Improving flowering and fruit quality in litchi

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Improving flowering and fruit quality in litchi Chapter · May 2016

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4 authors: Sanjay Kumar Singh

Amrendra Kumar

National Research Centre for Litchi


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Sushil Kumar Purbey

Swati Sharma

ICAR-National Research Centre on Litchi




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Improving Flowering and Fruit Quality in Litchi: Applying PGRs and Chemical Regulants Sanjay Kumar Singh, Amrendra Kumar, S K Purbey and Swati Sharma ICAR-National Research Centre on Litchi Flowering is the single most important event in the survival of angiosperms. Fruit bearing, arboreal species have been selected for cultivation primarily because of their palatable fruit characteristics and qualities that make them particularly attractive. They can be broadly categorized into two main groups, deciduous fruit tree species that grow in temperate climates and evergreen species that thrive in both tropical and subtropical climates. These two groups display phenologies that incorporate adaptations to each climate, including timing of flowering to avoid injurious conditions such as freezing winter temperatures in temperate regions and the desiccating conditions present during dry seasons in the tropics and subtropics. The availability of fresh litchi fruits in the market may be extended for another few days by utilizing other genotypes available in the litchi. However, much scope is not there as available genotypes differ little with regard to their maturity period (Ray and Sharma, 1986). Two pronged strategy may be employed to solve the problem i.e., either advancing the date of harvest or delaying the date of harvest. Still, there is no commercial method to be used for either advancing or delaying the harvesting time of litchi and thus extending the harvesting and marketing season. An alternative approach to induce early flowering and fruiting by using KNO3 has been successfully used in mango (Kumar et al., 2003). GA3 has been found to offer suitable means of controlling ripening process in litchi (Ray and Sharma, 1986) and in other fruit crops (Dilley, 1969). Evidence suggests that cytokinins retards sugar accumulation and pigmentation in litchi fruits. Yin et al., (2001) demonstrated inhibition of litchi fruit maturation and colouration following silver thiosulphate (STS) spray, indicated that ethylene is involved in the regulation of ripening events. Bagging of fruits including litchi can improve ripening and reduce physical damage. Flowering is very much related to various morphological (flushing time, shoot maturity), physiological and biochemical status of shoots especially C: N ratio, balance of endogenous auxins, cytokinins and gibberellins like substances and floral initiation process especially in warm subtropical region (Das et al., 2002). The relationship between flowering and vegetative flushing activity in winter is well established, however floral initiation takes place only after the shoot has undergone a period of vegetative dormancy. The growers are achieving more reliable flowering, especially in low-production cultivars by discouraging fall vegetative flushes, by insuring adequate age of the stems when the cool night temperatures occur in winter (Menzel, 1983). Flushing pattern and maturity of shoots influence flowering Litchi is an evergreen, recurrently flushing tree, and vegetative characters are very susceptible to environment and can change with difference in climate, soil or culture practices. Tree growth occurs as periodic, ephemeral flushes of shoots emerging from apical or lateral

resting buds before returning to a quiescent state. Periods of stem dormancy are short in young plants but can last more than 8 months between flushing episodes in mature trees. The three primary types of shoots (actively growing branch tips or laterals regardless of type of growth), that typically develop from dormant stems are vegetative (leaves only), generative (determinate inflorescences or panicles), or mixed (composed of both leaves and lateral inflorescences inserted at nodes). Vegetative flushes (growth occurring in numerous shoots, usually in sections of tree canopy or throughout the entire tree) of growth typically occur one to several times per year on individual stems (branch tips that are in rest). The frequencies of flushes that occur annually depend upon cultivar, size of the tree, and growing conditions (especially related to nitrogen and water availability). Reproductive flushes generally occur after extended periods of stem rest in the low-latitude tropics or immediately following periods of cool night temperatures in the higher latitude in tropics and subtropics. The flushing enlarges tree size and produce leaves for utilizing sunlight for carbohydrates synthesis which supports fruit development in the following seasons. Moreover, leaf flushing is one of the factors that counteract flowering process (Menzel and Simpson, 1992). The flushing of shoots in litchi is recurrent with cyclic flush growth. When new shoots emerge, they elongate, and the new leaves expand, subsequently, the terminal bud becomes dormant, with the leaves continuing to mature and accumulate chlorophyll. Flush growth after harvest is crucial for tree recovery and productivity for next season. New growth of shoot responds to low temperatures in winter and forms reproductive flush (Batten and Mc Conchie, 1995). However, new growth occurs only from a fully mature shoot. The maturity of flush in winter exerts a large influence on the flowering. The flush cycle is managed in such a way that the latest flushes are fully matured before winter, which maximizes flowering success. Hence, prediction of the flush cycle is needed so that precise and effective measures can be taken to manipulate it and is necessary to determine the progress of flush maturation, which is reflected by maturity of the new leaves. As leaves mature, they attain their full size, typical green colour, hard texture and optimal photosynthetic function. The poor fruit retention in litchi results from insufficient flushes on the bearing shoot, whereas poor flowering could occur when the bearing shoots produce immature flush and leaves in winter. The emerging inflorescence is initially similar to a vegetative flush and it is only when the lateral meristems develop into secondary inflorescences or start producing small leaves in the case of mixed shoots, it is possible to identify the shoot. The three flushing cycles in potted ‘Wai Chee’ litchi that consisted of a mean flushing duration of 20 days and an inter flushing period of 10 days. Each panicle produces ten to hundreds of small flowers (Menzel and Waite, 2005). Limited data suggested that cultivars with early fruit ripening had a lower alternate-bearing tendency than late ripening cultivars. Litchi leaves have a definite lifetime and 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. 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.

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. Fruit from the trees which flower very late in the cycle often do not fully mature. 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). Out of three flushes in litchi, early (after harvest), mid (August to October) and late (after November) season; the early and mid-season flushing influenced the yield, whereas the late season flushing do not contribute towards yield. Thus, the mid-season 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). A minimum cycle would be 6 to 8 weeks for flushing and 4 to 6 weeks between flushes; consequently, bearing shoot rarely completes more than two flushes between harvest and flower initiation in Australia (Batten and Lahav, 1994). 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. The vegetative flushing in the last week of November hardly produced any panicle in March apparently due to immaturity of these shoots to differentiate flower buds in the month of December and January and vegetative growth after September led to erratic bearing in litchi. The early and mid-season flushing influenced the yield, whereas the late season flushing did not have any contribution towards yield. The mid-season flush (appearing in August-October) is of more significance in Litchi 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 (Pareira et al., 2005). Bearing and fruit quality affected by PGRs applications

In litchi, yields are often irregular and suffer from alternate bearing. Productivity in offyears is unacceptably low and its yield and quality can be substantially improved by application of PGRs. The plant growth regulators primarily (PGRs) include auxin, gibberellin, cytokinin, ethylene, and abscisic acid (ABA). Secondarily it also includes florigens, anthesin, vernalin, morphactins, etc. Each growth regulators have various role and functions which contributes to economic of the farmers and horticulturists worldwide. The usage and dosage naphthalene acetic acid used in litchi trees: in the condition of lychee excessive growth, not germination, using 200-400 mg/L of naphthalene acetic acid

solution sprayed whole tree, can inhibit the growth of new shoots, increasing the flowers number, improve fruit yield. Research in Australia, China, Israel and South Africa has shown that synthetic auxin, 3-56 trichloro-2-phridyl-oxyacetic acid (3-5-6 TPA) applied as foliar sprays can reduce fruit drop and increase fruit size in different lychee cultivars. 3-5-6 TPA (applied at the 2, 4 and 6 g fruit mass stage at 0, 20, 40 and 60 mg/L) significantly increased fruit size and retention. However, the applications at the 2 g fruit mass stage at 40 and 60 mg/L resulted in the highest increases in fruit size and retention, respectively. Thus, a 3-5-6 TPA application in the range of 40 to 60 mg/L at the 2 g fruit mass stage can be recommended to improve fruit size and retention. It (50 ppm) reduced natural fruit drop. If applied too early in 'Tai So', it caused an increase in fruit drop. The TPA was most effective when natural fruit drop was high; reducing fruit drop from 74.7 to 34.9% in 'Kwai Mai Pink' and least effective when natural fruit drop was low. An increase in the percentage of fruit with poorly developed (chicken tongue) seed and slightly larger fruit size was also observed in treated trees. The litchi plants treated with ethrel (2 ml/L) will have highest C/N ratio (both in leaves and shoots before flowering), number of flowering panicles (71.58%), number of fruits per panicle at the initial stage (63.92) and also at harvest (23.09). However, the highest sex ratio (male: hermaphrodite) (3.26) of flowers found in untreated control plants and maximum percentage of fertile pollen was observed in plants treated with KNO3 (2%). The ethrel (2 ml/L) proved to be the most effective for flowering and fruit induction in litchi cv.‘Bombai’. (Mandal et al., 2014). GA3 (20 ppm) also was found effective treatment to increase fruit set, fruit retention and size of fruit being maximum of 42.18 per cent, 21.81 per cent and 3.64 cm x 2.84 cm, respectively. It also produced maximum number of fruits/tree (5327), weight of individual fruit (20. 66 g) and fruit yield per tree (104.55 kg). Interaction between borax 0.4 per cent and GA3 (20 ppm) exhibited in maximum retention of fruit (24.64 %) and fruit yield of 123.10 kg/tree (Kumar et al. 2009). Spray of Gibberellic acid (GA3) (ProGibb®, 20% of GA3) at 5 and 10 mg/l 14 days after full bloom (AFB) over 2 years increased fruit longitudinal and transversal diameter, and fruit, aril and pericarp weight (40–41 and 37–38 mm, and 27.3–28.4, 21.7–22.7 and 5.0– 5.3 g, respectively) compared with control (35–36 and 33–34 mm, and 22.3–22.4, 17.8–17.9 and 3.9–4.0 g) (Chang and Lin, 2006). KNO3 (4%) sprayed at 1 cm size of panicle (in the first week of February) and GA3 (20, 40 ppm) and BA (20, 40 ppm) applied two weeks before expected date of harvest (on 15 th May). KNO3 (4%) advanced the harvesting date only for 2 days in comparison to control. GA3 (20 and 40 ppm) delayed the harvest date for 2 and 5 days, respectively while BA (20 ppm and 40 ppm) delayed the harvest date for 5-6 days. In all the treated trees, fruit weight was found to be more than 21 g. Higher fruit quality attributes were recorded with GA3 (40 ppm) followed by GA3 (20 ppm) and reduced fruit cracking was also observed in trees which were sprayed with GA3 and BA. Higher dose of cultar (5 ml/m2 plant spread) proved better than the lower dose (3 ml/m2 plant spread) in controlling vegetative flush and increasing flowering and yield. Similarly, cultar (paclobutrazol) application 90 days before bud break was found to be more effective than

its application 60 days before bud break. Paclobutrazol, thus holds promise in increasing flowering, fruit set, yield and quality of fruits. Application of paclobutrazol (3 ml a.i./m2 canopy surface area) advanced the flower emergence by six to seven days. The paclobutrazol induced flowering in China. There is increase in C: N ratio and leaf water potential, by the paclobutrazol with drastic increase at the bud break. C: N ratio in shoot is positively related to ABA content in buds. The doses of 1.0 and 1.5 g of PBZ resulted in the reduction in the concentration of nitrogen and carbon in leaves and, therefore in C: N Ratio. The proportion of pure panicles can be increased by 4-fold with 0.1 g paclobutrazol spray in litchi cv. Xiangli. Paclobutrazol besides affecting gibberellins also increases ABA and cytokinin contents concomitant with C: N ratio and leaf water in mango buds to elicit flowering responses. TIBA (tri-iodobenzoic acid) is considered a polar auxin transport inhibitor and increases the endogenous cytokinin level in the lateral buds. There may be a positive relationship between cytokinin level and flower bud formation which may be due to the positive impact of TIBA (Negi et al. 2010). TIBA @ 1 g/L resulted in early panicle emergence, more flowering shoots percentage, more panicle length, and more fruit retention per panicle of the fruit. TIBA gave higher percentage of fertile pollen in both years (Mitra and Sanyal, 2001). Treatment of ethrel when early litchi had winter flushes at 400, 600, 800 and 1,000 ppm could remove winter flushes, but 800 ppm of ethrel could remove 95.6% of winter flushes, increasing C/N proportion to enable flowering, increasing fruit setting (28.1%), fruit yield (47.8%) compared with control, not affecting fruit quality and plant growth. Using ethrel of 1,000 ppm, which could remove winter flushes, dropped mature leaves, thereby affecting plant growth and development. The litchi plants sprayed with 1000-2000 dilution of Ethrel in late fall inhibited the shooting of new flushes and increased 29.7-36.7% of panicle formation. Need of Cincturing/Girdling The girdling treatment delayed the initiation of flowering and reduced about 15.9% of male flowers and increased 17.7% of hermaphrodite functioning as male flowers. However, girdling of the trunks also increased 31.2% of panicle formation. Ethrel treatment increased the yield of litchi fruits by 57.1%. 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 accumulation 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. Cincturing at the 3 mm deep resulted less flowering shoots percentage, low ascorbic content of the fruit and early harvest of the fruit. Cincturing the north and west side shoots showed induced flowering. Mineral nutrient requirement for flowering KNO3 increased flowering, number of fruits per panicle and yield. Potassium nitrate could replace the need for vegetative dormancy period, and induced higher flowering rates than plant growth regulators (Figure 1). The higher flowering resulted in higher yields, mainly in “off” years and thus produced highest yields also on 4-years basis, 52% higher than the control (Figure 2).

Fig.1: Effect of flower induction treatments on flowering shoots (%) in litchi trees in ‘off’-years.

Fig. 2: Effect of flower induction treatment on the yield of litchi trees in ‘off’-years. Zinc plays a vital role in the metabolic activities of plants. The principal functions of zinc in plant are as a metal activator of enzymes like dehydrogenase (pyridine nucleotide, glucose-6 phosphodiesterase, carbonic anhydrase etc). It is involved in the synthesis of tryptophane, a precursor of IAA. It is associated with water uptake and water retention in plant bodies. Boron on the other hand, is considered to be necessary for hormone metabolism, photosynthetic activities, cellular differentiation and water absorption in plant parts. It is also involved in reproduction, germination of pollen tube and fertilization. In case of boron deficiency, flowers are produced in less number and are mostly sterile; fruits are deformed and render themselves commercially useless. The application of borax 0.4 per cent resulted in maximum fruit set (42.50 per cent), fruit retention (22.60 per cent), size of fruit (3.72 cm x 2.90 cm), number of fruit per tree (5422), weight of individual fruit (20.91 gm) and fruit yield per tree (111.05 Kg). Aril percentage was high in borax 0.2 per cent and 2, 4-D 10 ppm. Minimum fruit crack of 10.91 per cent was observed in borax 0.4 per cent (Kumar et al. 2009).The application of micro-nutrients was beneficial in improving the fruit yield which was observed maximum under the trees treated with 1.0 per cent borax (Lal et al., 2010).

Foliar application of Zinc (0.6%), Copper (0.3%) and Boron (0.3%) was found to accelerate the growth and vigour of the plant (Babu and Singh, 2002). The foliar sprays of ZnSO4 @ 0.5, 1.0 and 1.5% on litchi considerably increased the fruit yield and reduced fruit drop. The maximum length and diameter of fruit is found with ZnSO4 at 0.4% spray whereas the weight of fruit was obtained highest in ZnSO4 at 0.2% and 0.4%. The fruit size and weight of fruit were increased greatly with borax applied at 0.4% and ZnSO4 at 1.0% through foliar spray (Rani and Brahmachari, 2001). Maximum edible percentage and minimum non-edible percentage in fruits was observed in treatment with 400 ppm SADH. Trees sprayed with 1.5 per cent potassium nitrate and 2.0 per cent calcium nitrate gave the highest fruit weight of 20.41 and 20.37 g, respectively. TSS, Ascorbic acid content, Total sugar, Juice percentage was found to be significantly higher by the sprays of borax at 1.0 per cent. Acidity was also lowest with the application of borax 1.0 per cent. Although the application of two sprays of the aqueous solution of 1.0 per cent borax technically proved to be most effective in improving yield and quality of fruits over control significantly, yet the most economic treatment proved to be the spraying of 0.5 per cent borax on litchi trees at 15 day interval during the period of growth and development of fruits. PGRs for extending post harvest life The synthetic cytokinin N-(2-chloro-4-pyridyl);N’-phenylurea (CPPU) at 5 – 10 mg l–1, applied to green or slightly red fruitlets (25 or 30 mm in diameter), delayed harvesting by 2–3 weeks compared with control trees. At harvest, CPPU-treated fruit that attained a red colour comparable to that of earlier harvested control fruit, were 20–25% larger with total soluable solid contents: titratable acidity (SSC:TA) ratios more than 50% higher than the controls. Despite their high SSC:TA ratios, CPPU-fruit stored well for 6 weeks at 1°C due to reduced browning, lower decay development and less aril discolouration, and maintained an acceptable flavour. These results suggest that CPPU can be used to extend the harvest season for litchi fruit. Silver thiosulphate gave a harvest delay of 8 days, however, a few brown spots on fruit skin were observed after the spray. Thus, applying various plant growth regulators and chemicals can help litchi orchardist to manage their orchard in such a way that it will have better quality production. It is mentioned here that above PGRs is effective in particular climate and its exact time of application must be known from researcher before orchard application.

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