruning of the immature shoot during the floral cycle. Inhibitory action can be simulated by exogenous application of gibberellins, whereas the long-term inhibitory action of endogenous gibberellins can be overcome with anti-gibberellins such as paclobutrazol. Emergence of pure panicles, mixed panicles i.e flowers + leaves and finally only leaves at the end of the floral cycle is a strong evidence for the cycle as well as for the interaction between the promoter and inhibitor.

The nutrient diversion hypothesis This hypothesis postulates that induction, whatever the nature of the involved factors, is a means of modifying the source/ sink relationships within the plant in such a way that the shoot apex receives a higher concentration of assimilates than under noninductive conditions. The inhibitory effect of non-induced leaves, positioned between induced leaves and the meristem. can be interpreted either by an inhibitor production (Schwabe, 1984) or on the basis that these leaves provide an alternate source of assimilates (Lang. 1965; Zeevaart et al., 1977). The concentration of sugar should be greater than that of nitrogenous compounds for flowering to take place. In mango except for cv. Baramasi it was found that higher starch reserve, total carbohydrates and C/N ratio in the shoots favoured flower initiation. Chacko and Ananthanarayana (1982) reported greater accumulation and metabolism of carbohydrates (particularly sucrose), protein and amino acids in the bark tissue at the time of flower initiation and an almost 4-fold enhancement in the specific activities of amylase and protease in mature (10-year old)

mango trees as compared with juvenile (3-year old) non-flowering trees. It was suggested that sugars play a regulatory role in floral induction, based on circumstantial evidence in mango (Mallik, 1951; Singh, 1960; Chacko and Ananthanarayanana, 1982; Rameshwar, 1989) and other species (Allsopp, 1965; Sachs, 1977; Mishra and Dhillon, 1978; Ramina et aL, 1979; Sachs et al., 1979; Bernier et al., 1981; Sachs and Hackett, 1983). The theory of photoassimilate diversion to the apical bud, presented by Sachs et al. (1979), is the basis for the carbohydrate-regulated flowering. Agents promoting assimilate supply to the meristem will appear as floral promoters. Some effects of exogenous PGRs on flowering may also sometimes be explained on the basis that they alter assimilate distribution in lower plants as in the case of cytokinin in Pharbitis nil (Ogawa and King, 1980). This theory has been supported by the evidence that many factors controlling flower initiation also influence photosynthesis and/or assimilate availability (Sachs and Hackett, 1983). Sucrose or glucose applications promote flowering in several photosensitive herbaceous plants, sometimes even in noninductive conditions (Bodson and Bernier, 1985). Further, evidence from photosensitive herbaceous plants suggests that there is an optimal timing input of assimilate supply to promote flower initiation. The sucrose level in the meristem of Sinapis increases before most other biochemical and cellular changes (Bernier, 1981; Bodson and Outlaw, 1985), ruling out the idea that this initial rise results from a higher demand of the activated meristem. It seems there is a greater sophistication in control than can be developed from mere assimilate diversion to receptor meristems. Thus in fruit trees, increased assimilate supply cannot be the sole signal for flower initiation.


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The model of multi-factorial control Floral evocation and morphogenesis can be achieved by the application of various chemicals including carbohydrates, PGR’s and PGR antagonists. Accordingly, Bernier et al. (1981a) proposed that several factors, promoters and inhibitors are involved in the control of flower initiation. This developmental step is believed to occur only when all factors are present in the apex at appropriate concentrations and times. While assimilates and PGRs are generally present in most plants, some of these compounds may be absent or present in sub or supra-optimal levels. Hence, each factor will not necessarily act in the same direction in all plants. Genetic variation, as well as past and present growing conditions, have resulted in different factors of the complex becoming the critical or limiting factors(s) in different species or in a given species in various environments. Work with exogenous application of PGRs is enormous and may not be possible to comprehend here.

Auxins Exogenous auxin can both inhibit and promote flower initiation in a number of fruit crops, and inhibition is far more widespread than promotion. In several plants, auxins are promotive at low doses and inhibitory at high doses. Inhibition at high doses might simply be related to a general growth inhibition (Jacobs, 1985) or an auxin-induced ethylene biosynthesis (Krekule et al., 1985). Studies invitro have confirmed that auxins do not simply oppose flowering: their presence in a certain concentration range is absolutely required if flowers are to be formed in various types of explants (Tran Thanh Van, 1980). In mango Chadha and Pal (1986), although concluded that auxin plays a role in

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floral induction, there is little evidence of this view. Chacko et al. (1972) reported a gradual increase in the levels of auxin-like substances extracted from stems of two mango cultivars from September to December when levels peaked. Because floral initiation occurs during this period (northern hemisphere), they concluded that a high level of auxin was necessary for floral initiation. In contrast, Chen (1987), using physico-chemical purification and detection methods, reported that the highest levels of indoleacetic acid (IAA) diffused from developing vegetative shoot tips. Auxin diffusion from similar shoot tips excised during bud rest, early panicle development and full flowering was approximately one quarter of that found during vegetative shoot development. Chacko et al. (1972) reported higher levels of extractable auxin-like compounds in shoots of ‘on’ year trees during autumn. Lal and Rani (1977) found no measurable differences in free IAA between shoot tips sampled in ‘on’ and ‘off years. The conflicting results reported here regarding the role of auxin in flowering of mango likely reflect inconsistencies in purification and analytical methodologies and use of field-grown trees from varying backgrounds and environments. The lack of consistent correlation between both endogenous levels and responses to exogenous auxin applications with mango flowering most likely reflects the lack of a direct role for this hormone in floral induction. Although decreasing auxin supply from these leaves as they age could explain periodic flushing, there are currently limited data to support this concept. Application of the synthetic auxin. naphthalene acetic acid (NAA), was reported to inhibit bud break of mango in Egypt (Bakr et al., 1981). However, Singh (1961); Singh and Singh (1963) and


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Pandey and Narwadkar (1984) observed no inhibition of bud break after application of auxin to mangoes. Singh and Singh (1973) reported that there was no lateral bud response following application of the auxintransport inhibitor, tri-idobenzoic acid (TIBA). Insufficient research has been conducted in this area to come to any conclusive statements regarding auxin inhibition of shoot initiation. It is also possible that other components. i.e. cytokinins from roots may interact with buds in regulating shoot initiation. Auxin may also be indirectly involved in stimulation of rootproduced cytokinin production through initiation of new root growth

Gibberellins GAs are the most extensively studied class of PGRs because they can elicit a flowering response in many LD and cold requiring rosette plants grown in noninductive conditions (Bemier et al.)., 1981a, b: Lang, 1965: Zeevaart, 1976). Although the critical role of GAs in the control of internode elongation is generally recognized (Zeevaart,1983), their participation in the control of flower initiation is a controversial matter (Bernier el al., 1981; Heild et al., 1987). In some rosette LDP, and in plants requiring cold treatment exogenous application of GAs, although promotes flowering they are found to be inhibitory of flower initiation in some perennial angiosperms, such as citrus, apple, the SDP strawberry, etc. (Bernier, 1988). There are several reasons for this apparent complexity. The important ones are (a) the effectiveness of various GAs is different in different species. In some plants the GA effect is enhanced or even only detectable, when GA is associated with an adjunct treatment, such as water stress or root pruning in Pinaceae (Pharis and King, 1985), (c) the timing of GA application was found to be

critical in many species (King of et al., 1987; Kinet et al., 1985), and (d) the GA response may be much influenced by the growing conditions, the effect being generally much greater in LD than in SD or at moderately low temperatures than at higher temperatures (Bernier et al.. 1981; Lang.1965). Gibberelic acid both native (endogenous) and applied (exogenous) has a clear inhibitive effect on flower bud induction and differentiation in citrus as in many other woody perennials (Badila et al., 1985; Britz et al., 1985). Inhibitors of GA synthesis. the growth retardants CCC and diaminozide enhance flower formation in lemons (Bodson and Remacle. 1987; Brulfert et al., 1985) in oranges (Chailakhyan et al., 1977) and in mangoes (Suryanarana and Rao,1977; Kurian and lyer,1993 a,b). Flowering in grape is a three step process (Srinivasan and Mullins, 1976): (a) formation of anlagen (undifferentiated primordia), (b) differentiation of inflorescence primordia, and (c) formation of flowers. It was shown that GA enhances the induction of the first step, leading later to differentiation of tendrils or inflorescences. It was suggested, however, that GA inhibits the second step leading from anlagen to inflorescences and thus promotes the development of vegetative tendrils. There have been numerous studies on the inhibitory effects of GA 3 on mango flowering (Singh, 1961; Kachru et al., 1972; Rajput and Singh, 1989; Nunez-Elisea and Davenport 1991; Osthuyse, 1991). Although GA3 inhibits flowering in mango. it is not clear whether it causes buds to develop vegetatively under floral-inductive conditions. Kachru et al. (1972) first reported a delay in flowering, which was quantitatively correlated with the concentration of GA3 applied in lanolin to apical buds. Bud break of resting buds treated


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS with the highest levels of GA3 was delayed until March and grew vegetatively, whereas resting buds treated with lower concentrations initiated growth earlier (during the cool, inductive period) and produced reproductive shoots. Similar results were observed by Tomer (1984). GA 3 did not inhibit induction of flowering, as evidenced by the production of axillary panicles, so long as cool, inductive temperatures were present during axillary shoot initiation. Late initiating buds which grew during warm, spring temperatures formed vegetative shoots. Multiple applications, even at lower rates, are more effective than a single application (Turnbull et al., 1996). Gibberellic acid treatment of mangoes has been recommended in the Canary Islands to delay flowering until after the danger of winter frost has passed (Galan-Sauco, 1990). In the subtropics of Australia, it is used to prevent flowering in newly planted trees during the spring so that the full growing period can be utilized for vegetative growth, thereby hastening orchard establishment (Davenport and NunezElisea,1997). Response to GA3 varies among cultivars, growing conditions and timing of application (Tomer, 1984; Osthuyse, 1995; Turnbull et al.. 1996.). For example, experiments were conducted in which trees planted at two different locations were simultaneously treated with the same concentration of GA3. Results showed a significantly greater response at one location compared to the other (Tomer, 1984; Turnbull et al., 1996). Plant response to GA3 also varies from year to year so that concentrations that are effective in delaying flowering in one year may not have an effect in the following season (Tomer, 1984; Turnbull et al., 1996). Conversely, it may be so effective that it delays flowering beyond the inductive window, resulting in a vegetative

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flush (Kachru et al., 1971, 1972; Davenport and Nunez-Elisea,1997). The variable response to applied GAs may be directly related to endogenous levels of the active gibberellin in buds at the time of application, to differential sensitivity of buds to GA3, depending on their position (apical versus axillary) or age (Nunez-Elisea and Davenport, 1991a). Efficacy is related to the timing of application, i.e., application immediately prior to normal shoot initiation appears to be the most effective (Davenport, 1993). The reports of endogenous gibberellins in young tissues, especially in buds, are difficult to interpret with respect to a regulatory role in bud break of flowering. Problems include sampling of tissues other than apical buds, i.e. whole shoots (Tongumpai et al., 1991), leaves (Poulos and Shanmugavelu, 1989; Sivagami et al., 1989) and xylem sap (Chen, 1987). Chen (1987) reported the highest levels of gibberellins in mango xylem sap during leaf differentiation and lower concentrations during rest, panicle emergence and full flowering. Clearly, more extensive work is needed to elucidate the role of gibberellins and other phytohormones in shoot initiation and induction. More importantly, they must also relate the endogenous levels in buds and leaves with physiological events occurring in individual shoots.

Cytokinins Exogenous cytokinins cause promotion and inhibition of flower initiation in a variety of species, although promotive effects are much more frequent than inhibitory ones (Bernier et al., 1981a,b). Cytokinin is an absolute requirement for flowering of explants from adult Passiflora plants, but juvenile explants do not flower even in its presence (Scorza and Janick, 1980).


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Chen (1987) described precocious bud break and flowering of mango shoots in response to an early October application of 100 ppm 6-Benzylaminopurine (BA). Full flowering was observed one month following application compared with three months later on non treated trees. Similar results were reported by Nunez-Elisea et al. (1990) using the synthetic cytokinin-like thiadiazuron. In mango. the lowest levels of putative transzeatin and its riboside were translocated from roots during the vegetative growth and resting stages, whereas the highest levels were measured during the early flowering and full bloom stages. In contrast, Paulas and Shanmugavelu (1989) observed no significant difference in cytokinin levels of the fourth and fifth leaves during resting bud and flowering stages. There was a substantial reduction in several cytokinins in mango leaves in the limp red leaf stage from trees treated with paclobutrazol. Concurrent with this response was suppression of bud initiation and reduced internode lengths for two years. In addition to repression of canopy growth through inhibition of gibberellin synthesis (Griggs et al., 1991). This class of compounds also causes reduction in feeder root development and formation of thick, blunt roots in numerous species (Bausher and Yelenosky, 1987; Burrows et al., 1992: Yelenosky et al., 1993), which possibly results in reduced cytokinin translocation to buds. The role of cytokinins in flowering is still unresolved. The few available reports draw conflicting conclusions, primarily due to sampling of different organs at noncomparable times or conditions. The elevated cytokinin levels found prior to and during flowering and the flowering response to applied BA led to the conclusion that cytokinins are involved in flowering of mango

(Chen, 1987), however, such a response can also be explained if cytokinins are involved in stimulation of bud break, not necessarily flowering per se.

Ethylene Smudging, i.e. continuous exposure of trees to smoke from burning leaves, has been utilized to stimulate flowering of mango in the Philippines. Only branches which have attained sufficient age or ‘ripeness to flower’ respond to smudging (Bueno and Valmayor 1974). Rodriguez (1932), investigating smokeinduced flowering of pineapple, first proposed that ethylene, generated by burning material, may stimulate flowering. Numerous investigations have since shown ethephon to be an effective floral promoter of some mango cultivars under specific conditions found in the low-latitude tropics (Das et al., 1989). Indirect support also comes from reports that KNO3 stimulated flowering of mango is mediated by increased levels of endogenous ethylene (Lopez et al., 1984). MosquedaVazquez and Avila-Resendiz (1985) reported that the efficacy of KNO3 was negated by CoCl2 and AgNO3 compounds which inhibit the synthesis and action of ethylene respectively when sprayed 1-4 h after KNO3. Davenport and Nunez-Elisea (1991 and 1997) reported elevated ethylene production in mango shoots in response to ethephon sprays without an accompanying floral response. The role of ethylene on flowering is till unresolved. Ethylene may simply stimulate shoot initiation through its ability to inhibit auxin transport in leaves and stems (Morgan and Gausman, 1966; Beyer and Morgan, 1971; Riov and Goren, 1979, 1980).

Abscisic acid Exogenous ABA is inhibitory in several SDPS’ and LDPs grown in inductive


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS conditions, and endogenous ABA in several photoperiodic species do not bear consistent relationships with day length. Bernier (1988), however, indicated that ABA does not appear as a major detriment in the floral transition, except perhaps in some species. He further suggested that ABA would be a general “background” inhibitor, produced more or less constantly irrespective of day length, its effect being overcome in inductive conditions by increased amounts of promoters.

induction of early flowering with greater intensity (Rajkumar et al., 2007 a,b,c); Ashok Kumar and Reddy (2006, a, b and 2008) on 5 varieties of mango, and Suresh kumar et al (2003 a, b) on Baneshan

There are reports from Andhra Pradesh farmers that flooding the field from July to November produced profuse and early flowering in mango. Under submerged conditions, increase in ABA synthesis was reported in several plant species (Hiron and Wright. 1973; Sivakumaran and Hall, 1978; Jackson and Hall, 1987), though ABA levels in mango were not estimated under anoxic conditions. It seems that ABA has got a role to play in flower induction during waterlogging. Conversely, it may be the increased ethylene production and translocation of food material to the shoots which created ideal conditions for flower induction.

Cultural Practices

Other chemical compounds A range of exogenous unrelated chemicals may affect flowering. Prominent among them are phenolics (Kandeler, 1985; Shinozaki et al., 1982), oligosaccharins (Tran Thanh Van, 1980), polyamines. and their conjugates with hydroxy cinnamic acids (Martin-Tanguy, 1985). Endogenous levels of polyamines and calcium were also found to change in relation to flowering. For the induction of flowering in mango H 3PO4, KH2PO4, K2HPO4, and KNO3 at 0.5% and 1.0 % either alone or in conjunction with paclobutrazol were used on mango cv Baneshan. It was found that H3PO4 @ 0.5% and KH2PO4 at 1% were superior in the

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Suresh Kumar et al., (2003 a, b), Ashok kumar and Reddy (2007) used salicylic acid and calcium nitrate for transduction of flowering stimulus with significant effect on mango cv Baneshan.

Besides environmental factors, some of the cultural practices like canopy management (pruning). moisture stress (with holding of irrigation), root pruning. deblossoming, defoliation and use of chemicals were found to be effective in regulating the flowering in different fruit crops.

Moisture stress (withholding of irrigation) The principle behind suspending the vegetative growth. or withholding irrigation is to provide rest to the plant, which results in accumulation of food in large quantity for enhancing flowering in the next season. In the absence of cool temperature (20 µmol/L) they, too, grew into shoots. The available information on the developmental pathways of anlagen have been combined and presented in diagrammatic form (Fig. 5). For purposes of description, anlagen which have produced a bract and two branches (inner arm and outer arm) are referred to as tendril primordia (Fig. 3, Stage 4).

The physiological basis of flower formation in the grapevine Flowering in plants is believed by many workers to be induced by a single substance, ‘florigen”, but others have suggested that the floral stimulus consists of two complementary components. According to Thimann, flowering is merely a developmental process under the control of the interplay of hormones, and Zeevaart has proposed that the requirement for a specific balance of hormones for flower formation is more readily applicable to woody perennials than to herbaceous annual plants. In summarizing 40 years of research on the ‘hormonal concept of flowering’ Chailakhyan concluded that the main function of gibberellins is to control the formation and growth of floral stems or inflorescence axes. The responses of grapevines to exogenous gibberellins and chlormequat are consistent with this view. Gibberellins are involved in the initiation of

Fig. 5. Developmental pathways of the Anlage


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS anlagen (formation of inflorescence axes) and are necessary for the growth of inflorescence axes, i.e., the extension growth of the twobranched anlagen (Stage 4). According to Carr two different inductive stimuli could be involved in the flowering of plants. One is the “primary induction” which is “Contagiously propagated” and the other is a “secondary induction” which occurs locally. Initiation of anlagen and tendril formation could be regarded as the “primary induction”, a condition which is permanent in grape cultivars which are perpetuated by vegetative propagation. The “secondary stimulus”, which is required annually for the direction of anlagen into the pathway of inflorescence development, is probably cytokinin. In nature, grapevines produce numerous anlagen but most grow into tendrils and only a few anlagen give rise to inflorescences. This suggests that gibberellin is readily available for initiation of Anlagen and for elongation of tendrils and that inflorescence formation is normally limited by

Fig. 6. A hypothetical scheme for the hormonal control of Anlage, tendril and inflorescence formation in the grapevine (Vitis vinifera L.)

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the cytokinin supply. The finding that repeated applications of cytokinin are required for transformation of tendrils into inflorescences suggests that a continuous influx of endogenous cytokinins into anlagen is needed for flower formation in the grapevine. A hypothetical scheme for the hormonal control of anlage, tendril and inflorescence formation in the grapevine is presented in Fig. 6. The postulated inhibitors in this scheme are endogenous compounds which mimic the effects of the synthetic growth retardant, chlormequat, i.e., inhibition of gibberellin biosynthesis and promotion of cytokinin biosynthesis.

CONCLUSION The flowering of Vitis vinifera spreads over two seasons. The formation of inflorescences and flowers in the grapevine involves three well-defined stages: 1. Formation of anlagen (Singular anlage). 2. Formation of inflorescence primordial. 3. Formation of flowers. Scanning electron microscope (SEM) is an ideal instrument for investigations of bud structure because it enables observations to be made at high magnification and with great depth of focus. The complex morphology of the grapevine shoot system and the origin of inflorescences have been clarified recently by scanning electron microscopy. In development of flowering include various stages (0 to 11) that show the changes in shape of organs at the time of development of flowering in grapevine. Different biochemical changes occurred in apices during the formation of Inflorescence Primordia. Hormonal aspects of flowering include regulation of analgen and tendril formation and differentiation of inflorescences. GA3 and Cytokinin are major hormones that regulate the flowering of grapes.



ENVIRONMENT DETERMINES SUCCESS OF NATURAL AND INDUCED OFF-SEASON FLOWERING IN MANGO Shailendra Rajan, V.K. Singh, Y.T.N. Reddy1, K.K. Upreti1, M.M. Burondkar2, A. Bhagwan3, R. Kennedy4, Pooja Saxena, Sakkthi Subramaniyam4 and S.R. Shivu Prasad1 Central Institute for Subtropical Horticulture, Rehmankhera, Lucknow. 1 Indian Institute of Horticultural Research, Bangalore. 2 Dr. Balasaheb Sawant Konkan Krishi Vidyapeeth, Dapoli, Maharashtra. 3 Fruit Research Station, Sangareddy- Medak, Andhra Pradesh. 4 Horticultural Research Station, Pechiparai, Kanyakumari, Tamil Nadu *Based on the findings of NAIP Subproject “Understanding the mechanism of off-season flowering and fruiting in mango under different environmental conditions”

INTRODUCTION Commerical off-season flower induction through chemicals, use of wide agroecological diversity and varietal wealth available across the country are long felt unmet needs for extending the mango season in India. Offseason cropping in mango is a natural and unique feature of certain tracts of Tamil Nadu. Besides the normal crop that matures from April to May, the trees of certain varieties also produce off-season crop from DecemberJanuary. The unusual phenomenon of regular off-season crop at Kanyakumari, which is the Southern most tip of Indian peninsula, is well known (Ram and Rajan, 2003; Kennedy et al., 2009). Survey conducted for commercial exploitation of off-season mango production in southern districts of Tamil Nadu indicated that off- season fruits of mango were produced from November to February besides the main crop and was a natural phenomenon in peninsular India that fetched higher price to growers than the main crop. With an increased understanding of agroecological dependence of varietal responses, effectiveness of chemicals for early induction of flowering and identification of nontraditional areas suitable for off-season mango production can increase area under commercial off-season mango production.

Information available on this aspect indicated that the off-season bearing, though a genetical character is also induced by favourable climatic conditions exhibiting unusual regular off-season crop at Kanyakumari and can be attributed to specific niche area. The bioclimatic factors responsible for this phenomernon were studied for utilizing the available diversity in agroecologies. For off-season induction through chemicals, all cultivars are not equaly responsive. Understanding of bioclimatic factors associated with off-season flowering is important to ascertain climatic requirements for the successful off-season flower induction through chemicals. Studies were conducted for elucidation of flowering mechanism vis-àvis climatic factors responsible for multiple and single flowering in mango for shifting maturity period with Environment x Management understanding. Understanding off-season flowering induced by chemicals like paclobutrazol and KNO3 is important for commercial exploitation of agro-ecology. Standardization of suitable doses and time of application of PBZ specific agroecological condition provides basis for developing package of practices for off-season production. This also helps in the modification of chemical treatments for off-season flower induction in relation with flowering negating factors like


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS rains and abnormal temperature. Development of area specific treatment schedules for flower inducing chemicals in geographical areas where higher benefits are achieved by the farmers with early crop production is directly linked with early flower induction.

Natural off-season flowering Off-season flowering phenological studies conducted at different parts of the country delineated areas of natural off-season flowering and fruiting and the phenomenon was prevalent in several parts of Tamilnadu and in limited areas of Andhra Pradesh. Neelum, Kalepad and Totapuri produce profuse flowering and fruiting in main and off-season at Kanyakumari. Off-season fruits of Totapuri and Kalepad are early and Neelum is comparatively late. Fruits are available for more than a month (Kennedy et al., 2009). At Chitoor, natural off-season flowering and fruiting in Rumani, Totapuri and Neelum was prevalent. Single cropping varieties, Neelum and Totapuri produced multiple crops at Kanyakumari and Chitoor, whereas at Dapoli, Bangalore, Sangareddy and Lucknow multiple cropping was not prevalent in these commercial varieties. Survey of mango orchards in different mango growing areas was conducted by consortia partners for delineating the areas with natural off-season flowering in commenrcial varieties. In Tamilnadu, offseason flowering was more prevalent in districts viz., Bhutapandi, Dindigul, Krishnagiri, Kuzhittura, Madurantakam, Nagercoil, Nattam, Periyakulam, Rajapalaiyam, Sattur, Sengottai, Takkalai, Tenkasi; and intermediate in districts viz., Ambasamudram, Attur, Denkanikota, Dharmapuri, Harur, Namakkal, Omalur, Palakkodu, Pennagaram, Perambalur,

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Ramanathapuram, Rasipuram, Salem, Sirkazhi, Tirunelveli, Turaiyur, however, low in Alangudi, Arantangi, Ariyalur, Aruppukottai, Karur, Kulattur, Kulittalai, Kumbakonam, Lalgudi, Mannargudi, Mayuram, Mudukulattur, Nagappattinam, Papanasam, Paramakkudi, Pattukkottai, Sankarankovil, Sankari, Tarangambadi, Thanjavur, Tiruchchirappalli, Tirumayam, Tirutturaippundi, Tiruvidaimarudur, Uttangarai and Uttiramerur districts (Kennedy, 2009). Off-season fruiting was recorded in Chitoor district (Andhra Pradesh) in Puttur and Sathivelu mandals. Studies in commercially grown cultivars in North and South Canara, Chikaballapur, Coorg, Kolar, Mysore and Ramanagar districts of Karnataka for occurrence of off-season flowering showed sporadic and sparse off-season flowering in the varieties such as Totapuri, Punasa, Niranjan and Royal Special. However, the fruit set was negligible during off-season in these varieties. Niche area for off-season production has been identified in Tamilnadu and Andhra Pradesh and in most of the Northern parts of the country (subtropical condition) multiple flowering in commercial varieties is rare and can not be commercialized even after early flower induction (Rajan et al., 2014).

Importance of bioclimatic factors in natural off season flowering Characterization of climatic condition for various mango varieties has been reported by Rajan (2008, 2013). Since, occurrence of natural off-season mango flowering phenology is sensitive to climatic conditions, an ecological niche modeling tool Maxent was used for studying the contribution of bioclimatic variables associated with suitable area for natural off-season flowering in commercial varieties. Among 19 bioclimatic


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS variables, annual mean temperature (40.4%), mean monthly temperature range (18.3%), min. temperature of coldest month (8.9%), annual precipitation (7.5%) and precipitation of wettest quarter (6.6%) had greater contribution in explaining variability in locations with regard to multiple flowering. Importance of mean monthly range in multiple flowering indicates the absence of extreme temperature regimes. The high value of this bioclimatic variable indicates low temperature in winters and high during summers and under subtropics its value may be high. These bioclimatic variables determine the phenological phases in mango and determine multiple flowering and synchrony in bloom. Suitable areas predicted for natural off-season flowering have been mapped (Fig. 1). The bioclimatic variables may become limiting factor for off-season flowering and independently only one factor may not be associated with the induction of off-season flowering (Rajan et al., 2014).

Off-season flower induction through chemicals Results revealed that advancement in flowering and harvest can be successfully achieved for commercial mango production with PBZ as soil application in several parts of the country whereas, early induction of flower in subtropics is possible but of no commercial value due to flower initiation when the temperature regimes are not suitable for panicle and fruit development (Burondkar, 2013; Bhagwan, et al., 2013, Swamy, 2012, Upreti, et al., 2013). At places, where PBZ can successfully induce early crop require precise cultural operations to backup this advanced harvesting of fruits and warrants induction of vegetative shoots for their sustainable conversion into flowering shoots to bear early crop regularly. This may be a part of

production technology for varieties like Alphonso.

Variable response of PBZ under different environmental conditions Early mango crop fetches better price than the main season harvest. Thus, paclobutrazol was used to demonstrate induction of early harvest at different geographical locations and varying responses were observed. The study has indicated that advancement of flowering and harvesting can be successfully achieved in southern states (Tamilnadu, Karnataka and Andhra Pradesh) and Konkan region, whereas, in Northern parts (Lucknow) of the country, induction of early flowering could not produce early crop harvest. The importance of early flowering has high commercial value under Konkan condition because of fetching premium price by early season harvested Alphonso, when produced before March. The lateritic soil condition and early paclobutrazol application can successfully produce early commercial Alphonso harvest. Paclobutrazol response for early harvest varied with the ecologies viz., Sangareddy-AP (13 weeks), Warangal-AP (7 weeks), Bangalore (4 weeks), Lucknow (0 week), Kanyakumari (9 weeks), DeogadMaharashtra (8 weeks), KotawadeMaharashtra (13 weeks). At Lucknow, though early flower but burst (Nov-Dec) was induced by PBZ application but early harvest could not be achieved because most of the panicle did not set fruits due to low night temperature of damaged during panicle developmental stage. Panicles emerging during late December were damaged due to cold injury. This clearly indicates that ecological conditions during panicle development play an important role for successful early harvest. An analysis of the bioclimatic factors indicated that


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS minimum temperature of winter months is most important limiting factor responsible for the failure of crop in early emerging panicles and can be used for mapping suitable areas for advancing harvest through PBZ application (Burondkar et al., 2013; Rajan et al., 2014). The analysis of off-season flowering– environment relationship was a central issue in this study. Presence-only modeling based on the known off-season flowering occurrences data together with predictor variables (bioclimatic). Nineteen bioclimatic variables with 30 seconds spatial resolution were downloaded from World-Clim dataset (www.worldclim.org), and used to find out the most influential variables associated with distribution of natural off-season flowering suitable areas. For such modeling, Maximum Entropy or Maxent was used because it performs extremely well in predicting occurrences in relation to other common approaches and it is also designed to integrate with GIS software. The analysis aimed on finding the largest spread (maximum entropy) in a geographic dataset of off-season flowering presence in relation to a set of environmental variables. Environmental layers data were used as raster data (ESRI ASCII grid format), to produce predictive maps of off-season flowering occurrences. Image files and as raster output was further manipulated in GIS software (Rajan et al., 2014). Natural off-season flowering areas with high probability was indicated in Kanyakumari, Theni, Dharmapuri, Thoothukkudi, Dindigul, Kancheepuram, Namakkal, Ramanathapuram, Salem, Virudhunagar, Tirunelveli, Pudukottai, Tiruchirapalli, Thiruvallur districts of Tamilnadu. Andhra Pradesh is another state exhibiting high possibility of off-season mango production particularly Chitoor, Prakasam and Nellore districts. 102

Areas suitable for off-season production and extended period of availability Success of off-season mango production is very much influenced by the climatic conditions, whether it is natural through suitable varieties and specific areas or through PBZ application time manipulation. Probability mapping for natural off-season production (Fig. 2) and extended period of availability through induction of flowering have indicated the role of bioclimatic factors. Higher annual temperature range and mean temperature of the coldest month which indicate that the temperature regime does not allow secondary vegetative and flowering mesostages at proper time when these mesostages can get suitable environment. In areas, where minimum temperature of the coldest month is 34.4°C) and low relative humidity of less than 20% during afternoon causes drying of flower resulting in yield reduction.

Flowering period and phases In general, seedling cashew plant starts flowering in three to five years while grafted trees come to flowering within 3 years. The

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flowering normally starts at the end of monsoon after the emergence of new growth flush, but its timing and duration are strongly influenced by temperature. Flowers are produced at the end of the new shoots. Thus, flowers and fruit are borne on the outer extremity of the canopy. Flower bud emergence in cashew initiates by the middle of September and continue until the end of February, the main season being October-November (Damodaran et al., 1965). Nambiar (1977) reported that the flowering season in cashew varies with country depending upon its altitude. The flowering season is from June to November in Tanzania with peak in AugustSeptember (Northwood, 1966). In coastal region and transitional zones of northeastern brazil (around 6 ÚS and up to 100m altitude), flowering lasts 4-6 months in the common type (from July/August to December/January) and 6-8 months (June/July to January/ February) in the precocious dwarf type (Barros et al., 1984; Barros 1988; Freitas 1994). The flowering period is from December to March with a peak in January-February in Central America (El Salvador) and West Africa. Two flowering periods were reported in Kenya, one from September to November and second from December to January (Agnoloni and Guiliani, 1977). Within India, the variation for flowering time was observed across different regions. In the west coast the peak flowering is in early January and the peak harvest is in early April (Rao, 1956) whereas in the east coast, the peak flowering is from mid January to mid February and the crop is harvested in the end of April (Dasarathi, 1958). Cashew shows the trend of late flowering and fruiting at higher elevation irrespective of latitude (Nambiar, 1977). For instance cashew flowering in Northeastern states gets delayed by 2-3 months and flowering is seen during April-June compare to other cashew growing regions of India


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS where the flowering period is November/ December to February/March. This is mainly due to reduction in temperature at higher altitudes. Generally flowering occurs in two or three typical phases and that appears in the intermediate stage is considered as the productive phase. Three distinct phases of flowering are observed in cashew (Pavithran and Ravindranathan, 1974). They are (i) the first male phase with 19-100 per cent male flowers, (ii) the mixed phase with 0 to 60 per cent male and 0 to 20 per cent hermaphrodite flowers and (iii) the second male phase with 0 to 6.7 per cent male flowers. Many other cashew workers have also found that flowers produced early in a panicle are by and large male. The duration of these flowering phases varies with genotype. The mean duration of flowering observed was 85.2 days in which the duration of first male phase was 2.4 days, mixed phase 69.4 days and second male phase 13 days. Based on the season of flowering cashew genotypes are classified as early (NovDec), mid (Dec-Jan) and late (Jan-Feb) flowering types.

Varietal response to flowering and fruiting Based on flowering and fruiting time, the cashew varieties have been categorized into three major groups i.e. i) early, ii) mid and iii) late types. The early flowering types will have emergence of new flushes immediately

after 10-15 days dry spell with bright sun shine in October-November. Those varieties may not require much soil moisture stress or vernelisation effect for flower bud initiation. A few varieties in this group get prolonged flowering if the rainfall continues after the flowering. Similarly, if prolonged rainfall during the flowering season can delay the flowering by 15-30 days in this group of varieties. Whereas, the mid season flowering types require more sun shine hours and a little chilling but may not require complete soil moisture stress for fruit bud differentiation and subsequent flowering. The mid season flowering varieties produce regular flowering (November-January) and fruiting in the season. However, depending on soil fertility and management practices, the flowering can be modified for this group of varieties. The late season varieties require soil moisture stress, low temperature and bright sunshine hours for initiation of flower buds and subsequent flowering in the month of January to March. However, early withdrawal of monsoon in season may advance the flowering in this group. The rain during November to December led to ordinate delay in flowering phase in late varieties. It can be inferred that cashew require relatively dry atmosphere with mild winter for better flowering. The major cashew varieties in above three groups are as below:

Cashew varieties based on flowering and fruiting season under West Coast region. Names of the varieties Early types NRCC Sel-2 Vengurla-1 Madakkathara-1 Ullal-4 Kanaka

Period of peak flowering

Flowering duration (months)

Peak fruiting

Oct – Nov Oct – Nov Oct – Nov Oct - Nov Oct – Nov

2-3 2 2 2 2-3

Feb – Mar Jan – Feb Jan – Feb Jan – Feb Jan – Mar


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Names of the varieties Mid season varieties Vengurla-4 Vengurla-3 Vengurla-7 Ullal-2 Ullal-3 VRI-3 K-22-1 Priyanka Dhana Late varieties Ullal-1 Bhaskara Madakkathara-2

Period of peak flowering

Flowering duration (months)

Peak fruiting

Nov – Dec Nov – Dec Nov – Dec Dec – Jan Nov – Dec Oct – Nov Nov – Dec Nov – Dec Dec – Jan

2-3 3-4 3-5 2-3 3-4 4-5 3-4 3-4 3-5

Jan – Mar Jan – Mar Feb – May Feb – Apr Jan – Apr Jan – May Jan – Apr Jan – Apr Jan – May

Dec – Feb Dec – Feb Jan – Feb

3-4 3-4 2-3

Mar – June Feb – May Mar - May

Floral biology The cashew flowers are small, white or light green at the time of opening, later turn to pink. Two kinds of flowers viz. hermaphrodite (bisexual/perfect) and male (staminate) are present in the same panicle. The perfect flowers are larger than staminate flowers (Damodaran et al., 1965). The flowers are pentamerous. The calyx is green and oval with five free sepals. The corolla is linear to lanceolate in shape, white or creamy white at the time of opening with five free petals. The external surface of sepals and petals is pubescent with simple hairs. The androecium consists of one fully developed stamen and 79 staminodes. The developed stamen has pink anther. The anther is basifixed, bi-lobed, dehisces through a slit between the two pollen sacs of each lobe. The staminodes possess short filaments and are hidden in the lower half of the open flower. The developed in the hermaphrodite flower has only short filament and its anther is far below the level of stigma. The pistil is dorsiventral; ovary is superior, reniform and monocarpellate. The style is long and slender, springs from distal margin of the

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ovary, tapering towards the end with slightly expanded stigma. The ovary is rudimentary in male flowers. It was suggested that the staminate flowers are derived from the ancestral hermaphrodite flowers by gradual reduction and loss of function of the gynoecium (Ascenso and Mota, 1972b). The anthesis is in between 9 am and 2 pm in India and hermaphrodite flowers open mostly between 9 and 11 am though some flowers open beyond this time. Staminate flowers were found to open very early in the morning and continue till about 2 pm. Over 80 per cent of the perfect flowers open between 10 am and 12 Noon. The peak period of dehiscence of anthers was from 9.30 to 11.30 am and the rate of dehiscence was slightly higher on the sunny side of the tree as compared to that on the shady side. The viability of pollen is usually high and it was 94 per cent in types studied and the stigma becomes receptive one day prior to anthesis and its receptivity stays for two days (Damodaran et al., 1966; Eradasappa et al., 2012 unpublished). In vitro germination of pollen was reported by Subbaiah et al. (1982)


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS and also germination of pollen grains up to 50 per cent has been observed on high sucrose medium at Directorate of Cashew Research, Puttur. The majority of male flowers open between 7 and 9 am while majority of bisexual flowers open between 8 am and 12 noon in the west coast region of India characterized by heavy rainfall and humid climate. Stigma is receptive throughout the day after anthesis of the flower (Rao and Hassan, 1957). The cashew produces scented flowers which attract pollinating insects mainly bees (Apis mellifera). The pollen grains of cashew are not easily carried by the wind (Paulino, 1992; Freitas, 1994; Freitas and Paxton, 1996). Reddi (1991) observed in the 20 inflorescences left open to insects bore 89 fruits, whereas those protected with butter paper bags (exclude insects and wind) or mosquito nets (exclude insects and allow wind) had no fruits formed. It was also confirmed the study that cashew pollen grains were sticky and were not released into the atmosphere as no pollen grains were trapped by the air sampler or by the stigmas of flowers left open to the wind. Hence, it was proved that the possibility of the wind acting as a pollinating agent was ruled out. It was reported that only pollens from large stamens of both staminate and perfect flowers are viable and play role in the reproduction. Staminodes (smaller stamens) do not produce viable pollen grains. The cashew is chiefly allogamous tree species because of its reproductive system. However, due to coincident flowering of the two kinds of flowers on the same tree and same panicle also favours self-pollination. Self–incompatibility hitherto was not reported among the species of the genus.

Inflorescence: flowers and sex ratio The inflorescence of cashew is called terminal panicle which bears both male

(staminate) and hermaphrodite (perfect) flowers in the same panicle. For this reason cashew is considered as andromonoecious species. The inflorescence may be conical, pyramidal or irregular in shape. Number of panicles per plant, flowers per panicle and distribution of male and hermaphrodite flowers (sex ratio) in each panicle vary significantly. Morada (1941) counted 3 to 11 branches in each panicle, depending on the vigor of the tree, with 40 to 100 individual flowers on each panicle branch or 120 to 1100 flowers with 90-99 per cent staminate flowers in one panicle. Rao and Hassan (1957) reported that 96 per cent of the flowers are staminate in a panicle; Bigger (1960) observed a ratio of 6:1 staminate to perfect flowers; Damodaran et al. (1966) reported perfect flowers from as low as 0.45 per cent to 24.9 per cent. The variations in these traits are observed due to genetic and environmental factors. Flowers are produced in gradual manner and hence each panicle may stay up to three months giving continuous fruits. The duration of flowering phase depends on the genotype and environmental conditions.

Fruit setting The cashew produces abundant flowers but only less than 10 per cent of which are hermaphrodite, about 85 per cent of the hermaphrodite flowers are fertilized under standard conditions and only 4-6 per cent of them reach maturity to give fruits, the remaining shed away at different stages of development. The fruit drop in cashew during the early stages of development is attributed to physiological reasons (Nothwood, 1966). Insects attack also plays an important role in immature fruit drop (Pillay and Pillai, 1975). Reddi (1987) reported that cashew plants can permit about 27 per cent of their well pollinated flowers to develop into fruits. But in nature only 10.5 per cent yield is possible


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS because of under-pollination and this was substantiated by stigmatic- pollen load analysis data. In nature about 25-72 per cent of the stigmas were found unpollinated due to limitation of pollinators leading to lower than potential yields. The yield increase of 157.8 per cent is possible if the flowers receive adequate pollen. Earlier workers also suggested that pollination in nature is inadequate (Rao, 1974; Kumaran et al., 1976a). Fruit set through bagging of panicles in two varieties of cashew, Bhaskara and Ullal-3 was observed at the Directorate of Cashew Research, Puttur, Karanataka, India indicating the possibility of self-fertilization to a limited extent. After pollination, the fruit takes 6 to 8 weeks to develop. The nut develops first and the apple fills out during the last fortnight before nut drop occurs. The nut drop continues for 6 to 8 weeks.

Apple and nut development The complete cashew fruit consists of two distinct portion i.e. lower portion (nut) and upper peduncle (pseudo fruit). The nut is grey coloured, kidney shaped achene (a dry one-seeded indehiscent fruit with the seed distinct from the fruit wall) consisting of epicarp, mesocarp, endocarp and a kernel wrapped by a peel (testa). The epicarp is smooth, coriaceous and grey or grayish green and it forms the epidermis. The mesocarp is thickest of three layers, spongy and features alveoli containing the cashew nut shell liquid (CNSL). The CNSL is sticky, resinous corrosive oil rich in phenolic compounds. The endocarp is hard and is formed of a compact mass of schlerenchymatous cells. These three layers form the thick shell, i.e., the pericarp which forms 45 to 50 per cent of the nut. The kernel, the edible part of nut is formed by two cotyledons forms 20 to 22 per cent of nut. The kernel is covered by a brown membranous

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testa (peel), which forms about 5 per cent of the weight of the nut. The peeling is one of the most important problems in the industrial processing of cashew nuts as it is very difficult to remove in as much as 20 per cent of the seeds. The nut size varies from 3 to 12g and the shelling percentage varies from 15-30 per cent. Peixoto (1960) mentioned nuts of 30g in Brazil. Proper filling and shelling percentage have direct impact on kernel recovery. Sometimes, thick nuts have thick shell instead of large kernels. Large nuts may also have cavities between kernel and shell and between two cotyledons. The cashew apple is a false fruit and it develops from the hypertrophied pedicel. The ratio between nut and apple is generally 1:8. The young apple is green or purple or purple green turning to green later. The apple becomes red or yellow or in between colour on ripening. When apple is ripened, it is an index that nut is able to harvest. The ripe apple has peculiar smell. The ripe apple contains about 60-85 per cent juice, which has about 10 per cent mostly invert sugar and 234-371 mg 100g-1 vitamin C. The apple is fleshy and juicy and varies in size, weight, shape, texture, colour and taste. The nut grows slowly in the initial stages and then accelerates to attain its maximum size by 28 days. In subsequent days, the nut size reduces as it matures and becomes visibly smaller (Damodaran et al., 1966). The cashew apple, in contrast, reaches its maximum size when it matures without any further change in size.

REFERENCES Agnoloni, M. and Giuliani, F. 1977. Cashew cultivation. Library of Tropical Agriculture, Ministry of Foreign Affairs. Institute Agronomic Per L’ Olhemare. p.168. Aliyu, O.M. and Awopetu, J.A. 2007. Chromosome studies in Cashew


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS (Anacardium occidentale L.). African Journal of Biotechnology, 6(2):131-136. Ascenso, J.C. and Mota, M.I. 1972b. Phylogenetic derivation of the cashew flower. Boletimda Sociedade Broteriana, 42:253-257. Baily, L.H. 1949. Mannual of cultivated plants. Pub.: MacMillan Co., New York (USA). Barros, L.M. 1991. Caracterizacao morfologica e isoenzymatica do cajueiro (Anacardium occidentale L.) Tipos comum e anao precoce, por meio de tecnicas multivariadas. Ph.D. Thesis, USP-ESALQ. p.256. Barros, L.M. 1988. Melhoramento. In: A Cultura do Cajueiro no Nordeste do Brazil (ed. Lima, VPMS), pp.321-355. BNB/ETENE, Fortaleza. Barros, L.M., Araujo, F.E., Almeida, J.I.L. and Teixeira, L.M.S. 1984. A cultura do cajueiro anaõ (Dwarf cashew crop). EPACE Document 2. Fortaleza, Ceara´, Brazil. Barros, L.M.1995. Botanica, origem e distribuicao geografica. In: Cajucultura: Modernas Technicas de Producao (Eds. J.P.P. Araujo and V.V. Silva). EMBRAPA-CNPAT, Fortuleza, pp.73-93. Behrens, R. 1998. About the spacing of cashew nut tree. Proceeding of the International Cashew and Coconut conference, 17-21 February 1997, Dares Salam, Tanzania. BioHybrids International Ltd., Reading, Uk. pp: 48-52. Bigger, M. 1990. Selenothrips rubrocinctus (Grand) and the floral biology of cashew in Tanganyika. East African Agriculture Journal, 25: 229-234. Damodaran, V.K., Abraham, J. and Alexander, K.M. 1965. The morphology and biology of the cashew flower I-Flowering habit, flowering season, morphology of the flower and sex ratio. Agricultural Research Journal of Kerala, 3(1 & 2): 23-28. Damodaran, V.K., Abraham, J. and Alexander, K.M. 1966. The morphology and biology of the cashew flower II - Anthesis, dehiscence, receptivity of stigma, pollination, fruit set and fruit development. Agricultural Research Journal of Kerala, 4: 78-84.

Darlington, C.D. and Janaki Ammal, E.K. 1945. Chromosome Atlas of Cultivated Plants. George Allen and Unwin, London, p.397. Dasarathi, T. B. 1958. A study of the blossom biology and growth features of cashew nut (Anacardium occidentale L.). M.Sc. Thesis. Andhra University, Waltair (unpublished). Freitas, B.M. 1994. Beekeeping and cashew in North-eastern Brazil: the balance of honey and nut production. Bee World, 75(4): 160168. Freitas, B.M. and Paxton, R.J. 1996. The role of wind and insects in cashew (Anacardium occidentale L.) pollination in NE Brazil. Journal of Agricultural Science, 126: 319-326. Hutchinson, J.J. and Dalziel, M. 1954. Flora of West Africa. Crown Agent for Overseas Government and Administration, Millbank, London, S.W. I. Vol. 1: 428-429. Jhonson, D.V. 1973. The botany, origin and spread of cashew (Anacardium occidentale L.). Journal of Plantation Crops, 1:1-7. Kumaran, P.M., Nayar, N.M., Nambiar, M.C., Mohan, E. and Vimala, B. 1976a. Cashewvarietal improvement. Central Plantation Crops Research Institute, Annual Report for 1975, Kasaragod, India p.125. Lima, D de A. 1954. Contribution to the study of the flora of perhembuco, Brazil. Mon. Univ. Rur. Pern. Recife 1. Mitchell, J.D. and Mori, S.A. 1987. The cashew and its relatives (Anacardium: Anacardiaceae). Memories on The New York Botanical Garden, 42:1-76. Morada, S.K. 1941. Cashew Culture. Philippines Journal of Agriculture. 12:89-103. Nambiar, M.C. 1977. Cashew. In Ecophysiology of Tropical Crops. Academic Press, Inc., San Francisco, pp.461-478. Nomisma 1994. The World Cashew Economy Oltremare Sp A, via Piemonte 5, Zola Predosa, Bologna, Italy, pp. 218. Nothwood, P.J. 1966. Some observations on the flowering and fruit-setting in the cashew (Anacardium occidentale L.). Tropical Agriculture (Trin.), 43:35-42.


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Ohler, J.G. 1979. Cashew. Kominklijk Institunt Voor de Tropen, Amsterdam, pp.1-260.

Rao, V.N.M. 1956. Multiply better yielding cashewnut. Indian Farming, 6:15-17.

Paula Pessoa, P.F.A., Leite, L.A. de S. and Pimentel, C.R.M. 1995. Situação atual e perspectivas da agroindústria do caju. p. 23 – 41. In: J.P.P de Araújo, and V.V. da Silva (org.) Cajucultura: Modernas técnicas de produção. Embrapa-CNPAT. Fortaleza.

Rao, V.N.M. 1974. Crop improvement of cashew. Mimeo. Report of the All India Summer Institute on Improvement and Management of Plantation Crops. Central Plantation Crops Research Institute, Kasaragod. pp.128-134.

Paulino, F.D.S. 1992. Polinizacao entomologica em cajueiro (Anacardium occidentale L.) no litoral de Pacajus, CE. Thesis M.Sc.USPESALQ, p.70.

Reddi E U B. 1987. Under-pollination: a major constraint of cashewnut production. Proceedings of the Indian National Science Academy, 53(3): 249-252.

Pavithran, K. and Ravindranathan, P.P. 1974. Studies on the floral biology in cashew, Anacardium occidentale L. Journal of Plantation Crops, 1: 32-33.

Reddi, E.U. B. 1991. Pollinating agent of cashewwind or insects? Indian Cashew Journal, 20(4): 13-18.

Pell, S.K. 2009. Anacardiaceae. Cashew family. In: The tree of life web project, http:// tolweb.org

Saroj, P.L. 2013. The Cashew : Issues, Challenges and Strategies. Cashew News. Pub. Directorate of Cashew Research, Puttur. P. 1-2.

Pillay, P.K.T. and Pillai, G.B. 1975. Note on the shedding of immature fruits in cashew. Indian Journal of Agricultural Sciences, 45:233234. Purseglove, J.W. 1968. Tropical Crops: Dicotyledons. Longman. Harlow, UK. Rao, V.N.M. and Hassan, M.V. 1957. Preliminary studies on the floral biology of cashew (Anacardium occidentale L.). Indian Journal of Agricultural Sciences, 27(3): 277-288.

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Sebastine, K.M. 1955. The emigrant economic plants of India (1) Anacardium occidentale L. Proceedings of Indian Academy of Sciences, 42: B.239-48. Tavares, S. 1959. Medeiras do nordeste do Brazil. Mon.Univ.Rur.Pern.Recife, 5:9-171. Thevet, A. 1558. Singularidades da Franca Antartica. Companhia Editora Nacional, Sao Paulo (Brazil) (1944).



DIFFERENTIAL SCOPE OF TRADITIONAL/ MOLECULAR BREEDING FOR REGULARITY IN BEARING HABIT OF FRUIT CROPS M.R. Dinesh and K.V. Ravishankar Indian Institute of Horticultural Research Hessarghatta, Banglore – 560 089, Karnataka

INTRODUCTION Genetic improvement is extremely difficult in perennial fruit crops due to the complex genetic nature. The germplasm collection, conservation and evaluation, which are a prerequisite for meaningful breeding programme, take a long time and area. Although the concept of core collection is very much valid, there is always a question mark when it comes to highly heterozygous crops as to whether the sample is good enough to represent the population. Due to the propagation by seeds, the large variability present needs to be evaluated for various characteristics. The genetics studies carried out in many of these crops are not conclusive and the progeny performance cannot be predicted. The biometrical methods to estimate the parameters viz., combining ability, heritability using the methodologies such as dill have proven to be a futile exercise to a very great extent. Parental selection, which is so vital for a successful breeding program is very difficult, as mainly selection has to be based upon the phenotype. Breeding for particular traits like biotic or abiotic stress has been difficult as the resistance is not found within the spp. and interspecific/intergeneric hybridization is difficult because of incompatibility barriers for eg., the ‘PRSV’ breeding program in papaya. In highly heterozygous crop like mango, there exists strong genotype x environment interaction, which alters the performance of improved varieties.

Fruit crops most of them being perennial are highly heterozygous. This comes in the way of improvement as understanding of the genetics and inheritance pattern of the quantitative traits become extremely difficult. Hence, the selection of parents in a breeding program becomes difficult. Parents when they are selected based on the phenotype and used in the breeding program, progeny performance or the manifestation of hybrid vigor becomes unpredictable. The progenies also are influenced to a great extent by the environment. However, one of the advantages of the heterozygosity is that in the F 1 generation itself segregation will be maximum and the desirable trait in the progenies can be fixed by vegetative propagation. Perennial crop breeding takes a long time. The seedling progenies take more than eight to nine years to fruit thereby making evaluation of the progenies long duration program. The absence of molecular markers and preselection indices in most of the crops is hampering the breeding programme. Several attempts have been made in crops like mango by vegetative propagation to induce early flowering through grafting (Kulkarni, 1991; Kulkarni, 1986 and Kulkarni, 1988 a) In most of the fruit crops, taxonomy is complex and the nomenclature ambiguity in crops like mango due to the large unevaluated variability has hindered improvement. The chromosomal aberrations in the case of seed propagated crops generally get deleted. But in vegetatively propagated crops these


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS aberrations get fixed ultimately resulting in undesirable recombinants. The presence of nucellar embryony in crops like citrus and mango interferes in the identification of zygotic seedlings. Hence, there is an urgent need to develop markers to identify them at the nursery stage. In some of the crops cross and self-incompatibility comes in the way of selecting parents for the breeding programme. Raising a large population, which is the basic necessity for selection, is extremely difficult and the large area needed for the evaluation is another hindrance in the breeding programme.

Bearing habit Many of the fruit crops viz., mango and jamun, are biennial bearers. In case of mango classification can be made on the basis of bearing as regular, irregular and alternate bearers. This difference of bearing habit also depends on the region of growing and prevailing climate. A classical example that can be given is the case of guava bearing in the northern region of the country and the peninsular region. In the northern region there is a clear cut flowering patterns, whereas, in the peninsular region the plant of guava is physiologically active throughout the year giving stray flowering with only one main season. The flowering in mango has remained an enigma as it largely depends on the genotype x environment interaction and the presence of growth regulators. However, there are varieties, which are early season, midseason and late season. In crops viz., apple, entire tree behaves in a particular way, whereas, in mango each branch seems to have its own physiology of flowering. In the case of papaya, flowering depends on the two sets of genetic factors; one, promoting sterility and another, promoting fertility, thus, causing differential flowering behavior (Storey, 1953).

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High heterozygosity In perennial fruit trees, biennial bearing is characterized by large yields of in ‘on’ years, and low yields, sometimes even no fruit, in ‘off ’ years. This phenomenon is present in many fruit tree crops, viz., nuts (hazelnuts, pecans, pistachios, and walnuts), temperate fruits (apple, apricot, pears, and prunes), subtropical fruits (avocados, citrus, and olives), tropical fruits (litchi and mango), and forest trees (beeches, oaks, pines, and spruces) (Monselise and Goldschmidt, 1982). For several years, many scientists have tried to understand this phenomenon in fruit crop trees especially in apple and citrus. However, the cause for alternate bearing is still largely unknown (Monselise and Goldschmidt, 1982; Bangerth, 2006, 2009). External factors (photo-period, temperature, and water stress), internal factors such as the carbon-to-nitrogen ratio and hormones [auxins, cytokinins (CKs), abscisic acid, ethylene, and gibberellins (GAs)], as well as interaction with other organs (leaves, terminal shoot growth, and fruit) affect flower formation in apple (Hanke et al., 2007; Bangerth, 2009). In apple, experiments using ‘Spencer Seedless’, which can bear both parthenocarpic and seeded fruit, suggested that seed development rather than nutritional competition may be a factor in alternate bearing (Chan and Cain, 1967; Neilsen and Dennis, 2000). The number of seeds per fruit or per bourse (flowering growth unit) has an effect on a biennial bearing, which can be overcome by a high vegetative growth rate of the bourse shoot itself (Chan and Cain, 1967; Grochowska and Karaszewska, 1976; Hoad, 1978; Neilsen and Dennis, 2000). Seed is known to contain relatively large amounts of hormones (Luckwill, 1974), and auxin [indole acetic acid (IAA)], GA, and CK have been


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS implicated separately and in combination, as being responsible for hormonal control of floral induction (FI). IAA and GA may act together or independently to inhibit FI in perennial fruit trees, whereas CK is likely to be the hormone enhancing FI (Bangerth, 2006). Although the spur (short fruiting shoot) tissues of biennial bearing apple cultivars receive more GA through the pedicel than annual bearing cultivars do (Hoad, 1978) and the peak activity of GA in apple seed coincides with FI (Luckwill, 1970), it has been difficult to obtain convincing evidence for the transport of GA from seed in sufficient quantities to inhibit FI. Bangerth (2006) proposed that auxin could be the mobile signal and might stimulate GA synthesis in the meristem. In this model, GA and auxin could potentially act as FI inhibiting signals working in concert, GA as the primary messenger that stimulates the synthesis/transport of the second messenger auxin. However, characterization and quantification of both GA and auxin in the meristem still need to be performed and, moreover, an inhibitory effect of GA/auxin and stimulation by CK on the expression of genes related to FI remain to be demonstrated (Bangerth, 2006).

Flowering peculiarity

pattern

in

mango-

The total number of flowers in a panicle may vary from 1000 to 6000, depending on the variety (Mukherjee, 1953). Initial fruit set in mango is directly related to the proportion of perfect flowers, although the final fruit set does not necessarily depend on this ratio (Iyer et al., 1989). It appears that the proportion of perfect flowers in a cultivar becomes critical for optimum fruit set only when the proportion drops to 1 per cent. Flowers begin to open early in the morning and anthesis has generally been

completed by noon. The greatest number of flowers opens between 9 and 10 a.m. Although the receptivity of the stigma continues for 72 h after anthesis, it is most receptive during the first 6 h; however, there are reports of stigma becoming receptive even before anthesis has occurred (Singh, 1960). The minimum time required for pollen grains to germinate is 1.5 h (Sen et al., 1946; Spencer and Kennard, 1955). Mango is cross-pollinated, which is affected by insects such as the common housefly, honeybees and thrips, and possibly by other insects through to a lesser extent. Pollination by wind and gravity has been suggested to occur in mango to some extent (Popenoe, 1917; Maheshwari, 1934; Malik, 1951). In nature, more than 50 per cent of the flowers do not receive any pollen. Some workers had suggested that self-pollination in certain cultivars can also occur quite frequently (Dijkm an and Soule, 1951). Studies by Issarakraisila and Considine (1994) have shown that for ‘Kensington’, a night temperature below 10oC results in pollen grains with low viability ( Mangifera indica L.). Scientia horticulturae, 39(2): 143-148. Lucas, M.R., Ehlers, J.D., Huynh, B.L., Diop, N.N., Roberts, P.A., and Close, T. J. 2013. Markers for breeding heat-tolerant cowpea. Molecular Breeding, 31(3): 529-536. Luckwill, L.C. 1974. A new look at the process of fruit bud formation in apple. Proc. 19 th Intern. Hort. Congr. 3:237-245 Luckwill, L.C. 1970. The control of growth and fruitfulness of apple trees. In:, Physiology of Tree Crops (Eds. L.C. Luckwill and C.V. Cutting). Academic Press, New York, pp. 237–254. Mimida, N., Ureshino, A., Tanaka, N., Shigeta, N., Sato, N., Moriya-Tanaka, Y., and Wada, M. 2011. Expression patterns of several floral genes during flower initiation in the apical buds of apple (Malus× domestica Borkh.) revealed by in situ hybridization. Plant cell reports, 30(8): 1485-1492. Mohamed, R. et al. 2006. Populus CEN/TFL1 regulates first onset of flowering, axillary meristem identity and dormancy release in Populus. Plant J. 62: 674–688. Monselise, S.P. and Goldschmidt, E.E. 1982. Alternate bearing in fruit trees. In: (Ed. J. Janick), Horticultural Reviews, 4: 128–173. Nakagawa, M., Honsho, C., Shinya, K., Kousuke, S., Naoki, U. (2012). Isolation and expression analysis of FLOWERING LOCUS T-like and gibberellin metabolism genes in biennialbearing mango trees. Scientia Horticulturae, 139:108-117. Putterill, J., Laurie, R. and Macknight, R. 2004. It’s time to flower: the genetic control of flowering time. Bioassays, 26:363373. Ramírez, F., and Davenport, T. L. 2010a. Mango (Mangifera indica L.) flowering physiology. Scientia Horticulturae, 126(2): 65-72.

Ramírez, F., and Davenport, T.L. 2012a. Reproductive biology (physiology) In: The case of mango. (Eds.S.G. Valavi, K. Rajmohan, J.N. Govil, K.V. Peter and G. Thottappilly) Mango: Vol. 1. Production and Processing Technology, Studium Press LLC, Houston, TX (2012), pp. 56–81. Ramírez, F., Davenport, T. L., Fischer, G., and Pinzón, J.C.A. 2010. The stem age required for floral induction of synchronized mango trees in the tropics. Hort. Science, 45(10): 1453-1458. Rhoades, M.W.et al. 2002. Prediction of plant microRNA targets. Cell, 110: 513–520. Ross, J.J., O’Neill, D.P., Smith, J.J., Kerckhoffs, L.H.J., Elliott, R.C. 2000. Evidence that auxin promotes gibberellin A1 biosynthesis in pea. The Plant Journal, 21: 547–552. Sánchez-Pérez, R., Dicenta, F., and MartínezGómez, P. 2012. Inheritance of chilling and heat requirements for flowering in almond and QTL analysis. Tree Genetics & Genomes, 8(2): 379-389. Segura, V., Cilas, C., Costes, E. 2008. Dissecting apple tree architecture into genetic, ontogenetic and environmental effects: mixed linear modeling of repeated spatial and temporal measures. New Phytologist, 178: 302–314. Segura, V., Cilas, C., Laurens, F., Costes, E. 2006. Phenotyping progenies for complex architectural traits: a strategy for 1-year-old apple trees (Malus3 domestica Borkh.). Tree Genetics and Genomes, 2: 140–151. Segura, V., Durel, C.E., Costes, E. 2009. Dissecting apple tree architecture into genetic, ontogenetic and environmental effects: QTL mapping. Tree Genetics and Genomes, 5: 165– 179. Shalom, L., Samuels, S., Zur, N., Shlizerman, L., Zemach, H., Weissberg, M., Sadka, A. 2012. Alternate bearing in citrus: changes in the expression of flowering control genes and in global gene expression in on-versus offcrop trees. PloS one, 7(10): 46930. Shen, L., Chen, Y., Su, X., Zhang, S., Pan, H., & Huang, M. 2012. Two FT orthologs from


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Populus simonii Carrière induce early flowering in Arabidopsis and poplar trees. Plant Cell, Tissue and Organ Culture (PCTOC), 108(3): 371-379. Spanudakis, E., Jackson, S. 2014. The role of microRNAs in the control of flowering time. Journal of Experimental Botany, 65(2): 365-380. Sung, S., Yu, G., An, G. 1999. Characterization of MdMADS2, a member of the SQUAMOSA subfamily of genes, in apple. Plant Physiology, 120: 969–978. Tan, F. and Swain, S.M. 2006. Genetics of flower initiation and development in annual and perennial plants. Physiologia Plantarum, 128: 8–17. Wada, M., Cao, Q., Kotoda, N., Soejima, J., Masuda, T. 2002. Apple has two orthologues of FLORICAULA/ LEAFY involved in flowering. Plant Molecular Biology, 49: 567– 577. Wang, J. W., Czech, B. and Weigel, D. 2009. miR156-regulated SPL transcription factors define an endogenous flowering pathway in Arabidopsis thaliana. Cell, 138 : 738–749. Wang, J.W. et al. 2011. miRNA control of vegetative phase change in trees. PLoS Genet., 7: e1002012. Wang, J.W., Czech, B., Weigel, D. 2009. miR156regulated SPL transcription factors define an endogenous flowering pathway in Arabidopsis thaliana. Cell, 138 : 738–749. Winterhagen, P., Tiyayon, P., Samach, A., Hegele,

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M., and Wünsche, J. N. (2013). Isolation and characterization of FLOWERING LOCUS Tsubforms and APETALA1 of the subtropical fruit tree Dimocarpus longan. Plant Physiology and Biochemistry, 71: 184-190. Wu, G et al. 2009. The sequential action of miR156 and miR172 regulates developmental timing in Arabidopsis. Cell, 138: 750–759. Wu, G. et al. 2009.The sequential action of miR156 and miR172 regulates developmental timing in Arabidopsis. Cell, 138 : 750–759. Wu, G., and Poethig, R.S. 2006.Temporal regulation of shoot development in Arabidopsis thaliana by miR156 and its target SPL3. Development, 133: 3539–3547. Xie, K et al. 2012. Gradual increase of miR156 regulates temporal expression changes of numerous genes during leaf development in rice. Plant Physiol., 158 : 1382–1394. Yamaguchi, A. et al. 2009. The microRNAregulated SBP-Box transcription factor SPL3 is a direct upstream activator of LEAFY, FRUITFULL, and APETALA1. Dev. Cell, 17: 268–278. Yeshitela, T., Robbertse, P.J., and Stassen, P.J.C. 2004. Effects of various inductive periods and chemicals on flowering and vegetative growth of ‘Tommy Atkins’ and ‘Keitt’mango (Mangifera indica) cultivars. New Zealand J. Crop Hort. Science, 32(2): 209215. Zhou, C.M., Wang, J.W. 2012. Regulation of Flowering Time by MicroRNAs. J. Genetics Genomics, 40 (5): 211-215.



MOLECULAR INSIGHTS INTO FLOWERING PATHWAY GENES IN MANGO Anju Bajpai, M. Muthukumar, V.K. Singh and S. Rajan Central Institute for Subtropical Horticulture, Rehmankhera, Lucknow 226 101, U.P.

INTRODUCTION Mango, Mangifera indica L., is an evergreen tropical fruit tree cultivated in the tropics and subtropics for its sweet luscious fruits. Given favorable growth conditions, the timing and intensity of flowering largely determines fruit productivity during a given season. Insight into phenomenon of flowering and fruiting has been of prime interest to scientists and growers for over a century. Efforts to elucidate the mechanisms of this critical biological event in mango and other model plant systems, have led to a better understanding of flowering at molecular, biochemical, and physiological. Despite enormous strides in this direction, flowering is still an unpredictable and irregular process in mango as in many other fruit crops. Most of the commercially grown varieties in North India, like Dasheheri, Safeda, Chausa and Langra are alternate bearers, while Amrapali bears fruit every year in the subtropics. Therefore irregular and alternate bearing in mango is a major problem faced by mango growers leading to unpredictable productivity. In many plant species, flowering is promoted by photoperiod, temperature or autonomous factors, or some combination thereof (Ausin et al., 2005), suggesting that flowering is triggered environmentally and genetically. Thus, to gain further insights into evolution and environmental adaptation, it is important to understand the regulation of seasonal flowering in plant species like mango,

exhibiting different flowering characteristics in varying agroclimates. Fruits like mango, grown in the subtropics (latitude 23°–30°) where substantial seasonal temperature changes occur, show floral induction from exposure to night temperatures of 10–15°C. Many cultivars flower erratically in the lowlatitude tropics, providing continuously warm temperatures with high soil and atmospheric moisture. Under such conditions, the age of stems is the dominant inductive factor (Ravishankar et al., 1979), and occasional cool night temperatures in the upper latitude tropics have a positive moderating effect (Davenport, 2003). The elucidation of flowering mechanism based environmental, physiological, biochemical and varietal determinants supported by gene expression in mango needs to be studied in detail in the background of physiological and biochemical signals.

Mango flowering model Flowering and fruit set are the most critical of all events occurring after establishment of a mango plant and understandably so, the floral initiation has been more extensively researched than any other tropical tree species in mango. Floral initiation occurs during late autumn and early winter; flower panicles emerge from the terminal and sub-terminal buds and grows continuously until anthesis occurs in the spring. A vast number of applied and fundamental studies have demonstrated the importance of light (through day length and


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS light-quality effects in fruit species) and temperature (through temperature and ambient temperature effects) as the main environmental regulators of flowering. However, other factors, including nutrient status, endogenous hormones, stress, and the developmental state of the plant, can also be important. Even with respect to light and temperature, great diversity in responsiveness exists within and between different plant species and among varieties in mango. These differences are important in the adaptation of varieties to particular latitudinal and climatic regions, and have also been extremely important for determining the environments and agronomic regimes under which particular variety can be most effectively grown. Besides the network of processes involved in flower formation during season other specific problems such as juvenility, detailed understanding of flower formation mechanisms during tree development, and relationship between two genetically different parts of the tree, rootstock and the scion, is also critical. All these phenomena stress the necessity to improve our knowledge on genetic factors controlling the processes of flowering formation in perennial fruit species with emphasis on mango Molecular biology of flowering in the facultative, long-day, model plant, Arabidopsis thaliana (Aksenova et al., 2006), has provided insight into the nature of the floral stimulus (FP). A network of four interacting genetic signaling pathways may result in flowering in response to photoperiodic, temperature, gibberellin and autonomous environmental cues (Boss et al., 2004; Putterill et al., 2004)(Fig.1). The photoperiodic pathway involves activation of the CONSTANS (CO) gene that encodes a zinc-finger protein, which in turn induces expression of the FLOWERING LOCUS T (FT) gene in the phloem tissue of leaves. FT is the terminal, integrating gene of 144

the four pathways regulating flowering in Arabidopsis. Its transcribed mRNA was initially thought to be the FP that is transported in phloem to buds (Huang et al., 2005); however, evidence indicates that the translated protein product of FT is translocated to Arabidopsis buds (Corbesieret al., 2007).Evidence of presence of analogous proteins encoded by Hd3a, an ortholog of FT in rice (Tamaki et al., 2007), and the aspen ortholog, PtFT1, which along with CO regulates the timing of flowering and growth cessation of Populus trichocarpa thus proves that FT is the FP. In the buds, the protein product of FT is thought to combine with the bZIP transcription factor (FD) protein to activate transcription of floral identity genes to begin floral expression (Abe et al., 2005). Similar mechanisms are likely to exist in mango. Studies with mango indicate that a FP is synthesized in leaves during exposure to cool, floral-inductive temperatures and moves to buds to induce flowering. Unlike receptor sites in buds requiring temperature for floral induction (Bernier et al., 1981), it is the mango leaves that appear to be the site of putative floral stimulus production. Complete defoliation of girdled branches during inductive conditions results in vegetative shoots instead of generative shoots, appearing to be transported over long distances from leafy branches to defoliated branches (NúñezEliseaet al., 1996).

Conservation of flowering genes in flowering plants Current research into the regulation of flowering is focused on progressive characterization of the genes participating in the control networks and clarification of gene interactions and their relationship with external inducers taking cues from model species like Arabidopsis. As a small, weedy annual, Arabidopsis is responsive to a wide


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS range of factors and has been invaluable in outlining the major genetic pathways that are likely to function in the control of flowering responses to photoperiod, temperature, and hormone responses (Amasino, 2004; Boss et al., 2004; Putterill et al., 2004). With the advent of genomic approaches in a range of model plant systems, the information gained from Arabidopsis is rapidly being extended into other species. A number of studies have already provided detailed phylogenetic descriptions of particular flowering-related gene families and/or functional analysis of individual genes in species such as Citrus, Malus, Dimocarpus, Prunus etc. Recently detailed analysis in citrus, indicated variation in differential expression of key metabolic and regulatory pathways genes, such as trehalose and flavonoid metabolism between ON- and OFF-crop trees. Among genes induced in OFF-crop trees was one homologous to Squamosa Promoter Binding-Like (SPL), which controls juvenile-to-adult and annual phase transitions, regulated by miR156. The expression pattern of SPLlike,miR156 and other flowering control genes suggested that fruit load affects bud fate(along with development and metabolism), a relatively long time before the flowering induction period. Photoperiod

Fig. 1: Conservation of flowering genes in flowering plants

Floral initiation in flowering plants occurs through the light, temperature, GA or the autonomous pathways. Pointed arrows represent positive regulation, ‘T’ arrows represent negative regulation, and both pointed and ‘T’ arrows represent positive and negative regulation. Under LD, photoreceptors stabilize CO allowing up-regulation of FT, the FT protein is transported from the leaf to the meristem where it interacts with floral meristem identity genes, leading to flowering. Temperatures cues suppresses the floral repressor FLC both in the meristem and the leaf, the autonomous pathway also suppresses FLC through several genes that act additively.

Native floral pathway integrators The transition from the vegetative phase to a reproductive phase is characterized by the induction and development of the meristem of the inflorescence, which will produce a collection of flowers. The plant must have a certain number of leaves and contain a certain level of total biomass, certain environmental conditions are also required that play an important part in the process. Molecular genetic studies have shown that at least three classes of homeotic floral pathway integrators/genes control the determination of floral meristems and organ identity in higher plants (Weigel and Meyerowitz 1994) Flowering Locus T (FT), Leafy (LFY), Suppresor Of Overexpression Of Constans1 (SOC1, also called Agamous-Like20)(Fig.2). These genes possess both common and independent functions in floral transition. SOC1 is a MADS-box-type gene, which integrates responses to photoperiod, tempearture and gibberellins (Blazquez et al., 1998).

CONSTANS(CO) Constans gene is controlled by the


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS circadian clock and photoperiod to regulate flowering time. It has been recently reported that constans gene is widely conserved in flowering plants and is responsible for production of a systemic signal. Previous research has shown that mango flowering is regulated by the interaction of temperature and leaf age but not by day-length, suggesting that a florigenic signal is up-regulated under low temperature conditions and transported to buds to induce production of flowering shoots. PCR validation of constans-like gene sequence in mango(validated in 48 Indian cvs )confirming presence of ortholog in mango. Further the cloned fragment of 634 bp was identified encoding a putative 221 aa polypeptide and containing an intron of 84 bp. The nucleotide sequence analysis showed that it has 36% homology with both the apple Constans-like protein-I gene (COL1) and its protein-II gene (COL2), and 40% homology with Arabidopsis COL0 gene. Further sequencing and characterization of the mango COL1 gene is underway(Zhang et al., 2005). The CO-Like proteins contain two segments of homology: a zinc finger containing region near their amino terminus and a CCT (CO, CO-Like, TOC1) domain near their carboxy terminus

Flowering Locus T (FT) FLT/FT can promote flowering in the plant photoperiod pathway and also facilitates temperature dependant flowering pathways and other ways to promote flowering. The expression of products of the FT gene is recognized as important parts of the flowering hormone and can induce flowering by long-distance transportation. Flowering loci time (FLT) is a small multi gene family which is under the control of constans (CON), photoperiod responsive gene and a negative regulator gene FLC which is inactivated by temperature. Recent studies 146

have identified homologs of Arabidopsis FLOWERING LOCUST (FT), to encode the floral inductive signal florigen (Corbesier et al., 2007; Tamaki et al., 2007), in several fruit trees such as citrus (Endo et al.,2005), grapevine (Vitis vinifera L.) (Boss et al., 2006; Sreekantan and Thomas, 2006), and apple (Malus domestica Borkh.) (Kotoda and Wada, 2005). These reports suggest that FT, AP1, and LFY, which are the key genes promoting flowering in Arabidopsis, are functionally conserved in fruit trees. The presence of this FLT multigene family was validated in 18 mango cvs where approx. 800 bp product was visualized. FLT gene sequence analysis based on BLAST homology had 82-100 per cent homology hits for FLT from cv. Alphonso,Litchi chinensis, Citrus species and Dimocarpus (Alphonso 634bp). The gene ontology is distantly related as evident from the phylogenetic tree of nucleotide sequence for varieties. Partial cDNA fragments of the FT homologous gene in mango amplified using degenerate primers that had been designed for isolating the FT ortholog from Prunus mume by Esumi et al. (2009) and the gene was designated as MiFT. So far only one FT homologue, MiFT, was isolated from mango, while some plant species contain more than one FT homologues. For example, citrus has three homologues of FT, and these genes have different expression patterns (Nishikawa et al., 2007). It is probable that mango has more than one FT homologues, but MiFT seems to be the only FT homologue expressed in mature mango leaves. The deduced amino acid sequence of MiFT showed high identity of the gene to other plant FT-like genes, such as PnFT2, MdFT2, CiFT2, Heading date 3a (Hd3a)and FT (81%, 81%, 80%, 75%and 72% identity, respectively). MiFT consists of 180 amino acids and conserves the single amino acid residues Try-89 and Gln-144 in the positions corresponding to Try-85 and Gln-


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS 140, respectively, in Arabidopsis Try-85/His88 and Gln-140/Asp-144 have been reported as key residues promoting flowering and distinguishing FT and TERMINAL FLOWER1 (TFL1) (Ahn et al., 2006). To clarify the relationships between MiFT and other FT/ TFL family members, a phylogenic tree of mango, Arabidopsis, grapevine, apple, orange (Citrus sinensis (L.) Osbeck), Lombardy poplar (Populus nigra L.), satsuma mandarin (C. unshiu Marc.), tomato (Solanum esculentum Dunal), and rice (Oryza sativa L.) was constructed using the bootstrap NJ method

Fig. 2. A model for the integration of regulatory pathways of flowering in Arabidopsis (Yamaguchi et al., 2005). Four mai n (photoperiod, tempera ture, autonomous and gibberellin) and additional (‘light quality’ and ‘repression’) pathways are shown with representative genes. Regulatory relationshi ps among Floral pa thw ay integrators FT, SOC1 a nd LFY by i nput pa thw ays is depic ted. Regula tion a t the transcriptional level is represented by solid arrows (promotion) and T-bars (repression). Arrows and T-bars to or from a dotted box with TSF and FT in it mean similar regulation of or by the two genes, while a T-bar from TFL2 to FT alone means regulation of only FT. Dotted arrow s mean modul ati on of ac tiv ity of the gene products or the machinery. Gray arrows represent regulatory relationships that are not directly analyzed in the present work.

with CLUSAL X. The phylogenic tree was divided into two clades represented by FT and TFL1. MiFT was classified into the FT clade, and most closely related to the CiFT clade. FT is strongly expressed in leaf vascular tissue under floral-inductive conditions, and the FT protein is transported from the leaf to the shoot apex, where it interacts with a basic-leucine zipper (bZIP) transcription factor, FLOWERING LOCUS D (FD), to activate the floral meristem identity gene AP1 (Corbesier et al., 2007). FT also up-regulates LFY via SUPPRESSOR OF OVEREXPRESSION OF CO1 (SOC1) (Moon et al.,2005) in Arabidopsis. Davenport (2007) suggested that the floralinductive signal in mango is generated in the leaves at cool temperature, and this putative floral-inductive signal is transported to the apical buds. MiFT fulfills these conditions as it was expressed only in the leaves of adult trees under floral-inductive cool temperature. Because of high identity to other plant FT homolog and conserved key amino acid sequences of FT, MiFT appears to be the flowering signal in mango.

Generalized hypothesis mechanism of FT action

for

The FT gene promotes the transition from vegetative to reproductive phase under photoperiodic regulation (Kardailsky et al., 1999; Kobayashi et al., 1999). Flowering Locus T (FT) genes encode proteins that function as the mobile floral signal, florigen. When light signal is perceived by leaves of the long-day plant Arabidopsis and the short-day plant rice, CO protein activates FT in leaf phloem (An et al., 2004; Ayre and Turgeon, 2004). Then, FT protein moves to the shoot apical meristem where it forms a complex with FLOWERING LOCUS D (FD) protein, which up-regulates the floral meristem identity gene AP1 to induce reproductive development (Abe et al., 2005 Corbesier et al., 2007; Tamaki et al.,


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS 2007). FT is also regulated by the temperature pathway. In cold-requiring accessions of Arabidopsis, the temperature pathway mediates low temperature signals that induce flowering by reducing the levels of the repressor FLOWERING LOCUS C (FLC), which up-regulates the expression of FT (Michaels and Amasino, 1999, 2001; Sheldon et al., 2000 ). Thus, FT serves as an important integrator of the photoperiod and temperature signals. There is extensive cross-talk between autonomous and temperature sensitive flowering pathways and ample evidence that genes associated with flowering regulation are highly conserved across species. Indeed, citrus genes homologous to Arabidopsis flowering control genes most likely possess similar functions and also in mango. For instance, overexpression of the citrus FLOWERING LOCUS T (FT), arabidopsis LEAFY (LFY) and arabidopsis APETALA1 (AP1) genes in citrus greatly reduced the juvenile period, allowing flowering at the seedling stage(Endo et al., 2005, Pena et al., 2001). FT was shown to be induced during the annual transition to floral development ( Nishikawa et al., 2007). In addition, FT transcript accumulated in trees subjected to low-temperature floral-inductive conditions. Overexpression of the citrus LFY, AP1 and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) genes in Arabidopsis resulted in phenotypes similar to those observed when the endogenous genes were overexpressed, and CsLFY and CsAP1 rescued Arabidopsis mutants in the respective genes ( Tan et al., 2007). Similar findings were demonstrated for the citrus TERMINAL FLOWER homolog (CsTFL). Inverse relationships were found between fruit load and the expression of FT, AP1 and SOC1 in the leaves of ‘Moncada’ mandarin, especially during the flowering induction period (Pillitteri et al., 2004; Munõz-Fambuena et al., 2003, Boss et al., 2004).

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LEAFY(LFY) The LFY gene is required for the specification of loral Meristem Identity in Arabidopsis. This is clearly deduced from the phenotype of LFY mutant plants, where the flowers are replaced by structures with shoot characteristics (Schultz and Haughn, 1991). LFY encodes a transcription factor that has so far been only found in the plant kingdom (Maizel et al., 2005). In contrast to most other types of transcription factors, LFY does not belong to a multigene family and most angiosperms contain only one LFY gene. Consistent with the phenotype of the mutant, LFY is strongly expressed throughout the young floral meristems from the earliest stages of development, in fact, up regulation of LFY in these meristems is crucial for them to acquire floral identity, as it activates the expression of AP1 and the floral meristem identity genes (Parcy et al., 1998). He expression of LFYis not absolutely confined to floral tissues and can also be detected at low levels in leaf primordia during the vegetative phase, and gradually increases until the floral transition (Bla´zquez et al., 1997). The actual level of LFY expression in the apex is considered to be a critical parameter that determines the time point at which the floral transition takes place and act as an integrator of the pathways controlling flowering time and the initiation of floral meristems (Bla´zquez and Weigel, 2000; Parcy, 2005). In fact, lfy mutants are slightly delayed in the vegetative-to-inflorescence transition (Bla´zquez et al., 1997).In agreement with its proposed roles in floral initiation, constitutive expression of LFY in arabidopsis causes early flowering and the transformation of all shoots into flowers, indicating that LFY is not only necessary, but also sufficient to confer floral identity to emerging shoot meristems (Weigel and Nilsson, 1995).



AGAMOUS (AG) AGAMOUS (AG) is a C-function floral organ identity gene, and encodes a transcription factor essential for reproductive organ development in plants. In addition, AG is required for meristem determinacy such that AG mutant flowers are indeterminate and produce an essentially endless number of floral whorls, repeating the basic pattern: (sepal, petal, petal)n(Bowman et al., 1991). AG encodes a transcription factor of the MADS-box super family whose representatives (over 100 published sequences) are also found in the other Eukaryotic kingdoms (TheiBen et al., 1996) and is expressed in stamen and carpel primordial in Arabisopsis. At later stages of development, AG is expressed in distinct regions of the reproductive organs. This suggests that AG might function during the maturation of stamens and carpels, as well as in their early development. However, the developmental processes that AG might control during organogenesis and the genes that are regulated by this factor are largely unknown. Since its isolation by Yanofsky et al. (1990), it has played a pivotal role in the study of flower development (Meyerowitz 1994). In plants, most of the MADS-box genes are expressed in reproductive organs, where they control different stages of inflorescence, flower and floral-organ development. Recently a MADS – box cDNA from mango encoding a protein of 254 residues was obtained and compared. Based on phylogenetic analysis, it is proposed that the MADS-box transcription factor expressed in mango fruit (MiMADS1) belongs to the SEP clade of MADS-box proteins. This need further validation in mango flowers.

APETALA 1(AP1) AP1 is the other main promoter of floral meristem identity. AP1 also encodes a

transcription factor but, in contrast to LFY, it belongs to a large multigene family, the MADSbox gene family (Mandel et al., 1992). Similarly to LFY, it is expressed throughout young floral meristems, shortly after the onset of LFY expression in these meristems (Mandel et al., 1992). In fact, AP1 (as well as CAL) is directly activated by LFY (Wagner et al., 1999).

WD WD1 (LWD1)/LWD2 as new clock proteins involved in photoperiod control were uncovered in an early-flowering Arabidopsis mutant defective in both LIGHT-REGULATED WD1 (LWD1) and LWD2, both of which encode WD (for Trp and Asp)-containing proteins. Their presence is essential for the proper expression phase and period length of both the oscillator and output genes known to participate in Arabidopsis photoperiod sensing. Validation of presence of WD 40 protein encoding region has been done for mango, necessitating its detailed investigation.

Floral transition: Enabling putative native homologs in perennial fruits The pathways that enable the floral transition regulate the expression of floral repressors that antagonize the pathways described above that promote the activation of the floral pathway integrators (Fig.2). The enabling pathways are viewed as regulating “meristem competence” (Bernier, 1988). High levels of the floral repressors keep the meristem “blind” to promotive floral signals. Different genes like FLC, TFL1 and SVP are supposed to be repressors of the floral pathway integrators (Boss et al., 2004)(Fig.3). These repressor genes are of particular interest in fruit tree breeding because they are responsible for the maintenance of juvenility. The down-regulation of floral repressor genes


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS results mostly in the activation of floral integrators and subsequently in the development of inflorescences and flowers. One of the best characterized floral repressor genes in fruit trees is TERMINAL FLOWER 1. The presence of a putative TFL1 homolog in the domesticated apple Malus domestica was firstly described by Kotoda et al. (2003).They isolated the coding region of MdTFL1 from cDNA ofthe apple cv. ‘Jonathan’. Based on the results of a Southern hybridization, the authors assumed the presence of multiple copies of MdTFL1 in the apple genome. This assumption was confirmed by Esumi et al. (2005) who found two types of cDNA for TFL1 homologs in six investigated Maloid species for apple, Japanese pear, European pear, quince, Chinese quince and loquat. The expression of TFL1 homologs of Japanese pear and quince revealed high level of expression was found in the apical meristem but it significantly recede just before floral differentiation. This could be an indication that a decrease in expression of these TFL1like genes induces floral initiation in Maloid species. Ectopic expression of CsTFL in Arabidopsis resulted in a significant delay in flowering. Furthermore, it was found that CsTFL expression is correlated with juvenility in Citrus (Pillitteri et al., 2004). It is assumed that down-regulation of CsTFL using a transgenic approach could be a powerful tool to reduce the juvenile stage and to induce early flowering. Based on the findings obtained from apple, orange and grapevine it could be ascertained that TFL1-like genes are present in perennial fruit tree crops, and that they have a comparable function to TFL1 in Arabidopsis. Another very interesting gene is MdJOINTLESS the predicted amino acid sequence of which is very similar to that of LeJOINTLESS of tomato and SVP of Arabidopsis. The primary role of LeJOINTLESS in tomato is to maintain the inflorescence state 150

by suppressing the sympodial program of development in inflorescence meristems. The SVP gene acts in contrast to LeJOINTLESS as a floral repressor. This gene acts in a dose dependent manner to delay flowering. Furthermore, it does not alter the effects of photoperiod or temperature on flowering time (Boss et al., 2004). Whether the function of MdJOINTLESS is more like LeJOINTLESS or more like SVP is unknown up to now.

Fig. 3: Pathways That Enable the Floral Transition (Boss et al., 2004) A central regulator of the enabling pathways is the floral repressor FLC. High levels of FLC repress the activity of the floral pathway integrators,and this antagonizes their activation by floral promotion pathways. Many genes are involved in regulating FLC expression. FCA, FY, FVE, FPA, and vernalization repress FLC (FLD and LD are not included here because they are not required in all genotypes). FRI, VIP3/4, ESD4, and EFSupregulate FLC. TFL1 and SVP also may antagonize the activation of the floral pathway integrators but are not included here because their regulation and interaction with FLC are unclear.

Ectopic expression of flowering genes in fruit trees Several key genes have been identified and described which regulate floral induction


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS and flower development in Arabidopsis. In this context two genes, LFY and AP1, necessary for the determination of the flower meristem identity was confirmed by constitutive over expression of the Arabidopsis LFY gene resulting in precocious flowering in rice, tobacco and hybrid aspen (Weigel and Nilsson 1995; Nilsson and Weigel 1997; He et al., 2000). Further, the LFY gene was successful used to accelerate the juvenile phase in citrus (Peña et al., 2001). After constitutive overexpression of the Arabidopsis AP1 gene early flowering was obtained in transgenic citrus (Peña et al. 2001) and tomato (Ellul et al., 2004). With the work published by Peña and Co-workers (Peña et al., 2001) the proof of principle was adduced that genes coming from an herbaceous plant as A. thaliana could be used to manipulate specific traits in fruit tree species. Starting from this fact several studies using the AP1 and LFY genes of Arabidopsis were performed on apple but up to now no early flowering was described .More successful was the work using the BpMADS4 of silver birch. This gene is similar to FUL of Arabidopsis and after constitutive overexpression of BpMADS4 precocious flowering was found in transgenic apple (Flachowsky et al., 2007). In BpMADS4 transgenic apple plants the juvenile stage was dramatically reduced. Several lines set up their first flowers during in vitro cultivation.Transgenic plants overexpressing the LEAFY (Weigel and Nilsson 1995) and CONSTANS (Simon et al., 1996) genes have been produced. These genes are sufficient to determine floral fate in lateral shoot meristems, with the consequence that flower development is induced precociously. This phenotype was also reported in plants overexpressing the phytochrome genes (Robson and Smith, 1997). In Arabidopsis, the acquisition of floral meristem identity (FMI) by these primordia is controlled by the

interaction of positive and negative regulators.

CONCLUSION The genetic control of flowering has been extensively studied in model herbaceous plant systems such as Arabidopsis. Although several genes have been shown to play important roles in the regulation of floral meristem identity in other species, LEAFY (LFY), Flowering Locus T(FLT and Constans(CO) which form the backbone of the network and, consequently, they are the ones whose role in the process has been best analyzed in Arabidopsis and whose homologues have been studied in mango.Among them, the Constans gene is controlled by the circadian clock and photoperiod to regulate flowering time. It has been recently reported that constans gene is widely conserved in photoperiodic plants and is responsible for production of a systemic signal and its presence has been confirmed in mango Preliminary results have revealed a constans-like gene sequence in mango having 36% homology with both the apple Constanslike protein-I gene (col1) and its protein-II gene (col2), and 40% homology with Arabidopsis col0 gene. Further sequencing and characterization of the mango COL1 gene is underway. Another FLOWERING LOCUS –like (MiFT) gene has been isolated from mango leaves. The FT gene is a floral pathway integrator gene whose function is to bring together the environmental and endogenous cues. Presence of transmembrane motifs and hydrophilic amino acid moiety implies its signal transduction ability. Another Meristem identity gene leafy implicated in flowering induction was also confirmed in mango cvs. Global assay can further, demonstrate role of promoting and enabling gene by analyzing the dynamic behavior of the shoot apex, across multiple time points and multiple genetic backgrounds in mango.


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Boss, P.K., Bastow, R.M., Mylne, J.S., Dean, C. 2004 Multiple pathways in the decision to flower: enabling, promoting, and resetting. Plant Cell. 16, S18-S31 Carmona,M.J., Cubas P., Martinez-Zapater, J.M., 2002. VFL, the grapevineFLORICAULA/ LEAFY ortholog, is expressed in meristematic regions independently of their fate. Plant Physiology. 130, 68-77 Corbesier, L., Vincent, C., Jang, S., Fornara, F., Fan, Q., Searle, I., Giakountis, A.,Farrona, S., Gissot, L., Turnbull, C., Coupland, G. 2007. FT protein movement contributes to long-distance signaling in floral induction of Arabidopsis. Science 316, 1030–1033. Davenport, T.L. 2003 .Management of flowering in three tropical and subtropical fruit tree species. HortScience.38:1331-1335. Davenportm T.L. 2006. Pruning strategies to maximizetropical mango production from the time of planting torestoration of old orchards. HortScience. 41:544-548. Davenport, T.L. 2007. Reproductive physiology of mango. Braz. J. Plant Physiol. 19(4):363-376. Endo, T., Shimada, T., Fujii, H., Kobayashi, Y., Araki, T.and Omura, M. 2005. Ectopic expression of an FT homolog from Citrus confers an early flowering phenotype on trifoliate orange (Poncirus trifoliata L. Raf.). Transgenic Research 14, 703-712. Esumi, T., Tao, R., Yonemori, K. 2005 Isolation of LEAFY and TERMINAL FLOWER 1 homologues from six fruit tree species in the subfamily Maloideae of the Rosaceae. Sexual Plant Reproduction 17, 277-287. Flachowsky, H,, Peil, A., Sopanen, T., Elo, A. and Hanke, V. 2007. Overexpression of BpMADS4 from silver birch (Betula pendula Roth.) induces early flowering in apple (Malus × domestica Borkh.). Plant Breeding 126, 137-145. He, Z.H., Zhu, Q., Dabi, T., Li, D.B., Weigel, D. and Lamb, C. 2000. Transformation of rice with the Arabidopsis floral regulator LEAFY causes early heading. Transgenic Research 9, 223-227.


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Huang. T, Böhlenius H, Eriksson S, Parcy F, Nilsson O 2005 The mRNA ofthe Arabidopsis gene FT moves from leaf to shoot apex and induces flowering.Science. 309, 1694-1696. Kardailsky, I., Shukla, V.K,. Ahn, J.H., Dagenais ,N., Christensen, S.K., Nguyen,J.T., Chory, J., Harrison, M.J., Weigel, D. 1999. Activation tagging of the floral inducer FT. Science 286, 1962-1965 Kobayashi Y, Kaya H, Goto K, Iwabuchi, M. and Araki, T. 1999. A pair of related genes with antagonistic roles in mediating flowering signals. Science 286,1960-1962 Kotoda, N. and Wada, M. 2005. MdTFL1, a TFL1like gene of apple, retards the transition from the vegetative to reproductive phase in transgenic Arabidopsis.Plant Science. 168, 95-104 Kotoda N, Wada. M., Komori, S., Kidou, S., Abe, K., Masuda. T., Soejima. J. 2000. Expression pattern of homologues of floral meristem identity genes LFY and AP1 during flower development in apple. Journal of the American Society for Horticultural Science. 125, 398-403. Mandel ,M.A., Yanofsky, M.F. 1995. The Arabidopsis Agl8 Mads box gene is expressedin inflorescence meristems and is negatively regulated by Apetala1.Plant Cell. 7, 1763-1771 Matsuda, N., Ikeda K, Kurosaka M, Isuzugawa K, Endo T, Omura M,TakashinaT 2006 In vitro flowering on transgenic pears (Pyrus communisL.) expressing CiFT, a Citrus ortholog of the Arabidopsis FT gene. Abstract Book of the 3rd Intl. Rosaceae Genomics Conf., 19-20 March, 2006. Napier,New Zealand, p 45. Michaels SD, Amasino RM 1999. FLOWERING LOCUS C encodes a novel MADS domain protein that acts as a repressor of flowering. Plant Cell 11,949-956. Moon, J, Suh S.S., Lee H, Choi, K.R., Hong, C.B., Paek, N.C., Kim, S.G., Lee I. 2000 The SOC1 MADS-box gene integrates vernalisation and gibberellin,signals for flowering in Arabidopsis. Plant Journal. 35, 613-623.

Muñoz-Fambuena, N., Mesejo, C., Gonzez-Mas, M.C., Primo-Millo, E., Agust M., Iglesias, D.J. 2011. Fruit regulates seasonal expression of flowering genes in alternatebearing ‘Moncada’ mandarin. Ann. Bot. 108, 511–519. Nishikawa, F., Endo, T., Shimada, T., Fujii, H., Shimizu, T., Omura, M., Ikoma, Y., 2007. Increased CiFT abundance in the stem correlates with floral inductionby low temperature in Satsuma mandarin (Citrus unshiu Marc.). J. Exp. Bot. 58,3915–3927. Nuń˜ez-Elisea, R., Davenport, T.L., Caldeira, M.L. 1996. Control of bud morphogenesis in mango (Mangifera indica L.) by girdling, defoliation and temperature modification. J. Hortic. Sci. 71, 25–40. Parcy F, Nilsson O, Busch MA, Lee I, Weigel D. 1998. A genetic framework for floral patterning. Nature. 395(6702):561-6. Pillitteri, L.J. ,Carol J. Lovatt, and Linda L. Walling. 2004. Isolation and Characterization of a TERMINAL FLOWER Homolog and Its Correlation with Juvenility in Citrus. Plant Physiology, Vol. 135, 1–12. Peña L, Martin-Trillo M, Juarez J, Pina JA, Navarro L, Martinez-Zapater JM 2001 Constitutive expression of Arabidopsis LEAFY or APETALA1genes in citrus reduces their generation time. Nature Biotechnology 19, 263-267. Putterill, J., Laurie, R., and Macknight, R. 2004. It’s time to flower: The genetic control of flowering time. Bioessays 26: 363–373. Ravishankar, H., Rao, M.M. and Bojappa, K.M., 1979. Fruit-bud differentiation in mango ‘Alphonso’ and’ Totapuri’ under mild tropical rainy conditions. Scientia Hortic., 10: 95—99. Schmid, M., Uhlenhaut, N.H., Godard, F., Demar, M., Bressan, R., Weigel, D.,Lohmann, J.U. 2003. Dissection of floral induction pathways using global expression analysis. Development 130, 6001-6012. Schultz, E. A. and Haughn, G.W. 1991.LEAFY, a Homeotic Gene That Regulates


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Wada, M., Cao, Q.F., Kotoda,N., Soejima, J. and Masuda, T, 2002. Apple has two orthologues of FLORICAULA/LEAFY involved in flowering. Plant MolecularBiology 49, 567-577. Walton, E.F., Podivinsky, E., Wu, R.M. 2001. Bimodal patterns of floral gene expression over the two seasons that kiwifruit flowers develop. Physiologia Plantarum. 111, 396-404.

Sreekantan L and Thomas M.R. 2006. VvFT and VvMADS8, the grapevine homologues of the floral integrators FT and SOC1, have unique expression patterns in grapevine and hasten flowering in Arabidopsis. Functional Plant Biology. 33, 1129-1139.

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Sung, S.K., Yu, G.H., Nam, J., Jeong, D.H., An, G. 2000. Developmentally regulated expression of two MADS-box genes, MdMADS3 and MdMADS4, in the morphogenesis of flower buds and fruits in apple. Planta. 210, 519-528. Tamaki, S., Matsuo, S., Wong, H.L., Yokoi, S., Shimamoto, K., 2007. Hd3a protein is a mobile flowering signal in rice. Science. 316, 1033–1036. Tan, X., Calderon-Villalobos, L. I., Sharon, M., Zheng, C., Robinson, C. V., Estelle, M. and Zheng, N.2007.Mechanism of auxin perception by the TIR1ubiquitin ligase. Nature 446 , 640-645. Theißen G, Becker A, Di Rosa A, Kanno, A., Kim, J.T., Munster, T., Winter, K.U. and Saedler, H. 2000. A short history of MADS-box genes in plants. Plant Molecular Biology 42, 115-149. Van der Linden C.G., Vosman, B., Smulders, M.J.M. 2002. Cloning and characterization of four apple MADS box genes isolated from vegetative tissue.Journal of Experimental Botany. 53, 1025-1036.

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ENGINEERING CROP IMPROVEMENT THROUGH RNAI Sangeeta Saxena Babasaheb Bhimrao Ambedkar University (A Central Universiity), Lucknow, U.P.

INTRODUCTION

RNA-interference in flowering

RNAi (RNA-interference) holds a lot of potential for crop improvement in this era of plant molecular biology and genetic engineering. In order to provide food security, improvement of crops both with respect to quality and quantity is demand of the day. Today, the RNAi as a technology is used to target many plant genes for down regulating or silencing the expression of a particular gene whether it is constitutive, stress induced , stage or tissue specific etc.. It includes endogenously induced gene silencing effects of miRNA as well as silencing triggered by foreign dsRNA like siRNA. RNAi is a technology that is homology dependent i.e. specificity is sequence-based and depends on the sequence of one strand of the dsRNA corresponding to part or all of a specific gene transcript. The dsRNA binds with a protein complex DICER which cleaves it into short fragments with a few unpaired overhung bases at both ends. The short dsRNA fragments (siRNA or miRNA) integrate with another active protein complex RISC. Consequently, one of the RNA strands (anti-guide strand) is degraded while the other is selected as a guide strand which remains bound to RISC complex. When a complementary mRNA is located by an RISC bound guide strand, it binds to it and is cleaved and degraded. This RNAi technology has not only helped both plant scientist and breeders to produce improved crop varieties but now has become a powerful tool for functional genomics, determining the function of all the genes in the plant genome, male sterility, disease and pathogen resistance etc.

Now it is reported that RNAi plays a major role in the developmental process in plants like formation of leaves, flowers, flowering time etc. which are complex processes regulated through an array of proteins and environmental factors. The developmental pathways in plants include the passage from seed germination to an adult stage, marked initially by formation of vegetative structures, different floral and reproductive organs once it enters in the reproductive phase. RNAi through an extensive network of short interfering RNA molecules is found to be involved in regulating the developmental timings in plants for flowering. One of the example cited here illustrating the role of miRNA in flower development is that of miRNA 172. In Arabidopsis, miR172 acts on several proteins known to play role in floral repression (Wu et al., 2009; Zhu et al., 2011; Xie et al., 2012) and due to increase in action of miR172 the floral repressors are reduced resulting in floral developmental phase. The flowering time in angiosperms is one of the most critical stages for reproductive success in them. The flowering commences when there is a switch from vegetative to reproductive phase in response to certain environmental signals. The flowering time is controlled by several endogenous and environmental pathways, with about 180 genes responsible for controlling flowering time is shown in Arabidopsis (Zhu et al., 2011). miR319 is also found to play a significant role in flowering in addition to leaf morphogenesis


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS and is thus one of the critical conserved miRNA for development, growth, morphogenesis, and reproduction in plants (Nag et al., 2009; Schommer et al., 2012). It is also reported that RNAi mediated gene silencing of the MdTFL1 gene in apple induces early flowering (Szankowski et al ., 2009).

Other applications of RNAi 1.

2.

Crop Improvement/ Modulation of agronomically important traits (Warthmann et al., 2008). Resistance to viruses ((Tenllado et al., 2004; Qi-Wen et al., 2006).

3.

Plant growth development and stress resistance (Bosheng Li et al.,2003).

4.

Respone to abiotic stresses. (Ines Trindade et al., 2010).

5.

Low glutenin rice variety (Kusuba et al., 2003)

6.

Insect pest resistance (Alexey et al. (2008,Rosso et al., 2009)

7. 8.

Transgenic corn (Baum et al., 2007). Bt cotton (Mao et al., 2007).

9.

Gene expression studies/ functional genomics etc.

In the present lecture although various application of RNAi in crop improvement will be discussed, role of miRNA and siRNA in flower development shall be emphasized. The above mentioned applications are still restricted to laboratory experiments and RNAi based transgenic plant products have not appeared in the market commercially yet.

REFERENCES Baum, J. A., Bogaert, T., Clinton, W., Heck, G. R., Feldmann, P., Ilagan, O., Johnson, S., Plaetinck, G., Munyikwa, T., Pleau, M., Vaughn, T. & Roberts, J. 2007. Control of

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coleopteran insect pests through RNA interference. Nature Biotechnology, 25, 13221326. Kusaba, M., Miyahara, K., Lida, S., Fukuoka, H., Takario, T. Sassa, H., Nishimura, M. and Nishio, T. 2003. Low glutenin content 1: a dominant mutation that suppresses the glutenin multigene family via RNA silencing in rice. Plant Cell, 15: 1455-1467 Nag, A., King, S. and Jack, T. 2009. Mir319a targeting of TCP4 is critical for petal growth and development in Arabidopsis. PNAS., 106, 22534–225393 Qi-Wen Niu, Shih-Shun, Lin., Jose Luis Reyes, Kuan-Chun Chen, Hui-Wen Wu, ShyiDong Yeh and Nam-Hai, Chua 2006. Expression of artificial microRNAs in transgenic Arabidopsis thaliana confers virus resistance Nat Biotechnol., 24 (11):1420-1428 Rosso, M. N., Jones, J. T. and Abad, P. 2009. RNAi and functional genomics in plant parasitic nematodes. Annual Review of Phytopathology, 47 : 207-232. Schommer, C., Bresso, E.G. and Spinelli, S.V.2009 Role of MicroRNA miR319 in Plant Development. Signaling and Communication in Plants 15, DOI 10.1007/ 978-3-642-27384-1_2. Szankowski, I.S., Waidmann, A., ElDin Saad Omar, H., Flachowsky, C., Hättasch, M.V. Hanke 2009. RNAi-Silencing of MdTFL1 Induces Early Flowering in Apple; In proceeding of: Proc. 1st IS on Biotechnol. of Fruit Species, Volume: Acta Hort., 839, ISHS 2009 Tenllado, F., Llave, C. and Díaz-Ruíz, J. R. 2004. RNA interference as a new biotechnological tool for the control of virus diseases in plants. Virus Research, 102, 85-96 Wang, J.-W., Hong, G.-J., Tao, X.-Y., Wang, L.-J., Huang, Y.-P. and Chen, X.-Y. 2007. Silencing a cotton bollworm P450 monooxygenase gene by plant-mediated RNAi impairs larval tolerance of gossypol. Nature Biotechnology, 25, 1307-1313.


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Warthmann, N., Chen, H., Ossowski, S., Weigel, D. and Herve, P .2008. Highly Specific Gene Silencing by Artificial miRNAs in Rice. Plos one , 3 (3): 1829. Wu, G., Park, M.Y. and Conway, S.R. 2009 . The sequential action of miR156 and miR172 regulates developmental timing in Arabidopsis. Cell, 21:138 (4): 750– 759.

Xie, K., Shen, J. and Hou, X. 2012. Gradual Increase of miR156 Regulates Temporal Expression Changes of Numerous Genes during Leaf Development in Rice. Plant Physiology, 158: 1382–1394. Zhu, Q.H. and Helliwell, C.A. 2012. Regulation of flowering time and floral patterning by miR172. Journal of Experimental Botany, 62 (2): 487–495.


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MOLECULAR EVENTS DURING FLOWER INDUCTION IN MANGO Manish Srivastav, S. K. Singh and A. K. Singh Division of Fruits and Horticultural Technology Indian Agricultural Research Institute, New Delhi-110 012

INTRODUCTION Flowering and fruit set are the most critical of all events occurring after establishment of a tree crop. Under favourable growth conditions, the time and quantum of flowering greatly determines the yield during a given season. Floral induction is of vital importance from a practical viewpoint, particularly for cultivated fruit trees, because it determines to a considerable extent the success of commercial orchards by its influence on fruit quantity and quality. Floral induction in mature fruit trees constitutes a morphogenetic transition of stem cells in apical, as well as lateral central meristems into differentiated floral cells. This transition implies the activation and transcription of a great number of genes. Considerable advances have been made recently in deciphering the molecular genetic mechanisms that result in the morphogenetic transition from vegetative to a reproductive stage. This progress has only been possible through the use of a few model plants, like Antirrhinum and Arabidopsis and the obtained basic results with these plants can obviously be applied to many annual/ biennial plants. However, whether this emerging molecular-genetic model can fully explain recent experimental results obtained for floral induction in perennial plants, particularly angiosperm trees, seems doubtful. This regulation of floral induction is significantly different in perennial compared to annual/biennial plants insofar as the floral promoter in annual/biennial plants induces all the above-ground meristems to flower in the same season, whereas in perennial plants a sophisticated regulatory system consisting

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of many different factors, finely tunes floral induction so that only a proportion of meristems will be transformed into flowers at any one time. One of the main and most important characteristics of mature perennial plants is to maintain some of their aboveground buds/meristems in a vegetative state, whereas annual/biennial plants, when induced to flower, consume them all at once. Floral induction in Arabidopsis and most certainly in all other annual/ biennial plants is induced by exogenous and/or endogenous cues, which initiate a sequence of gene expressions, including the flowering integrator gene FT, or orthologs of it, in leaves and subsequently its protein presumably moves via the phloem into responsive meristems where it induces the expression of floral identity genes and thus flowering. Thus, the FT protein is presently considered as the long time hypothetical ‘Florigen’ and a similar mechanism may exist in perennial plants as well, because a number of the genes found to be involved in floral induction in Arabidopsis have also been detected in perennial trees, although sometimes with different functions. This basic molecular-genetic model of floral induction ‘level one- regulation’ explains the basic regulatory mechanism for floral induction shared by both groups of plants. However, in addition a ‘level-tworegulation’ of floral induction was seemingly present in perennials from the beginning and obviously necessary for the more plastic quantitative floral induction found in these plants. ‘Level-two-regulation’ would be involved in floral induction of perennial


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS plants in a way that (i) a great number of exogenous and endogenous factors participate in the floral induction process to ensure that prevailing conditions would be able to influence floral induction and (ii) a floral promoter, no matter how strong, would not be able to transform all the above-ground meristems into floral meristems. The mechanism(s) by which perennial plant perform these functions obviously differs in temporal as well as spatial ways between various species and cultivars and is greatly modified by different horticultural treatments.

Facts about mango flowering Floral initiation and induction Mango flowering is a key reproductive event for the production of fruit. Initiation is the onset of shoot development, regardless of the type of shoot evoked. It involves cell division and elongation of cells in leaf primordia (vegetative shoots), lateral meristems (generative shoots) or both (mixed shoots) in the nodes of the resting buds, and is followed by cell divisions in the apical meristem to form more nodes (Davenport, 2009). Shoot initiation can be stimulated by environmental factors, such as the change from dry to rainy season in the tropics and a shift from cool to warm temperatures. Initiation can also be stimulated by anthropogenic factors such as pruning, irrigation, application of nitrogen substances and/or fertilizers and exposure to ethylene. However, Reece et al. (1949) realized that a putative signal, which triggers initiation of shoot development, is separate and different from the inductive signal that determines the fate of the shoot. Shoot initiation in mango, i.e. initiation of bud break, must occur before induction can determine the type of shoot to be evoked in those buds. They are different physiological events that lead to the formation

of reproductive, vegetative, or mixed shoots. Many herbaceous plants are photoperiodic, that is they flower in response to day length. Photoperiod is sensed in the leaves, with longday (LD) and short-day (SD) plants flowering in response to the change in the dark period, requiring short and long dark periods, respectively. In contrast, Davenport (1995) found that photoperiod had no effect on the vegetative or floral state of axillary buds in mango, and cool inductive temperatures 180 C day/100C night caused floral initiation in container grown mango. Induction in mango is the temporary commitment of buds to evoke a particular developmental pathway (i.e. vegetative shoot, generative shoot or mixed shoot) when growth is initiated (Davenport, 2009). Coincident with shoot initiation, induction occurs based on the conditions present at the time of initiation (Davenport, 2000). Although conditions suitable for floral induction may be present before shoot initiation in tropical fruit trees, determination of the inductive conditions in buds is not made until initiation occurs. Mango growth is not continuous. It occurs as discontinuous, ephemeral flushes of shoots from apical or lateral buds of resting stems. Vegetative flushes typically occur one to several times per year on individual stems. The numbers of flushes that occur annually, including the flowering flush, depend upon size of tree, growing conditions, and cultivar (Davenport, 2000). Mango flowering is thought to be determined by a short-lived, temperatureregulated florigenic promoter (FP). The FP has been shown to be synthesized in leaves and transported to buds via phloem based on the observed requirement of leaves for mango flowering (Reece et al., 1949; Singh, 1959, Davenport et al., 2006 & 2009). Through defoliation, girdling and decapitation experiments in mango established the requirement for leaf factors for floral induction


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS and grafting experiments demonstrated transmission of the stimulus from an induced donor stem to receiver stems (Kulkarni, 1991). A substance thought to offset the influence of the florigenic promoter is the putative vegetative promoter (VP), which appears to be regulated by stem age. Vegetative or reproductive (generative and mixed shoot) induction appears to be governed by the ratio of both components, not their absolute concentration in buds at the time of shoot initiation. Therefore, regardless of the endogenous levels of the individual components perceived in buds at the time of shoot initiation, floral and vegetative inductive responses can be effectively explained by the ratio of the FP and VP (Davenport, 2000). When the putative ratio of the FP and VP increases to a critical threshold level due to high FP as a result of low temperatures in the subtropics, or decreased VP levels in stems of advanced age compared with the basal level of FP in the tropics, it results in floral induction when shoots are initiated in stems. Overall, high FP/VP ratios when shoot initiation occurs may be conducive to induction of generative shoots, whereas low ratios may be conductive to induction of vegetative shoots, and at intermediate levels, mixed shoots are induced. FP appears to be upregulated during exposure to cool night temperatures below 180 C in subtropical conditions; however, there appears to be a basal level present at all times regardless of temperature in order to regulate flowering during warm temperature conditions of the tropics. Floral induction of mango shoots at the time of shoot initiation in subtropical latitudes is, thus, strongly influenced by cool winter temperatures but moderated by the age of the resting stems from which they emerge. In the tropics, floral induction of shoots occurs only in terminal stems that have attained sufficient time in rest since the previous flush of at least four months.

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The hormonal control model, which proposes that floral or vegetative induction of initiating shoots involves interaction of the FP and VP was thoroughly studied in mango during cool temperatures in subtropical field conditions. Under those conditions, only 1/4 of a leaf per stem was sufficient to induce 95 per cent reproductive shoots when initiated in the tested stems. One half of a leaf or more caused 100 per cent reproductive shoots to form. It is proposed that more FP is synthesized in leaves under cool temperature conditions than during warm tropical conditions with a lower basal level of FP. Reece et al. (1949) documented how the FP apparently moved down the stems of a leafy branch and up into defoliated branches, which resulted in floral induction. Davenport (2006) suggested that during early panicle development in cool, floral inductive temperatures, demonstrated movement of the FP from deblossomed donor stems bearing 1– 5 leaves to induce flowering in initiating buds on nearby leafless, deblossomed receiver stems borne on two forks of bifurcated branches. Branches with designated deblossomed donor stems bearing no leaves produced only vegetative shoots on the donor and in all receiver stems Davenport (2006). This result confirmed that leaves are required for synthesis of FP to cause a flowering response. Five leaves in the donor stems produced 100 per cent flowering shoots in all donors and receivers. Intermediate numbers of leaves on the deblossomed donor stems displayed a pattern of decreasing proportions of reproductive shoots and increasing proportions of vegetative shoots with increasing distance of deblossomed receiver stems from the donor stems. The further the receiver stems were from the donor stem and the fewer the number of leaves on the donor stem, the lower the proportion of reproductive shoots induced in buds. This contrasted with increasing reciprocal proportions of vegetative


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS shoots with increasing distance from the donor. FP is translocated to buds via phloem. Its movement was determined to reach more than 100 cm from one stem to another along branches under cool, floral inductive subtropical conditions.

Conceptual flowering models in mango Conceptual flowering models for mango elaborate the physiological basis of floral induction. The first two models present a carbohydrate regulated mechanism of flowering in mango, however, the second two models propose that flowering and vegetative growth are under hormonal regulation.

Molecular basis of flowering in mango Advances in molecular biology of flowering in the facultative, long-day, model

herbaceous plant, Arabidopsis thaliana, has provided new insights into the nature of the floral stimulus. Activation of the CONSTANS (CO) gene encodes a protein, which in turn induces expression of the FLOWERING LOCUS T (FT) gene localized in phloem tissue in vascular veins of leaves. The protein product of FT acts as the florigenic component, that is translocated to Arabidopsis buds (Corbesier et al., 2007). This conclusion is supported by translocation from leaves to buds of an analogous protein encoded by Hd3a, a rice ortholog of FT, which appears to be the florigen operating in that crop (Tamaki et al., 2007), and the aspen ortholog, PtFT1, which along with CONSTANS was demonstrated to regulate the timing of flowering and growth cessation of Populus trichocarpa (Bohlenius et al., 2006). Once translocated to buds, the protein product of FT is thought to combine with the bZIP

Mango Flowering Model

Fig. 1. Conceptual flowering model of mango. The model summarizes the proposed roles for various phytohormones in initiation of shoot growth and in defining the vegetative or reproductive outcome of that growth (induction). Single lines in the scheme are promotive and double lines are inhibitory.


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS transcription factor (FD) protein to activate transcription of floral identity genes, such as APETALA1 (AP1) to begin floral expression (Abe et al., 2005; Wigge et al., 2005). Similar mechanisms may be active in mango but with greatly altered dynamics of gene expression. Zhang et al. (2005) and Davenport et al. (2006) isolated a CONSTANS-like gene (MiCOL) from mango leaf DNA by a combination of genomic walking and PCR methods. CONSTANS is a circadian expression gene interacting with the photoperiodic pathway in Arabidopsis (Putterill et al., 2004). This gene is central to activation of the FT gene in Arabidopsis during long days, but because mango is nonphotoperiodic, the role of this gene in mango flowering systems remains unclear. The mango ortholog has 79 per cent, 76 per cent, and 62 per cent homology with two apple CONSTANS genes, MdCOL2 and MdCOL1, and the Arabidopsis CONSTANS gene (AtCO), respectively. Expression of floral pathway integrator genes results in the activation of genes called ‘‘floral meristem identity genes,’’ that confer floral identity to new emergent meristems and activate ‘‘floral organ identity genes’’ leading to an appropriate development of floral organs (Liu et al., 2009). Efforts to isolate the FT or homologous gene responsible for synthesis of the protein, FP, however, have, thus far, been unsuccessful. In addition, the MiFT gene, a homolog of FLOWERING LOCUS T, has been isolated from mango leaves and has been proposed to be a putative flowering signal in mango because of (1) its great identity with other plant FT-like genes, (2) the presence of conserved key amino acid residues of FT, (3) an exclusive upregulated expression in leaves of adult trees exposed to cool temperatures, and (4) consistency of results that show that the expression of this gene is directly correlated

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with flowering induction (de los SantosVillalobos et al., 2012; Nakagawa et al. 2012). Similar to the SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1), FT is a floral pathway integrator gene whose function is to integrate environmental and endogenous signals such as gibberellins, autonomous, vernalization, thermosensorial, and photoperiod responses (Castro et al., 2011).

REFERENCES Abe, M., Kobayashi, Y., Yamamoto, S., Daimon, Y., Yamaguchi, A., Ikeda, Y., Ichinoki, H., Notaguchi, M., Goto, K., Araki, T. 2005. FD, a bZIP protein mediating signals from the floral pathway integrator FT at the shoot apex. Science, 309:1052-56. Bohlenius, H., Huang, T., Charbonnel-Campaa, L., Brunner, A.M., Jansson, S., Strauss, S.H., Nilsson, O. 2006. CO /FT Regulatory module controls timing of flowering and seasonal growth cessation in trees. Science, 312:1040-43. Castro, Marýń I., Loef, I., Bartetzko, L., Searle, I., Coupland, G., Stitt, M., Osuna, D. 2011. Nitrate regulates floral induction in Arabidopsis, acting independently of light, gibberellin and autonomous pathways. Planta, 233:539–52 Chacko, E.K. 1991. Mango flowering—still an enigma. Acta Hortc, 291:12–21 Corbesier, L., Vincent, C., Jang, S., Fornara, F., Fan, Q., Searle, I., Giakountis, A., Farrona, S., Gissot, L., Turnbull, C.G.N., Coupland, G. 2007. FT protein movement contributes to long-distance signaling in floral induction of Arabidopsis. Science, 316:103033. Davenport, T.L. 2000. Processes influencing floral initiation and bloom: the role of phytohormones in a conceptual flowering model. Hort. Technol., 10:733-39. Davenport, T.L. 2009. Reproductive physiology. In: The mango: botany production and uses, 2nd


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS edn. (ed. R.E. Litz). CAB International, Wallingford, pp 97–169. Davenport, T.L., Ramos, L., Alani, A. 1995. Evidence for a transmissible florigenic promoter in mango. In: Proceedings 22 nd Annual Meeting of the Plant Growth Regulation Society of America. Minneapolis, pp.159. Davenport, T.L., Ying, Z., Kulkarni, V., White, T.L. 2006. Evidence for a translocatable florigenic promoter in mango. Sci. Hort. 110:150-159. Davenport, T.L., Zhang, T., Ying, Z. 2006. Isolation of potentially regulating mango flowering. Proceedings of the 33rd annual meeting of the Plant Growth Regulation Society of America, Quebec City, Canada, July 9–13, 2006. Plant Growth Regulation Society of America, Alexandria, pp 109–110. de los Santos-Villalobos, S., Parra-Cota, F.I., deFolter, S., Pena-Cabriales, J.J. 2012. Primers to amplify flowering locus T (FT) transcript in mango (Mangifera indica) and their potential use in other angiosperms. Plant OMICS 5:453–457 gloeosporioides. World J Microbiol Biotechnol, 28:2615-23. Liu, C., Thong, Z., Yu, H. 2009. Coming into bloom: the specification of floral meristems. Development, 136:3379-91

Nakagawa, M., Honsho, C., Kanzaki, S., Shimizu, K., Utsunomiya, N. 2012. Isolation and expression analysis of flowering locus t-like and gibberellin metabolism genes in biennial-bearing mango trees. Sci. Hortic., 139:108–17. Putterill, J., Laurie, R., Macknight, R. 2004. It’s time to flower: the genetic control of flowering time. Bioassays, 26:363–373 Reece, P.C., Furr, J.R., Cooper, W.C. 1949. Further studies of floral induction in the Haden mango (Mangifera indica L.). Am. J. Bot., 36:734-40. Singh, L.B. 1959. Movement of flowering substances in the mango (Mangifera indica L.) leaves. Hort. Adv. 3:2027. Tamaki, S., Matsuo, S., Wong, H.L., Yokoi, S., Shimamoto, K. 2007. Hd3a protein is a mobile flowering signal in rice. Science, 316:1033-36. Wigge, P.A., Kim, M.C., Jaeger, K.E., Busch, W., Schmid, M., Lohmann, J.U., Weigel, D. 2005. Integration of spatial and temporal information during floral induction in Arabidopsis. Science, 309:105659. Zhang, T., Ying, Z., Davenport, T.L. 2005. Isolation and characterization of a CONSTANS-like gene in mango (Abstract). Plant Biology, p.151


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REGULATORY ROLES OF PHYTOHORMONES AND CARBOHYDRATES OF FLOWERING IN MANGO K.K. Upreti, S.R. Shivu Prasad and G. Bindu Indian Institute of Horticultural Research Hessaraghatta Lake Post, Bangalore – 560 089, Karnataka

INTRODUCTION Flowering is decisive factor in the productivity of mango (Mangifera indica L.). The process associated with mango involves shoot initiation followed by floral differentiation of apical bud, and panicle emergence (Murti and Upreti, 2000). All these developmental events occur in most of the mango cultivars sometimes during OctoberDecember under tropical as well as subtropical conditions. The induction of floral bud formation has strong links to prevailing environmental conditions and age of terminal resting shoots (Davenport, 2007; 2009) as under tropical locations, the flower induction occurs in response to age of previous year shoot, while cool inductive conditions are vital to floral induction under sub-tropical conditions. It is documented that a low temperature around 15-18°C and 6-8 months old matured shoots have a strong possibility for floral growth initiation (Nunez-Elisea and Davenport, 1991; 1995; Murti and Upreti, 2000). Ramirez and Davenport (2010) illustrated the basic mechanism underlying mango flowering, involving an interaction between putative temperature dependent florigenic promoter and an age regulated vegetative promoter, with a high ratio in favour of florigenic promoter under low temperature conditions contributing to floral development. It is found that the florigenic promoter that is graft transferable and short-lived has potential to move long distances during cool conditions and carbohydrates in the donor tissues are anticipated as driving force in the transport

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of florigenic promoter (Davenport et al., 2006). However, the exact nature of florigenic promoter and mechanism by which it elicit floral responses is still not elucidated. It is found that the florigenic promoter has strong link to phytohormonal factors, which act in association with carbohydrate production and supply during differentiation for expression of floral responses (Davenport, 2009; Murti and Upreti, 2000). Phytohormones are considered intrinsic signal molecules produced within the plant, and occur in extremely low concentrations. These regulate various cellular physiological processes and optimize metabolic activity in targeted cells locally and in other locations of the plant upon transportation. Flowering has strong links to the phytohormonal synthesis and balance in the developing reproductive organs. In mango, correlative evidences have been provided for the regulation of floral process by phytohormones more specifically by gibberellins employing exogenous applications of growth regulators. Some evidences of phytohormonal involvement are also available from measurements of phytohormones in various organs during flowering time. Besides, carbohydrates reserves depicted as key energy producing chemicals also play important role floral induction process in many crop species. The increased capacity of leaf phloem loading system is contributory to floral induction. Based on the postulate suggested by Sachs and Hackett (1983) that increased assimilate supply to the shoot apex


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS contributed to floral initiation, the strategic role for carbohydrates in the flowering process was established. Thus, the adequate availability or supply of carbohydrate reserves is crucial to floral bud development and floral initiation. This is well supported from the fact that a high endogenous ratio of carbon to nitrogen ratio in plants is stimulatory to flowering whereas a low C : N ratio favours vegetative growth (Corbesier et al., 2002). In mango, Singh (1960) demonstrated that initiation of flowering mainly depends on maintenance of higher C/N ratio. This builtup in C:N ratio vital for floral growth points towards definite increases in carbohydrates. Evidences also point on role of gibberellins in the carbohydrate mobilization by stimulating their degradation to hexoses (Jacobsen and Chandler, 1987). Thus, a reduction in gibberellins important to induction of flowering could favour carbohydrate accumulation for eliciting of flowering. Davenport (2009) suggested that the maturity of terminal shoots and accumulation of carbohydrates in the shoot apex are in some way linked to the synthesis of the floral stimulus.

Role of gibberellins Gibberellins are considered derivatives of tetracyclic diterpenoid compounds and exhibit wide array of physiological activities. In many perennial fruit species including mango, gibberellins have been shown to suppress floral process (Davenport, 2009; Murti and Upreti, 2000). The floral inhibitory response of gibberellins depends upon concentrations, growth stage, and climatic conditions of the location. Kachru et al. (1971) found that higher GA3 concentrations applied on bud of On year Dashahari mango tree just before flower bud differentiation inhibited flowering to greater extent than the at lower concentration. The gibberrellin application in

some varieties also delayed emergence of panicle by 4-6 weeks with higher concentration causing longer delay (NunezElisea and Davenport, 1991). Nunez-Elisea and Davenport (1998) further reported that the mango buds initiated inflorescences despite GA3 treatment, when morphogenesis occurred during exposure to cool, floral-inductive temperatures. GA 3 treatment resulted in vegetative shoot production only when buds differentiated during exposure to warm temperature conditions. Thus, GA3 delayed inflorescence initiation but did not cause vegetative morphogenesis when bud differentiation occurred in cool temperatures. In contrast to delaying inflorescence initiation in cool temperatures, GA 3 did not delay vegetative growth during warm temperatures, thereby revealing that GA3 prevents initiation of reproductive shoots of mango rather than inhibiting floral induction. Further, the differential responses of gibberellins are attributed as the consequences of prevailing endogenous concentrations levels of gibberellins in differentiating buds during application, variations in uptake pattern, besides bud sensitivities, age of shoots and cultural practices. There are limited evidences to show the mechanisms involved in the inhibition of floral initiation by gibberellins. It is believed that increased gibberellins might enhance or maintain the synthesis and production of other hormones and/or modify assimilate partitioning to suit for inhibitions in flowering. Limited attempts have been made in understanding the molecular events involved in the inhibition of floral initiation by gibberellins in mango. Several investigations on role of endogenous gibberellins in relation to mango flowering have been carried out and most of investigations have conclusively proved that increasing levels of gibberellins are inhibitory to flowering of mango. Abdel Rahim et al.


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS (2011) reported decline in GA1+3+20 during floral development based on comparison between off-year and on-year of flowering in mango cultivars like Miska, Mahmoudi and Toto Combo growing in Sudan. Tongumpai et al. (1991) observed increasing levels of gibberellins in whole stem over 16 weeks prior to vegetative shoot emergence and decreasing levels over the same period prior to panicle development. GA1, GA3, GA4 and GA7 were the most abundant gibberellins in apical stem bud (Shivu Prasad, 2014) and their consistent decrease in growing buds contributed to floral induction. Concentration of GA3 increased with in buds with increase in stem age. Chen (1987) found highest level of gibberellins in sap during leaf differentiation and lowered at rest, panicle emergence and full flowering. Also the endogenous level of gibberellins in mango was high in “off’ year shoot-tips than in “on” year shoot-tips, suggesting that the erratic flowering or failure of flowering during the “off’ year may be associated with a higher gibberellins levels in the shoot-tips. The role of gibberellins in mango flowering is further confirmed from the finding of Upreti et al. (2013) and Abdel Rahim et al. (2011) that paclobutrazol inhibited gibberellins in mango buds concomitant with profuse induction in flowering.

Role of auxins Auxins influence flowering in many perennial plants and increasing trends in auxins in many perennials is vital to floral induction. However, their direct role in mango flowering is still not conclusive. It is believed that these act in association with other phytohormones like ethylene, cytokinin or gibberellins through manipulation in cell elongation process. Lal and Ram (1977) reported that the shoot tip of Dashehari during flower bud differentiation several fold higher auxins in the “On” year than the “Off” year. 166

The increased in auxins is related to lower IAA oxidase activity and ogibberellin at flowering (Chacko et al., 1970). Further blocking auxin transport by TIBA induced flowering in Alphonso mango by arresting apical dominance. We presume that maintenance of high auxins is vital for floral growth possibly by its action on cell elongation process in the event of declined gibberellins.

Role of cytokinins Cytokinins are compounds with a structure resembling adenine which promotes cell division. These compounds are considered important regulator of shoot meristematic activity and their high production in apical meristem during active growth facilitates reproductive morphogenesis. Chemically, primary cytokinins are N6-substituted purine derivatives. Numerous reports ascribe a stimulatory or inhibitory function to cytokinins in different developmental processes including flowering. The perennial crops lack definite evidences with respect their involvement in flowering process. We witnessed distinct accumulation of cytokinins in buds prior or during floral bud development in mango (Upreti et al., 2013) and is well supported by induction of flowering in mango by externally applied cytokinins (Nunez-Elisea, 1990). In another studies, Murti and Upreti (1998) observed high cytokinin activity corresponding to zeatin riboside (ZR) and zeatin (Z) in the growing leaves of regularly flowering cv. Totapuri at flowering time as compared to Langra in its ‘Off’ year. The increase in cytokinins is either due to stimulated synthesis of cytokinins that are transported to shoots or arresting of cytokinin degradation. As side chain, 2-methyl-but-2en-1-ol in cytokinin moity are derived from isoprenoid pathway which also regulates gibberellins biosynthesis, it is obvious that the


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS declining gibberellins would facilitate cytokinin accumulation for floral induction. Further, support for cytokinin increase is derived from its increase by paclobutrazol during flowering vis-a-vis decline in gibberellins (Upreti et al., 2013). Further evidence for cytokinin involvement in mango flower induction is deduced from cytokinin, benzyl adenine induced floral bud formation in mango (Chen 1985). The increased cytokinin helped mango trees in maintaining high leaf water potential during floral induction.

Role of ethylene The fact that smudging and external applications of ethrel stimulates mango flowering suggests ethylene plays important role in floral induction. This was confirmed subsequently from the analysis of endogenous ethylene concentration during flowering (Chen, 1985; Nunez-Elisea, 1991). We also found higher ethylene concentration in Totapuri and Neelum (regular) at flowering stage compared to juvenile Langra (biennial) during flowering (Murti and Upreti, 1996).Various indirect evidences linked to ethylene production such as extrusion of latex in terminal buds at flower initiation and leaf epinasty near apex during panicle growth also confirm involvement of ethylene in mango flowering process. Besides, KNO3 has been shown to stimulate flowering under tropical condition in number of mango cultivars. As KNO 3 is suggested to induce ethylene production and efficacy of KNO 3 is suppressed by ethylene biosynthesis inhibitors, the involvement of ethylene appear an important factor in mango flower process. However, Davenport and Nunez-Elisea (1990) reported contrasting findings wherein no measurable differences ethylene concentration in Florida grown mango cv. Keitt compared to base values during floral growth and ethrel

and not KNO 3 was found effective in increasing flowering. Such differences may be reflection of cultivars, growing condition and stage of analysis.

Role of abscisic acid Abscisic acid is a sesquiterpene derivative, which typically regulate numerous developmental processes and has an inhibitory effect on cell elongation. It also regulates adaptive stress responses in plants. As stress conditions are required floral morphogenesis, its increased concentrations is expected to facilitate floral growth though stress adaptive mechanism involving osmotic adjustment and synthesis of stress responsive genes. It also has influence on flowering through is effects on sucrose metabolism. In mango, studies dealing with ABA role in floral inductions have not been made in great detail. Chacko (1968) was first to report the presence of certain inhibitors similar to abscisic acid in mango shoots. His findings that the shoots of ‘Dashehari’ during ‘On’ year and ‘Totapuri’ trees had relatively higher levels of this inhibitors during flower bud initiation than the shoots of ‘Dashehari’ in ‘off’ trees indicated that the inhibitors are important in the initiation of flowering in mango. Further, the observation that defoliation of ringed shoots of ‘Dashehari’ and ‘Janardhan Pasand’ ‘On’ trees activates vegetative buds in such shoots, suggested that the inhibitor produced in the leaves is necessary for checking vegetative growth (Singh, 1971). Since the abscisic acid is antagonistic to both gibberellins and auxins, thereby affecting cell elongation and thereby providing conditions for floral bud differentiation. Upreti et al. (2013) found profound accumulation of abscisic acid in paclobutrazol untreated and treated trees of Totapuri during pre-burst stages and concluded its possible significance in creating situation for floral growth in differentiating


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS buds. The increase in abscisic acid is the result of induction in its biosynthesis as a result of modifications in the isoprenoid pathway which is partially common in ABA and gibberellins biosyntheses. The high ABA levels are expected to induce bud dormancy, which consequently help in floral bud formation as flowering in mango is found to occur on buds at rest. Significant positive relationship between ABA and C : N ratio support its involvement in floral inductions possibly via carbohydrate mobilization (Upreti et al., 2013).

Role of carbohydrates The requirement of high C : N ratio for floral initiation, induction in C : N ratio by paclobutrazol (Upreti et al., 2013) and induction of flowering through girdling (Davenport, 2009) depicts that increase in carbohydrate availability is important attribute to floral initiation in mango. The C : N ratio differed with growth of shoots in the varieties, which reveals its dependence upon environmental conditions and prevailing metabolic balance. The positive association of floral bud initiation with C : N ratio shows that the increase in carbohydrate availability and translocation is vital to the floral initiation in mango (Shivu Prasad, 2014). Thus, shoots with higher carbohydrate content are expected to favour flower initiation provided inductive conditions are prevailed. For this a critical level of carbohydrate is desired to express flowering favourable activity. As reproductive growth is a high energy requiring developmental event, the requirement of high carbohydrate demand at flowering is obvious. We presume an expected balance in certain carbohydrates for eliciting flowering responses by suitably influencing some associated enzymes. The increase in carbohydrates are concomitant with changes in phytohormones and we expect that declining gibberellins levels would favour 168

built of simple carbohydrates, as one of principal effect of gibberellins is to mobilize carbohydrates by stimulating their degradation to simple sugars. Thus, an environment where gibberellins are high, no starch accumulation can take place. However, gibberellins concentration needs to fall below threshold levels to show carbohydrate accumulation tendency and floral initiation. Distinct differences in carbohydrate pattern is seen in growing shoots and with approach of flowering consistently higher production of total sugars and reducing sugars in apical buds of untreated as well as paclobutrazol treated trees was witnessed with peak concentration available at bud burst (Shivu Prasad et al., 2014). Paclobutrazol induced increase in soluble sugars at flowering has also been reported in mango by Abdel Rahim et al. (2011). The increased carbohydrates demand is due to the outcome of enhanced photosynthetic rate as result of increased photosynthetic efficiency required for encouraging reproductive development process. In addition, Davenport (2007) believed occurrence of putative florigenic promoter in mango leaves that is loaded into the phloem and actively translocated by mass flow generated by high concentration of photoassimilates for the induction of floral differentiation. Furthermore, the directional movement of sugars from photosynthesizing leaves to tissues requires high energy and as the floral inductive process is high energy consuming metabolic process; the requirement of high soluble sugars for the energy supply for floral development is well justified. The mass flow of assimilated sugars from the leaves might help in the transport of a florigenic promoter to facilitate production of generative buds. Koch (2004) reported that the carbohydrates serve as signaling molecules for sugar responsive genes, leading to different physiological responses such as


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS turgor driven cell expansion and defense responses. As one of the factor required for facilitating floral bud morphogenesis is drought, the increase in soluble sugars are expected to prepare the buds for the floral initiation through inductions in stress tolerance owing to osmoprotectant nature of carbohydrates. Starch is one of the basic reserves of carbohydrates that accumulate in chloroplasts of photosynthesizing leaves. The increase in starch content more profoundly in the leaves than buds at different pheno-phases and their declining levels at bud break stage indicated its involvement in the enhanced soluble sugar levels (Shivu Prasad et al., 2014). It showed that increased starch accumulation in the mango shoots is important attribute to the expression of floral responses. Jacobsen and Chandler (1987) reported that gibberellins arrest starch accumulation by promoting the breakdown and the mobilization of starch. Thus, the observed increase in starch could be the effect of the lowered gibberellins content. We witnessed considerably decreased gibberellins in mango buds and leaves as buds reached bursting stage (Upreti et al., 2013). Soluble sugars such as sucrose, glucose and fructose are important substrates of metabolism that help the plants in many developmental and physiological events (Koch, 2004). These sugars regulated the import of carbon to metabolically active sink for sustained plant growth. Corbesier et al. (1998) opined that the treatments that induce flowering might also lead to increased transport of soluble sugars from leaves to the apical meristem for floral induction. The increased sugars help in satisfying the energy requirements of trees for metabolically active processes like floral bud differentiation. Thus, the consistently increasing levels of sucrose, glucose and fructose in the apical buds in paclobutrazol untreated and treated trees with

advancement in floral bud growth are speculated as the result of increased synthesis and/or mobilization of soluble sugars following rising metabolic demand of developing floral buds. The Bernier et al. (1993) report that soluble sugars act as a signal in the processes linked to flowering lend supported to this. Monerri et al. (2011) reported high level of these sugars in the growing shoots of citrus before the onset of flowering. In support of our results, it has been reported that hexose concentration exhibits seasonal changes with strong accumulation before blooming in cherry (McCamant, 1988) and before bud break in peach (Maurel et al., 2004). Thus increased levels of sugars such as sucrose and glucose might be of significance in eliciting floral response in mango. Besides, that gibberellins act functionally antagonistic to sucrose, and gibberellins overcome the inhibitory effect imposed by glucose and sucrose further strengthened our contention. Distinct induction in amylase activity in leaves and buds during floral bud formation and the induction in amylase activities might contribute to higher levels of glucose. The gibberellins are required for induction in amylase activity in certain tissues of some plants and as paclobutrazol treated trees showed reduction in gibberellins (Upreti et al., 2013), the induction in amylase activity might not be related to reduction in gibberellins. Further, gradual decline in amylase activity from 510 to 515 phase is helpful in contributing starch accumulation for activating floral bud differentiation. Acid invertase and SS are illustrated as important sucrose degrading enzymes and SPS as a sucrose synthesizing enzyme. A balance among the sucrose degrading and synthesizing enzymes is expected to regulate the metabolism and supply of sucrose along with glucose and fructose in sustaining the growth of developing sinks. Shivu Prasad (2014)


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS experienced induction in the activities of acid invertase and SPS more drastically than the SS by paclobutrazol application in the developing floral buds; the enzyme activities were high at bud burst phase. Moreover, carbohydrate metabolism appears to be more complex since various other enzymes may also be involved in their metabolism. Thus, more detailed investigations are needed to explain explicitly the role of carbohydrates in the induction of mango flowering. Besides the links by which hormones control the sugar balance needs to be established in delineating the inductive effects of carbohydrates in mango flowering. Thus, we suggest that the interaction between the optimal level of carbohydrates in buds and putative floral stimulus to trigger floral induction is decisive to floral initiation in mango.

FUTURE PROJECTIONS 

CONCLUSION Flower bud differentiation and floral initiation in mango denotes distinct changes in phytohormones and mobilization of carbohydrates from source to sink, which depend by climatic conditions, shoot age and size, besides genetic characters. Consistent decline in gibberellins with profound increase in cytokinins and abscisic acid in combination with sufficient built-up of carbohydrates in the buds approaching bud burst stage ensure floral inductions in mango. The accumulation of abscisic acid in buds at floral initiation is contributory in optimizing leaf water potential and sap flow besides optimizing carbohydrate availability and cytokinins in sustaining differentiation activity in growing buds. Not all gibberellins exhibits similar physiological activity to elicit floral response and nature and type of gibberellins are variety dependent. Distinct carbohydrate accumulation takes place as buds attain floral differentiation phase and it possible phytohormones like

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gibberellins and abscisic acid may have link in facilitating carbohydrate accumulation. The floral bud differentiation is expected to starts from 5 to 7 months before the actual flowering, for which 6-8 months old shoots with sufficient carbohydrate reserves are important. The information on timing of floral bud differentiation is vital under a particular set of climatic conditions for a variety, to enable growers to schedule the manuring, irrigation and other cultural operations to have better yield. Paclobutrazol induced increase in early flowering is the result of increase in C : N ratio, leaf water potential and distinct decreases in gibberellins at floral bud growth. In eliciting floral growth, it also favoured increase in cytokinins and abscisic acid.

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Understanding the role of environmental factors in relation to floral bud differentiation in terms of identification and characterization of flowering stimulus for explaining flowering process. Delineating regulatory mechanism to flower induction at cellular and molecular levels. Association and link between phytohormones and carbohydrates in revealing floral initiation. Defining role and contribution of stored and current photo assimilates to flowering.

LITERATURE CITED Abdel Rahim, A.O.S., Elamin, O.M. and Bangerth, F.K. 2011. Effects of paclobutrazol (PBZ) on floral induction and associated hormonal and metabolic changes of biennially bearing mango (Mangifera indica L.) cultivars during off year. ARPN Journal of Agric. Biol. Sci., 6: 55-67.


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Bernier, G., Havelange, A., Houssa, C., Petitjean, A. and Lejeune, P. 1993. Physiological signals that induce flowering. Plant Cell, 5: 1147-1155.

cereals. In: Plant Hormones and their Role in Plant Growth and Development (ed. P.J. Davies). pp. 164-193. Martinus Nijhoff Publishers, Boston (USA).

Chacko, E.K. 1968. Studies on physiology of flowering and fruit growth in mango (Mangifera indica L. ). Ph. D. Thesis, IARI, New Delhi, India.

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Kachru, R.B., Singh, R.N. and Chacko, E.K. 1971. Inhibition of flowering in mango (Mangifera indica L.) by gibberellic acid. Hort. Science, 6:140–141. Koch, K. 2004. Sucrose metabolism: regulatory mechanisms and pivotal roles in sugar sensing and plant development. Current Opin. Plant Biol., 7: 235-246. Lal, K. and Ram, S. 1977. Auxins of mango shoot – tip and their significance in flowering. Pantnagar J. Res., 2:31-35. Maurel, K., Leite, G.B., Bonhomme, M., Guilliot, A., Regeau, R., Petel, G. and Sakr, S. 2004. Trophic control of bud break in peach (Prunus persica) trees: a possible role of hexoses. Tree Physiol., 24: 579-588. McCamant, T. 1988. Utilization and transport of storage carbohydrates in sweet cherry. MS Thesis. Washington State University, Pullman (USA). Monerri, C., Fortunato-Almeida, A., Molina, R.V., Nebauer, S.G. and Garcia-Luis, A. 2011. Relation of carbohydrate reserves with the forthcoming crop, flower formation and photosynthetic rate, in the alternate bearing ‘Salustiana’ sweet orange (Citrus sinensis L.). Scientia Hort., 129: 71-78. Murti, G.S.R. and Upreti, K.K. 1998.Changes in the levels of endogenous hormones in relation to shoot vigour in mango (Mangifera indica L.). Plant Physiol. & Biochem., 25(2): 167171. Murti, G.S.R. and Upreti, K.K. 2000. Plant hormones. In: Advances in Plant Physiology, Vol. 3 (ed. A. Hemantaranjan), pp 109-148, Scientific Publishers, Jodhpur (India).


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Murti, G.S.R. and Upreti, K.K. 2000. Plant hormones. In: Advances in Plant Physiology, vol. 3, (Ed. A. Hemantaranjan), Scientific Publishers, Jodhpur, India, pp. 109148.

Sachs, R.M. and Hackett, W.P. 1983. Source-sink relationships and flowering. In: Strategies of Plant Reproduction (ed. W.J. Meudt). pp 263-272. Allanheld, Osmun, Ottawa (Canada).

Nunez-Elisea, R. and Davenport, T.L. 1991. Requirement for mature leaves during floral induction and floral transition in developing shoots of mango. Acta Hort., 296: 33–37, 1991.

Shivu Prasad, S.R., Reddy, Y.T.N., Upreti, K.K. and Rajeshwara, A.N. 2014. Studies on changes in carbohydrate metabolism in regular bearing and off season bearing cultivars of mango (Mangifera indica L.) during flowering. International J. Fruit Science (in press).

Nunez-Elisea, R. and Davenport, T. L. 1998. Gibberellin and temperature effects on dormancy release and shoot morphogenesis of mango. Scientia Hort., 77: 11-21. Nunez-Elisea, R. and Davenport, T.L. 1995. Effect of leaf age, duration of cool temperature treatment, and photoperiod on bud dormancy release and floral initiation in mango. Scientia Hort., 62: 63-73. Nunez-Elisea, R., Caldeira, M. L. and Davenport, T. L. 1990. Thidiazuron effects on growth initiation and expression in mango (Mangifera indica L.). Hort. Science, 25:11671168 Ramirez, F. and Davenport, T.L. 2010. Mango (Mangifera indica L.) flowering physiology. Scientia Hort., 126: 65-72.

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Singh, L.B. 1977. Mango. In: Ecophysiology of Tropical Crops (ed. P.T. Alvim, T.T. Kozlowski). pp. 479-485, Academic Press, New York (USA). Singh, R.N. 1971. Biennial bearing in fruit trees. ICAR Tech. Bull. (Agri.) No., 30. Ind. Council Agri. Res., New Delhi. Tongumpai, P., Jutamanee, K. and Subhadrabandhu, S. 1991. Effect of paclobutrazol on flowering of mango cv. ‘Khiew Sawoey’. Acta Hort., 291: 67–79. Upreti, K.K., Reddy, Y.T.N., Shivu Prasad, S.R., Bindu, G.V. and Jayaram, H.L. 2013. Hormonal changes in response to paclobutrazol induced early flowering in mango cv. Totapuri. Scientia Hort., 150: 414418.



PHYSIOLOGY OF FLOWERING IN LITCHI IN RELATION TO SHOOT MATURITY Vishal Nath and Sanjay Kumar Singh National Research Centre on Litchi (ICAR) Musahari Farm, Muzaffarpur 842 002, Bihar

ABSTRACT Inconsistent flowering in litchi tree is a major problem in all growing areas of the world. Litchi trees flowers when early flush development coincides with cool temperature and other factors such as age of the stems, maturity of flushes and vegetative dormancy in upcoming season. Vegetative flushing during winter reduce flowering and pruning of young flushes in early December, stimulate flowering. Lower the temperature, chances of flowering in mature shoots increased with increased in level of total phenol content, total non structural carbohydrates and restricted leaf nitrogen level (1.75-1.85%) before flower initiation. Vegetative growth in the 1-2 months prior to panicle emergence completely eliminates flowering. Leaves next to the inflorescence are more important for yield than the older leaves. Shoots emerged during August and November found to bear panicles in month of February. Locality with warm winter (daily maximum temperature above 25 0C) is avoided for litchi culture. Various methods of controlling flush cycle like girdling, water stress, growth retardants and flush killers promotes flowering. Fluctuation in starch concentration in small branches correlates very well to vegetative growth and fruiting. Increased leaf potassium content improves photosynthesis rate, WUE and stomatal conductance of litchi plants. Thirty days before flower bud formation, ABA increased markedly and the total cytokinin content increased in the xylem sap reaching maximum during flower bud formation and full bloom.

INTRODUCTION Fruit crops have been a matter of extensive research in recent years because of

their importance to agriculture, the human diet and lively hood security. Some aspects of flowering in trees make them especially challenging for physiologists, breeders and growers. First, the juvenile phase, which lasts for several years during which time no flowering or fruiting occurs; second, interactions between vegetative growth, flowers and fruit of the previous year on floral initiation in the current year, affect growers through phenomena such as biennial bearing, and make interpretation of research data difficult for scientists (Wilkie et al., 2008). The litchi (Litchi chinensis Sonn.), which is an important commercial crop in India due to its high demand in the season and export potentiality, has not yet attended the status of major crop due to the problem of low and irregular bearing habit. Besides a rich source of vitamin C, litchi contains a fair amount of Phosphorus, Calcium, Iron, Vitamins A and B (Ahmad, 1956). Litchi is an evergreen tree with medium to large, much branched, round topped canopy reaching up to 15 meters or more height when allowed to grow naturally under optimum soil and climatic conditions. Vegetative characters of litchi trees are very much susceptible to environment and can change with difference in climate, soil or cultural practices. The quality and productivity of litchi crop is determined by various physiological and environmental factors at a particular place notable among are emergence pattern and timing of new flush, maturity of shoot to bear panicle and health of shoot/panicle to bear and sustain the fruits till maturity.


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Litchi flowering to fruit development Flowers, in particular the female flower, are the predecessor to a litchi fruit. When the ovary of a female flower comes into contact with pollen from male flowers and fertilized the embryo develops into the fruit, provided pollination is successful. Most varieties do not flower or fruit consistently every year, especially the non-commercial varieties, may go many years without producing much fruit. Flowering in litchi trees occurs once a year in the spring on a physiological mature shoots which inturn resultant of 3-4 growth cycle (flush) in the year. Understanding this process is a key factor in managing litchi for optimal fruit production. Panicle bearing shoot in litchi grows in “recurrent terminal flushes”, which means that they grow from the end of branches in periodic spurts separated by short intervals of dormancy. Young litchi trees flush as many as 5-6 or more times in a year, whereas mature fruit bearing trees flush 2-3 times in a year with a bloom flush in the spring. The interval of dormancy between successive flushes is minimum 6 weeks (Das et al., 2003) and can be much longer depending on the tree size, age, weather conditions, growing conditions and variety (Table 1).

Flower bud differentiation

formation

and

Litchi must experience bud break of 2mm to 4mm during an extended period of cool weather. Litchi flowers during the spring months (north) and September (south), when the mean temperatures in preceding months are consistently below 200 threshold which is required for bloom formation during March– April in the northern hemisphere and AugustSeptember in the southern hemisphere. During warm winter (average temperatures above 200 C) most litchi trees will grow vegetatively and not produce flowers. It has

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been generally established that if the mean daily temperature is above 200C, new growth will be vegetative (i.e. leaves and branches), whereas if the mean temperatures are below this temperature flower panicles will form from emergent buds (Singh et. al., 2012). This process is known as flower bud differentiation and is a function of internal plant hormone levels, and prevailing environmental conditions. When the buds first emerge, they are a mixture of flower and leaf buds. As the bud continues to grow, the leaves fall off and an inflorescence develops, if the temperatures remain low. If the temperatures remain high, a mixed inflorescence with both flowers and leaves can develop. Solution for getting forced flower panicles during the winter months through bud break by pruning prior at the onset of an extended cold period generally called as flush removal/tip removal has been quite effective but cumbersome and tedious. At the same time the problem with this approach is that the remaining leaves left after the pruning is too old to support a good crop because the photosynthetic capacity and nutrient and energy output of the leaves diminishes with age.

Flush emergence and flowering Litchi leaves have a definite lifetime and is shed periodically. With a situation of winter vegetative growth flush, selective pinching/ or pruning of the growth flush by leaving some new leaves to support fruit development can be done for better flowering. A better strategy is to time your postharvest pruning so as to insure bud break during the cooler season. When a litchi tree flowers, the flowering panicle emerges 4-6 weeks after initiation has already taken place as showy multi flowered cluster, known as a panicle, on the end of branches (terminal inflorescence). It is believed that litchi needs a period of vegetative dormancy to initiate floral buds.


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Flower buds emerge in December and sometimes as early as November. The buds develop into a panicle during December and January. The flowers, which are borne on these panicles develop in February through March. Fruit from the trees which flower very late in the cycle often do not fully mature. A fully developed panicle consists of a main stem or spine known as a rachis, with lateral (axial) branches. These branches are covered with one or more spikelets each having three small greenish yellow non-fragrant flowers approximately 2 to 3 mm in length. Litchi flowers do not have petals, but they do possess the typical anatomical components of a flower: ovary, style, stigma and anthers. A panicle can be 30-45 cm feet in length or more long and have as many as 3000 flowers, although only a small percentage of these are ever pollinated (100-200). The number and percentage of the different types of flowers in litchi vary greatly with cultivar, environmental conditions, tree and nature of panicle within a tree. The production of functional female flowers varies between 10 and 60 per cent (Singh, et al., 2012). Flowers are usually produced in later winter or early spring and there are three types of flowers, which open in succession on the same panicle.

Flowering in response of various stresses Water stress has been thought to induce flowering in litchi but there is no conclusive evidence that water stress is directly involved in inductive processes as has been found in citrus (Menzel, 1983). The water stress is required to induce dormancy, which promotes flowering (Thunyarpar, 1998). Cool temperature are known to play an important role in stimulating flowering but other factors also play important role i.e. age of the shoots, since flushes are also suspected of influencing the tree’s response to cool temperature

(Davenport et al., 1999). Litchi being subtropical fruits crop, cool temperature became a key trigger of flower induction (FI). Due to cool temperature treatment a clear raise of cytokinins (CKs) in buds is opposed by a drop in gibberellins (GAs) and auxin (IAA). Deficit irrigation can enhance fruit quality by raising dry matter percentage and sugar content. Furthermore, controlled water deficit has been used as a technique to stimulate blossoming in litchi.

Flowering in response to flush maturity Flowering is very much related to emergence of flushes and its maturity. Flushing refers to the emergence of new shoots on the comparatively older shoots. The duration and interval of successive ûushes in litchi seems to be strongly dependent on the vigor of the tree, pruning practices, irrigation regimes radiation, and temperature. The flushing enlarges tree size and produce leaves for utilizing sunlight for carbohydrates synthesis, which supports fruit development in the ensuing seasons. Moreover, leaf flushing was one of the factors that counteract flowering process (Menzel and Simpson, 1992). Flushes of vegetative growth occur on groups of stem borne on scaffolding branches in isolated section of tree canopy. Flushing stems are usually connected at some common branch point within the tree limbs (Davenport, 2009). Appearance of enlarged leaf primordia and lateral meristems on the elongating main axis are the first indications of floral differentiation in litchi. The emerging inflorescence is initially similar to a vegetative flush and when the lateral meristem develop into secondary inflorescences or start producing small leaves (as in the case of mixed shoots), each panicle produces ten to hundreds of small flowers (Menzel and Waite, 2005).


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS The relationship between flowering and vegetative flushing activity in winter is well established in litchi. The shoot must be of high quality i.e. must have plenty of leaves, good built up of carbohydrates and above all matures on time. The winter flushes are not allowed as these do not flowers in upcoming season. Failure of shoot to bloom is generally attributed to an insufficient degree of dormancy required for initiation of flower bud formation. Floral initiation as the first step in the productivity of litchi plants in warm subtropical region (Das et al., 2003) is governed by shoot maturity and sufficient nutrient reserve in the shoot.

Out of three flushes in litchi, early (after harvest), mid (August to October) and late (after November) season; the early and midseason flushing influenced the yield, whereas the late season flushing do not contribute towards yield. Thus, the midseason flush (appearing in August-October) is of more significance in cultivars Bedana, Bombai and Deshi, whereas the early season flush (appearing in July) is the desirable vegetative flush in the rest of the cultivars with respect to yield (Pereira et al., 2005). The floral initiation takes place only after the shoot has undergone a period of vegetative dormancy (Menzel, 1983). There is minimum cycle of 6 to 8 weeks for ûushing and 4 to 6 weeks between ûushes is needed for litchi. In Australia, bearing shoot of litchi rarely completes more than two ûushes between harvest and ûower initiation (Batten and Lahav, 1994).

Fig.1 Flush emergence on secondary branches and mature flush of litchi on which flowering is expected in upcoming season

Source sink relationship for improved litchi production The relation between developing fruits (sink) with mother soil base (source) is well

Table 1. Pattern of emergence of different flushes in litchi cv. Shahi Flushing Pattern

% of total No. of Shoots

No 2nd flush and 3rd flush emerging during 1st to 31st December, 2nd flush emerging during 20th to 31st August and 3rd flush emerging during 1st to 31st December 2nd flush emerging during 1st to 20th September and 3rd flush emerging during 1st to 31st December 2nd flush emerging after 20th September and 3rd flush emerging during to 31st December 2nd flush emerging after 20th September and 3rd flush emerging during 1st to 31st December

6.0

% of bearing panicle 55.55

30.0

100.00

8.0

66.66

28.0

55.00

28.0

66.00

(Das et al., 2003)

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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS established in litchi. The development and transfer of nutrients from source to ultimate sink (fruit) has been very crucial. Generally, most perennial fruit trees do not flower when they are in vegetative growth. The intraplant variation in flushing and shoot growth pattern influences the overall floriferousness of the litchi plants (Singh et al., 2012). Under normal circumstances, one of three shoots initiates growth from apical or axillary buds in resting stem. Vegetative shoots produce only leaves at each node; generative shoots give rise to inflorescences; and mixed shoot bear both leaves and inflorescences at each node. There is importance of flushing management in terms of the bearing shoot for flowering and fruiting in litchi, and poor fruit retention would result from insufficient flushes on the bearing shoot, whereas poor flowering occurs when the bearing shoots produce immature flush and leaves in winter.

Flowering in response to mechanical barriers Closed girdling, spiral girdling led to increase in flowering in litchi with increases in soluble sugars and starch content in the shoot. Girdling of trunks or primary branches inhibits the downward transport of photosynthates, and promotes the accumulation of photosynthates in the upper canopy. Girdling of branches having 3 to 4 cm diameter or foliar application of 0.5 g paclobutrazol + 0.4 g of ethephon per litre with hardened flush in September (North) promote flowering in unproductive litchi trees.

Flowering in response to nutrition The relationship between the nutrition of fruit trees and fruit quality indices has been well documented (Dris et al., 1999). The right nutrient balance is essential to maintain fruit quality. Nutrients with the most notable

influence on fruit quality are nitrogen (N), phosphorus (P), potassium (K), and calcium (Ca) (Fallahi et al., 1985). The relationship between the leaf nutrients and fruit quality attributes showed positive relationships between leaf potassium (K) and anthocyanin content and titratable acidity (TA); leaf phosphorus (P) and pericarp, leaf nitrogen (N) and fruit weight; leaf calcium (Ca) and fruit firmness (Shivakumar and Korsten, 2007). Generally, the flower bud initiation in litchi starts in December and completed by the end of January. After harvest, the N contents in leaves and stalks rose while P, K contents in them continued to decline. The N content in xylem significantly increased at the preheading stage, but the P, K contents significantly decreased, and only P content significantly declined at the pre-blossoming stage, while N, P contents significantly rose after harvest. After harvest, the N contents in leaves and stalks rose, while P and K contents in them continued to decline. The N content in xylem increase at the pre-heading stage, but the P and K contents significantly decreased, and only P content significantly decline at the pre-blossoming stage, while N and P contents rose after harvest.

Flowering in relation to weather parameters The duration and interval of growth in litchi are strongly related to environmental conditions, with optimum leaf area production occurring at about 29°C (Batten and Lahav 1994). Variation in leaf flushing and reproductive activity of litchi may be due to variation in microclimate, soil nutrient (especially N) and insect attack which influences the endogenous rythem of each tree (Menzel and Simpson, 1992). Vegetative flushing in the 4-6 weeks period before the


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS time of panicle emergence eliminates flowering in spring (Menzel et al., 1988).

primordial leaves develop to form true compound leaves. If favourable conditions persists, through the initiation and differentiation of new nodes, the new primordial leaves develop into compound leaves at the distal part of the shoot. Vegetative shoot takes 6 weeks or longer, depending on the weather for flushing. During this period, the apex produces about eight leaves before returning to rest.

Initiation of mixed shoots in litchi occurs in mild weather, at temperature lower than those needed for purely vegetative shoots and higher than those for purely floral shoots. Both leaf primordial and lateral meristems develop, resulting in shoots with a leaf and an inflorescence at each node. Transition shoots commonly appear in litchi when shoot emerge during rapidly changing temperatures. These initiate one type of shoot, either vegetative or generative, which finish as the generative (Batten and McConchie, 1995).

Biochemical changes during flowering The changes in biochemical constituents in shoot like carbohydrates, phenols, soluble protein and amino acids in relation to flushing

In warm weather, the pre existing

Table 2. Biochemical changes associated with flushing and panicle emergence in litchi cv. Shahi Biochemical constituent

Carbohydrate (%) Total phenols (mg/100g) Total soluble protein (%) Total free amino acids (mg/g) L- Proline (mg/100g) LPhenylalanine (mg/100g) DL-Alanine (mg/100g) DlTryptophane (mg/100g)

1st flush 2nd Flush 3rd flush C.D. st st nd st nd rd at 5 Previous 1 Previous 1 2 Previous 1 2 3 season State season stage stage season stage stage stage % flush flush flush 9.26 4.92 9.54 6.23 5.61 6.71 6.32 7.21 4.87 1.114 0.36

0.24

0.54

0.50

0.29

0.61

0.57

0.5

0.29 0.355

0.18

0.29

0.19

0.28

0.36

0.14

0.19

0.23

0.34 0.118

0.86

1.28

0.38

0.62

0.85

0.68

0.64

0.79

1.07 0.214

0.82

0.34

0.19

0.18

0.65

0.22

0.92

0.28

0.29 0.168

0.16

0.31

0.29

0.52

0.21

0.85

0.51

0.37

0.18 0.131

0.00

1.19

0.52

0.55

0.24

0.37

0.39

0.29

0.28 0.089

0.16

0.65

0.43

0.36

0.58

0.14

0.12

0.23

0.24 0.139

(Das et al., 2004)

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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS and panicle initiation would help in developing a proper understanding of the panicle initiation process in litchi (Das et al., 2004) (Table 2). We hypothesized that a bearing shoot comprised of three to four flushes and its carbohydrate reserves are essential for adequate cluster production. Leaves close to inflorescences records lower rates of mitochondrial respiration (Rd) and net photosynthesis (Anet), and lower stomatal conductance (gs) and quantum efficiency of photosystem II under actinic light than vegetative shoot leaves. Leaf nitrogen concentration, generally decreased from the beginning until the end of flowering, had lower N in leaves close to inflorescences than in vegetative shoot leaves. However, these differences and changes are counterbalanced by an increase in leaf mass-to-area ratio so that leaf nitrogen per unit leaf area (Na) remained nearly constant during the whole flowering period, except in leaves close to panicles bearing set fruits. low Anet in leaves close to inflorescences is probably due to neither to changes in Na nor to a decrease in Rubisco activity induced by low gs, but rather to a decrease in electron flow in PS II. This

decrease is not directly associated with higher starch or soluble sugar contents. (Urban et al., 2004). The greatest constraints of litchi flowering is to get high beneficial commercial production, which can be overcome by breeding new cultivars or study physiology of flowering and we can try to modify the response by cultural practices. In litchi, the available carbohydrate as total non structural carbohydrate or starch is accumulated before flower initiation and leaf flushing (Thunyarpar, 1998). Young litchi shoot has relatively low rates of photo assimilation until the leaves are fully expanded and dark green and depends on assimilates from elsewhere in the plant. During leaf expansion, translocation of assimilates to the shoot occurs at the expense of the roots (Hieke et al., 2002). Starch concentrations of the lower stem and roots decreases as the young red leaves expanded, and increased as the fully expanded leaves turned dark green. Chlorophyll concentrations and net CO2 assimilation rate are high in the fully expanded dark green leaves (Hieke et al., 2002)

Fig.2. Flush emergence and flowering in litchi; a.) New flush emergence, b.) Flowering on September Flush, c.) Flowers ready for pollination.


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Starch concentration in the leaves is higher than that in the terminal shoots of the light flowering trees. It is suggested that carbohydrate distribution pattern may serve as an indication for the judging of the floral induction effect in litchi. Concentration of soluble sugars increases from November to December and then decreased in January, while the starch concentration increases progressively, especially in the upper parts of the canopy (Houbin et al., 2004). Starch concentrations in the heavy flowering trees are highest in small branches and decreased acropetally and basipetally, whereas the concentrations of soluble sugars record highest in the terminal shoots. The contribution of fruit photosynthesis to reproductive growth varies across species, environment and fruit type, but ranges from 5 to 15 per cent for many fruit trees. The developing fruit of ‘Tai So’ depend primarily on current CO2 assimilation from leaves rather than on stored carbohydrates. There is increase in cytokinin activity in the buds during flower bud differentiation in litchi. In dormant buds, the endogenous cytokinin content remains low, and the buds do not respond to exogenous cytokinin application. However, application of kinetin promotes flower bud differentiation after completion of bud dormancy. Thus, it can be referred as an indication that the increase in endogenous cytokinin levels during flower bud differentiation may be correlative rather than the cause of flower bud initiation (Chen, 1991). Flush growth should be restricted to 0.6– 2.0 cm in October-November and that leaves should be removed from flush growth > 10 cm. These practices prevent alternate fruit set and stabilise yield in litchi.

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REFERENCES Ahmad, S. 1956. The Litchi Leaflet. No. 122. Ayub Agric. Res. Inst. Faisalabad–Pakistan. Batten, D.J. and Lahav, E. 1994. Base temperature for growth processes of lychee, a recurrently flushing tree, are similar but optima differ. Aust. J. Plant Physiol., 21:589– 602. Chen, Wen, Saw 1991. Changes in Cytokinins before and during Early Flower Bud Differentiation in Lychee (Litchi chinensis Sonn.). Plant Physiol., 96:1203-1206. Das, B; Nath, V., Rai, M. and Dey, P. 2003. Investigation on flushing and panicle overgance in litchi under sub-humid subtropical plateau region of eastern India. Indian Journal of Horticulture, 61: 1-15. Davenport, T.I. 2009. Reproductive physiology. In: The Mango, Botany, Production and Uses (Ed. R.E. Litz,). 2 nd. CAB International Wallingford, UK. pp. 97-169. Davenport, T.L.; Li, Y. and Zheng 1999. Towards reliable flowering in lychee (Litchi chinensis Sonn.) in South Florida. Proc. Fla. Sta. Hort. Soc., 112:182-184. Hieke, S.; Menzel, C. M. and Lüdders, P. 2002. Shoot development, chlorophyll, gas exchange and carbohydrates in lychee seedlings (Litchi chinensis). Tree Physiology, 22:947–953. Jones, H.G. and Tardieu, F. 1998. Modelling water relations of horticultural crops: a review. Scientia Hort., 74: 21-46. Menzel, C.M. and Simpson, D.R. 1992. Growth, flowering and yield of litchi cultivars. Scientia Hort., 49:243-254. Menzel, C.M., Carseldine, M.L. and Simpson, D.R. 1988. Crop development and leaf nitrogen in lychee in sub-tropical queensland. Aust. J. Exp. Agric., 28:793-800. Pereira, L.S., Pathak, P. and Mitra, S.K. 2005. Relation between flushing cycles and flowering in different litchi cultivars. Indian Journal of Horticulture, 62(2):141-144.


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Singh, G., Nath V., Pandey, S.D., Ray, P.K. and Singh, H.S. 2012. The Litchi. FAO, Rome. Sivakumar, D. and Lise Korsten 2007. Relating Leaf Nutrient Status to Fruit Quality Attributes in Litchi cv. ‘Mauritius’. Journal of Plant Nutrition, 30: 1727–1735. Spreer,W., Nagle, M., Neidhart, S., Carle, R., Ongprasertand, S. and Muller, J. 2007. Effect of regulated deficit irrigation and partial root zone drying on the quality of mango fruits (Mangifera indica L., cv. ‘Chok Anan’). Agr. Water Manage, 88 : 173-180. Thunyapar, T. 1998. Physiological aspects on flowering of lychee and Longan: A Review.

J. Japan. Soc. Hort. Sci., 67(6): 1161-1163. Turner, D.W. 1994. Bananas and plantains. In: The Handbook of Environmental Physiology of Fruit Crops. Vol. II. Subtropical and Tropical Crops. (Eds. B.S. Schaffer and P.C. Andersen). CRC Press, Boca Raton, FL, pp. 37–64. Urban, L., Lu, P. and Thibaud, R. 2004. Inhibitory effect of flowering and early fruit growth on leaf photosynthesis in mango. Tree Physiology, 24:387–399. Wilkie, John, D., Sedgley, M. and Olesen, T. 2008. Regulation of floral initiation in horticultural trees. Journal of Experimental Botany, 59(12): 3215–3228.


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CANOPY MANAGEMENT AND EFFECTS OF PRUNING ON FLOWERING TENDENCIES IN FRUIT TREES W.S. Dhillon and Anirudh Thakur1 Punjab Horticultural Post- harvest Technology Centre, PAU Campus, Ludhiana-141 004 (Panjab) 1 Department of Fruit Sciences, PAU, Ludhiana-141 004 (Panjab) In plant kingdom, management of canopy architecture is a critical component to improve crop performance by increasing the magnitude of partitioning of dry matter towards reproductive phase. In general, management of canopy architecture deals with positioning and maintenance of plant’s framework in relation to optimum productivity of quality fruits. Canopy management is the most important fruit plant management practice. Training and pruning of fruit trees are the specialized horticultural operations. Training of the Pear trees should be done in such a manner that sufficient air and light gets penetrated inside the foliage to facilitate proper coloration and development of fruit of superior quality. Sufficient attention must be given to training of young plants to an appropriate system of training. The formation of photosynthates is the basis of plant growth and production. Net photosynthesis is influenced by environmental factors viz; light, temperature, CO2 concentration, water, fertility of the soil, etc. as well as by plant-related factors (morphology, structure and age of the leaf, presence of sinks, etc. (Proietti et al., 2000). Since whole-tree photosynthesis is primarily light limited (Lakso 1980), manipulation of canopy architecture to enhance global light interception is a major objective of all planting systems (Lakso and Corelli-Grappadelli 1992; Sansavini and Corelli-Grappadelli 1992; Tustin et al. 1988, 1998; Wagenmakers et al., 1991). In fruit trees, fruit yield and quality depend on the light microclimate. At the orchard and tree scales, fruit yield of healthy

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and well-watered trees is related to total light interception (Jackson 1980, Palmer 1989, Robinson and Lakso 1991) because photosynthetic carbon fixation depends mainly on the sunlight captured by a tree or an orchard. Plant performance can be understood as the crucial link between its phenotype and its ecological success and the form becomes ecologically and evolutionary relevant when it affects performance (Koehl 1996).

Basic principles management

of

canopy

Considering inherent characteristics and management factors constant, the productivity and quality of fruits largely depend upon tree vigour and weather parameters particularly light interception, prevailing temperature and humidity as well as air flow. The crux of the canopy management lies in the fact, as to how best we can manipulate the tree vigour to utilize natural resources efficiently for improving productivity and quality and to minimize the adverse effect of weather parameters. The proper sunlight exposure to foliage and fruits and prevailing temperature play vital role in photosynthesis, fruit bud differentiation, ripening and fruit quality etc., while increased air flow reduces disease pressure. The high humidity is congenial for pest and disease problems. Similarly, there are various undesirable influences of shading like promotion of herbaceous character, increases pH, reduces inflorescence initiation, suppress fruit set, slow fruit growth and ripening. Some


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS basic considerations in management of canopy architecture are:  Develop strong and desired structure and vigour.  Maximising light penetration in and outside the canopy  Avoidance of microclimate build-up congenial for diseases and pest  Optimizing productivity and quality of fruits  Prone to mechanization and feasibility in cultural operations  Crop regulation and crop diversification The study of plant architecture emerged as a new scientific discipline about 30 years ago. The architecture of a plant depends on the nature and on the relative arrangement of each of its parts; it is, at any given time, the expression of equilibrium between endogenous growth processes and exogenous constraints exerted by the environment. It aims at to identify these endogenous processes and to separate them from the plasticity of their expression resulting from external influences by means of observation and experimentation. Plant architectural analysis has proved to be one of the most efficient means currently available for the study of the organization of complex arborescent plants. Architectural concepts appear to be of particular interest for the understanding of crown construction in trees.

Objectives of canopy architecture 





To make maximize utilization of light as light has key role in flower induction as well as in fruit development through carbohydrate synthesis. Provide the basic tree form and to aid the development of a strong tree framework by encouraging strong wide crotch angles. To encourage tree for longer living and precocious bearing.

  

  

  

To expose maximum leaf surface area to sun. Permit proper levels of light and air distribution to the tree interior. To direct the growth of the tree so that various cultural operations such as spraying and harvesting. Achieve orchard uniformity. Produce the proper amount of well distributed fruiting wood. Encourage a structurally sound tree by removing branches with weak narrow crotch angles or those with diseased, damaged, or unproductive wood. Minimize tendencies toward biennial bearing. To accommodate more number of trees per unit area to increase the yield. To reduce the juvenility period of the fruit

Plant structure and light capture The rate of canopy photosynthesis depends on the biochemical capacities of the leaves as well as on the distribution of light within the tree canopy. Canopy management aims at modification in crown architecture for overall light harvesting and the efficiency of light harvesting. The total leaf area of plant canopy is most important factor that affects the absorbed radiation. Similarly, the distribution and arrangement of leaves within a plant canopy also strongly modify the light harvesting efficiency of unit foliage area (Cescatti and Niinemets 2004). The shape of the plant crown can be illustrated by the size, the ratio of height to width, and the shape of its contour. The intrinsic architectural pattern of the cultivar itself (Sansavini and Corelli- Grappadelli 1992) from upright highly branched scaffolds to low-branched tip-bearing cultivars (Lespinasse and Delort 1986). Because the solar inclination angle decreases from equator to pole, crowns with differing height to width


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS ratio have inherently varying efficiencies of light interception. Specifically, in high latitudes, light penetrates from high solar inclination angles, implying that beam path lengths become increasingly longer with increasing crown flatness. The beam path lengths are similar throughout the entire canopy for the narrow, vertically extended crowns that maximize the direct light interception of entire crown in high latitudes (Kuuluvainen 1992). It is further important that the crown shape can vary at any given height to width ratio. For low-solar inclination angles, the beam path length strongly increases with canopy depth for narrow ellipsoidal crowns (Valladares and Niinemets, 2007). However, the beam path length is essentially the same for narrow conical crowns, in which the branches in lower canopy positions reach farther from the stem, implying that such crown can be very efficient at low latitudes. In general, the more extended the cone, the larger is the fraction of irradiance captured (Jahnke and Lawrence 1965). Horizontal leaves at the top of the crown exhibit their maximum light interception efficiency at noon and summer season of the year when irradiance in sunny environments is well above the light saturation point for photosynthesis. Typically, foliage photosynthetic capacity (Amax) increases two- to fourfold from the bottom to the top of the canopy (Meir et al. 2002; Niinemets et al. 2006). Therefore, the superior light capture of horizontal leaves in high light usually translates into a negligible increase of potential carbon gain. In general, the effective light penetration into the tree canopy is approximately one meter. Based upon this fact, the canopy of a large tree can be broken down into three zones with regards to light penetration. The top portion of the tree receives 60 to 100 per cent full sunlight; zone two

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receives 30 to 59 per cent full sunlight and zone three receives less than 30 per cent full sunlight. Once light levels drop below 30 per cent of full sunlight, flower-bud formation is reduced, spur vigour is lost and fruit that is produced in this zone is small and of poor quality. With time, fruit production will decline in this area as a result of fruit spur death. Zone three is a non-productive zone and the size of this zone is influenced by tree size, form and pruning. This area of inadequate light can vary as much as 25 per cent in a large central leader tree to as little as 1.6 per cent in a dwarf central leader tree. The smaller area of a non-productive zone is one of the reasons why smaller trees can be more productive than large trees.

Light interception and utilization Interception of light in fruit plant canopies varies according to size, angle, orientation and surface features of the photosynthetic organ(s). Shade plants can increase their interception of light by producing larger leaves. Shade loving plants have larger leaves as compared to sunlit plants and hence some of the largest leaves are produced by plants found in rainforest understorey’s. The size leaf can change with respect to its position on the tree within individual plant, smaller leaves being produced near the top where radiation are maximum, and larger leaves towards the interior and base where light levels are lower. Similarly the light interception can be modified by changing the angle/orientation of the leaf. Vertical arrangements increase interception of light at low sun angles during early morning or late afternoon, and reduce interception at solar noon when radiation levels are highest. However, leaves that are arranged horizontally will intercept light throughout the day with maximum interception at noon.



Light Interception in relation to planting density Light exposure is also known to influence flower bud differentiation, fruit set, fruit colour and quality and can induce anatomical and physiological differences between leaves formed in shade or light. For any given training system, orchard design (i.e. row arrangement) is strictly related to planting density. The relationship between the number of trees per hectare and productivity, however, is not linear. Fruit quality declines at higher planting densities and also can negatively affect the fruit productivity. In double and triple row designs, difficulties are in orchard management, with effects on costs and fruit quality. Total light interception of an orchard can be raised by increasing the density of the canopy (i.e. increasing its LAI without increasing canopy volume), the height of the trees (in relation to free alley width), or by increasing the number of trees (of smaller size) per hectare. Increasing canopy density will cause an increase in the percentage of total light intercepted (F), although at high LAI values it will cause a reduction of well illuminated canopy volume, i.e. the volume of canopy capable of producing quality fruits. In apple Palmer (1980) calculated the LAI for three different training systems, palmate, slender spindle and full field. The LAI values for the three systems were 1.6, 1.6 and 1.9 respectively, and the fraction of the total light intercepted was 53 per cent for both the palmate and the slender spindle and 66 per cent for full field. Increasing the height of the trees will increase light interception particularly for trees of triangular section. If LAI is held constant, increasing tree height may improve light distribution within the canopy, particularly at high LAI values this will lower canopy density. The relationship between tree height, plant spacing is critical. Rows too far apart will cause reduction in

interception because more light will miss the tree altogether. On the other hand, in overly close rows mutual shading will occur between rows, thereby reducing the amount of illuminated canopy of the whole orchard.

Factors affecting horticultural plant architectural systems 1. 2. 3. 4. 5.

Cultivar/rootstock combination Tree density Tree arrangement Support system Tree training

Training system and photosynthesis response Training systems which typically aim at increasing light interception by the canopy— e.g. Lincoln Canopy and, to a lesser extent, Vtrellis and Y-trellis—often result in excessive annual, vertical growth on the exposed sides of scaffolds (Palmer and Warrington, 2000). The most common tree forms that apple trees are trained are Globular – is characteristic of large open centered trees where the most productive portion of the tree is top third, where the fruit is less accessible; Conical or pyramidal - this would be characteristic of a Christmas tree shape with an open framework. The top of the tree does not shade the bottom branches and a major part of the bearing surface is close to the ground. The open framework will allow light to penetrate well into the canopy; Horizontal canopy where the thickness of the canopy is limited to about 1 m, which allows for effective light penetration to the full canopy. The Lincoln canopy is a good example of this tree form; Y or V form - allows for maximum light penetration while providing growth control and influencing productivity. The Tatura V trellis and the New York Y trellis are examples of this form. Open-center (Vase) system: The main trunk


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS least 45 cm from the ground. Additional scaffold limbs should be separated along the trunk by a minimum of 20 cm and be well distributed around the trunk. When the leader becomes too tall to harvest, it should be headed back into two-year old wood. Branches that have shade in excess should be removed. Maintain the cone shape of the tree. Remove shoots that are not productive.

is allowed to grow up to 75 cm by cutting within a year of planting. All side branches are headed back and resemble a conical shape. This system lacks strong crotches and provides weak frame work and as such is less satisfactory. However, it may be favoured for more sunlight for better colouration of the inside fruits. But under sub-tropical conditions where sunshine is plenty and there are strong winds during summer, this system is not suitable in view of the weak framework and other obvious defects. It is low density planting system (100-200 trees acre-1)

Modified central leader: It is a hybrid of open and central leader system. It is first trained like central leader by allowing stem to grow for the first two years, and then headed back at 75 cm height. Lateral branches are allowed to grow and cut back as in open centre system. With this system, the height of tree is lowered as the length of the main trunk is reduced. The scaffold branches are encouraged to become larger and grow to greater length. The trees possess strong crotches and a durable frame work. The system suits most of the commercial fruit trees because the height of the tree is comparatively less, which facilitates operation like spraying, pruning, harvesting, etc. It is medium density planting system (250400 trees/ acre).

Entral leader: Make proper selection and practice proper training of the scaffold branches. The first scaffold limb should be at

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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Solaxe training system: Trees are grown as a central leader with branches tied down to 120º to remove vigour and encourage precocity (Fig.5). Branches are seldom pruned except to remove young limbs that are too closely spaced. Limited branch renewal helps to improve light penetration, as does the creation of a light tunnel next to the trunk where all buds within 30 to 40 cm of the trunk are removed. Where adequate branching is lacking, buds are notched or Promalin® applications are made to increase branching. As the tree reaches 3.5 to 4 m the top is bent to the horizontal so the maximum height can be maintained. Lack of pruning and branch bending makes this a very precocious system. Little pruning also means that bacterial canker infection is generally low. Crop load and fruit size are controlled by spur removal. The number of spurs left per branch is determined by the productivity of the variety and the diameter of the branch. ‘Bing’ branches are often thinned to approximately 10 cm between spurs and ‘Van’ branches thinned to 20 cm. Spur removal and branch bending makes this a highly intensive system and potentially a very expensive system to establish and maintain. Vertical axis system: In the vertical axis system, the trees are trained and maintained in a narrow pyramidal shape with a dominant central leader to maximize light penetration within the tree canopy. The central leader is trained to grow vertically to a height of about 10 feet. In this system, few pruning cuts are made during the first three years after planting until the trees have begun to grow together. Thereafter, lateral branches are periodically renewed by cutting into 2-year-old or older growth. Trees are supported by a trellis, consisting of a conduit or a wooden post at each tree with at least one wire connecting the tops of the posts.

Slender spindle: Apple trees trained to the slender spindle system have more of a conical shape than the pyramidal shape of a central leader or spindle bush tree. This shape is achieved by limiting lateral limb growth through partial or total removal. A 45° cut (Fig. 10) is used when removing limbs in order to promote a new lateral from the same location on the trunk. Limbs are trained to or below the horizontal position in order to control tree vigor and induce early fruit production. The slender spindle system lends itself to high density plantings on dwarf rootstocks with a tree height of 2 m or less. Tree density can vary from 2000 to 5000 trees per hectare depending upon the use of single row or multi-row bed plantings. It is small, conical, centre leader tree of only 2 m in height and maximum diameter of 1.5 m. Spindles starts early cropping with little pruning and horizontal bending of laterals. High density (700-1100 trees acre-1) to very high density (super spindle 1500-2000 trees acre-1) planting with slender conical canopy and dwarfing rootstock (M.9 size) supported by posts vigour controlled by bending central leader. Spindle bush: Basically this training system is similar to the 155 system in that a central leader training method is used to develop a cone shaped tree supported by a post or wire


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support system. The training form is suitable for medium-to-medium high density planting with tree height varying from to 2to 3 meters in height and spread. This tree size necessitates the development of a permanent set of scaffold limbs in the bottom third of the tree canopy. Early cropping is desirable where good growth is being obtained in order to control tree vigour and retain the mature tree to its allotted tree spacing. Espalier: The goal of espalier training is to create a work of art confined to a specific space; as such, it requires heavy pruning to control shoots on top of horizontal limbs. This system is similar to Kniffan system in grapes. The tree forms produced are usually two dimensional since frequently a wall or fence provides the background of the trellis. All

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designs require support system, at least in the formative training. When forming espaliers, one should take into account the species and the vigour of the plan. The space between horizontal limbs, for example, is wider for peach trees (20 to 24 inches or 50.8 to 61 cm) than for pear trees (12 inches or 30.5 cm). About three tiers of limbs are adequate for small plants, but vigorous plants can have more. All bending should be done when the limbs are still flexible. A balance should be maintained between limbs on either side of the central axis by keeping opposite limbs at each equal in length. The limbs should be tied closely to the support or trellis, as already mentioned. Espaliers may be formal or informal in design. Horizontal espalier: The horizontal espalier training system consists of a set of horizontal wire trellis attached to walls, fences, or posts. When starting from a seedling pant, it is cut just below the fruit wire. This practice causes new shoots to develop from lateral buds. Two lateral shoots of equal vigour are selected and trained on stakes tied diagonally to the wires and tied. Stakes may not be necessary. Horizontally limbs are developed by first heading the plant just below each wire. Growth toward the wall should be pruned. Horizontal espaliers produce uneven vigour in the plant. The whole process is repeated to



   

Rows are spaced 5-6 m apart with a distance of 3-4 m between trees. Height of the tree will remain around 5 m. Trees are trained on 4 wire system, the wire being spaced at one meter intervals. The trees when fully grown consist of a central leader and four pair of framework branches that are supported

Advantages of palmette system    

form the next tier of lateral branches. The ends of the lower scaffold branches usually lose vigour. Once established, side shoots will be produced, first on the lower limbs. These shoots are pruned in summer to form fruiting spurs in the next season. As fruiting spurs increase in number over the years, they should be thinned out to avoid overcrowding and reduced plant vigour. Palmette system: The palmette training system is the variation of the espalier system whereby plants are trained at about a 400 angle instead of having horizontal branches. The candelabra palmette training system uses a lattice framework consisting of horizontal and vertical arms to create balanced and attractive trees. This system improved orchard productivity inducing earlier bearing and enabling higher planting densities. Semi-high density planting system refers to 400-800 trees acre-1.

Main characteristics 

This method has been widely adopted in modern commercial planting In Italy, France and other European countries.



It produces high quality and high quantity fruits. It is well suited to all the conditions (species, environment, rootstock/cv etc.) Reduce need for summer pruning. Low capital investment. Capable of high light interception and distribution.

Juvenile phase of tree development: The juvenile period is the period elapsing between seed germination and first flowering of the seedling? During the juvenile phase of plant development meristems acquire reproductive competence, becoming able to sense and respond to signals that induce flowering. Within a species, the onset of flowering can vary tremendously, either because of differences in the environment or because of genetic differences. Fruit tree seedlings in their juvenile period show a number of anatomical and morphological characters which disappear or change with time. Leaves differ from those in the adult phase as to size (smaller), width (narrower), serration (sharper), cell size (larger). Beside this, thorns are present during the juvenile period of the tree and the angle between side shoots and main stem is wide. However, the attainment of the flowering stage and the disappearance of juvenile symptoms do not necessarily occur simultaneously in all seedlings of a given progeny.


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Transition flowering

from

vegetative

to

It is well established that there exists a transition period between juvenile and adult period. The end of the juvenile period is indicated by the attainment of the ability to flower and the actual production of flowers is the first evidence that plant is in the adult phase. However, the end of the juvenile period and the first appearance of flowers may not

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coincide. Thus, seedlings do not flower because of other factors; even through the seedlings have attained the ability to flower. This period of transition is also defined as the adult vegetative phase. The adult vegetative phase is the most important phase for breeders as during this phase most floral-inducing techniques are applied successfully. Observations on several fruit tree species have shown that seedling vigour and juvenile


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS period are inversely related. Stem diameter of apple seedlings is inversely correlated with the duration of the juvenile period (the thicker, the shorter) and initial productivity of the seedling (the thicker, the higher). This inverse correlation exists also for trees on rootstocks, i.e. between stem diameter and unproductive period. It was shown that adult seedlings after having budded on a rootstock flowered sooner when the juvenile period has been shorter. Evaluation of the juvenile phase of seedlings shows that the lowest bud of a seedling which may be an indicator of the point of transition to the adult phase occurred at a height of 1.8-2m on greenhouse plants in crab apple. Later studies indicate that the stage of development is better measured by node number than by height of the seedling, thus the transition occurred at about 75th to 80th node. It is estimated that apple seedlings

attained the height at which flower buds were formed 9-12 months after germination. To force flowering in apple progenies, seedlings were grown as single-shoot plants under optimum greenhouse conditions, manually defoliated and planted in the field after chilling. According to a study on the dynamics of polyphenolic compounds, the lowest flowering node on seedlings was found at around 122nd node under natural conditions, in other words the seedlings had reached the reproductive phase. However, in response to application of plant growth regulators, such as BA and ethephon, flowering was induced at the lowest node, node 77, indicating that the seedlings had been in the adult vegetative phase, i.e. transition phase. Based on these studies it was concluded that the transition points from juvenile to adult vegetative and from adult vegetative to reproductive phase

Ontogenesis in apple seedlings


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS would be around node 77 and 122, respectively. Once fruit trees have passed the juvenile phase and reached an adult phase of reproductive competence, a portion of shoot meristems will initiate flowers each year. Upon the transition from the juvenile phase to the reproductive phase, apple shoots begin producing flower buds that contain inflorescences with bracts and floral meristems. Shoots develop in a defined pattern that has specific vegetative and floral bud locations. Fruit buds in apple are borne terminally on fruiting spurs and/or terminally or laterally on long shoots. Whether the mechanism regulating competence in adult tree meristems is the same as that is responsible for the acquisition of competence in the juvenile to adult transition remains to be elucidated.

Current knowledge on ontogenetic phases of development in apple Woody plants are pruned to maintain a desired size and shape and to promote a certain type of growth. Ornamental plants are pruned to improve the aesthetic quality of the plant, but fruit trees are pruned to improve fruit quality by encouraging an appropriate balance between vegetative (wood) and reproductive (fruiting) growth. Annual pruning of fruit trees always reduces yield, but enhances fruit quality. Pruning increases fruit size because excess flower buds are removed and pruning encourages the growth of new shoots with high-quality flower buds. Pruning improves light penetration into the canopy, and light is required for flower-bud development, fruit set and growth, and red colour development. Pruning also makes the canopy more open and improves pest control by allowing better spray penetration into the tree; air movement throughout the canopy is increased, which improves drying conditions

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and reduces severity of many diseases. Pruning fruit trees is somewhat of an art based on an understanding of plant physiology and development. In other words, if we understand how plants grow and how they will respond to different types of plant manipulations, we can alter vegetative growth and fruiting to obtain trees and fruit with desirable characteristics. A basic understanding of certain aspects of plant physiology is a prerequisite to understanding pruning. Unlike animals, plants continue to increase in size throughout their lives. There are only two ways plants can grow. Primary growth is the increase in length of shoots and roots, and is responsible for increases in canopy height and width.

Secondary growth is the increase in thickness of stems and roots. Both types of growth require cell division followed by cell enlargement and differentiation. Buds: Buds are important to the vegetative and reproductive growth of trees. Fruit tree training and, to a lesser extent, pruning primarily involves bud manipulation. Buds are actually undeveloped shoots. When a vegetative bud is sliced longitudinally during the winter and viewed under magnification, the apical meristem at the tip, leaf primordial (developing leaves), axillary meristems, developing axillary buds, and pro-cambial tissue (tissue that will develop into the cambium) are all visible. Buds on fruit trees usually have about seven leaves and initial shoot elongation in the spring results from cell expansion. During late June and July some of the shoot apices will flatten out and develop into flower buds. Flower buds are actually modified shoots and the various flower tissues (petals, stigmas,


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS anthers, etc.) are actually modified leaves. Although the process of switching from vegetative to reproductive buds is not fully understood, hormones that can be influenced by environmental factors, stresses, and plant nutrition control the process. There are several things we can do to influence whether or not a bud becomes a flower bud or remains vegetative. In general, factors that favour rapid growth, such as high nitrogen levels in the shoot tissues, inhibit the development of flower buds. Applying growth-promoting plant growth regulators such as gibberellins usually inhibits flowerbud induction, whereas ethylene may promote flowerbud development. Mild stresses such as shoot bending and water stress may also promote flowerbud development. Producing annual crops of high-quality fruit requires a balance between reproductive and vegetative growth. Fruit producers use various techniques, including pruning, branch bending, and plant growth-regulator sprays, to manipulate tree growth and flowering. Often these techniques affect bud dormancy, so knowledge of buds and bud dormancy is essential if we are to understand how pruning influences tree growth. It is also important to be able to identify the different types of buds on a tree, especially to distinguish between flower and vegetative buds.

Pruning facts Pruning refers to the removal of any vegetative plant part to regulate the production and maintain the balance between vegetative and reproductive growth. Pruning involves both art and science, Art in making the pruning cut properly and science in knowing how and when to prune for maximum benefits. Pruning is a dwarfing process: Pruning increases vegetative growth near the pruning cut and this gives the illusion that pruning

stimulates growth. However, the weight of a tree that was pruned annually is always less than the weight of a non-pruned tree. Pruning reduces yield: Pruning removes wood with flower buds, and thus potential fruit. Yield from pruned trees is nearly always less than yield from non-pruned trees, but fruit quality is improved by pruning. Pruning improves fruit size by increasing the amount of leaf area per fruit. Pruning improves light distribution throughout the tree, which is important for the development of fruit red colour and sugar levels. Pruning delays fruiting: Pruning encourages vegetative growth rather than reproductive growth in young trees. A non-pruned tree will always flower and produce fruit earlier in the life of the tree than a pruned tree. The reason young trees are pruned is to induce branches to develop where they are wanted and to develop a strong tree structure that will support large crops as the tree matures. As a tree matures, the physiology changes from vegetative growth to reproductive growth. To obtain high annual yields of mature trees, it is important to minimize fruiting until trees have nearly filled their space. Pruning is one technique used to delay fruiting of young trees. Summer pruning: Summer pruning involves the selective removal of leafy shoots during the growing season. Responses to summer pruning vary with time of pruning, severity of pruning, tree vigour, geographical location, and variety. Several researchers evaluated summer pruning during the 1980s and several general statements can be made about the practice. Summer pruning reduces within-tree shade and usually improves fruit red colour development and sometimes improves flower bud development. Summer pruning removes leaves that produce photosynthates (sugars) for growth of all tree parts. Summer pruning


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS sometimes reduces fruit size and sugar levels. Due to reduced whole-tree photosynthesis, summer pruning suppresses lateseason trunk enlargement and root growth. Summer pruning does not suppress shoot elongation the following season. Summer pruning reduces late-season photosynthesis, and theoretically should reduce the accumulation of reserve carbohydrates within the tree that are used for early season growth. However, results from most pruning experiments indicate that the response to a certain type of pruning cut will be the same regardless of the time of year the cut was made.

Objectives of pruning 1.

Reduce tree size

Pruning increases vegetative growth at pruning cut and this gives the illusion that pruning stimulates growth. However, the weight of a tree that was pruned annually is always less than the weight of a non-pruned tree. 2. Control tree shape 3. Make trees structurally strong 4. Improve fruit quality Yield from pruned trees is lesser than yield from non-pruned trees. Pruning improves fruit size and quality by increasing leaf area per fruit. 5. Improve light penetration  Improves fruit colour  Improves flower bud initiation & flowering in the consequent season  Helps in pest control 6. Improve light penetration  Flower bud initiation  Fruit colour  Pest control  Facilitate cultural operations  Keep the crop close to the ground 7. Removal of diseased wood

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Physiological factors affected by pruning Photosynthesis: The sunlight intercepted by the tree canopy is of prime importance for the production of qualitative and quantitative yield. Light is the chief source of energy for photosynthesis in which carbon dioxide from the air and water from the soil are combined in the leaves for the formation of the basic food for the tree growth and its bearing capacity. Light becomes limiting when there is overcrowding of shoots and pruning therefore becomes necessary for improvement of access of light. The aim of pruning is to maximize the sunlight impingement on the tree canopy. Sunlight not only influences flowering and fruit set but also enhances the fruit quality and colour development. Apical dominance: The suppression of lateral bud growth by the terminal bud is known as apical dominance. Apical dominance dependent upon hormonal balance, explains many of the growth characteristics of trees and their responses to pruning. The main growth hormone that regulates the branching is auxins produced in the terminal bud which moves down the plant system to inhibit lateral bud break. Removal of the terminal bud destroys apical dominance so that one or several lateral buds will commence to grow and branching results. Vigorous shoots called water sprouts or suckers show extreme apical dominance with no side-branch development. Apical dominance however varies somewhat with vigour and variety. Carbohydrate: Nitrogen ratio: The balance between tree growth and fruitfulness depends upon a relationship between carbohydrates and nitrogenous compounds within the tree. When both of these are present in optimum quantity, adequate growth of the tree with corresponding high yield takes place. But when both are low, the growth of citrus trees and the yields are adversely affected. Even in


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS case when the balance of the two is somehow altered then again yields are adversely affected. A tree low in carbohydrates and high in nitrogen tends to produce vigorous vegetative growth at the expense of its fruit production capacity. Since carbohydrates are manufactured and stored in the leaves, heavy pruning which removes a large portion of the leaf area can result in this kind of condition. Efforts should therefore be made so that the C: N ratio is not disturbed due to excessive pruning. Too much nitrogen after severe pruning can aggravate the problem by causing thick and puffy fruit peel. Thus in such cases, when heavy pruning is done, the nitrogen applications should be adjusted according to the severity of pruning. Reducing nitrogen application avoids an imbalance when heavy pruning is done. Omitting a nitrogen application before heavy pruning and possibly after will reduce both costs and excessive vegetative growth. In case the pruning is done only for the maintenance of canopy it should not affect fertilizer requirements of the tree unit. Flowering behaviour: Pruning of young fruit trees at flowering does not inhibit flower formation much since the flowering process once initiated is not suppressed easily. Pruning encourages more flow of nutrients and water to the remaining shoots which flower and that is how the percentage of flowers that develop to form fruits is increased invariably. As long as a balance between loss of potential bearing surface and the nutrient supply is kept at optimum pruning always encourages better bearing. The extent of pruning alone or the amount of thinning and pruning to be practiced is to be decided by the grower to get more output by minimum input for a larger number of years. Alternate bearing behaviour: Some citrus groves tend to have a bearing habit with alternating high and low yields. A heavy crop

of fruit usually depletes the carbohydrate levels and results in a low crop and heavy vegetative growth during the following year. In case heavy pruning is done after a heavy crop, it additionally stimulates vegetative growth the following year as the carbohydrate supply has been reduced and the capacity to resupply is low. This may result in poor fruit quality. Pruning after a light crop and before an expected heavy crop should help reduce alternate bearing. Hence pruning should be done only as per requirement after heavy / low crop load. Orientation of branches: The orientation of branches in space has a marked effect on growth and fruiting. A decrease in growth rate and an increase in flowering occur when branches bend to a horizontal position. A possible explanation for this phenomenon is a change in the distribution of growth substances and carbohydrates. Favouring horizontal branches over upright ones should result in better growth control and more fruit production. Fruit yield and quality: Fruit size is very important in fruits that are consumed fresh. Smaller fruit sizes results in economic loss to the growers. Some cultivars grown for fresh fruit tend to set very heavy crops of small fruit in some years and very light crops the next year. Pruning after a heavy crop can result in alternate bearing and thus in a small yield of poor quality fruit the following year. Hedging and/or topping after a light crop and before an expected heavy crop can reduce the number of fruit with a corresponding increase in fruit size and also reduce alternate bearing. The grower may elect to speculate and prune before an expected large crop is set or wait until after fruit-set so that the amount of fruitset can be more accurately determined. The latter should be done before the fruit has attained appreciable size. Since later fruit removal could result in a crop reduction


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS without a compensating fruit size increase. Pruning improves the size and colour of fruits if the leaf to fruit ratio is not lowered to a great extent since the pruning operation essentially controls photosynthetic surface and through it the physiological activities of the plant connected directly or indirectly with the leaf.

Components of woody tree pruning Analysing branching: Shoot polymorphism is not frequent in tropical trees as the evergreen habit is not conducive to development of short shoots, however it may occur in tropical environments which are dry, disturbed or otherwise exposed as in species of Acacia, Bumelia, Ximenia etc. Sylleptic shoots: Syllepsis is the continuous development of a lateral from a terminal meristem to establish a branch without an evident intervening period of rest of the lateral meristem and the branches so developed are referred as sylleptic branches. Sylleptic branching is a common feature in dry land fruit crops and in pomegranate it is related to productivity. The sylleptic shoots mainly develop during the early developmental years such as feathers in nursery and these are considered to be of advantage for young tree establishment. Sylleptic branching helps these plants to produce a dense canopy during the short period favourable for growth following monsoon showers in arid and semi-arid regions (Kurian and Reddy, 1999). Proleptic shoots: Prolepsis is the development of a lateral from a terminal meristem to establish a branch with some intervening period of rest of the lateral meristem and the branches so developed are referred to as proleptic branches. In temperate fruits trees, the distribution of laterals most commonly corresponds to an acrotonic distribution. Sylleptic branch is synchronous in its

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development with its parent axis but a proleptic branch is not. Shoot types: Usually two main shoot categories are reported; 1) Short shoots, and 2) Long shoots: Short shoots (brachyblasts): limited number of organs and life span. Short shoots contains resting bud (preformed organ) which do not elongate after bursting bud. In pome fruit species, short shoots have been named “bards” when they are strictly vegetative or “spurs” when they are usually floral.

Long shoots are of two types’ i.e. medium and long Preformed organs whose internode elongate: these shoots have limited final length and have been considered to be intermediate category i.e. meso-blasts.  Preformed organs followed by new formed organs resulting in apical growth: These shoots result from both inter-nodal growth of the preformed shoots and apical growth which produces a new formed part and generally form longer shoots also named auxi-blasts. These shoots also sometimes refer to water shoots when growth is extended and/or rate is high. Intra- species tree variability: In some fruit plants like apple there exists variability. Fruit trees exhibit a polymorphic development of shoots. Bernhard (1961) reported four types (I to IV) of apple cultivars on the basis of overall tree growth and their fruiting types. The plant of type I cultivar bear fruits on spurs that are branched on old wood and type IV cultivars bear fruit on terminal portion of the shoots including water shoots (Costes et al, 2006). The type I apple cultivars are columnar in shape and most of the apple varieties fall in type II category (Lespinasse, 1992). Role of cuts in tree shape: The growth pattern 



Type I

type II

type III

type IV

Apple ideo-types from spur (type I) to weeping trees (type IV)

of a tree can be modified by the type and severity of pruning cuts. In fruit plants two type of pruning cuts are described i.e. thinning cuts and heading cuts. Thinning cuts: These Thinning cuts are given at a portion where a branch/shoot originates. These cuts are given to open up canopy while the tree maintains its natural shape. More light penetrates a plant that has been thinned and interior branches and foliage will be retained nearer the centre of a tree. Heading cuts: Heading cut implies to shortening of the branch to bud or cutting stem back to a stub or lateral branch. Heading cuts removes apical dominance and facilitates the growth of lateral buds. Headed back plant puts up profuse growth and the natural form of tree is lost. Heading results in;  Releases lateral buds from apical dominance  Increases number & length of shoots  Decreases fruit spur formation  Results in more upright growth habit  Decreases fruit fullness  Reduces carbohydrate reserves  Decreases calcium & magnesium, increases nitrogen  Stimulates shoot growth Bending: Bending or tying down branches is

often used with two objectives. One is to maintain the tree in the allotted space in relation with the tree management system. It is preferred to heading cuts for the control of tree growth and shape and is currently used in particular training procedures, as described for Solaxe system of training. A second objective of bending is to reduce vegetative growth of the branch and promote flowering. However, the effects of bending on flowering and fruiting remain controversial and, depending on the experiment, orienting entire trees or individual branches.

Fruit bearing habit and pruning An accurate knowledge of fruit bearing habit is a necessary to prune fruit plants to harvest the good of pruning 1. Apple and pear bear fruit on spurs. Two or more years are required for their development. The spurs will become unfruitful, or even die, if over-shaded. Once a spur is lost on any part of the tree it can never be replaced there but, must be produced further out on the tree. 2. Peach, nectarines and some of the sour cherry varieties bear crop on the shoots produced during the preceding summer. Hence, the production of these shoots must be encouraged by pruning.


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS 3.

Grape, bramble, persimmon and quince do not have separate fruit buds during preceding winter. These crops bloom and bear fruit on current season growth which arises from lateral buds formed the preceding summer.

Bearing habit of fruits 







 



Apple and Pear: it developed terminally on 1- year old shoot and spurs and rarely laterally on 1- year old shoot. The bud developed to inflorescence Quince: it developed laterally and terminally on 1-year-old shoot. Flowers are solitary (each bud produce 1 flower). Loquat: it developed terminally on 1year-old shoot. The bud developed to inflorescence Almond, Apricot, Cherries and Plum: it develops laterally on 1- year old shoot and spurs Peach and Nectarine: it develops laterally on one year old shoot Walnut: Male: It is simple and developed laterally on 1-year old shoot, the bud developed to inflorescences. Female: It is mixed and developed terminally and/ or laterally on one year old shoot, the bud developed to shoot at the end developed inflorescence. Grapes: Flower bud is compound and developed laterally on 1-year old shoot (cane), the primary bud developed to shoot with leaves, tendrils and inflorescences.

Use of pruning to induce good flowering in fruit crops (case studies) 1.

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In grapes, pruning and canopy, management is equally important. Proper correct pruning creates long term vine structure Good canopy management results in good sunlight penetration. Good flowering, high yield and quality.

2.

Pruning of grapevines is recommended anytime after leaf fall, which may occur late fall or throughout the winter. Once the leaves fall, the vascular system becomes inactive and plugs up. Before this time, minerals and carbohydrates are transferred from the leaves into the permanent, woody structures of the vine for winter storage. For this reason, pruning before leaf fall can affect storage leading to mineral deficiencies and poor bud maturation, which can affect the growth of the vine and the crop in the following season. Timing of pruning within the dormant season may also affect the time of bud break. Vines pruned very late in the season usually start spring growth slightly later than those pruned mid-dormancy. Such a delay in bud break may be desirable in frost prone areas. Vigorous and dense grapevines require more labour for canopy management and tend to create excess shade, decreasing fruit quality. Winter pruning level, shoot thinning and leaf removal influence the overall density of the canopy and the subsequent degree of shade in the canopy which effects fruit yield and quality. Induction of flowering in guava by pruning under ultra high density systems: Meadow Orchard System is a new concept of guava planting which has been developed for the first time in India at Central Institute for Subtropical Horticulture, Lucknow. The planting is done at 2.0 m (row to row) x 1.0 m (plant to plant), which gives a density of 5000 plants per hectare. Initially, the trees are pruned and trained to allow maximum production of quality fruits during the first year. A single trunk tree with no interfering branches up to 30 - 40 cm from the ground level is desirable to make



3.

dwarf tree architecture. After a period of 1-2 months of planting, all the trees are topped at a uniform height of30-40 cm from the ground level for initiation of new growth below the cut ends. No side shoot or branch should remain after topping. This is done to make a single trunk straight up to 40 cm height. After 15-20 days of topping, new shoots emerge. In general, 3~4 shoots are retained from below the cut point after topping. As shoots mature generally after a period of 3-4 months, they are reduced by 50 per cent of their total length so that new shoots emerge below the cut point. This is done to attain the desired tree canopy architecture and strong framework. The emerged shoots are allowed to grow for 3 - 4 months before they are again pruned of 50 per cent. After pruning, new shoots emerge on which flowering takes place. Tip pruning for synchronous flowering in mango under warm tropics: Mango flowering is a key reproductive event for the production of fruit. Shoot initiation is the first event that takes place for mangoes to flower. Shoot initiation in mango can be stimulated by environment, pruning, and irrigation, application of nitrogen substances and/ or fertilizers and exposure to ethylene. Cool temperatures during winters induce mango flowering under subtropical and upper-latitude tropical conditions. Under subtropical conditions, only 1/4 leaf per stem provided sufficient florigenic promoter (FP) to induce flowering in 95 per cent of initiating lateral shoots. Under tropical conditions, the same area of leaf surface only induce flowering in 11% lateral shoots. In subtropical condition s the translocation of florigenic promoter was

4.

greater due to its higher concentration. Tip pruning and the use of KNO3 has been used effectively in the warm tropics to induce synchronous out-of-season flowering in mango. Tip pruning is defined as pruning terminal stems anywhere from near the terminal apex to a point down the stem that is no larger than 1 cm in diameter. Tip pruning is ideally used to synchronize vegetative flush events in the canopy. Flushes will occur at once in all stems throughout the canopy if the entire canopy is tip pruned. Lateral stems produced by tip pruning can be initiated to grow by foliar applications of ethephon or a nitrate salt such as potassium, calcium or ammonium nitrate in warm temperatures (>20 æ%C night) if remain in rest for 4-5 months. Spray applications of KNO3 should be made about 5 months after tip pruning trees and following that at 2-week intervals until flowering is achieved. Tip pruning not only causes a uniform flush of growth throughout the canopy, it removes growth and flowerinhibiting factors in stems derived from the previous seasons’ flowering and fruiting panicles (Davenport, 2006). Moreover, it increases annual yield 4–5 fold due to increased numbers of resulting lateral stems while eliminating alternate bearing in prone varieties. Role of pruning in flowering and fruiting in peach and nectarines: The successful pruner must understand how a tree grows and how it will respond to various types of pruning cuts. It is also important to observe the results of pruning. There are two types of buds on a peach tree. The terminal bud at the end of a shoot is always vegetative and sequent years. A number of axillary buds on vigorous current season’s shoots


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS (greater than 2 feet long) grow to produce secondary shoots. Such shoots are not very fruitful because fruit buds do not develop at many nodes on secondary shoots. The ideal fruiting shoot is 12 to 24 inches long and 3/16 to 1/4 inch thick at its base, and it has no secondary shoots. Proper pruning, fertilization, irrigation, and fruit thinning must be practiced to ensure enough shoot growth each year to produce adequate fruit buds for the following season. The energy for plant growth comes from light. Leaves intercept light and the light energy is converted to chemical energy in the process of photosynthesis. The chemical energy is in the form of carbohydrates, which are transported around in the tree and used for growth. Results from shade experiments in USA indicate that the critical light level for flower bud development in peach is about 20% full sun. For maximum flower bud development, shoots must be exposed to light during June and early July. High light levels during late July, August and September will not influence flower bud formation. Tree architecture and canopy management is an art in perennial fruit trees which offers the way to shape the plants in air to get a desired size and strong frame work of the plant. The plant is opened-up to the sun light and allows the air to pass through the centre of the canopy, and is free from the attack of insects and pests. The main objective is to reduce juvenility, to maintain equal balance of vegetative and floral buds, and to get regular yields with high quality product for longer period of time. Annual pruning improves light distribution throughout the tree, which is necessary for the development of flower buds and fruit. To produce large, well-colored fruit, with high sugar levels, all regions of the tree

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must receive at least 25% full sun. The fruiting surface of poorly pruned trees will move farther from the tree center each year, which results in reduced yields and increased production costs.

REFERENCES READINGS

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Ashraf, N. and Ashraf, M. 2014. Summer pruning in fruit trees. African Journal of Agricultural 9(2): 206210. Bakshi, J.C., Uppal, D.K. and Khajuria, H.N. 1997. The pruning of fruit trees and vines. Kalyani publishers, Ludhiana.156p. Bernhard, R. 1961. Mise à fruits et alternance chez les arbres fruitiers. p. 91–116. Congrès pomologiques. INRA, Paris. Cescatti, A. and Niinemets, Ü. 2004. Sunlight capture. Leaf to landscape. In: Photosynthetic Adaptation. Chloroplast to Landscape (eds W.K. Smith, T.C. Vogelmann & C. Chritchley) pp. 42–85. Springer Verlag, Berlin, Germany. Costes, E., Lauri, P.E. and Regnard, J.L. 2006. Analysing fruit tree architecture: Implications for tree management and fruit production. (Eds. J Janik). Horticultural Reviews, 32: 1-47. Davenport, T.L. 2009. Reproductive physiology. In: (Ed. R.E. Litz). The Mango: Botany Production and Uses, 2nd edition. CAB International, Wallingford, UK, pp. 97–169. Davenport, T.L., Ramo, L., Alani, A. 1995. Evidence for a transmissible florigenic promoter in mango. In: Proceedings of the 22nd Annual Meeting of the Plant Growth Regulation Society of America, pp.159. Jackson, J.E. 1980. Light interception and utilization by orchard systems. Hortic Rev., 2: 208–267. Koehl, M.A.R. 1996. When does morphology matter? Annual Review of Ecology and Systematics, 27: 501–542. Kuuluvainen, T. 1992. Tree architectures adapted to efficient light utilization—is there a basis for latitudinal gradients. Oikos 65: 275–284. Lakso, A.N. 1980. Aspects of canopy


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS photosynthesis and productivity in the apple tree. Acta Hortic., 114:100–109. Lakso, A.N. and Corelli-Grappadelli, L. 1992. Implications of pruning and training practices to carbon partitioning and fruit development in apple. Acta Hortic, 322:231– 239. Kurian, R.J. and Reddy, Y.N. 1999. Pattern of Shoot Growth in Zizyphus mauritiana and Z. oenoplia. Annals of Botany, 84: 289-295. Lespinasse, Y. 1992. Breeding apple tree: aims and methods. Proc. Joint Conf. of the EAPR Breeding and varietal assessment section and the Eucarpia Potato section: 103–110. Lespinasse, J.M. and Delort, F. 1986. Apple tree management in vertical axis: appraisal after ten years of experiments. Acta Hortic 160:120–155. Lespinasse, J.M. and Delort, J.F. 1993. Regulation of fruiting in apple. Role of the bourse and crowned brindles. Acta Hortic., 349:229–246 Meir, P., Kruijt, B., Broadmeadow, M., Barbosa, E., Kull, O., Carswell F, Nobre A and Jarvis P G 2002. Acclimation of photosynthetic capacity to irradiance in tree canopies in relation to leaf nitrogen concentration and leaf mass per unit area. Plant, Cell & Environment, 25, 343–357. Morini, R.P. 2009. Physiology of pruning fruit trees. Publication No. 422-025. Virginia Polytechnic Institute and State University, Virginia, USA. Niinemets, Ü., Cescatti, A. and Christian, R. 2004. Constraints on light interception efficiency due to shoot architecture in broadleaved Nothofagus species. Tree Physiology, 24, 617– 630. Palmer, J.W. 1980. Computed effects of spacing on light interception and distribution within hedgerow trees in relation to productivity. Acta Hortic, 114:80–88 Palmer, J.W., Warrington, I.J. 2000. Underlying principles of successful apple planting

systems. Acta Hortic, 513:357–363. Pratibha, Shant Lal and Goswami, A.K. 2013. Effect of pruning and planting systems on growth, flowering, fruiting and yield of guava cv. Sardar. Indian J. Hort., 70(4): 496500. Proiettia, P., Palliottia, A., Famiania, F., Antognozzia, E., Ferrantib, F., Andreuttib, R., Frenguelli, G. 2000. Influence of leaf position, fruit and light availability on photosynthesis of two chestnut genotypes. Scientia Horticulturae, 85 : 63-73. Ramirez, F. and Davenport, T.L. 2010. Mango (Mangifera indica L.) flowering physiology. Scientia Horticulturae, 126: 65–72. Sansavini, S. and Corelli-Grappadelli, L. 1992. Canopy efficiency of apple as affected by microclimatic factors and tree structure. Acta Hortic., 322:69–77. Singh, G. 2008. High density planting in guava. CISH, Lucknow 21p. Tustin, D.S., Cashmore, W.M., Bensley, R.B. 1998. The influence of orchard row canopy discontinuity on irradiance and leaf area distribution in apple trees. J Hortic Sci Biotechnol 73:289–297. Tustin, D.S., Hirst, P.M., Warrington, I.J. 1988. Influence of orientation and position of fruiting laterals on canopy light penetration, yield, and fruit quality of ‘Granny Smith’ apple. J Am Soc Hortic Sci., 113:693–699. Valladares, F. and Niinemets, U. 2007. The architecture of plant crowns: from design rules to light capture and performance (Eds. FI Pugnaire, F. Valladares). Handbook of functional plant ecology. Taylor and Francis, New York pp 101-149. Wagenmakers, P.S., Nijsse, F., De, Gendt, C.M.E. 1991. Planting systems and light climate. Research Station for Fruit Growing, Wilhelminadorp, The Netherlands. Ann Rep : 39–40.


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PRUNING IN GUAVA (PSIDIUM GUAJAVA L.) AND APPRAISAL OF CONSEQUENT FLOWERING PHENOLOGY USING MODIFIED BBCH SCALE : SOURCE-SINK RELATIONSHIPS V.K. Singh, H. Ravishankar , Anurag Singh and Manoj Kumar Soni Central Institute for Subtropical Horticulture, Lucknow-226101, U.P.

ABSTRACT The guava (Psidium guajava L.) is an evergreen fruit species well adapted to a wide range of soils and agro climates and is acclaimed as ‘Super fruit’ owing to its high nutritional and nutraceutical profile. The crop presents well defined phenological stages during growth and flowering, depending upon climatic conditions which of course is amenable to manipulater through cultural interventions especially irrigation. Tree management strategy to increase shoot numbers (fruiting units) and induce profuse flowering for crop manipulation is very important for profitable guava cultivation. Under the changing climatic scenario and adoption of hi-tech horticultural practices, there is an urgent need to modify BBCH scale vis a vis phenophases under location specific climatic, soil and pruning conditions. Pruning operations impact the normal BBCH scale rating. The characterization of phenological stages is essential to achieve high fruit quality, since management practices like pruning, application of fertilizers, thinning, other management practices, harvesting time etc. depend upon the recognition of certain critical phenological stages impacting productivity. Therefore, this study was carried out with the objective to describe the modified phenological growth stages of guava in terms of temporal arrangement based on BBCH scale resulting from pruning operations at Central Institute for Subtropical Horticulture, Lucknow during 201112 and 2012-13. The guava cv. ‘Lalit’ having pink pulp and prolific bearing habit that has found favor with the orchardists especially in HDP systems in Maharashtra was selected for the collection of phenological data, analyzed and interpretation in appraising the suitability of BBCH scale in order to describe phenological

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patterns under pruning’s along with changing weather parameters. Variations in shoots emergence representing principal growth stages viz., vegetative bud emergence, shoots, leaves, flowers and fruits development was observed as a result of pruning operations during the months of February, May and September. It was observed that the duration between the pruning and the bud sprout ranged from 11 to 15 days during different times of pruning’s in a year. In contrast, the unpruned trees showed bud emergence in 23 days. The duration of flowering ranged 78 to 93 days from the opening of the flower and took 150 and 153 days for the fruit maturity in the pruning’s carried out during February and September as compared to unpruned control (129146 days). Interestingly, May pruning showed a different trend beginning sprouting in 7 days as compared to unpruned (3 days). The 50 per cent flowering was hastened and occurred in 43 days and took 136 days for fruit maturity. This may be due to the fact that May pruning produced the fruits during November to January and the prevailing low temperatures delayed the process of fruit maturity at the same time increasing the fruit size with better quality with higher yields arising from efficient and prolonged sink activity under low temperatures. Hence, it can be inferred from the present study that more the amount of assimilates diverted to the fruits (sinks) more is the time taken for the attainment of full size and vice versa. This clearly indicated the effect of pruning though delayed the emergence of buds but hastened the post-flowering phenophases due to increased source and reduced sink as a consequence of thinning and tip pinching operations and efficient translocation of photosynthates in the pruned shoots to the potential sinks (fruitlets). The impact of weather parameters impacting degree days in relation to


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS modified BBCH scale was also estimated for better understanding of flowering phenology in this study.

INTRODUCTION The guava (Psidium guajava L.) is an evergreen fruit species well adapted to a wide range of soils and shows a unique nutritional profile as a rich source of Vitamin C and also contains high amount of Vitamin A, phosphorous and calcium and iron content (Singh and Singh, 1998). The guava trees have well defined phenological stages and for achieving successful guava cultivation, a tree management strategy to increase shoot numbers (fruiting units) and induce profuse flowering for yield enhancement is a very important factor. It is based on the fact that flowering in guava is borne on current season recently mature vegetative shoots, either from lateral buds on older wood or at the shoot terminals. Under natural conditions, guava tree produces flowers and fruits thrice in a year in Northern India. The spring season flowering begins during February-March for harvesting during July-September (rainy season). Likewise, monsoon season flowering begins during June-July and fruiting during November-January (winter season) as well as winter flowering occurs during October and fruiting during March-April. During post juvenile period guava undergoes several phenological changes which depend on plant genotype as well as on climatic conditions. Depending on season, the period from flowering to fruit ripening is 20 to 28 weeks as it is adapted to areas with hot summers and cool winters. In some areas, an average monthly maximum temperature higher than 32°C and a minimum temperature below 3°C are regarded as restrictive for guava cultivation. Temperatures of up to 45 °C can be tolerated, although the highest yields are usually recorded at mean temperatures of 23

to 28°C. Optimum vegetative growth occurs between 15 and 28°C (Crane and Balerdi, 2005). Depending on the cultivar, the mean summer temperatures higher than 16 °C are needed for the trees to flower and bear fruit successfully. For successful management of specific developmental periods is crucial for good yield. The sequence of all periodical events involved in a plant life cycle is known as ‘phenology’. Several phenological indicators are used to monitor and evaluate plant development, however, the interval between blooming and fruit set is one of the most important phenological stage (Villalpando and Ruý´z, 1993; Schwartz, 1999). Growing degree days (abbreviated as GDD or DD) is calculated by assigning a heat value to each day. The values are added together to give an estimate of the amount of seasonal growth of trees. Guava fruit growth curve has a double sigmoid shape presenting three different growing phases (Rathore, 1976, Mercado-Silva et al., 1998 and Selvaraj et al., 1999). It was observed that the first phase corresponds to an accelerated growth, beginning a few days after anthesis and goes on for 45 or 60 days during the rainy season/winter and during spring, respectively. The second is relatively slow and last about 30 days, except during spring when it extends up to 60 days and hardening occur at this growing phase. In the third phase an exponential increase of fruit growing rate resulting in increased fruit diameter and length is observed. This period last for 30, 60 and 90 days in rainy season, winter and spring respectively. After fruit growth its external colour changes until complete maturation (Somarriba, 1985 and Laguado et al., 1999). Each cultural practice, alone or in combination, can influence flower bud formation by forcing the trees into vegetative growth. Crop cycling should be initiated immediately after a crop is harvested


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS or when the next cycled crop is desired. Pruning is an important tool in crop cycling, for continuous fruit production throughout the year and increase yield and profit (Singh et. al., 2007). The new BBCH General Scale, unified previous codes that were employed for some temperate and sub-tropical fruit species (Salazar et al., 2006; Meier et al., 1994; Rajan et al., 2011). In 1945 Fleckinger defined “phenological stages” as external physiological changes occurring at specific periods of time, which coincide with the natural growth cycle. This method is basically a decimal system that identifies different developmental stages by a two-digit code. While the first digit refers to its major stages using values between zero and nine, the second digit, also scaled from zero to nine, relates to its secondary stages. Under the changing climatic scenario and adoption of hi-tech horticultural practices including pruning, there is an urgent need to redefine BBCH scale vis a vis phenophases under location specific climatic, soil condition, pruning intensity and time. Once the phenological stages of guava are clearly identified, it will be easier to assess the best timing for its canopy architecture management through pruning for enhanced quality yield. Phenology of guava according to the traditional Fleckinger Code and the modified BBCH General Scale is described in this paper under changing climatic condition for planning pruning time. The guava (P. guajava L.) cv. Lalit, a prolific bearer having pink flesh and highly suitable for processing was undertaken to describe the phenological stages of, using the traditional nomenclature described by Fleckinger (1945) and to relate them to the BBCH General Scale in pruned or unpruned trees for assessing the best period for field operations to get high yield with best quality fruits of guava under North Indian conditions. 204

MATERIALS AND METHOD A guava orchard located at Central Institute for Subtropical Horticulture, Rehmankhera, Lucknow (elevation of 128 m above sea level and situated between 26.55 oN latitude and 80.59 oE, having coarse loam soil, mixed hyperthermic family of Typic Ustochrepts pH 7.8, low total N 12 ppm and low K 1 canopy diameter, NAA @ 80 ppm) and fruit set improving chemicals (Spermidine @ 0.01 mM, Spermine @ 0.1 mM, Boron -20% @1.25gm.l-1) on flowering, fruit set and yield of mango cv. Banganpalli, was conducted at Fruit Research Station, Sangareddy, Dr. YSRHU, A.P. The design adopted was Randomized Block Design with factorial concept with three replications per treatment. Mango cv. Banganpalli trees were applied with plant growth regulators and fruit set improving chemicals alone and in combinations. Vegetative parameters like number of new flushes (number), internodal length (cm), flowering parameters like time taken for panicle initiation (days), days taken flowering, flowering (%), number of fruits panicle-1, number of fruits tree-1, fruit weight ( g fruit-1) and yield (kg tree -1) were recorded. Trees applied with paclobutrazol alone significantly reduced the vegetative growth in terms of minimum number of new flushes and internodal length, compared to control trees. Paclobutrazol alone and in combinations with fruit set improving chemical significantly minimized the number of days taken for panicle initiation and increased the number of days taken for 50 per cent and 100 per cent flowering, duration of flowering along with increase in flowering percentage, panicle length and breadth when compare to control trees. Significantly highest fruits panicle-1, fruit tree -1 and yield was recorded in paclobutrazol (39% over control) applied trees and spermidine (39% over control) and boron (37% over control) applied trees alone compare to control. Boron and Spermidine alone could able to significantly increase the fruit panicle-1 and final retention of

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fruits and increased the fruit weight reflecting in the overall increase in yield by 37 and 28 per cent respectively. Among the combinations, trees sprayed with paclobutrazol and boron or spermidine has equally increased the yield by 47 per cent, when compared with control. The combination of paclobutrazol and spermidine increased the yield by 14.2 per cent and 14.37 per cent over the paclobutrazol or spermidine used alone, respectively. Paclobutrazol with its increases in all flowering parameters and Spermidine with its increase in fruit retention.panicle-1 has increased the overall yield by 47 per cent, when used in combinations. However, the maximum benefit cost ratio was recorded in trees sprayed with NAA and Boron applied trees compare to any other combination and control.

INTRODUCTION Mango (Mangifera indica) is the premier fruit among the tropical fruits and has been in cultivation in the Indian subcontinent since several centuries. Although, India is the leading mango producing country, the development of mango orchards as an established industry has remained a distant goal and per hectare yields (2.45 t ha-1) are low in spite of great potential (Anon, 2010). There are number of reasons for the poor productivity, of which alternate or biennial bearing habit of most of the choicest commercial varieties of India is one of the important factors. However, there is tremendous scope to boost the productivity, if this problem can be managed properly.


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS The mango cv. Banganpalli is the choicest export quality variety, which is commercially grown in Andhra Pradesh and it occupies 70 per cent of mango area. The major mango cv. Banganpalli growing districts in Andhra Pradesh are Krishna, Chittoor, Medak, Ananthapur, Adilabad, Karimnagar, East Godavari, West Godavari and Ranga Reddy (Anon, 2010). It is a moderate to heavy bearer and is considered to be fairly regular. According to Rao (1997), it appears that there is no such variety as ‘regular bearer’ in its true sense, since all varieties or hybrids express the bienniality in varying degree. At best, the so called ‘regular bearers’ could be classified as ‘weekly biennials’ i.e., if they carry a heavy load of crop in one year, they show the tendency towards reduced yields in the following year. Because of this erratic behavior, Banganpalli is also classified under ‘weakly biennial’ varieties. Hence, this variety needs proper management and crop regulation (Kumar Raj et al., 2005). The flowering phenomenon in mango appears to be a complex one. Research workers engaged in the field have not appreciably established the critical factors responsible for this phenomenon. Recommendations of horticultural scientists have not paved the way for a satisfactory solution to this problem. However, on account of continued research, this problem is better understood now than before. Since, most of the earlier studies were aimed at developing agrotechniques to promote regular cropping, enough knowledge on the physiology of flowering is lacking. However, the studies of Davenport (2007), on the evidence of involvement of leaf generated floral stimulus have opened up new vistas in the direction of research on physiology of flowering in mango. There are several reasons for poor

productivity in mango cv. Banganpalli in Andhra Pradesh. Among them, poor and erratic flowering coupled with poor or nil fruit set in mango cv. Banganpalli is one of the major reasons for poor productivity. The flowering and fruit set in mango is majorly influenced by the temperature during flowering (Davenport, 2007). Floral induction of mango occurs during bud dormancy in cool temperatures around 150C and that warm temperatures near 30 0C prevented floral initiation of induced buds (Nunez-Elisea and Davenport, 1995). A certain number of days below 13 0 C are required for optimum flowering in mango cv. Alphonso (Rao, 1998). A night temperature of less than 150C for 3-4 weeks is necessary for mango to flower and a night temperature above 140C is needed for proper fruit set (Davenport, 2003). Mango cv. Keitt was sensitive towards low temperature for flower induction (Yeshtela et al., 2004). The climatic changes especially temperature during flowering and fruit set period has been attributed to erratic flowering and poor fruit set in mango cv. Banganpalli (Bhagwan et al., 2013) in Andhra Pradesh. Modulation of flowering and fruit set by spraying of various hormones and chemicals is the best alternative to mitigate or reduce the climate change effect on mango. Various chemicals and plant growth regulators application have been standardized for enhancing and uniform flowering in mango. Application of paclobutrazol @ 3ml m-1 canopy diameter was found to improve the flowering about 38 per cent in mango cv. Banganpalli (Bhagwan et al., 2013). The effect of paclobutrazol in improving flowering per cent was due to its anti gibberellins activity (Quinlin and Richardson, 1984). Spraying of NAA @ of 50100 ppm has shown the effect in early flowering (Davenport, 2007) in mango. Naphthalene acetic acid (NAA), an auxin


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS group of plant growth regulator was found to have an effect on the flower promoting activity in mango (Beyer, 1976). Polyamines form a class of aliphatic amines that are ubiquitous in living organisms and are known to have role in a wide range of biological processes including plant growth and development (Pandey et al., 2000). Putrescine, spermidine and spermine are the major forms of polyamines which are biosynthesised from orginine or ornithine. Polyamines arise from a common metabolic intermediate pathway as of ethylene and are believed to act antagonistically to ethylene in several physiological process like stress, senescence etc. (Anon., 2004). Recently, polyamines have been attributed to play a role in the fruit set of many crops including mango. For improving the fruit set and fruit retention, spraying of various polyamines like spermine @ 0.1 mM and spermidine @0.01mM at full bloom stage were standardized in mango cv. Kensington Pride. Polyamines like spermine and spermidine increases the fruit set by improving the floral organs development, pollination, fertilization (Aman Ullah Malik et al.,2006) and fruit retention by anti ethylene activity (Brown, 1997). Among the micronutrients, spraying of Boron at full bloom stage has significantly improved fruit set in mango (Zong Runi and Dong, 2000) by enhancing the pollen grain germination and pollen tube elongation which consequently leads to better fruit set (Saleh and El-Monem, 2003). Even though, plant growth regulators on flowering and fruit set improving chemicals on fruit set of mango have been standardized, no work has been carried out on the combination of both flower enhancing plant growth regulators and fruit set improving chemicals on yield of mango cv. Banganpalli

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along with cost benefit ratio for successful commercialization of these plant growth regulators and chemicals. Keeping the above information in view, the present investigation is proposed with the objective in to study the interaction and synergistic effects of flower enhancing plant growth regulators and fruit set improving chemicals on flowering, fruit set and yield of mango cv. Banganpalli

MATERIALS AND METHODS The experiment was initiated on ten years old, well grown, uniform statured trees of mango cv. Banganpalli. The trees were spaced at 8m and planted in square system. Treatment trees were selected by random numbers and the experiment design was laid out in factorial randomised block design (Oliver, 1965) with 3 replications and one plant per replication. All cultural practices like fertilizers, spraying of pesticides, fungicides and irrigation were uniformly practiced in experimental trees. The flower enhancing plant growth regulators were taken as factor-1 and fruit set improving chemical as factor-2 with following treatmental combinations.

Treatments FACTOR-1 (Flower enhancing PGR) (3) P1 - Paclobutrazol diameter

@ 3ml.m -1 canopy

P2 - NAA @ 80 ppm P0 - Untreated control FACTOR-2 (Fruit set improving Chemicals) (4) F1 -

Spermidine @ 0.01 mM

F2 - Spermine @ 0.1mM F3 - Borax – (Boron -20%) @ 1.25gr.l-1 F0 -

Untreated control



Treatment combinations T1

P1F1

-

T2

P1F2

-

T3

P1F3

-

T4 T5 T6 T7 T8 T9 T10 T11 T12

P1F0 P2F1 P2F2 P2F3 P2F0 P0F1 P0F2 P0F3 P0F0

-

Application of PBZ 3ml.m-1 canopy diameter along with spraying of spermidine 0.01 mM Application of PBZ 3ml.m-1 canopy diameter along with spraying of spermine 0.1mM Application of PBZ 3ml.m-1 canopy diameter along with spraying of boron 1.25gm.lit-1 Application of PBZ 3ml.m-1 canopy diameter alone Spraying of NAA 80 ppm along with spraying of spermidine 0.01 mM Spraying of NAA 80 ppm along with spraying of spermine 0.1mM Spraying of NAA 80 ppm along with spraying of boron 1.25gm.lit-1 Spraying of NAA 80 ppm alone Spraying of spermidine 0.01 mM alone Spraying of spermine 0.1 mM alone Spraying of boron 1.25gm.lit-1 alone Absolute control

Method and time of application of treatments Paclobutrazol concentration was calculated based on the diameter of the tree, and applied @ 3 ml m-1 of canopy diameter (Bhagwan et al., 2013). The required paclobutrazol was dissolved in 10 litre of water. 75 mg of NAA was dissolved in 50 ml of ethanol and diluted it in 1 litres of water to get 80 ppm of NAA. 1.45 mg of spermidine was dissolved in 1 litre of water to get 0.01 mM of spermidine. 20mg of spermine was dissolved in 1 litre of water to get 0.1 mM of spermine. 1.25 gm of boron (20%) was dissolved in 1 litre of water to get 1.25 g l-1 of boron. Paclobutrazol was applied as soil collar drench. Ten holes were made at 2 feet away from tree trunk, and the prepared paclobutrazol solution was poured equally in the holes. The trees were irrigated before the application of paclobutrazol. Paclobutrazol was applied 120 days before bud break (Bhagwan et al., 2013). Ten litres of NAA 80 ppm solution was sprayed per tree 30 days

before flowering (Davenport, 2007). Ten litres each of spermidine 0.01mM and spermine 0.1 mM per tree was sprayed during full bloom stage (Aman ullah malik and Zora singh 2006). Ten litres of boron 1.25 g lit-1 was sprayed during full bloom stage (Sanna et al., 2005). The above chemicals and plant growth regulators were sprayed to observe the flowering, fruit set and yield of the trees.

Observation recorded Vegetative parameters The number of new flushes of the tree canopy was recorded and expressed in number as number of new flushes. The data was recorded on October, 15th, November 5th and November 30 th of 2011. The length between two internodes was measured and expressed in centimetres as internodal length. The internodal lengths of ten randomly selected (North, South, East and West directions) shoots were recorded and the mean was calculated. The number of days


213

PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS taken for panicle initiation from the day of spraying was recorded and expressed as time taken for initiation of panicle emergence after spraying.

Flowering parameters Fifty shoots were randomly tagged (from North, South, East and West directions) and all the flowering parameters were recorded. The mean number of days taken for initiation of panicle emergence after spraying was computed. The number of days taken from spraying to 50 per cent flowering i.e., till half of the tagged shoots flowered was recorded as time taken for 50 per cent flowering. The mean number of days taken for initiation of panicle emergence after spraying was computed. The number of days taken from spraying to 100 percent flowering i.e., till total tagged shoots flowered was recorded as time taken for 100 per cent flowering. The mean number of days taken for initiation of panicle emergence after spraying was computed. The number of tagged shoots which had flowered was recorded and expressed as percentage. The length and breath of the panicle was recorded and expressed in terms of centimeters as panicle length and breath. The panicle lengths and fruit set of ten randomly selected (North, South, East and West directions) shoots were recorded and the mean was calculated. The number of days taken from the date of panicle initiation to fruit formation of panicle at mustard stage was recorded was expressed as number of days taken for fruit set from panicle initiation. The mean number of days taken for fruit set after panicle initiation was computed. An average of 5 fruited panicles was considered for calculating the average number of fruits panicle-1 at the time of fruit set stage and expressed as fruit set panicle -1. The total number of fruits harvested tree-1 was counted after harvest and expressed as number of fruits tree-1. 214

Yield parameters The total number of fruits harvested treewas counted after harvest and expressed as number of fruits.tree-1.The average fruit weight was computed by dividing the total yield (kg tree -1) and number of fruit tree -1 of the respective treatment. The total weight of fruits produced by a tree was recorded to obtain the fruit yield tree-1 and expressed in kilograms. The number of days taken from the date of panicle initiation to harvest was recorded and expressed as days taken from panicle initiation to harvesting. Fifty shoots were randomly tagged (from north, south, east and west directions) and the panicle initiation was recorded. The mean number of days taken for harvesting of tree after panicle emergence was computed. Benefit cost ratio was calculated by estimating ratio of the cost of treatments and other cultural practices cost and yield (in terms of value) per tree. The data were subjected to statistical analysis as per the procedure out lined by Panse and Sukhatme (1985). 1

RESULTS AND DISCUSSION Vegetative parameters Vegetative growth in mango comprises of induction of cyclic new flush and increase in internodal length (Davenport, 2007). Hence, vegetative growth in mango includes both the emergence of new flush and increase in internodal length. After the cessation of the vegetative growth, mango undergoes dormant period coinciding with the low temperatures and subsequent induction of initiation of flower bud. Hence, mango has distinct vegetative and reproductive phases. Various plant growth regulators have varying effect on the vegetative growth of the mango cv. Banganpalli in the present investigation. There was a significant difference


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Flowering of mango was associated with reduced vegetative growth and available evidence strongly suggest that flower initiation depends on the presence of an unknown flower promoting factor or factors synthesised in the leaves. At the same time, there are other factors in the shoots which work against the flowering factor or factors. Further, evidence suggests that a group of hormones called gibberellins act as inhibitors of flowering (Voon et al., 1991). GA3 is a vegetative growth promoting hormone and paclobutrazol displays an anti-gibberellic activity. Hence, in the present investigation the observed reduction in vegetative growth in terms of reduction in number of new flushes and reduced intermodal length in paclobutrazol applied trees (Table 1 and 2) were due to anti gibberellic activity of paclobutrazol. NAA found to be significantly reducing the vegetative growth. Similar reduction in vegetative growth was observed by (Wahdan et al., 2011) in mango cv. Succary Abiad. As NAA was found to have flowering promoting activity (Oksher et al., 1980), the observed reduction in vegetative growth in present

among the plant growth regulators with respect to number of new flushes (Table 1) on October 15th and November 5th. Number of new flushes were increased gradually from October 15th to November 5th and reduced by November 30th. Paclobutraol and NAA have significantly minimised the number of new flushes when compared to control (Table 1). Similar reduction in number of new flushes or vegetative shoots in mango cv. Alphonso was earlier reported, when trees were sprayed with paclobutrazol at 3000 ppm (Rao et al., 1997), and in mango cv. Irwin (Orwintinee et al., 2008), Adil et al. (2011) which is often induced by a lower activity of GA3 (Voon et al., 1991). There was a significant difference observed among the plant growth regulators with respect to the internodal length (Table 2). Paclobutrazol and NAA significantly reduced the internodal length compare to control. Similar reduction in internodal length was obtained with application of paclobutrazol in mango cv. Irwin (Orwintinee et al., 2008), and in mango cv. Dashehari (Ram and Tripathi, 1993).

Table 1. Effect of flower enhancing plant growth regulators and fruit set improving chemicals on number of new flushes (no) of mango cv. Banganpalli. Treat

Oct 15th P1 P2 P0 Mean P1 F1 15.33b 29.33c 32.66c 25.77 8.00 b F2 30.66c 28.66c 21.33 26.88 11.3 b F3 2.33a 11.66a 9.00a 7.66a 0.00 a F0 9.66a 5.66a 19.66 11.66 1.33 a Mean 14.49a 18.82a 20.66 5.16a F-Test S. Em ± CD at (5%) Factor * 1.916 5.621 Factor F F Factor * 1.659 4.868 Factor P P F×P * 3.319 9.736 F×P

Nov 5th P2 P0 8.33 b 17.33c 5.66 a 10.33 8.66 b 4.33a 1.66 a 3.66a 6.07a 8.91b F-Test S. Em ± * 1.138 *

0.985

*

1.971

Nov 30th P2 P0 Mean 2.00a 1.66a 2.33 2.00a 3.66b 2.55 5.00b 3.33a 3.66 4.00b 2.00a 3.00 3.25 2.66 CD at F-Test S. Em CD at (5%) ± (5%) 3.339 Factor * 0.392 NS F 2.891 Factor * 0.339 NS P 5.783 F×P * 0.679 1.992

Mean 11.22b 9.10b 4.33a 2.21a

P1 3.33a 2.00a 2.66a 3.00a 2.74


215

PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Table 2. Effect of flower enhancing plant growth regulators and fruit set improving chemicals on internodal length (cm) of mango cv. Banganpalli. Treatment

F1 - Spermidine 0.01mM F2 - Spermine 0.1mM F3 - Boron 1.25g l-1 F0 - Control Mean Factor F Factor P F×P

P1 – PBZ 3 ml m-1 7.91a 8.18a 8.49a 7.38a 7.99a F - Test * * *

Internodal length P2 – NAA P0 – Control 80 ppm 8.53b 7.99a 8.35a 7.81a 9.00b 9.06b 8.49a 9.85c 8.59b 8.67b S. Em ± 0.222 0.192 0.385

Mean 8.14 8.11 8.85 8.57 CD at (5%) NS 0.565 1.131

Figures with same alphabets did not differ significantly. ** Significant at (p= 0.01 LOS), *Significant at (p= 0.05 LOS), NS- Non Significant. Values were compared with respective C.D values.

investigation may to due to inhibitory effect of flower promoting factors on vegetative growth in plants, because of NAA is a flowering hormone (Beyer, 1976).

Flowering parameters

flowering early when compare to control. Further, the reduction in the vegetative growth in terms of number of new flushes and intermodal length with PBZ application in the present investigation might have resulted in early flowering.

There was a significant difference among flower enhancing plant growth regulators with respect to time taken for panicle initiation after spraying of plant growth regulators (Table 3). Paclobutrazol significantly reduce the number of days taken for panicle initiation compare to control. Similar early panicle initiation was earlier reported by in mango cv. Baneshan (Kumar et al., 2005) and in mango cv. Alphonso (Rao et al., 1997) when trees were treated with PBZ @ 3000 ppm. Orwintinee et al. (2008) and Adil et al. (2011) also found similar earliness in mango flowering in mango cv. Irwin when trees were treated with PBZ @ 1 gm. a.i. tree-1, and PBZ @ 2.5 a.i. tree -1 respectively. Paclobutrazol with its anti– gibberellic activity in the present study might have initiated the

Paclobutrazol significantly increased the time taken for 50 per cent flowering (Table 4) and 100 per cent flowering (Table 5) compare to control. Once, panicle initiation has taken place, there was no effect of paclobutrazol and NAA on reducing the time taken for 50 per cent flowering, 100 per cent flowering and per cent of flowering compare to control. Similar increase in full bloom period was earlier observed by Khader et al. (1989) with paclobutrazol application in mango. Further, the increase in number of days taken for 50 per cent and 100 per cent flowering has prolonged the flowering period which might have ultimately resulted in better pollination and fruit set in paclobutrazol and NAA applied trees (Table 7).

216


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Table 3. Effect of flower enhancing plant growth regulators and fruit set improving chemicals on number of days taken for panicle initiation of mango cv. Banganpalli. Treatment

F1 - Spermidine 0.01mM F2 - Spermine 0.1mM F3 - Boron 1.25 g l-1 F0 - Control Mean Factor F Factor P F×P

P1 - PBZ 3 ml m-1 45.00b 40.00a 40.00a 36.66a 40.41a F - Test * * *

P2 – NAA 80 ppm 44.66b 55.00c 47.00b 39.66a 46.58b

Days P0 – Control 59.00c 48.33b 44.33a 56.00c 51.915c S. Em ± 1.535 1.329 2.658

Mean 49.55b 47.77a 43.77a 44.10a CD at (5%) 4.502 3.899 7.798

Figures with same alphabets did not differ significantly. ** Significant at (p= 0.01 LOS), *Significant at (p= 0.05 LOS). Values were compared with respective C.D values

There was significant difference among the plant growth regulator with respect to per cent of flowering on December 20th, December 26th, January 3rd, January 10th (Table 5). The per cent of flowering was taken on December 20th, December 26th, January 3rd, January 10th,

January 20th and February 1st. There was a gradual increase in per cent of flowering with increasing in the time intervals. Paclobutrazol application and NAA spray has significantly increased the per cent flowering compare to control (Table 5). However, the paclobutrazol

Table 4. Effect of flower enhancing plant growth regulators and fruit set improving chemicals on time taken for 50 per cent flowering from panicle initiation of mango cv. Banganpalli. Treatment

Days

F1 - Spermidine 0.01 mM F2 - Spermine 0.1 mM F3 - Boron 1.25 g l-1 F0 - Control Mean Factor F Factor P F×P

P1 - PBZ 3 ml m-1 29.33c 30.33c 30.00c 29.33c 29.74b F - Test * * *

P2 – NAA 80 ppm 31.33c 29.00b 27.33b 27.66b 28.83b

P0 – Control

Mean

20.00a 27.66b 25.00b 21.00a 23.41a

26.88 28.99 27.44 25.99

S. Em ± 0.836 0.724 1.448

CD at (5%) NS 2.124 4.248



217

PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Table 5. Effect of flower enhancing plant growth regulators and fruit set improving chemicals on time taken for 100 per cent flowering from panicle initiation of mango cv. Banganpalli. Treatment

Days


P1 - PBZ 3 ml m-1 46.00b 44.33b 40.66a 43.33b 43.58b F - Test * * *

P2 – NAA 80 ppm 39.33a 46.00b 39.33a 43.66b 42.08b

P0 – Control

Mean

45.33b 34.66a 38.33a 35.33a 38.41a

43.55 41.66 39.44 40.77

S. Em ± 1.197 1.036 2.073

CD at (5%) NS 3.040 6.081


was significantly more effective in increasing the flowering percentage. Gibberellins, a group of plant growth hormones were reported to be inhibitory to flowering in mango and the available evidence suggests the flower promotive effect of paclobutrazol in mango

due to its anti - gibberellin activity (Quinlan and Richardson, 1984). Hence, in the present investigation the increase in the per cent (%) flowering of mango by paclobutrazol was due to its anti-gibberellin activity. The similar findings of increase in per cent flowering (%)

Table 6. Effect of flower enhancing plant growth regulators and fruit set improving chemicals on number of days taken for fruit set from panicle initiation of mango cv. Banganpalli. Treatment

Days


P1 - PBZ 3 ml m-1 55.66b 59.66b 58.00b 62.00c 58.83c F - Test * * *

P2 – NAA 80 ppm 56.00b 48.33a 54.33b 60.66c 54.83b

P0 – Control

Mean

45.66a 53.33b 53.33b 46.33a 49.66a

52.44 53.77 55.22 56.22

S. Em ± 1.251 1.083 2.167


218


CD at (5%) NS 3.179 6.358

PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS by application of PBZ was earlier reported by Rao et al. (1997) in mango cv. Alphonso, by Shinde et al. (2001) in mango cv. Alphonso, by Burondkar et al. (2000) in mango cv. Alphonso, by Vijayalaxmi and Srinivasan (2000) in mango cv. Alphonso, by Kumar et al. (2005) in mango cv. Baneshan, Orwintiner et al. (2008) and by Muhammad Nafeez et al. (2010) in mango cv. Irwin. The NAA spray has also significantly increased the flowering in mango cv. Banganpalli in the present investigation when compared with the control. Similar increase in flowering with spraying of NAA was reported in mango cv. Succary Abiad NAA, which is considered as flowering hormones in some crops might have increased the latent flowering factors in the mango and resulted in overall increase in flowering in mango cv. Banganpalli when compared to control in the present investigation. There was significant difference among the plant growth regulators with respect to panicle length (Table 7). Paclobutrazol and NAA significantly increased the panicle length compare to control. Similar increase in panicle length with the application of paclobutrazol in mango was reported by

Desai and Chundawat (1994) in mango, Vijayalaxmi and Srinivasan (1998) in mango cv. Alphonso, when trees treated with PBZ @ 10 ml tree-1. There was a significant difference among plant growth regulator with respect to panicle breadth (Table.8). Paclobutrazol could able to increase the panicle breadth compare to control and NAA (8). However, Winston (1992) in mango cv. Kensington and Orwintiner et al. (2008) in mango cv. Irwin reported that the panicles of paclobutrazol treated trees were considerably shorter than those of control trees. The discrepancy in the finding of present investigation to the earlier reports regarding panicle may be due to varietal change, time of applications and dosage of paclobutrazol. However, increase in panicle length and breadth of paclobutrazol treated trees might be beneficial for increase the number of hermaphrodite flowers per panicle. This may cause for better fruit set over the control.

Effect on fruit set parameters There was a significant difference among plant growth regulators with respect to number of days taken for fruit set from panicle initiation (Table 6). Paclobutrazol

Table 7. Effect of flower enhancing plant growth regulators and fruit set improving chemicals on panicle length (cm) of mango cv. Banganpalli. Treatment P1 - PBZ 3 ml m-1 F1 - Spermidine 0.01mM F2 - Spermine 0.1mM F3 - Boron 1.25g l-1 F0 - Control Mean Factor F Factor P F×P

17.36b 17.10b 14.40a 17.73b 16.64b F -Test * * *

Panicle length (cm) P2 - NAA 80 P0 - Control ppm 16.16b 16.00b 15.33a 15.96b 15.86a S. Em ± 0.544 0.471 0.943

13.76a 16.30b 16.50b 12.63a 14.79a CD at (5%) NS 1.384 2.768


Mean 15.76 16.46 15.41 15.44

219

PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Table 8. Effect of flower enhancing plant growth regulators and fruit set improving chemicals on panicle breadth (cm) of mango cv. Banganpalli. Treatment

F1 - Spermidine 0.01mM F2 - Spermine 0.1mM F3 - Boron 1.25g.l-1 F0 - Control Mean Factor F Factor P F×P

P1 - PBZ 3 ml m-1 12.06b 12.20b 11.90b 13.10c 12.31b F - Test * * *

Panicle breadth (cm) P2 - NAA 80 P0 – Control ppm 9.866a 9.36a b 11.16 12.46b a 9.93b 11.70b b 11.66 10.23a a 10.65 10.93a S. Em ± CD at (5%) 0.334 0.981 0.289 0.849 0.579 1.699

Mean 10.42a 11.94b 11.17a 11.66b

Figures with same alphabets did not differ significantly. ** Significant at (p= 0.01 LOS), *Significant at (p= 0.05 LOS). Values were compared with respective C.D values.

could not able to reduce the time taken for fruit set after panicle initiation compare to control. This may be due to increase in time taken for full bloom stage of paclobutrazol treated trees (Table 5) and early panicle initiation compared to control (Table 3). However, increase in days taken for fruit set from panicle initiation might be beneficial for better fruit set and fruit retention in paclobutrazol treated trees. There was significant difference among plant growth regulators with respect to fruit set panicle-1 (Table 9). Paclobutrazol could able to increase fruit set panicle-1 compared to control and NAA (Table 10). This may be due to increase of number of perfect flowers per panicle. Similar increase in fruit set panicle-1 in response to paclobutrazol application was recorded by GoGuey (1990) in mango cv. Valencin, Iyer and Kurian (1992) in cv. Alphonso, Zora Singh et al. (2000) in cv. Dashehari, Cardenas an Rojas (2003) in mango cv. Tommy Atkins, Kumar et al. (2005) in cv. Baneshan and Orwintinee et al. (2008) in mango cv. Irwin. The prolonged flowering 220

period (time taken for 100 % flowers from panicle initiation (Table 5) might have caused for better fruit set in paclobutrazol treated trees compare to control.

Effect on yield parameters Yield parameters like number of fruits tree-1, fruit weight (gm), yield (kg tree-1) and number of days taken for harvesting from panicle initiation were recorded in two experiments. There was a significant difference among plant growth regulators with respect to the number of fruits tree-1 (Table 10). Paclobutrazol application has significantly increased the number of fruits per tree compare to control and NAA spray (Table 10). Similar increase in number of fruits tree-1 was earlier reported by Kumar et al. (2005) in mango cv. Baneshan, Cardenas and Rojas (2003) in mango cv. Tommy Atkins, Orwintinee et al. (2008) in mango cv. Irwin, Kumbhar et al. (2007) in mango cv. Kesar. Paclobutrazol application significantly increases flowering percentage (Table 6) and better fruit set per panicle (Table 9) compared


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Table 9. Effect of flower enhancing plant growth regulators and fruit set improving chemicals on number of fruit set per panicle of mango cv. Banganpalli. Treatment

F1 - Spermidine 0.01 mM F2 - Spermine 0.1 mM F3 - Boron 1.25 g.l-1 F0 - Control Mean Factor F Factor P F×P

P1 - PBZ 3 ml m-1 5.80b 5.40b 6.40d 6.20c 5.95c F - Test * * *

Fruits in number P2 – NAA P0 – Control 80 ppm 5.60b 5.53b a 5.20 5.20a c 5.86 5.86c 5.80b 4.86a 5.61b 5.36a S. Em ± 0.085 0.074 0.148

Mean 5.64b 5.26a 6.04c 5.62b CD at (5%) 0.251 0.217 0.434


to control and NAA spray. These may cause for increase in the total number of fruits per tree by PBZ application. The similar correlation between intensity of flowering, perfect flowers and better fruit set and subsequent increase in total number of fruits per tree and yield was earlier reported by Burondkar and Gunjate, (1993) in mango.

There was significant difference among plant growth regulators with respect to fruit weight (gm) (Table 11) and yield (Table 12). Paclobutrazol and NAA were both equally increased the fruit weight and yield. Similar increase in fruit weight was earlier reported by Nav Prem Singh (2002) in mango cv. Dashehari treated with 100 ppm of NAA.

Table 10. Effect of flower enhancing plant growth regulators and fruit set improving chemicals on total number of fruits per tree of mango cv. Banganpalli. Treatment



Fruits in number P2 – NAA P0 – Control 80 ppm 152.66b 131.33a a 116.00 137.33b b 148.33 139.66b a 118.00 114.66a a 133.74 130.74a S. Em ± 4.366 3.781 7.562

Mean 146.99b 132.99a 140.77b 127.66a CD at (5%) 12.806 11.091 22.182



221

PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Table 11. Effect of flower enhancing plant growth regulators and fruit set improving chemicals on fruit weight (g) of mango cv. Banganpalli. Treatment


P1 - PBZ 3 ml m-1 320.00b 284.00b 273.66a 291.33b 289.74a F - Test * * *

Fruit weight (g) P2 – NAA P0 – Control 80 ppm 318.00b 239.00a b 318.00 268.00a 331.66c 303.33b 240.66a 268.66a 302.08b 269.74a S. Em ± 8.143 7.052 14.104

Mean 289.00a 290.00a 302.88b 266.88a CD at (5%) 23.885 20.685 41.370


Paclobutrazol also increased the fruit weight in mango cv. Baneshan (Kumar et al., 2005) The increased in intensity of flowering, better fruit set and fruit weight in paclobutrazol treated trees have ultimately increased the yield of mango by 42.17 per cent. Burondkar and Gunjate (1993) has also found

similar correlation between flowering, fruit set, fruit weight and yield of mango in response to paclobutrazol application. Similar increased in yield of mango in response to paclobutrazol application was obtained by various worker like Singh and Dhillan (1992) in cv. Kensington pride, Zora Singh and

Table 12. Effect of flower enhancing plant growth regulators and fruit set improving chemicals on yield (kg) of mango cv. Banganpalli. Treatment



Yield (kg.tree-1) P2 – NAA P0 – Control 80 ppm 48.54b 31.38a a 36.88 36.80a 49.19b 42.36b 28.36a 30.80a 40.75b 35.33a S. Em ± 1.893 1.639 3.279


222


Mean 43.38b 38.34a 42.77b 34.32a CD at (5%) 5.552 4.808 9.617

PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Dhillon (1992) in cv. Dashehari, Iyer and Kurian (1992), Ram and Tripathi (1993) in cv. Dashehari, Desai and Chundawat (1994) in Alphonso, Shinde et al. (2002) in cv. Alphonso, Kumar et al. (2005) in Beneshan, Orwintinee et al. (2008). There was a significance difference among plant growth regulators with respect to number of days taken from panicle initiation to harvesting (Table 13). Paclobutrazol could able to minimize the number of days taken from panicle initiation to harvesting, compare to control. Shu (1999) revealed that warm temperatures (31o/ 25oC) hastened growth rates of panicles and flowers, shortened flowering duration and life span of flowers in cultivars like Haden, Irwin, Keitt etc. Warm temp also increased the rates of percentage of anther dehiscence and pollination. Shinde et al. (2001) reported that the total heat units required for maturation of fruits in mango. In the present investigation paclobutrazol treated trees resulted in early panicle initiation and delayed to get full bloom

stage and caused delay in fruit set compare to control, which might have got exposed to more heat units (or) required degree days well in advance of other and resulted in early maturity of fruits. Similar findings were obtained by, GoGuey (1990), Singh and Dhillon (1992) in mango treated with paclobutrazol.

Fruit set improving chemicals impact on mango cv. Banganapalli There was no significant difference among fruit set improving chemicals with respect to number of days taken for harvesting from panicle initiation (Table 8), however, there was a significant difference among fruit set improving chemicals with respect to number of fruits tree-1 (Table 10). Spermidine and boron were significantly effective in increasing the number of fruits tree-1 compare to control and spermine. 1

The increase in the number of fruits treeby application of polyamines like spermidine

Table 13. Effect of flower enhancing plant growth regulators and fruit set improving chemicals on number of days taken from panicle initiation to harvesting of mango cv. Banganpalli. Treatment


P1 - PBZ 3 ml m-1 109.00a 117.66b 116.33a 127.33c 117.58a F - Test * * *

Days in number P2 – NAA P0 – Control 80 ppm 113.66a 121.66b 122.33b 121.33b 120.66b 116.66a 119.66b 131.33c 119.07a 122.74b S. Em ± 1.573 1.362 2.724

Mean 114.77a 120.44b 117.88a 126.10c CD at (5%) 4.613 3.995 7.991



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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS and spermine may be due to improvement in embryo development (Ponce et al., 2002), increased viability of the ovules and a prolonged pollination period (Crisosto et al., 1988). There is substantial evidence to support that ethylene is the main trigger in abscission process (Brown, 1997) and polyamines are considered as anti-ethylene substances (Apelbaum et al., 1981), being the likely competitors of precursors of ethylene (Sadenosyl methionine). Hence, exogenous application of polyamines has been reported to improve fruit retention in olive (Rugini and Mencuccini, 1985), and in mango (Singh and Singh, 1995), by increase in number of fruit.panicle-1. As earlier discussed boron is essential for stigma receptivity, pollen tube germination and growth (Nyomora and brown, 1997). The increase in yield by spraying of boron in the present investigation is due to better fruit set and increase in number of fruits per panicle. Similar increase in number of fruits per tree with boron was earlier reported by Kampol et al. (2001) in mango cv. Namdoknai, Sanna et al. (2005) in mango cv. Fagrikalan and Ramzy et al. (2011) in mango. There was significant difference observed among fruit set improving chemicals with respect to fruit weight and yield. Boron, spermine and spermidine could able to increase the fruit weight compare to control (Table 11). Spermidine could able to increase

yield (kg tree-1) compared to control. Boron and spermine found to be at par with spermidine (Table 12). Spermidine and spermine were significantly effective in increasing the yield compare to control and boron (Table 12). This increase in yield may be due to increase in total number of fruits per tree and increase in average fruit weight. The similar increase in yield was earlier reported by Abd El-Migged et al. (2002) spraying with boron in olive, Sanna et al. (2005) with boron spray in mango, Zongruni and Dong (2000) with boron spray in mango (Ramzy et al., 2011) with boric acid application in mango, application with polyamines in apple (Costa and Bagni, 1983), application with polyamines in mango (Singh and Singh, 1995), application with polyamines in mango cv. Kensington pride (Malik and Zora Singh, 2006) and application with polyamines in cannino apricot (Enas et al., 2010). There was significant difference among fruit set improving chemicals with respect to number of days taken for harvesting from panicle initiation stage. Spermidine and boron significantly minimized number of days taken for harvesting from panicle initiation compare to control (Table 13). This minimization in number of days taken for harvesting from panicle initiation is may be due to early fruit set, pollen tube germination and growth (Nyomora and Brown, 1997).

Table 14. Effect of flower enhancing plant growth regulators and fruit set improving chemicals on benefit cost ratio of mango cv. Banganpalli. Treatment

F1 - Spermidine 0.01 mM F2 - Spermine 0.1 mM F3 - Boron 1.25 g.l-1 F0 - Control Mean

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P1 - PBZ 3 ml m-1 1.82 0.28 1.15 1.97 1.30

Benefit : Cost P2 – NAA P0 – Control 80 ppm 2.71 1.35 0.12 0.29 3.06 2.80 1.33 1.53 1.80 1.53


Mean 1.96 0.23 2.33 1.54


Synergistic effect of flower enhancing plant growth regulators and chemicals combination with fruit set improving chemicals on mango Synergistic effects on fruit set parameters There was significant difference among the interactions of flower enhancing plant growth regulator and fruit set improving chemicals (Table 9). Flower enhancing plant growth regulators in combination with fruit set improving chemicals could not able to reduce the number of days taken for fruit set from panicle initiation compare to control. This increase in days may be due to increase in days taken for full bloom stage. However, these may further cause for better fruit set by providing prolonged pollination period by the effect of polyamines (Crisosto, 1988). There was significant difference among the interactions between flower enhancing plant growth regulators and fruit set improving chemicals with respect to fruit set panicle-1 (Table 9). Paclobutrazol combination with spermidine could able to increase fruits panicle-1 significantly when compared to control. Paclobutrazol could helps in getting more number of perfect flowers and thus further helps in better fruit set in paclobutrazol treated trees compare to control (Kumar et al., 2005). Polyamines like spermidine may increase the fruit set per panicle by improving embryo development (Ponce et al., 2002), increase viability of the ovule and prolonged pollination period (Crisosto, 1988) there by increasing the pollen germination and pollen tube growth (Wolukan et al., 2004). These may cause for better fruit set panicle -1 in spermidine treatment compare to control. Paclobutrazol along with spermidine because of their fruit set improving properties, might have caused

increase in number of fruits per panicle synergistically compare to their individual application and control. The similar synergistic effect in increasing the number of fruits panicle-1 was earlier reported by Kumar et al. (2005). Combination of paclobutrazol along with Ca (NO3)2 increases number of fruits per panicle compares to their individual application in mango cv. Baneshan. Sanna et al. (2005) reported that combination of sucrose along with Boric acid enhanced fruit set panicle-1 compared to individual application of chemicals in mango cv. Fagri kalan.

Synergistic effects on yield parameters Flower enhancing plant growth regulators combinations with fruit set improving chemicals significantly increased the number of fruits tree -1 (Table 10). Paclobutrazol combination with spermidine could able to increase the number of fruits tree1 compare to control (Table 10). Paclobutrazol could helps in getting more number of reproductive shoots to tree (Rao et al., 1997, Kumbhar et al., 2007, Muhammad Nefees et al., 2010, Adil et al., 2011), and also increase the perfect flowers per panicle (Kumar et al., 2005). Spermidine (polyamines) as earlier discussed cause for better fruit set by increasing the embryo development (Ponce et al., 2002), by increase the viability of ovules and prolonged pollination period (Crisosto, 1988), and increased the harvested fruits per tree by increase the fruit retention, possibly by inhibiting endogenous ethylene biosynthesis, which is the known trigger in abscission (Brown, 1997). The flower enhancing ability of paclobutrazol and fruit set improving property of spermidine has synergistically increased the overall number of fruits harvested per tree when compared to their individual effect. Similar synergistic increase in number of fruits harvested per tree was earlier reported by Kumar et al. (2005) with


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS the application of paclobutrazol along with Ca (NO3)2 in mango cv. Baneshan. Sanna et al. (2005) also obtained similar results with sucrose in combination with potassium citrate. NAA combination with boron could able to increase significantly the fruit weight compare to control and individual application (Table 11). NAA might have increased the fruit weight (Table 11) by increasing the fruit pulp content and fruit size. The similar increase in fruit weight by Boron application was earlier reported by Sanna et al. (2005) and Ramzy et al. (2011) in mango. In the interaction of NAA along with boron because of their both fruit weight improving properties, might have caused for increase in fruit weight synergistically compare to their individual application and control. The similar synergistic effects in increasing the fruit weight were earlier reported by Sanna et al. (2005) with sucrose along with boric acid. Kumar et al. (2005) also reported that paclobutrazol along with phosphorus chemicals increase fruit weight synergistically in combination compare to individual application. There was significant difference among the interactions between flower enhancing plant growth regulators and fruit set improving chemicals with respect to yield (kg tree-1). Paclobutrazol in combination with spermidine could able to increase the yield (kg tree-1) compare to control (Table 12). Paclobutrazol as earlier discussed helps in getting more number of reproductive shoots (Muhamad Nafes et al., 2010) and also increases the perfect flowers per panicle (Kumar et al., 2005) in mango. Spermidine could able to help in increasing fruit set and fruit retention (Malik and Zora Singh, 2006) in mango and also improves the average fruit weight (Eanas et al., 2010). In the interaction of paclobutrazol along with spermidine

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synergistically increase the yield (kg tree-1) by flower enhancing nature of paclobutrazol and fruit set, fruit retention and fruit weight increasing behaviour of spermidine could helps synergistically in getting more yield per tree compare to their individual application and control. Similar synergistic effect on increasing the yield was earlier reported by Sanna et al. (2005) with sucrose along with potassium citrate.

Benefit cost ratio In the interactions of the flower enhancing plant growth regulators combine with fruit set improving chemicals the maximum benefit cost ratio was obtained by NAA along with boron compare to control and other treatments (Table 14). This may be due to chemical cost of per kg or lit was lesser compare to other chemicals which were used in interactions.

REFERENCES Adil, O.S., Osman, A. R., Elamin, M and Bangerth 2011. Effect of paclobutrzol on floral induction and associated hormonal and metabolic changes of biennially bearing mango (Mangifera indica L.) cultivars during off year. APRN Journal of Agricultural and Biological Science., 6 (2), Feb. Malik, A.U. and Zora Singh 2006. Improved fruit retention, yield and fruit quality in mango with exogenous application of polyamines. Scientia Horticulturae, 110:167-174. Anonymous 2004. Annual Report, Indian Institute of Horticulture Research, Bangalore. Anonymous 2010. Annual Report, National Horticulture Board. Pp.86-95. Apelbaum, A. Burgoon, A.C., Andrew, J.D., Liberman, M. Ben-Arie, R. and Matto, A.K. 1981. Polyamines inhibit biosynthesis of ethylene in higher plant tissue and fruit protoplast. Plant Physiol. 68: 453–456. Beyer, E.M.J. 1976. A potent inhibitor of ethylene


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS action in plants. Plant Physiol., 58: 268-271. Bhagwan, A., Vanajalatha, K., Sarkar, S.K., Girwani, A. and Misra, A.K. 2013. Standerdization of dose and time of soil application of Cultar on flowering and yield in mango cv. Banganpalli. Journal of Ecofriendly Agriculture, 8 (1): 39-43. Brown, K.M. 1997. Ethylene and abscission. Physiol. Plant 100: 567–576. Burondkar, M.M. and Gunjate, R.J. 1993. Control of vegetative growth and induction of early and regular cropping in mango with paclobutrazol. Acta Hort., 341: 206-215. Cardenas, K. Rojas, E. 2003. Effect of paclobutrazol and nitrates of potassium and calcium on the development of the mango ‘Tommy Atkins’. Bioagro, 15: 2:83 -90. Crisosto, C.H. 1988. Putrescine influences ovule senescence, fertilization time, and fruit set in ‘Comice’ pear. J. Am. Soc. Hort. Sci., 113: 708–712. Davenport, T.L. 2003. Management of flowering in three tropical and subtropical fruit tree species. Hort. Science, 38: 1331-1335. Davenport, T.L. 2007. Reproductive physiology of mango. Braz. J. Plant Physiol, 19(4):363376. Desai, M.M. and Chundawat, B.S. 1994. Regulation of flowering in mango by paclobutrazol. Indian Journal of Horticulture, 51(1): 9-15. Enas, A.M., Ali, S.M. Sarrwy, A. and Hassan, H.S.A. 2010. Improving Canino Apricot Trees Productivity by Foliar Spraying with Polyamines. Journal of Applied Sciences Research, 6(9): 1359-1365. GoGuey, T. 1990. The effects of repeated application of cultar (Paclobutrazol) to Mangifera indica L. Var. Valencia. Fruits (Paris), 45(6): 599-607. Kumar, Raj, M Reddy, Y N, Chandrasekhar, R. Srihari, D. 2005 Effect of foliar application of chemicals and plant growth regulators on flowering of unpruned mango trees of cv. Baneshan. Journal of Research ANGRAU, 33: 2, 6-11. Kumbhar, A.R. Gunjate, R.T. and Amim, S.M. 2007.

Comparision of cultar and austar as source of paclobutrazol for flowering and fruiting in Kesar in Mango. Acta Hort., 820, Proc. 8th Int. Mango symposium. Moti Singh A S Chaudhary A S and Prasad M 1987 A note on the effect of some plant regulators on fruit retention in mango (Mangifera indica L). Haryana J. Hort. Sci. 15 (3/4): 221 (Hort. Abst. 51 (3):2200). Muhammad, N., Muhammad, F. Saeed A., Khan, M.A. Jamil, M. and Aslam, M.N. 2010. Paclobutrazol Soil Drenching Suppresses Vegetative Growth, Reduces Malformation, and Increases Production in Mango. International Journal of Fruit Science, 10: 431– 440. Singh, N.P. 2002. Effect of chemicals and plant bioregulators on the promotion of flowering and fruiting in mango cv. Dusehari. Ph.D Thesis submitted to the Punjab Agricultural University, Ludhiana. Nunez-Elisea, R. and Davenport, T.L. 1995. Effect of leaf age, duration of cool temperature treatment and photoperiod on bud dormancy release and floral initiation in mango. Scientia Hort., 62: 63-73. Nyomora, A.M.S. and Brown, P.H. 1997. Fall foliar-applied boron increases tissue boron concentration and nut set of almond. J. Amer. Soc. Hort. Sci., 122(3): 405-410. Quinlin, J.D. and Richardson, P.J. 1984 Effect of Paclobutrazol on apple shoot growth. Acta Horticulture, 146:105-110. Orwintinee Chusri, Naoko Koza, Tatsushi Ogata, Hirokazu Higuchi and Yoshimi, Yonemoto 2008. Application of paclobutrazol for flowering and fruit production of Irwin mango (Mangifera indica L.) in Okinawa. Trop. Agr. Develop, 52(3): 69-73. Pandey, S. Ranade, S.A. Nagar, P.K. and Kumar, N. 2000. Role of polyamines and ethylene as modulators of plant senescence. Journal of Biosciences, 25:291-299. Ponce, M.T., Guiñazú, M. and Tizio, R. 2002. Effect of putrescine on embryo development in the stenospermocarpic grape cvs. Emperatriz and Fantasy. Vitis, 41:53–54.


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Ram, S. and Tripathi, P.C. 1993. Effect of cultar on flowering and fruiting in high density Dashehari mango trees. Indian Journal of Horticulture, 50(4):292-295. Ramzy, G. Stino Habashy, S. A. and Kelani, R.A. 2011. Productivity and fruit quality of three mango cultivars in relation to foliar spray of calcium, zinc, boron and potassium. Journal of Horticultaral Science & Ornamenta Plant, 3 (2): 91-98. Rao, M.M., Srihari, D., Patil, V.S. Madalageri, M.B. 1997. Further studies on chemical induction of flowering directly on fruited shoots in off phase Alphonso mango trees. Karnataka J. Sci., 10(2): 598-601. Rao, M.M. 1998. Role of low night temperature days in fruit bud differentiation in mango trees under mild tropical rainy climatic conditions. Karnataka Journal of Agricultural Sciences, 11(4) : 1142-1144. Saleh, M.M. and El-Monem, E.A. 2003. Improving the productivity of Fagri Kalan mango trees grown under sandy soil conditions using potassium, boron and sucrose as foliar spray. Ann. Agric. Sci., 48L :747-756. Sanna Ebeed and Abd El-Migeed, M.M.M. 2005. Effect of Spraying Sucrose and Some Nutrient Elements on Fagri Kalan Mango Trees. Journal of Applied Sciencse Research 1(5): 341-346. Shinde, A.K., Dalvi, M., Godse, S., Patil, B. and Pujari, K. 2002. Evaluation of chemical and growth regulatory for post harvest treatment of fruits in Alphonso mango. VII International Mango Symposium, Recife, Brazil, p.77. Shinde, A.K., Burondkar, M.M., Bhingrade, R.T., Waghmare, G.M., Rangwala, A.D. and Wagh, R.G. 2001. Heat unit requirement for fruit maturity in mango varieties. Indian Journal of Plant Physiology, 6(2): 194-196. Shu, Z. H. 1999. Effect of temperature on the flowering biology and fertilization of

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mangoes (Mangifera indica L.). Journal of Applied Horticulture, Lucknow. 1(2): 79-83. Singh, Z. and Dhillon, B.S. 1992. Effect of paclobutrazol on floral malformation, yield and quality of mango (Mangifera indica L.). Acta Horticulturae, 296: 51-54. Vijayalakshmi, D. and Srinivasan, P.S. 1998. Induction of flowering in off year mango cv. Alphonso as influenced by chemicals and growth regulators. Ann. Plant Physiol., 12(2): 93-97. Voon, C.H.C., Pitakpaivan and Tan, S.J. 1991. Mango cropping manipulation with cultar. Acta Horticulture, 291:219-228. Wolukau, J.N.S.L., Zhang, G.H., Xu and Chen, D. 2004. The effect of temperature, polyamines and polyamine synthesis inhibitor on in vitro pollen germination and pollen tube growth of Prunus mume. Sci. Hort., 99: 289299. Yeshitela, T.P.J., Robbertse and Stassen, P.J.C. 2004. Effects of various inductive periods and chemicals on flowering and vegetative growth of ‘Tommy Atkins’ and ‘Keitt’ mango (Mangifera indica) cultivars. New Zealand Journal of Crop and Horticultural Science., 32: 209-215. Zongruni, and Dong, R. 2000. Effect of boron on blossom, Embryo development and yield of mango. J. Yunnan Agric. University,15: 6365. Zora Singh and Dhillon, B.S. 1992. Effect of paclobutrazol on floral malformation, yield and quality of mango (Mangifera indica L.). Acta Horticulture, 296: 51-53. Zora Singh, Singh, Z., Muller, W., Polency, F., Verheyden, C. and Webster, A.D. 2000. Effect of (2 RS, RS) paclobutrazol on tree vigour, flowering, fruit set and yield in mango. Proceeding of International Conference on Integrated fruit production, Leuven, Belgium 27 July-1 August. Acta Horticulture, 525:459-462(Abst.).



INDUCTION OF MANGO OFF-SEASON FLOWERING THROUGH CHEMICAL AND CANOPY MANAGEMENT IN PENINSULAR INDIA T. N. Balamohan and A. Nithya Devi Horticultural College and Research Institute for Women Tiruchirappalli – 620 009 (T.N.) Email: [email protected], [email protected]

INTRODUCTION The Mango (Mangifera indica L.), member of family Anacardiaceae, is amongst the most important tropical fruit of the world. Indo – Burma-Siam regions and Philippines are considered to be the probable places of origin of mango. Besides delicious taste and excellent flavour, mango is rich in vitamins and minerals. Mango has been under cultivation for more than 4000 years in India. India continues to be the largest mango producing country of the world, accounting for more than 50 per cent of the world production. Flowering is the first of several events that set the stage for mango production each year. Given favorable growth conditions, the timing and intensity of flowering greatly determines when and how much fruits would be produced during a given season. Insight into this phenomenon has been of prime interest to scientists and growers for over a century.

South Indian scenario of mango flowering In South India, mango generally starts flowering from December- January and yields from April to July during normal rainfall years. If rainfall is excess, fruiting would be shifted accordingly by a month or two. During on years, there will be a huge arrival of mangoes from June to July leading to glut, resulting in slashed price, leaving farmers with very low profit. The long felt need of the farmers of Tamil Nadu is to produce mangoes in off-season in

order to fetch a rewarding profit. Several attempts were made to identify mango varieties yielding off-season and the ways to induce off-season fruits. There are reports about varieties yielding off-season fruits but not consistently. Therefore, most of the mango workers feel that the induction of flowers either through canopy management or through chemicals would be more reliable than selection of off-season varieties.

Flower induction through canopy management Though many reasons are attributed for low productivity, poor canopy management is considered as one of the major limiting factors in mango production. Being an evergreen tree, mango is seldom pruned in India, which leads to over-crowding of branches resulting in poor penetration of sunlight causing low productivity coupled with inferior quality fruits. Regular training and pruning operations are very much essential to have a productive canopy. The extent of pruning has an impact on the flowering and fruiting. Mango trees under ultra high density planting system have to be pruned every year to avoid interlocking. Severe pruning i.e., total removal of past seasons’ growth resulted in poor flowering (Gopu et al., 2013). Davenport (2007) reported that shoot initiation is stimulated by pruning, defoliation, irrigation during dry conditions, application of nitrogen fertilizer, and other


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS factors, e.g., exposure to ethylene or a shift from cool to warm temperatures. Frequent flush events occur in young trees and in mature trees in conditions of high nitrogen and abundance of water. Other factors that stimulate initiation of shoot development include stem pruning, defoliation, foliar nitrogen sprays and ethylene. Induction, controlling the type of shoots that are evoked upon initiation, appears to be governed by the interaction of a putative temperature-regulated florigenic promoter (FP) and an age-dependent vegetative promoter (VP) (Davenport and Núñez-Eliséa, 1997; Davenport, 2003, 2008).

Flower induction through nitrogen manipulation High nitrogen levels, especially under well-watered conditions, are conducive to initiation of frequent vegetative flushes. Nitrogenous fertilizers should never be applied nearer to the time of pruning which would induce second flushes before the stems have achieved sufficient maturity. Reduction of vegetative flushes can be accomplished by limiting nitrogen fertilizer application to trees until the desired flowering time. It is critical to maintain the annual leaf nitrogen levels sufficiently low to discourage unwanted vegetative growth during the period approaching the desired flowering date. Davenport (2003 & 2006) correlated high leaf nitrogen levels with frequent vegetative flushes in mango. Hence, It is advisable that leaf analyses for nitrogen levels should be conducted on the last flush of leaves at least once or preferably, twice a year. If one analysis is conducted, it should be done just prior to the synchronizing prune. An observation of Davanport (2007) says that the leaf nitrogen levels for mango should be 1.1 to 1.4 per cent at the time of synchronizing prune event in order to avoid possible second flushes.

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Flower induction by chemicals Application of chemicals like potassium nitrate from 1 to 8 per cent (Davenport, 2003), urea 2.0 per cent, ethylene 125 to 1000 ppm (Dutcher, 1972; Chacko et al., 1974), 6-benzyl amino purine 100 ppm (Chen, 1987), P333 (paclobutrazol) @ 1.25 to 10g a.i/tree (Tandel and Patel, 2011) were found to have a positive impact on the induction of flowering in mango. Earlier works on floral manipulation in mango plants, revealed that floral initiation in trees is controlled by a range of factors which includes environmental stimuli, developmental cues and other interactions with vegetative growth and PGRs and it is also apparent that rarely one factor can be considered in isolation. Research in trees is expensive and slow and it has often been focused as a limitation to production in perennial trees like mango. So, adoption of a particular practice could be recommended strongly only after thorough assessment of different methods/practices and continuous research efforts. Paclobutrazol sold in the tropics under the trade name Cultar (Syngenta Corp., also available from several Chinese manufacturers and distributors), reduces the period of dormancy which is necessary to allow floral induction during warm temperature conditions by approximately one month (Davenport, 2003), thus increases the potential to produce reproductive shoots in younger stems upon shoot initiation. Application of paclobutrazol or uniconazole [Sumitomo Chemical Co. (international) or Valent Corp. (USA)], triazole compounds that inhibit synthesis of kaurene oxidase in the gibberellin-synthesis pathway (Dalziel and Lawrence, 1984; Rademacher, 1991), stimulates the production of flowering shoots during these weakly inductive conditions (Burondkar and Gunjate, 1993; Tongumpai et


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS al., 1991; Voon et al., 1991; Nartvaranant et al., 2000; Yeshitela et al., 2004). Thus, field application of paclobutrazol to trees bearing one-month-old mango shoots produced inflorescences from those stems when bud break was initiated three months later by a foliar application of KNO3 (Davenport, 2003).

experience has shown that about half that amount is needed if applied during the dry season. It takes at least 90 days for either product to exert an effect in trees (Nartvaranant et al., 2000). Earlier initiation of flushes results in formation of vegetative shoots so it is important to avoid growing conditions that promote the initiation of frequent flushes when paclobutrazol is applied.

The triazole plant growth retardants, paclobutrazol (Cultar, Zeneca Corp.) and uniconazole (Sumitomo or Valent Corp.) inhibit gibberellin biosynthesis (Rademacher, 1991) and therefore, reduce the levels of the putative vegetative promoter which is thought to be a gibberellin. Both products are effective for assisting in floral induction with uniconazole being more effective than paclobutrazol. The triazole products provide the flexibility needed to shift the flowering time of the more-difficult-to-manage cultivars like ‘Tommy Atkins’ to any week of the year with less concern for early vegetative flushes. For this reason, Cultar has been widely marketed throughout the tropics to stimulate mango flowering. Either product should be applied after the onset of re-growth following pruning (1-1.5 months after prune date) depending upon cultivar. Paclobutrazol should be applied as a soil drench containing 1 to 1.5 grams of active ingredient per meter of canopy diameter (Nartvaranant et al., 2000) if applied during the rainy season, but personal

Methodology The experimental site Pochampalli taluk is geographically located at 12° 20' N latitude, 78° 22' E longitude at an altitude of 300 m above mean sea level. The annual average rainfall was 830mm. The soil in the experimental field was dark reddish brown, sandy loam. Induction of off-season flowering in mango in the project site was taken up as farmers’ participatory research. The farmers growing mango cv. Bangalora were selected to take up the research trials in their field. A group of 25 farmers from Gurugapatti, Pochampalli, Krishnagiri district registered under the NAIP scheme on “A value chain on mango and guava for domestic and export markets” participated in the research programme for off-season mango production in order to fetch a premium price. The regular

Table 1. Leaf nutrient content in mango cv. Bangalora (15-25 years old) during August 2011 Leaf nitrogen content (in %)

No. of farmers

T1

> 2.5

12

T2

1.4-2.4

8

T3

< 1.4

5

Treatment

Fertilizer applied Adopted recommended dose of N, P & K (1:1:1 kg/tree/year) Adopted 200% recommended N along with recommended dose of P & K (2:1:1 kg/tree/year) Adopted 250% recommended N along with recommended dose of P & K (2.5:1:1 kg/tree/year)


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Table 2. Flowering percentage and yield observed in mango cv. Bangalora (15-25 years old) Treatment

Leaf nitrogen content range during August (%) > 2.5 1.4-2.2 < 1.4

T1 T2 T3

Flowering percentage during June-July

Calculated Yield ha-1 (t) (Oct.-Dec.)

70 83 89

14 17 20

flowering season (December-January) was skipped by encouraging vegetative shoots in the season. Leaf analysis was done during August in order to find the nitrogen content and also to decide the amount of nitrogen to be applied to induce vegetative growth. Trees having > 2.5 per cent leaf nitrogen content were applied with the normal dose of fertilizers, between 1.4 to 2.4 per cent were applied with 200 per cent and 100 cm). Shoots having 5 leaves - 100 % generative shoots Shoots having 0 leaves

- 100 % vegetative shoots

Shoots having 1-3 leaves

- decreased proportion of genera

Growth retardants and its role in flowering of mango First break through in the commercial feasibility of Tree Growth Retardants (TGR) was in 1970’s in USA used in arboriculture on a large scale was the formulations of cell elongation inhibitors, paclobutrazol, uniconazol and flurpirimidol for trunk

injection. The active ingredients of these formulations were unquestionably effective in reducing the tree growth. But, after several years of application problems associated with trunk injection like cracks in the cambium, weeping from injection holes, wood discolouration and compartmentalization around the wholes led to the limited use. Uniconazol and flurpirimadol were removed from the tree care market. Satisfactory performance of paclobutrazol as growth retardant initiating early flowering as well as several benefits of tree health resulted in rebound in the use.

Paclobutrazol and its effect on flowering In commercial mango plantations, it is desirable to control the vegetative growth and canopy size to get uniform and regular flowering. Manipulation in physiological activity by use of plant growth regulators is considered important determinant of productivity enhancement in a number of fruit crops. Among the chemicals suggested, paclobutrazol is considered as one of the important plant growth retardant, which restricts vegetative growth and induce flowering in many fruit species including mango (Yadav et al., 2005). The first report about the use of PBZ on mango came from India in Dashaheri and Banganapalli (Kulakarni, 1988). The Paclobutrazol applied as soil drench @ 3.0 ml/m of canopy diameter during the third week of August advanced the fruit harvest period by 22 days as compared to untreated trees by promoting early flowering in mango cv. Totapari. The effectiveness of paclobutrazol is found to as the result of decline in gibberellins in buds and increase in ABA, cytokinins and C:N ratio in the shoots (Upreti et al., 2013). Soil application of PBZ, use of root


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS pruning and PBZ bark painting hold great promises in induction of early and profuse flowering in cv. Alphonso. PBZ also found to increase chlorophyll content, checks the transpirational losses and helps in maintaining better plant water balance (Rakshe and Nigade, 2013). Hussen et al. (2012) studied that, the paclobutrazol accelerate the induction of flowering as indicated by the increase in percentage of flowering plants, more flowers, faster rate of flower emergence, more petals and higher yield in 20 accessions of mango hybrids of 3 years planted at 4×4 meters spacing. Rahim et al. (2011) studied the hormonal changes in response to paclobutrazol application in biennial bearing mango cvs. Miska, Mahmoudi and Totocombo. The

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increased levels of starch, cytokinins and ABA and decreased levels of gibberellins and auxins were observed during the floral induction period. Tandel and Patel (2011), studied, the number of fruits per tree and fruit yield per tree and per hectare were recorded maximum in cvs. Alphonso, Kesar and Rajapuri mango varieties drenched with paclobutrazol @ 5 g ai per tree. Soil drench application of paclobutrazol at 7500 ppm and 10000 ppm on 15 th October caused earlier panicle emergence by 19 days and advanced harvesting by 15 days in mango cv. Amrapali compared with control. PBZ at 7500 ppm gave highest yield, heavier fruit and improved fruit quality (Babul and Rahim, 2012).



Mode of action of PBZ One of the major roles of gibberellins in tree is the stimulation of cell elongation. When GA production is inhibited cells do not elongate but cell division still occurs and same number of leaves and internodes comprised into a shorter length. PBZ blocks the terpenoid pathway at several steps inhibiting the gibberellins synthesis.

results in shunting of the intermediate compounds to the production of phytol, an essential part of chrlorophyll molecule. 5.

Reduced water stress: Abscissic acid also produced through the terpenoid pathway. Treatment with PBZ promotes the production of ABA much like phytol production. PBZ also interferes with the normal breakdown of ABA. The combined effect on both production and breakdown of ABA results in enhanced concentration of ABA in leaves. ABA causes stomata to close, reduces the shoot growth and reduces the water loss through transpiration.

6.

Reduces the fungal diseases: the fungistatic property of paclobutrazol is due to inhibition of steroid production in fungi through the terpenoid pathway.

Method of application PBZ can be applied as foliar spray or as a soil drench to mango trees (Tongumpai et al., 1991). PBZ is a systemic growth retardant and can be taken up by plant roots or through lenticels and bark eruptions, while foliar spray through shoot tips, young stems and leaves (Voon et al., 1991). Best method is soil application because of its low solubility and long residual activity (Davenport & NunezElisea, 1997).

Advantages of PBZ application 1.

2.

3.

4.

Growth reduction: Reduction in shoot growth by paclobutrazol is primarily as a consequence of reduced intermodal elongation associated with the GA biosynthesis inhibition and increasing the synthesis of inhibitors like ABA. Flower initiation: PBZ initiates early flowering by mimic the effect of environmental factors on flowering and reduces the age dependency of shoots for early and profuse flowering. Increased root density: PBZ treated plants shows a higher root to shoot ratio, primarily due to drastic reduction in shoot growth. Greener leaves: chlorophyll content increases with PBZ application. PBZ blocks the production of gibberellins,

Disadvantages of PBZ: 1. 2.

Soil pollution Residual effect in fruits

3.

Compressed panicles leading to the development of diseases like Powdery mildew and anthracnose.

4.

If irrigation system fails major scaffolding branches are killed. Reduces the soil micro flora

5.

CONCLUSION Mango is one of the most amenable of the tropical fruit trees to floral manipulation. Paclobutrazol is considered as one of the important plant growth retardant which can stimulate or mimic the effect of environmental factors on flowering and reduces the age dependency of shoots for early and profuse flowering.


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REFERENCES Babul, C. Sarker and Rahim, M.A. 2012. Vegetative growth, harvesting time, yield and quality of Mango (Mangifera indica L.) as influenced by soil drench application of paclobutrazol. Bangladesh J. Agric.Res., 37(2):335-348. Chacko, E.K. 1968. Studies on the physiology of flowering and fruit growth in mango (Mangifera indica L.). Ph.D Thesis submitted to P.G. School of IARI. Chen, J.Z., Zhao, H., Chen, J.L. and Zhao, H.Y. 1999. Advances in research on flower bud differentiation in mango. South China Fruits 28(2):34-35. Chen, W.S. 1987. Endogenous growth substances in relation to shoot growth and flower bud development of mango. J. Amer. Soc. Hort.Sci., 112: 360-363. Chowdhary, J.N. and Rudra, P. 1971. Physiological studies on chemical control of growth and flowering in mango (Mangifera indica). Indian Agril., 5: 127-135. Corbesier, L., Vincent,C., Jang, S., Fornara,F., Fan, Q., Searle, I., Giakountis, A., Farrona, S., Crissot, L., Turnball, C.G.N. and Coupland, G., 2007. FT protein movement contributes to long – distance signaling in floral induction of Arabidopsis. Science, 316: 10301033. Farrona, S., Crissot, L., Turnball, C.G.N. and Coupland, G. 2007. FT protein movement contributes to long – distance signaling in floral induction of Arabidopsis. Science, 316: 1030-1033. Davenport, T.L. 2007. Reproductive physiology of mango. Brazilian J. Plant. Physiol., 19(4): 363-376. Hetherington, S.E. 1997. Profiling of photosynthetic competence in mango fruit. J. Hort.Sci., 72: 755-763. Jogande, A.O. and Chowdhary, K.G. 2001. Seasonal changes in abscissic acid content and its role in flowering in mango (Mangifera indica L.). Orissa J. Hort., 29(1): 4649.

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Jyothi, M.H., Ravindra, S., Suresh, E., Soppin, R. and Ekbote, S. 2000. Biochemical changes in the leaf of bearing and non bearing trees of some mango (Mangifera indica L.) varieties/ hybrids. Adv. Agril. Res. India, 10:17-23. Lei, B., Xie, Z., Zang, A., Xu, W., Zhang, C., Liu, C. and Wang, S. 2010. Tree growth characteristics and flower bud differentiation of sweet cherry (Prunus avium L.) under different climate conditions in China. Hort. Sci. (Prague), 37: 6-13. Neluheni, K.O. 2005. Seasonal patterns of vegetative growth and photosynthesis in mango (Mangifera indica L.) trees. M.Sc. Thesis submitted to the University of Pretoria. Nunezelsea , R. and Davenport, T.L. 1992. Requirement of mature leaves during floral induction and floral transition in developing shoots of mango. Acta. Hort., 296:33-47. Rahim, A.O.S., Osman, M.E. and Fritzk. B. 2011. Effect of paclobutrazol (PBZ) on floral induction and associated hormonal and metabolic changes of biennially bearing mango (Mangifera indica L.) cultivars during off year. ARPN. J. Agri. Bio. Sci., 6(2): 55-67. Rakshe, M.V. and Nigade, P.M. 2013. Pre and post flowering physiological behavior of Alphonso mango leaves as influenced by stem girdling, root pruning and chemicals. Bioinfolet, 10(3B): 979-982. Palanichamy, V., Reddy, N.N., Babu, S., Emmanuel Selvraj, Aranganathan and Mitra B. 2012. Determination of time period of flower bud differentiation and associated histological and biochemical changes in mango hybrids. Res. J. Pharm. Biol. Chem. Sci.,3(2): 271-289. Palanichamy, V. Bhaskar Mitra, Arabi Mohammad Saleh and Deep Sankar, P. 2011. Studies on flower bud differentiation in mango (Mangifera indica L.). Res. Pl. Biol., 4: 55-67. Ramirez F. and Davenport T.L. 2010. Mango


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS (Mangifera indica L.) flowering physiology. Scientia Horticulture, 126:65-72. Rao, M.M. 1998. Role of low night temperature days in flower bud differentiation in mango trees under mild tropical rainy climatic conditions. Karnataka.J. Agric.Sci., 11(4): 11421144. Patil, P.B., Rao, M.M., Srinivasan, C.N., Bhaskar, P.W. and Nalwadi, V.G. 1992. Physiological and biochemical factors associated with fruit – bud – differentiation in Alphonso mango: V- total free phenols and polyphenol oxidase. Karnataka J. Agric.Sci., 5(4): 338-342. Sen, P.K. 1943. The bearing problem of mango and how to control it. Indian J. Hort. 1: 48-71. Shankara Swamy, J. 2012. Flowering manipulation in mango: A science comes of age. J. Today’s Bio. Sci.: Research and Review, 1(1): 122-137. Singh, R.N. 1960. Studies on the differentiation and development of fruit buds in mango (Mangifera indica L.).IV. Periodical changes in the chemical composition of shoots and their relation with flower bud differentiation. Hort. Adv.4: 48-59.

Singh, R.N. 1971. Biennial bearing in fruit trees accent on mango and apples. Indian Council of Agric. Res.Tech. Bull., 30: 47. Tandel, Y.N. and Patel, N.L. 2011. Effect of chemicals on growth, yield and economics of mango (Mangifera indica L). Karnataka J. Agric.Sci., 24 (3): 362-365. Tongampai, P., Jutamanee, K. and Subhadrabandu, S. 1991. Effect of paclobutrazol on flowering of mango cv. Khiew Saway. Acta. Hort., 291: 67-70. Upreti, K.K., Reddy, Y.T.N., Shivu Prasad, S.R., Bindu, G.V., Jayaram, H.L and Rajan, S. 2013. Hormonal changes in response to paclobutrazol induced early flowering in mango cv. Totapuri. Scientia Horticulture, 150: 414-418. Voon, C.H., Pitakpivan, C., Tan, S.J. 1991. Mango cropping manipulation with cultar. Acta. Hort., 291: 219-228. William, R. C. 2010. Response of cambial and shoot growth in trees treated with paclobutrazol. J. Arboric., 30:137-145. Yadav, R.K., Rai, N., Yadav, D.S., and Asati, B.S. 2005. Use of paclobutrazol in Horticultural crops – A review. Agric. Rev., 26: 124-132.


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UNLOCKING MYSTERY OF PHASE CHANGE AND FLOWERING IN LITCHI (LITCHI CHINENSIS SONN.) CULTIVARS Rajesh Kumar National Research Centre on Litchi Muzaffarpur-842 002, Bihar E mail : [email protected]

ABSTRACT The study on phenology and flowering in litchi indicated that irrespective of cultivars, growth in the form of flushes occurred in sequential pattern either naturally and/or under forced condition with varied re-growth frequency (extension growth). The observed lag phase seems to be an intrinsic part of shoot development that suppresses further bud development, shows the restricted phase of vegetative growth. This lag phase have been also found to be influenced by weather parameters (mainly low temperature ( Mallika (23.7%)> Chaosa & Kesar (19.2 %) > Langra (15.6%) and malformation trend was Amrapali (44.3%)> Dashehari & Bombay Green (20.1%)> Kesar (19.3%)> Langra & Chausa (17.8%)> Mallika (10.6%). This trend might be due to varietal response with weather parameters. These results are in accordance with findings of Raheel et al. (2011) in mango. Hopper population during flowering was maximum in Amrapali and least in Kesar (Mishra et al., 2011-12).

findings of Zhong (1998), Lad et al. (1999), Singh (2009) and Puche et al. (2012) in mango.

Mean temperature and relative humidity during different phenophase viz., flowering span (19.4oC & 52 % RH), fruiting span (30oC & 45 % RH), flowering to maturity (24.5oC & 48 % RH) were congenial during 2013 and mango varieties like Amrapali, Bombay Green, Dashehari, Mallika and Langra gave good crop but in Chausa and Kesar 2013 showed off year. During 2014, Amrapali and Mallika have good flowering and fruit set in comparison to other varieties. Rainfall during flowering damaged the crop and heavy wind velocity during fruiting caused heavy incidence of fruit drop. The results of the present findings are in the agreement with the

Anonymous, 1998. The mango. Bulletin of Central Institute for Sub-tropical Horticulture, Lucknow, p.1.

Calculated heat unit as growing degree days over the base temperature from flowering to fruiting recorded maximum in Chausa (2429.5) and minimum in Bombay Green (1935.3). Yield and heat unit efficiency -2013, maximum was registered in Dashehari followed by Mallika, Langra, Amrapali and minimum in Chausa (Table-3). Thus, the performance of the varieties Amrapali and Mallika were found to be promising in terms of flowering and fruiting behavior consistently at the Banswara conditions of Rajasthan.

REFERENCES

Bally, I.S.E., Harris, M. and Whiley, A.W., 2000. Effect of water stress on flowering and yield of ‘Kensington Pride’ mango (Mangifera indica L.). Acta Horticulturae, 509:277-281. Lad, B.L., Pujari, K.H. and Magdum, M.B. 1999. Effect of thermoperiodic changes on flowering behaviour in mango under coastal climate of Maharashtra. Annals of Plant Physiology, 13 (1): 38-46. Mishra, A.K., Pandey, G. and Rakesh Chandra (2011). Proceedings of the 20 th Group Worker’s Meeting of AICRP on (STF), CISH, Lucknow: 1-108.


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Mishra, A.K., Pandey, G. and Rakesh Chandra 2011-2012. Annual Report, AICRP (STF), CISH, Lucknow, India :1-168. Puche, M., Perez Macias, M., Soto, E., Figueroa, R., Gutierrez, M. and Avilan Rovira, L. 2012. Minimum temperature an environmental determinant in the floral initiation of mango. Revista Cientifica UDO Agricola. 12(1):83-90. Raheel Anwar, Ahmad, Saeed, Rajwana, I.A., Khan, A.S., Noor-un-Nisa and Nafees, Memon Muhammad. 2011. Phenological growth patterns and floral malformation of mango (Mangifera indica L.) tree under subtropical climate. Pakistan Journal of

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Agricultural Sciences.48 (2): 109-115. Sarolia, D.K., Singh, V. and Kaushik, R.A. 201213 & 2013-14. Annual Reports, AICRP on Sub Tropical Fruits, Department of Horticulture, Rajasthan College of Agriculture, MPUAT, Udaipur-313 001 (Rajasthan):1-60. Singh, Z. 2009. Gibberellin type and time of application influence fruit set and retention in mango. Acta Horticulturae, 820: 407-412. Zhong, SiQiang 1998. Analysis of the meteorological factors which caused the great reduction of mango production in Guangxi province in 1997 and the strategy. South China Fruits,.27 (4): 29-30.



OFF SEASON FLOWERING AND FRUITING IN MANGO UNDER ANDAMAN CONDITIONS T. Damodaran and S. Rajan1 Central Soil Salinity Research Institute, RRS, Lucknow, U.P. 1 Central Institute of Subtropical Horticulture, Lucknow, U.P.

INTRODUCTION Mango (Mangifera indica L.) originated in the Indo-Burma region during the earlier period of the Cretaceous era (Yonemori et al., 2002) and then gradually spread to the tropical and subtropical regions of the world. India is considered being the primary centre of diversity along with its status as the centre of origin of mango along with Myanmar and Malaysian region. Presently, the sub-continent harbours more than 1000 mango cultivars and represents the biggest mango germ pool in the world. Mango cultivars are divided into two groups based on their origin. Indian type (monoembryonic seed race) and Indo Chinese type (polyembryonic seed race) (Crane et al., 1997; Iyer and Degani, 1997). Flowering and fruit set are the most important phases that determine the mango productivity (Litz, 1997). The Indian sub-continent with distinct variable agro-climatic conditions of warm tropical, humid tropical and sub-tropical conditions nurtured a wide source of variability in the bearing habit of mango varieties (Damodaran et al., 2012). Most of the tropical varieties exhibited regular bearing character, while it was reverse with the varieties of the sub-tropics, which flowers by the stimulation model of cool temperature and age of the last vegetative flush (Davenport, 2003). Earlier studies on mango flowering considered the tropical and the sub-tropical conditions of the climate in correlating with the bearing behavior of the trees, while, there was little emphasis to arrive a flowering physiology model including the climatic

variability of the humid tropics of equatorial regions and the embryonic (mono and polyembryony) races. In this paper the findings on flowering behavior of the polyembryonic and mono-embryonic mango accessions of the Andaman and Nicobar Islands and their strategies for further utilization is briefly summarized.

Diversity in mango accessions in humid tropical island ecosystem of the Indian sub-continent Andaman and Nicobar islands are one of the most important zones of variability in mangoes offering choice of selection for wide range of economical traits (Yadav and Rajan, 1993, Ram and Rajan, 2003, Damodaran et al., 2012). The islands are situated about 1200 km away from mainland India in the Bay of Bengal. They form an arched string of about 572 islands and isles stretching from Burma in the north to Sumatra in the south between 6o and 14o N latitudes and 92 o and 94o E longitudes. They are known as diverse hot spot of native mangoes (Kapoor and Bhamniya, 2003). Due to the long history of mango cultivation in these islands cultivars from Myanmmar and Thailand were introduced by early settlers and migrants, which in due course generated a broad genetic base through open pollination with existing mango cultivars of the islands. In the Andaman Islands flowering occurs in May–August, September– November and December–March. However, major flowering season where fruits are


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS available in markets for consumption is from September to November and December to March (Damodaran et al., 2007). Mango cultivars both polyembryonic and monoembryonic were found to coexist spreading from Havelock islands in the south to the Diglipur in the North Andaman (Damodaran et al., 2009). Initial exploratory surveys were first conducted in 1998, followed by survey for identification of of-season flowering accessions during 2004. Later, post tsunami collections of mango accessions for specific traits like tolerance to salinity, sodicity and regular bearing behavior were carried out from Havelock Islands in the south to the Diglipur in the North Andaman (Fig. 1). A total of 40 mango types collected and catalogued from the tsunami affected regions of South Andaman. Flowering in wild mangoes occurs in October and the fruiting gets completed by early March. Among the wild types M. andamanica is regular bearers while, M. comptosperma and M. griffithi are biennial bearers (Damodaran et al., 2012a). Genetic diversity among 4 wild mango species and 29 genotypes/cultivars of polyembryony and monoembryony mangoes of the Andaman Islands were analyzed using

biochemical, RAPD and ISSR (Inter Simple Sequence Repeat) markers. A total of 335 ISSR markers were scored, of which 213 markers were polymorphic. These markers were used to estimate the genetic similarity among accessions using Dice similarity co-efficient. Similarity values ranged between 2–70 per cent with an average of 34per cent. The sampled genotypes/accessions were divided into 3 prominent groups of 4 (wild), 14 (monoembryonic) and 15 (polyembryonic) differentiating the polyembryonic from monoembryonic accessions and the wild mango species (Fig. 1). The analysis separated the differentially flowering polyembryony genotypes from the early flowering monoembryony types for their exploitation in genetic improvement programmes or selection in the regions of tropical Island ecosystem.

Evaluation of polyembryonic varieties for off-season flowering The 15 polyembryonic varieties along with the other varieties like Neelam, Banglora, Kurrukan and Rumani were evaluated for their off-season flowering ability and impact

Fig. 1. Dendrogram was generated using unweighted pairgroup method with arithmetic average analysis and Principal Coordinate Analysis (Damodaran et al., 2012).

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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS of environment in the bearing habit. In India, Rumani, Banglora, Neelum and Ali Pasand showed off-season flowering by bearing twice or thrice in a year under Kanyakumari conditions (Ram and Rajan, 2003) while, these accessions flowered and fruited only once a year under Andaman conditions. Moreover, the yield of these accessions produced lower yields when compared with the polyembryonic local selections (Damodaran et al., 2000). Among the 15 polyembryonic accessions, the accessions like ML-2, GPL-1, GPL-3, ML-3, ML-7, CJ-1 and ML-6 flowered twice a year (June-August and November– April) showing higher yields. Earlier, specific bands responsible for multiple flowering using RAPD markers were assigned for genes responsible for differential flowering accessions of the Andaman Islands. Also the genetic diversity studies using 150 RAPD markers separated the polyembryonic varieties of the Andaman Islands with the off-season flowering varieties like Neelam and Banglora (Damodaran et al., 2007).

Salinity Research Institute, Lucknow, India. Monoembryonic accessions were excluded from screening because of their segregating nature and limited possibility for getting true to type material by seeds and stress tolerance potential. The accessions ML-6 and CJ-1 showed flowering during September-October, which fruited to maturity in December and January. The accession ML-2, ML-6 and GPL1 exhibited tolerance to sodicity and established good vegetative vigour as compared to control check of 13-1. These accessions also recorded regular bearing and off-season flowering under the island ecosystem of humid tropics (Damodaran et al., 2013).

The selected 15 polyembryony accessions (Table 1) were recollected and evaluated for their reaction to sodium toxicity and flowering under field conditions of subtropical Indo-Gangetic plains at Central Soil

Crane, J.H., Bally, I.E., Mosqueda-Vazquez, R.V. and Tomer, E. 1997. Crop production. In: The mango: Botany, production and uses (ed. R.E. Litz), Wallingford, UK, CAB International. pp. 203-256.

The polyembryonic accessions like ML2, CJ-1, ML-6 and GPL-1 that explicit regular bearing trait along with salt tolerance form a rich source of genes for multiple traits of interest in including them as a donor parent in mango improvement programmes.

REFERENCES


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FUSARIUM MANGIFERAE INDUCED STRESS ETHYLENE CAUSES FLORAL MALFORMATION OF MANGO : A SCANNING ELECTRON MICROSCOPIC STUDY Varsha Rani, Archana Singh, Mohammad Wahid Ansari1, Alok Shukla, Ramesh Chandra Pant and Gurdeep Bains Department of Plant Physiology, College of Basic Sciences and Humanities, G.B Pant University of Agriculture and Technology, Pantnagar 263145, Uttarakhand 1 Plant Molecular Biology Group, International Centre for Genetic Engineering and Biotechnology, New Delhi [email protected]

ABSTRACT Malformation disorder of mango has remained a major concern among Plant physiologist, Horticulturists and Plant Pathologists due to its yield limiting nature in several mango growing provinces of the world. Depending on the plant part affected it may be vegetative or floral in nature. It has been suggested that the disorder may be due abiotic or biotic factors such as mites, virus, fungus etc. Being mysterious, its etiology has not yet been resolved, but it is being strongly argued that stress ethylene liberated from Fusarium mangiferae are thought to be the chief causal factors of this disease. Scanning electron microscopy has revealed the presence of cottony growth on the surface of malformed floral bud. It has been credited that these fungal pathogen leads to surge of stress ethylene production in mango plants which causes deviation from normal metabolism, resulting in abnormal warty morphology of malformed floral bud.

INTRODUCTION Malformation disorder of mango has remained a major concern among Plant Physiologist, Horticulturists and Plant Pathologists due to its yield limiting nature in several mango growing provinces of the world. Being mysterious, its etiology has yet not been resolved, but it is being strongly argued that stress ethylene liberated from 282

Fusarium mangiferae is thought to be the chief causal factors of this disease. Scanning electron microscopy has revealed the presence of cottony growth on the surface of malformed floral bud. It has been credited that this fungal pathogen leads to surge of stress ethylene production in mango plants which causes deviation from normal metabolism, resulting in abnormal warty morphology of malformed floral bud. Scanning electron microscopic study of healthy and malformed floral bud of mango cv. Baramasi to observe the presence of fungal mycelium on the floral bud surface and to analyse the difference in morphology of healthy and malformed floral bud.

MATERIAL AND METHODS Floral buds of cv. Baramasi were collected from mango orchard (Department of Plant Physiology) G.B Pant University of Agriculture and Technology, Pantnagar, India.

Scanning Electron Microscopy of mango floral bud a.

Primary Fixation: The tissue samples were fixed using 2.5% Glutaraldehyde for 24 hours at 4 o C


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS b.

c.

Dehydration: To remove water from the tissues, ascending grades of acetone (30%, 50%, 70%, 80% and 90%) were used for 15 minutes at 4 o C. Drying: Sample was transferred from organic dehydration medium (acetone) to drying medium (liquid CO 2) in a chamber which was cooled and put under pressure. When the dehydrating agent had been completely removed and impregnated with liquid CO 2, the chamber was warmed up to the point (critical point) where the density of drying medium was same in both the liquid and gas phase. Phase boundary disappear and CO 2 be released gradually to avoid condensation. The sample was then dried. Most commonly used media for Critical Point Drying :

CO2 -C.P. 31.5 oC at 1100 p.s.i (pressure) or o

Freon 13 – C.P. 28.8 C at 560 p.s.i (pressure) d. Mounting: Specimen were then mounted on Aluminum stubs with conductive paint or adhesive tape e. Coating: Specimen was coated with a thin layer (30-40nm) of metal conductor to increase its electrical conductivity. For this the specimen either undergoes thermal evaporation or sputter coating. Sputter coating was done by using gold (35nm thick film). The specimen was then observed in Scanning Electron

Microscope (JEOL, JSM-6610 LV)

RESULTS AND DISCUSSION Morphological features of healthy floral bud of mango Scanning electron micrograph has revealed that the surface of healthy floral bud is free from cottony mycelial growth, with large and swollen cells. Also it possesses large number of longer epidermal hairs. (Fig 1-3)

Morphological features of malformed floral bud of mango Scanning electron micrograph has revealed small, wavy and shrinked cells covered with cottony growth of fungal mycelium and possesses lesser number of short epidermal hairs. (Fig 4-6). Similar observations have been made by Usha et al., 1997 and Waffa Haggag, 2010.

CONCLUSION Appearance of cottony fungal mycelium on malformed floral buds represented an initial stage of the disorder. This fungal pathogen is supposed to bring morphological alteration on buds and floral parts and alteration of metabolic pathway, via production of stress ethylene as the symptoms of malformed panicles are similar to those caused by ethylene.

Electron micrographs of healthy mango floral bud


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Electron micrographs of malformed mango floral bud

REFERENCES Singh, Z. and Dhillon, B.S. 1990. Comparative developmental morphology of normal and malformed floral organs of mango (Mangifera indica L.). Tropic. Agric. 67: 143148. Rani, V., Ansari, M.W, Shukla, A, Tuteja, N. and Bains, G. 2013. Fused lobed anther and

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hooked stigma affect pollination, fertilization and fruit set in mango, A scanning electron microscopy study. Plant Signal Behav 8: e23167. Kvas, M., Steenkamp, E. T., Adawi, A. O. Al, Deadman, M. L., Jahwari, A. A. Al, Marasas, W. F. O. 2008. Fusarium mangiferae associated with mango malformation in the Sultanate of Oman. Eur. J. Plant Pathol., 121: 195-199.



SURVEILLANCE OF POLLINATORS AND THEIR BEHAVIOUR IN MANGO FLOWERS D. Anitha Kumari, Jyothirmayee Madhavi, A. Bhagwan and M. Raj Kumar Grape Research Station, DRYSR Horticulture University, Rajendranagar, Hyderabad, Andhra Pradesh E-mail : [email protected]

ABSTRACT Mango, Mangifera indica, is the king of fruits in India and is one of the popular fruits in the world due to its attractive colour, delicious taste and excellent nutritional properties. Mango is not only known for its sweet fragrance and flavour, but also due to the increasing domestic demand and export potential of the fruit. Fruit set in mango is dependent on successful pollination, which depends on the availability of quality of pollen, the presence of pollinators in sufficient number and optimal weather conditions. Typically, mango flowers are pollinated through pollinators viz. flies, butterflies and moths and wind,. Systematic surveillance was done in the mango orchard at Fruit Research Station, Sangareddy, Andhra Pradesh and pollinators were observed and recorded during peak flowering stage in fifty tagged inflorescences in five trees. Foraging behaviour of pollinators were observed on mango flowers for 7 am to 9 am and 4 pm to 6 pm. Most of these visiting insects belonged to the orders diptera and hymenoptera. The important pollinators are honey bees (Apis dorsata, A. florae, A. cerana indica), Meliponas sp., Coccinella septumpunctata, housefly (Musca nebulo) and other moths and butterflies. Among the pollinators, honey bee was found to be the major pollinator (30%). The maximum population of different pollinators were recorded during 5th meteorological week (8.5) and there after the number of pollinator decreased. The maximum number of pollinators were observed in the medium height of the tree. The pollinators activity was maximum in the north direction followed by east and west direction. The

population of pollinators was recorded maximum in the full bloom flowering stage of mango and population of pollinators is negatively correlated with mean temperature (r value=-0.34991) and relative humidity (0.12655). There was no fruit set on completely bagged panicles. Some setting took place when bags were opened for 24, 48, and 72 hours in bloom. Insecticidal spraying affected activity of the pollinators and thus, fruit set.

INTRODUCTION Despite profuse flowering in mango, the fruits carried to maturity are comparatively meager. Pollination is major yield-limiting constraint, due to the large number of flowers on trees and low fruit set. Studies on pollinators on mango indicated that large native insect species were shown to pollinate mango in northern Australia. Most mango cultivars are self-fertile but benefit from cross pollination. Flowers open in the morning about 8 am and anthesis is generally completed by noon. Receptivity of the flowers usually lasts up to about 72 hrs. Although, only one stamen per flower produces pollen, large number of flowers on the tree assures an abundant supply of pollen. Adequate pollinators are needed for pollen transfer to increase fruit set. Mango flowers may be pollinated by flies, bees, thrips and other insects, with flies probably the most important (Singh, 1954; Free and Williams, 1976). The kinds and biology of pollinators of mangos have been studied in India and Israel


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS and their results demonstrated that insects of the Diptera and Hymenoptera play major roles in pollination. The pollinators, in decreasing order of efficiency, were wasps, bees, large ants and large flies. Large Diptera and the native bee, Trigona sp., frequently move from tree to tree and thus, were probably the most effective cross pollinators. Of randomly selected hermaphrodite mango flowers only 36 per cent were pollinated (Singh, 1988; Bhatia et al., 1995; Singh, 1997; Dag and Gazit, 2000). Major pollinating insects of mango was found to be from order diptera i.e. Meliopona sp., Syrphus sp., housefly and a few beetles viz. Coccinella septumpunctata. Effective pollination by honey bees requires 3 to 6 colonies per acre (Gajendra Singh, 2006). In present communication, the role of pollinators on fruit set in mango in relation to the occurrence of high and low temperatures is discussed.

MATERIALS AND METHODS Systematic surveillance was taken up in the mango orchard for pollinators in mango cv. Banganpalli during the flowering period at Fruit Research Station, Sangareddy, Andhra Pradesh, during 2009-11. The flowering period was between December to January during both the years. Weekly observation on pollinators were recorded on 50 panicles per tree from 10 randomly selected trees at different height of the tree from all the four directions (north, south, east and west) in a fixed plot at three different heights on the tree (upper height 4-6 m; medium height 2-4 m and lower height 0-2 m) and the field was kept free from pesticide sprays. Foraging behaviour of pollinators was observed on mango flowers for 7 am to 9 am and 4 pm to 6 pm. It was found that the most efficient pollinators were those that carried large numbers of pollen grains on their

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thoraces and used a short proboscis or short mouth parts to feed on nectar. Data was correlated with weather parameters.

RESULTS AND DISCUSSION Systematic surveillance was done in the mango orchard at Fruit Research Station, Sangareddy and pollinators were observed and recorded during peak flowering stage. The important pollinators are honey bees (Apis dorsata, A. florae, A. cerana indica) stingless bees (Trigona sp., Melipones sp., Coccinella septumpunctata) housefly (Musca nebulo) and other moths and butterflies. Among the pollinators, honey bee was found to be the major pollinator (35.8%). The maximum population of different pollinators were recorded during 5th meteorological week (8.5) and there after the number of pollinator decreased. The maximum numbers of pollinators were observed in the medium height of the tree. The pollinators activity was maximum in the north direction followed by east and west direction. The population of pollinators was maximum in the full bloom flowering stage of mango and population of pollinators is negatively correlated with mean temperature (r value= 0.34991) and relative humidity (-0.1265) (Table 1). Studies conducted on major pollinating insects of mango indicated that major pollinators were found to be from order Diptera, that is, Meliopona sp, Syrphus sp. A few beetles especially Coccinella septumpunctata was quite important. Rhynchaenus mangiferae Marsh, although a pest helped in pollination and increased fruit setting when its population was below the damaging level. Presence of Hymenoptera and honey bee was negligible (Table 2,3). There was no fruit set on completely bagged panicles. Some setting took place when bags were opened for 24, 48,


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Table 1. Observations on insect pollinators in relation to weather parameters in mango at Fruit Research Station, Sangareddy during 2009-2011. Std week

Temperature Min 0

Relative Humidity % FN AN

Max

Rain fall (mm)

Upper height (4-6 m) E W N S

Lower height (upto 2m) E W N S

Total

0

( C) ( C) 1(Jan) 12.4 29.6 95.5 31.9 2 8.8 31.4 95.2 11.8 3 11.8 33.3 88.7 16.6 4 12.8 33.1 86.3 16.9 5(Feb) 14.3 33.1 82.3 19.5 6 13.3 34.7 74.4 11.9 7 16.5 34.0 64.5 19.3 8 19.5 33.8 86.5 29.7 R value -0.3499 -0.2608 -0.1265 -0.02911

0 0 0 0 0 0 0 0

0.5 0.5 0.5 0.9 0.6 0.7 0.6 0.5

Table 2. Percentage of pollinators (different orders) observed on mango flowers at Fruit Research Station, Sangareddy during 2009-2011. Pollinator Honey bees (Hymenoptera) House flies, Blue flies Blow flies (Diptera) Coccinellid Beetles (Coleoptera) Butterflies (Lepidoptera) Others

Percentage 35.8 30.3 25.6 5.4 5.3

Table 3. Diversity of pollinators on mango flowers at Fruit Research Station, Sangareddy during 2009-2011. Common name European honey bee Gaint honey bee Indian honey bee Wasp Syrphid Blue bottle fly Monarch butterfly Cabbage butterfly Lady bird beetle

Middle height (2-4m) E W N S

0.4 0.5 0.3 0.3 0.5 0.9 0.6 0.6

0.3 0.5 0.6 0.7 0.5 0.8 0.6 0.3

0.4 0.8 0.3 0.6 0.4 0.6 0.7 0.6

1.1 0.6 0.7 0.7 0.5 0.8 0.8 1.1

0.4 0.4 0.6 0.6 0.7 0.9 0.8 0.4

0.2 0.3 0.6 0.7 0.6 0.6 0.6 0.8

0.4 0.7 0.6 0.6 0.4 0.9 0.8 0.4

0.4 0.9 0.8 0.8 0.9 1.1 1.0 0.8

0.4 0.4 0.5 0.5 0.4 0.9 0.8 0.6

0.5 0.6 1.0 0.6 0.5 0.8 0.8 0.5

0.3 0.9 0.8 0.8 0.3 0.5 0.7 0.3

5.3 7.1 7.3 7.8 6.3 9.5 8.8 6.9

and 72 hours in bloom and also in insect released bags. Insecticidal spraying affected activity of the pollinators and thus fruit set (Gajendra Singh, 2006). The present studies were in confirmation with above results. Thus, it may be concluded that most of these insects belonged to the orders diptera and hymenoptera. The important pollinators are honey bees (Apis dorsata, A. florae, A. cerana indica), Meliponas sp., Coccinella septumpunctata), housefly (Musca nebulo) and other moths and butterflies. Conservation of pollinators during flowering time helps in increased fruit set and yields by avoiding insecticidal sprays during flowering period.

Scientific name

Order

Apis mellifera

Hymenoptera

LITERATURE CITED

Apis dorsata

Hymenoptera

Bhatia, R., Gupta, D., Chandel, J.S. and Sharma. N.K. 1995. Relative abundance of insect visitors on flowers of major subtropical fruits in Himachal Pradesh and their effect on fruit set. Indian Journal of Agricultural Sciences, 65: 907-912.

Apis cerana indica Hymenoptera Vespula oientalis Calliphora

Hymenoptera Diptera Diptera

Danius pleippus

Lepidoptera

Pieris rapae

Lepidoptera

Coccinella septumpunctata

Coleoptera

Dag, A., and Gazit, S. 2000. Mango pollinators in Israel. Journal of Applied Horticulture, 2 : 3943. Anderson, D.L., Sedgley, M., Short, J. R. T. and Allwood, A. J. Insect pollination of mango in northern Australia, Australian Journal of Agricultural Research, 33(3) 541 – 548.


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS Free, J.B. and Williams, I.H. 1976. Insect pollination of Anacardioum occidentale L., Mangifera indica L.,Blighia sapida Koening and Persea americana Mill. Trop. Agric., 53: 125139. Gajendra Singh 2006. Insect pollinators of mango and their role in fruit setting. Acta Horticulturae, 231: II International Symposium on Mango. Singh, R.N. 1954. Studies on floral biology and

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subsequent production of fruits in the mango (Mangifera indica L.) varieties Dushehari and Langra. Indian Journal of Horticulture, 11: 69-88. Singh, G. 1988. Insect pollinators of mango and their role in fruit setting. Acta Horticulturae, 231: 629-632. Singh, G. 1997. Pollination, pollinators and fruit setting in mango. Acta Horticulturae.. 455: 116-123.



PHYSIOLOGY OF FLOWERING IN BANANA M.M.Mustaffa and I. Ravi National Research Centre for Banana, Trichy, Tamil Nadu

INTRODUCTION Banana (Musa sp.) is the most important fruit crop in India. Its year round availability, affordability, varietal range, taste, nutritive and medicinal value makes it the favourite fruit among all classes of people. It has also good export potential. Basically, bananas have occupied the status of commercial crop. Traditional banana growers, with the exception of few large companies, are responsible for most production world-wide. Bananas and plantains (Musa spp.) are grown in more than a hundred tropical and subtropical countries and provide staple food for hundreds of millions of people. Bananas and plantains are grown in around 130 countries around the world, exhibiting a spectacular production of 122.85 million tons (FAOSTAT 2012). India alone produces 31.5 million tons on an area of 0.85 million ha. India is the largest producer in the world, followed by China, The Philippines, Brazil and Ecuador. Around 87% of all the bananas grown worldwide are produced by smallscale farmers for home consumption or for sale in local and regional markets, while the remaining 13%, mainly dessert bananas, are traded internationally. Bananas originated from South East Asia, a primary centre of diversification of banana crop and where the earliest domestication has occurred (Simmonds, 1962). This is an area bordered on the west by India and on the east by Samoa, Fiji and other South Pacific islands (Simmonds, 1966). Musa acuminata is said to have originated from Malaysia, while the hardy Musa balbisiana originated from Indochina. The low land areas

of West Africa contain the world’s largest range of genetic diversity in plantains (Musa AAB) (Ortiz and Vuylsteke, 1994). Conversely in East Africa, bananas are highly evolved into an important zone of secondary genetic diversity for the East African highland bananas (Musa AAA) (Smale, 2006).

Morphology of Banana Bananas are large perennial herbs with an underground stem called a corm, which is the true stem of the banana plant. The corm also consists of the apical meristem from which the leaves and ultimately the flowers are initiated. On average, each plant produces 35 to 50 leaves in its growth cycle. When the banana plant formed an average 40 leaves (within 8 to 14 months), the terminal vegetative bud converts into reproductive structure ie., inflorescence which grows and elongates through the centre of the pseudostem emerging at the top in the centre of the leaf cluster. The inflorescence is a compound spike of female and male flowers arranged in groups. Each group consists of 2 rows of flowers, one above the other, closely appressed to each other, and the whole collection is covered by a large subtending bract. The bracts and their axillary groups of flowers are arranged spirally round the axis and the bracts become closely overlapping each other forming a tight conical inflorescence at the tip. The lower bracts of the axis produce female flowers; the middle few bracts consists of neuter flowers (absent in some cultivars), whilst at the tip of the inflorescence male flowers are present (Purseglove, 1972). In M. schizocarpa, M. acuminata ssp. banksii and M. acuminata ssp. errans only hermaphrodite


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS flowers are produced (Sharrock et al., 2001). The female inflorescences develop into fingers that form the bunch. Banana bunches consists of four to 12 hands (clusters), each with at least 10 fingers. In wild bananas, both male and female flowers produce abundant nectar and pollen whereas in cultivated bananas, many clones lack pollen. Banana pollen is tiny and sticky, coated with waxes and proteins held in place by sculpture elements. The quantity of pollen is an important factor to enhance the germination potential of pollen grains (Dumpe and Ortiz, 1996). The female flowers have ovaries that develop first by parthenocarpy (without fertilization) to form pulp which is the edible part of the fruit. However, wild bananas exhibit cross pollination and ultimately fertilization to form seeds instead of pulp (non-parthenocarpic).

Vegetative growth The ‘apparent’ aerial shoot of banana known as the pseudostem, is composed of rolled and enclosing bases of large number of leaves. This aerial shoot is born on a subterranean stem (corm), which grows slowly and horizontally to a length of about 0.3 m. Aerial shoots (suckers or followers) arise from lateral buds on the corm. Each shoot is determinate (Norman et al., 1984). Mechanically the aerial stem (a sympodium) is completely dependent on the leaf sheaths for support, reaching a height of 2–8m in cultivated varieties. The actual stem is at or below the soil level. The apex initiates the leaf primordia, which develop into leaves that rapidly encircle the shoot apex. The growth in these lateral organs overshadows that in the vegetative apex to create an immense photosynthetic structure. Successive internodes are difficult to discern because of their condensation. This condition changes on flowering when a massive true erect stem forms (Barker and Steward, 1962; Karamura 290

and Karamura, 1995; Simmonds, 1966). The area of individual leaves of dessert cultivars can reach 2–3 m2 and the total leaf area of a plant 17–25 m2 (Stover and Simmonds, 1987). In ratoon crops, the leaf area index (L) varies from 2 to more than 6 depending on the cultivar, season and plant density. A value for L of 4.5 is associated with the maximum use of photosynthetically active radiation (Turner 1990, quoting others), and corresponds to about 90% of the incoming solar radiation being intercepted by the leaf canopy (Turner et al., 2007).

Development of inflorescence and reproductive system In banana, the inflorescence is initiated at the apex of the vegetative plant and subsequently the nodes of flowers become the hands of fruit begin to differentiate. The first three to 18 nodes of the inflorescence form female flowers that become the fruit of commerce. At the time of bunch initiation about 11 leaves are present within the pseudostem (Summerville, 1944). After these leaves emerge the bunch appears at the top of the pseudostem at anthesis. In lowland tropical areas, floral initiation occurs after 30–40 leaves have been produced. This occurs at the apex of the rhizome, which is located within 0.3m of the soil surface, following which the aerial stem begins to elongate pushing through the center of the pseudostem until it is visible at the top (a process known as shooting). The floral phase is considered to extend from floral initiation to inflorescence (bunch) and emergence from the throat of the pseudostem (the start of the fruiting phase), although the fruit actually exist before they appear external to the plant (Karamura and Karamura, 1995; Simmonds, 1966). The total number of leaves produced till flowering varies with cultivars. For


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS example, in banana cvs. Poovan, Nendran, and Ney Poovan produce on an average of 31.8, 38.4 and 41.2 leaves respectively. It appears that the number of leaves produced is varied according to variety and locality (Nambisan 1972). The plants retained with lower number of leaves (6-9) showed delayed shooting, whereas early shooting was observed in plants with high number of leaves (12-18). The period of maturity of bunches from shooting was early in plants having more number of functional leaves (Shanmugavelu, 1978). In banana, flower induction stimulus is not yet known, and flowering can occur at any time of the year, the inflorescence is a spike with stout peduncles on which flowers are arranged in nodal clusters in two rows on transverse cushions (crown). The first nodes of flowers are female, while the last nodes are male. The fruits grow from the female flowers with/without pollination (Purselove, 1972). In cultivated varieties, the inflorescence on emergence behaves geotropically which results in each banana bunch (or stem) hanging in a pendulous position. Mechanically the aerial stem is entirely dependent on the surrounding leaf sheaths for its support. Day-neutral plants do not depend on photoperiod for floral induction (Lincoln et al., 1982) and banana falls into this category. Bunches emerge (anthesis) at any time of the year where the plant is grown, although the number of bunches emerging may be influenced seasonally by environmental and edaphic factors. If photoperiod does not influence bunch initiation and development of the plant can be described by growingdegree-days. However, Turner and Hunt (1987) pointed out that for banana cv. ‘Williams’ (AAA, Cavendish subgroup) growing in the subtropics, the GDD was not

the same for three different planting dates suggesting some other factor, perhaps photoperiod, was involved in bunch initiation. Lassoudière (1978) demonstrated variation in GDD in cv. ‘Poyo’ (AAA, Cavendish subgroup) grown in Ivory Coast over five years. More importantly there was variation in the GDD between planting dates within locations where the crops planted earliest in the year had the least GDD. From these data, it is likely that a factor other than temperature is influencing bunch initiation in bananas, a similar conclusion reached by Turner and Hunt (1987) for cv. ‘Williams’ in a sub-tropical environment. In Honduras (15ºN) Dens et al. (2008) found that removal of the bunch and leaves on the parent hastened the development of the ratoon crop in long days but the same treatment had no effect on development when conducted during short days. They concluded that an environmental factor was contributing to floral induction in banana because the effect of the treatment in hastening development of the ratoon was overridden in the season with shorter days. While banana is currently regarded as dayneutral for floral induction because it does not depend on photoperiod for flowering, there is evidence that environmental factors delay floral development, independent of growingdegree-days. If this factor was short photoperiod, then bananas may be classified as quantitative long day plants.

Flower development The inflorescence is a terminal spike comprising of a series of nodes of flower clusters (hands) that are subtended by bracts. The female flowers occupy the basal nodes and the male flowers the apical nodes. The female ovary is inferior with three locules that each contains an axile placenta. The ovules


291

PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS are in two or four rows in each locule. Floral initiation begins when the indeterminate vegetative apex is transformed into a determinate reproductive apex; the shoot apex ceases to produce leaves and starts to produce floral parts. The inflorescence bears five to 15 or more clusters of female flowers and 150 to 300 clusters of male flowers. Summerville (1944) proposed that the upper limit of inflorescence size was set by the size of the meristem at the time of transformation. Thus at floral initiation environmental conditions that affect general vegetative development will affect fruit production. This notion has yet to be tested experimentally although within a cultivar, large plants produce large bunches of fruit. Within the inflorescence the transformation from female to male flowers is marked by a sudden decline in ovary length that is first noticeable when the inflorescence is midway up the pseudostem and the female ovaries have reached approximately 10 mm in length. The sequence of floral initation, formation of the ovule primordium and the megaspore mother cell occurs while the inflorescence is inside the pseudostem. Consequently, when the inflorescence emerges they are almost at anthesis. When the inflorescence is midway up the pseudostem the megasporangium (ovule) is differentiating, it appears as a rounded protuberance growing at right angles from the placental wall. It is at first atropus and by differential growth becomes anatropous with its micropyle pointing towards the placental wall. The inner integuments have already formed when the archesporium arises from any sub-epidermal cell near the summit of the nucellus. It is easily distinguished from the surrounding cells by its relatively large size and becomes the megaspore mother cell. The differentiation of the archesporium takes place

292

before the differentiation of the outer integument and when the megasporangium is half anatropous. The ovules have almost attained maximum size when the megaspore mother cell begins to divide. When the inflorescence protrudes from the pseudostem the gametophyte or embryo sac has differentiated and the nuclei are in their respective positions ready for fertilization (Fortescue and Turner, 2005). The development of the female flowers inside the pseudostem spans 12-13 weeks in the tropics and is up to twice as long in the sub-tropics. Any effect of environmental conditions during this time will be reflected in the shape and anatomy of the fruit.

Fruit growth The interval between inflorescence (bunch) emergence and harvest is seasonally variable ranging in subtropical South Africa, for example, from 108 days after flowering in early December (summer) to 200 days in early May (autumn), and leading to corresponding uneven fruit production during the year. By tagging inflorescence emergence every two weeks, Robinson and Nel (1984) found that it was possible to predict harvest dates based on historical records. There were also differences in bunch mass depending on the time of flowering, linked to the minimum temperatures prevailing at flower initiation. For example, Robinson (1982), again in South Africa, reported how inflorescences that emerged from plants in November produced bunches, which were small and malformed. This was explained as the effect of low temperatures at the time the flowers were being initiated in June. In the sub-tropics, an individual mean bunch mass of 50 kg is possible from ratoon crops (cv. ‘Williams’ AAA Cavendish subgroup,). By comparison the corresponding weight in the tropics is 30–


PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS 35 kg (Robinson and Nel, 1989). A bunch contains a cluster of fruits at a node (known as a hand), which in turn is composed of individual fruits (or fingers). The effects of drought at this time are illustrated by the results of an experiment in the Canary Islands (28æ%37Ń). When water was withheld for 63 days from flower emergence, before re-watering (cv. ‘Grande Naine’ AAA Cavendish subgroup) finger number remained constant (not surprisingly) compared with the control, but finger length and diameter were both reduced (by 9%). Total bunch fresh weights were reduced by 41%, from 30 to 17 kg plant”1. Drought also delayed fruit maturity (Mahouachi, 2007).

Effect of abiotic stress on flower and fruit development 1. Soil Moisture deficit stress on flower initiation Holder and Gumbs (1982) reported a study on the effects of the timing of irrigation during floral initiation on female flower production (cv. ‘Robusta’ AAA Cavendish subgroup) on a clay loam soil in St Lucia (14æ%N). A continuous non-limiting supply of water during the ‘dry’ season from December to July increased the number of flowers produced on the plant crop. Relieving water deficits after 120 d, for a period of 60 d, during the period of estimated floral initiation and early differentiation had a similar effect, but also increased the number of female flowers per inflorescence compared with the continuously watered treatment. There was evidence of enhanced growth rates (pseudostem girth), for a period of 50 d, following the relief of the water deficit, which made up for the earlier effects of drought. Positive linear correlations were observed between the final (240 d after planting)

pseudostem diameter (range 50–58 mm at 0.60 m above the ground) and the number of female flowers per inflorescence (range 100–160; r2 = 81%, n =9). Similarly, female flower production was correlated with the rate of increase in the diameter of the pseudostem (1– 4 mm d”1) during the period 150–181 d after planting (r2 = 85%, n = 9). 2. Low temperature on flower development There are three critical times in the reproductive biology of Musa when it is sensitive to damage by low temperature. Firstly, low temperature affects the differentiation of the ovaries and associated tissues soon after floral initiation. Secondly it affects the ovaries, when the carpels and stamens are forming midway up the pseudostem. Thirdly, it affects the differentiation of the megasporangium three to six weeks before anthesis. Morphological and anatomical evidence suggests that the development of the flower in banana is sensitive to low temperature when the ovary is differentiating (Fahn et al., 1961), when the perianth and stamens are forming (White, 1928) and when the megasporangium is differentiating (Fortescue and Turner, 2005). These studies have been conducted mainly on triploid AAA clones of the Cavendish subgroup. Low temperature when the ovary is differentiating is associated with deformed fruit that are not suitable for marketing. Internally these fruits are characterized by a reduced number of locules in the ovaries and in some flowers there are no locules at all. Flowers with reduced locules develop into undersized fruit while those with no locules form very small fruit no larger than the ovaries of neuter or male flowers (Fahn et al., 1961). Cool temperatures at the time of megasporogenesis and embryo sac formation can lead to malformations in the ovule itself. Low temperature (3-18ºC) reduced the size of


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PHYSIOLOGY OF FLOWERING IN PERENNIAL FRUIT CROPS ovules and caused them to have a rounder shape than normal ovules. In addition, the nucellus and nucellar cap protruded through the micropyle. These deformations were observed in ovules in bunches growing in the autumn, winter and spring in the subtropics. Fortescue and Turner (2005) suggested that megasporangium formation was particularly sensitive to low temperature and that low temperatures need not last for more than a night or two. 3. Fruit growth and soil water deficit In a field experiment conducted at NRCB, Trichy farm concluded that irrigation at flowering critical period for normal fruit development otherwise, soil moisture deficit stress may decreases the bunch weight in Robusta (42.07%), Karpuravalli (25%) and in Rasthali (18.83%) and also affect the finger growth (length as well as circumference) resulted in poor marketable bunch. Mahouachi (2008), in a field study on cv. ‘Grand Nain’ (AAA, Cavendish subgroup), examined the effects of soil water deficit on the growth and nutrient concentrations of fruit during the first two months after bunching and then for a further three weeks after the plants had been rewatered. Soil water content at 15 cm depth and 40 cm from the irrigation drip line decreased exponentially from 33 to 15 per cent during 63 d of drying. Upon re-watering, the soil water content did not increase instantaneously, but increased linearly and did not reach field capacity until 20 d later. From the data of Mahouachi (2008) we calculated the effects of the soil water deficit on rates of fruit growth and rates of accumulation of K in the fruit. In well-watered plots the fruit grew (fresh and dry weights) exponentially for the 83 d of measurement. For the first 63 d the relative growth rate (FW) was

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1.1 per cent per day and in the last 20 d it increased to 1.6% per day. This pattern of growth was similar in the fruit on plants subjected to soil drying, but the rate was reduced by 30% during soil drying (0-63 d) and by 11 per cent during re-watering (63-83 d). Even so, the fruit was still growing after 63 d of drying. The net photosynthesis of the leaves had been reduced by 80 per cent at this time. Soil water deficit reduced the rates of accumulation of fresh weight and dry weight by 39 per cent and the accumulation of K by 57 per cent. Soil drying reduced the accumulation of water and K in the fruit and the K concentration fell by 19%, from 186 to 151 mmol K per ‘cell sap’ volume. Re-watering fully restored the rate of K uptake by the fruit but the accumulation of dry matter was 17 per cent less than control and the fresh weight was 30 per cent less. These data suggest that the fruit adjusts its growth rate to the supply of water available and that some of this adjustment may be related to maintaining a sufficient concentration of K in the fruit tissues. This mechanism allows the fruit to increase its absolute growth rate and complete its development, despite dwindling supplies of water. Commercially, soil drying reduces fruit size, which is often a criterion for markets, and this effect begins soon after soil drying commences. Nonetheless, the fruit continues to grow, albeit at a slower rate, whereas in a similar situation, the emerging leaf on vegetative plants are likely to stop elongating. For fruit to grow as the soil dries it must be able to attract water by having a more negative water potential than other organs of the plant. This might be achieved by decreasing its osmotic potential through the accumulation of solutes. Since soil drying reduced the amount of K entering the fruit in the experiment of Mahouachi (2008), any decrease in osmotic potential is not caused by K and must be attributed to other osmolytes, perhaps sugars



CONCLUSION

Gowen). London, Chapman and Hall.

The banana is day neutral for floral induction, but photoperiods of less than 12 h are associated with a slowing in the rate of bunch initiation that is independent of temperature expressed as growing degree days. This may contribute to seasonal variations in banana flowering, even in more tropical environments with moderate temperatures.Banana flowering was considered as day neutral but it needs to be confirmed across cultivated genotypes. There was less or no report on phytohormones with flowering physiology. These are areas to be studied to understand the flowering and management purpose. In banana floral primordial initiation, flower and fruit developments are sensitive to soil moisture deficit and chilling stress. These stages are to be taken care as they are very critical for normal inflorescence and fruit development.

SELECTED REFERENCES Barker, W.G. and Steward, F.C. 1962. Growth and Development of the Banana Plant II. The Transition from the Vegetative to the Floral Shoot in Musa acuminata cv. Gros Michel. Ann Bot (1962) 26 (3): 413-423

Mahouachi, J. 2007. Growth and mineral nutrient content of developing fruit on banana plants (Musa acuminate AAA, ‘Grand Nain’) subject to later stress and recovery. Journal of Horticultural Science and Biotechnology, 82:839–844. Mohan Ram, H.Y., Manasi Ram, H. and Steward F.C. 1962. Growth and Development of the Banana Plant 3. A. The Origin of the Inflorescence and the Development of the Flowers: B. The tructure and Development of the Fruit. Annals of Botany, 26(4): 657673 Robinson, J C., Anderson, T. and Eckstein, K. 1992. The influence of functional leaf removal at flower emergence on components of yield and photosynthetic compensation in banana. Journal of Horticultural Science, 67:403–410. Simmonds, N.W. 1998. Tropical crops and their improvement. In : Agriculture in the Tropics 3rd edition, 257–293 (Eds C. C. Webster and P. N. Wilson). Oxford, Blackwell Science. Simmonds, N.W. and Shepherd, K. 1955. The taxonomy and origins of the cultivated bananas. Journal of the Linnaian Society, 55:302–312. Stover, R.H. and Simmonds, N.W. 1987. Bananas 3rd edition, Harlow, Longman pp.468.

Holder, G.D. and Gumbs, F.A. 1983. Effects of nitrogen and irrigation on the growth and yield of bananas. Tropical Agriculture, (Trinidad) 60:179–183.

Summerville, W.A.T. 1944. Studies on nutrition as qualified by development in Musa cavendishii Lamb. Queensland J. Agric. Sci. 1:1-127.

Karamura, E.B. and Karamura, D.A. 1995. Banana morphology – part II: the aerial shoot. In Bananas and Plantains, 190–205 (Ed. S.

Turner, D.W. 1998. Ecophysiology of bananas: The generation and functioning of the leaf system. Acta Hort. 490 : 211-221.


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