influence of bulb storage temperature on dormancy and flowering of ...

Influence of Bulb Storage Temperature on Dormancy and Flowering of Veltheimia bracteata Johan L. Ehlers 1, Pieter J. Jansen van Vuuren 1 and Liesl Morey 2 1 2 Department of Agricultural Management Biometry Group Technikon Pretoria Agricultural Research Council Private Bag X680 P O Box 8783 Pretoria, 0001 Arcadia, 0007 South Africa. South Africa. Tel: +27-12-318-4156 Tel: +27-12-342-9969 Fax: +27-12-318-5969 Fax: +27-12-342-9969 e-mail: [email protected] e-mail: [email protected] Keywords: flowering dates, storage temperatures, Veltheimia. Abstract Veltheimia bracteata is a bulbous plant indigenous to South Africa. Under natural growing conditions it is evergreen and flowers during June to Septembe r. It was found that dormancy and flowering was influenced by storage temperature in the Netherlands where it is grown as a dormant bulb which is planted in summer to flower from December to February. Plants of three different clones were lifted, defoliated, dried off for three weeks under greenhouse conditions, then stored at four different constant temperatures for eight weeks, after which the bulbs were planted and grown under greenhouse conditions. The dates of first emergence of new vegetative growth, first emergence of the inflorescence and opening of the first flower were recorded. Due to limited material only two storage temperature treatments were assigned to each clone. Storage at 15o C and 20o C retarded emergence by five and three weeks respectively; storage at 25o C slightly accelerated emergence, while storage at 30o C accelerated emergence but caused damage to the bulbs as was evidenced by loss of almost 50 percent of the bulbs. Emergence of the inflorescence of the defoliated controls only occurred in clone ‘Lemon Flame’ and was retarded compared to untreated controls. The only treated bulbs to flower were those of ‘Lemon Flame’ stored at 15o C, which flowered 3,28 weeks after the untreated control. The severe difference in reaction of the different clones has resulted in the trial being repeated with ‘Lemon Flame’ this season in order to clarify the results. INTRODUCTION Veltheimia bracteata Harv. ex Bark. is an attractive, evergreen indigenous bulbous plant with potential as a commercial pot plant and cut flower. It produces a single raceme of dusky pink flowers during winter. A lemon yellow flowered variety also exists. Since consumer demand for plants and flowers differ during different times of the year, the flowering date and the ability to manipulate the flowering date of a particular plant is of vital importance for the possible commercial success of the plant (Jansen van Vuuren & Ehlers, 1998). It was reported by Van Leeuwen & van der Weijden (1997) that in the Netherlands V. bracteata was grown as a dormant bulb which is planted in summer to flower in winter from December to January. Working with a single clone, they found that bulb dormancy and flowering was influenced by the bulb storage temperature resulting in generally deleterious effects with storage temperatures below 20o C and above 25o C. Jansen van Vuuren & Ehlers (1998) also reported that experiments with non-clonal material showed that bulb dormancy and flowering were similarly influenced by bulb storage temperature. They also found that initiation of the inflorescence occurred earlier than the start of the storage treatments of both these investigations and concluded that some of the deleterious results of various storage temperatures could be ascribed to damage to the already initiated inflorescences and growing points, rather than its influence on the initiation of these structures. The work reported here represents the results of a greenhouse trial to investigate the influence of storage temperatures on the flowering behaviour of V. Proc. 8th Int. Symp. on Flowerbulbs Eds. G. Littlejohn et al. Acta Hort. 570, ISHS 2002

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bracteata. MATERIALS AND METHODS Four clones of different origin were used in this trail. They were Clone L (obtained from van Leeuwen in Lisse, Netherlands); ‘Lemon Flame’ (obtained from Kirstenbosch, Cape Province); Clone R (obtained from ARC Institute for Horticultural and Vegetable Crops, Roodeplaat, Gauteng) and Clone A (produced in vitro in the Tissue Culture Laboratory of Technikon Pretoria). Forty plants of each clone which had flowered during the previous flowering season were selected at the stage before initiation of the new inflorescence and ten plants each were treated as follows: Treatment 1: Removal of the old inflorescence. Treatment 2: Removal of the old inflorescence and foliage. Treatment 3: Removal of the old inflorescence and foliage followed by lifting, three weeks drying off on the greenhouse bench (Mean temperature 18o C) followed by storage for eight weeks at a constant 15o C before planting in 150mm plastic pots and growth in the greenhouse. Treatment 4: The same as Treatment 3, except that the bulbs were stored at a constant 20o C. Treatment 5: The same as Treatment 3, except that the bulbs were stored at a constant 25o C, Treatment 6: The same as Treatment 3, except that the bulbs were stored at a constant 30o C. The temperature range was determined to include the upper and lower limits which gave poor results as reported by van Leeuwen & van der Weijden (1997) and Jansen van Vuuren & Ehlers (1998). Due to the limited number of bulbs available, each treatment could not be applied to each clone. Treatments 1 and 2 were applied to all four clones and then two of the four storage temperatures were systematically applied to clones A, ‘Yellow Flame’ and R randomly, while all six treatments were applied to clone L. Two bulbs of clone L were sampled at the start of the storage period and then at fortnightly intervals to the end of the storage period for dissection, fixation, processing followed by sectioning, staining and microscopic examination to follow the development of the bulbs during the storage period according to the method of Jansen van Vuuren and Ehlers (1998). After the storage period of eight weeks the other treated bulbs were planted in pots and arranged in a randomised block design. The trial was monitored every second day for emergence of vegetative growth, emergence of the inflorescence and opening of the first flower of each inflorescence. Treatment 1 could not be accurately monitored for emergence of vegetative growth because the evergreen nature of V. bracteata makes the determination of the first emergence of new growth of a plant with foliage an imprecise observation. RESULTS AND DISCUSSION The results of the histological study of the growing points were negative. Despite trial runs with non-clonal material to verify the applicability of the standard histological method as modified and reported previously, no success was obtained in getting efficient wax infiltration of the fixed and processed material. As a result no sections suitable for microscopic examination could be obtained. The replacement of xylol with benzene as non-polar solvent in the process had no effect. Wax imbedding under vacuum and increasing the percentage of beeswax in the wax mixture was also unsuccessful. The emergence of the bulbs, emergence of inflorescences and opening of the first flower of each inflorescence were recorded and the cumulative results of all aspects of all treatments showed a clear ‘S’ shaped pattern with initial slow emergence or opening which speeds up before slowing down to approach a limit. These patterns were modelled by means of the Generalised Logistic Curve using the Genstat 5 Release 3 Statistics Package (Payne, 1993). The Generalised Logistic Curve gave the best fit with between 95,1% and 100,0% variance being accounted for. According to Horgan (1999) the generalised formula for the Generalised 178

Logistic Curve is:

C

Y = A+ (1 + Te

1 − B ( x− M ) T

)

where Y= number of emerged bulbs/emerged inflorescences/ first flowers open; X= time (weeks); B=maximum emergence/flowering rate; A+C= maximum number of emerged bulbs/inflorescence/first flowers open; and M = tM = point of inflexion (point at which the maximum emergence/flower opening occurs. An analysis of Variance of the emergence, emergence of inflorescences and opening of first flowers was done at the point of inflexion of each clone for each temperature treatment. Data was tested for normality of distribution of residuals and homogeneity of variances. Specific treatments were significant at p=0,05. The results are summarised in Table 1. Emergence of Vegetative Growth Bulbs of Clone A which were stored at 30o C started emerging at the same time as those stored at 25o C; both starting to emerge about four weeks before the control. Storage at 30o C resulted in a 50% loss of bulbs stored at that temperature. Storage at 15o C and 20o C resulted in a five and four week delay in emergence compared to the control of Clone R. ‘Lemon Flame’ stored at 15o C showed a seven week delay in emergence compared to the control bulbs. The bulbs of ‘Lemon Flame’ which were stored at 30o C only emerged ten weeks after the control bulbs. This long delay could be ascribed to the fact that the much smaller ‘Lemon Flame’ bulbs did not survive the elevated storage temperature well. Sixty percent of them were killed and the survivors resumed growth by developing offsets and not by development of the terminal bud. Emergence of the Inflorescence The point of inflexion for emergence of the inflorescence for the untreated controls of the three clones (A, ‘Lemon Flame’ and R) lay within a three week period with Clone R first, ‘Lemon Flame’ second and Clone A last to emerge. Of the defoliated controls, only ‘Lemon Flame’ showed emergence of its inflorescence, with its point of inflexion 2,75 weeks before the untreated control. None of the bulbs which were stored at the various constant temperatures developed inflorescences except ‘Lemon Flame’, stored at 15o C which showed emergence of inflorescences 7,27 weeks after the defoliated control. Opening of First Flowers The point of inflexion for opening of the first flower of the inflorescence for the untreated controls did not differ significantly and was about eleven weeks after the emergence of the inflorescence. The defoliated control of ‘Lemon Flame’ took 1,87 weeks longer than the untreated control to reach its inflexion point. The bulbs of ‘Lemon Flame’ which were stored at a constant 15o C reached the point of inflexion for opening of the first flowers 3,28 weeks after the untreated control, but only 1,64 weeks after the defoliated control. Rough modelling of the emergence data indicates that storage of the bulbs within the range of 15o to 25o C results in a delay of emergence at the lower end of the range and accelerated development at the higher end of the range with the upper limit between 25o and 30o C. These results differ from those reported by van Leeuwen & van der Weijden (1997) and Jansen van Vuuren & Ehlers (1998). The results do however offer an explanation for the anomaly in the results of the former authors, where early lifted bulbs stored at 17o C showed delayed emergence compared to similar bulbs stored at 25o C. This result was reversed with bulbs lifted at a later stage. It can be postulated that the early lifted bulbs were lifted prior to initiation of the inflorescence and vegetative development. Regarding flowering behaviour it is clear that the reaction of the different clones of V. bracteata which were used in this trail to the different treatments were so divergent that it is not 179

possible to deduce a general pattern of reaction to the treatments. The results also show that the histological study of the bulbs of Clone L would in all probability only be applicable to Clone L. It is however clear that storage at 30o C was not a practical storage treatment for any of the clones exposed to that treatment due to the unacceptable loss of 50 percent or more of the bulbs treated in this manner. The flowering reaction of ‘Lemon Flame’ to an extent mirrors the reaction of vegetative development and it appears that lower storage temperatures result in the longest delay. This hypothesis will be tested during the 1999/2000 season when the trial will be repeated with ‘Lemon Flame’ as only clone and the discontinuation of the 30o C storage temperature as a treatment. ACKNOWLEDGEMENTS Technikon Pretoria and the National Research Foundation for funding of the project. Literature Cited Horgan, G.W. 1999. Growth Curve Modelling. Biomathematics and Statistics Scotland, UK. http://www.bioss.sari.ac.uk/smart/ Jansen van Vuuren, P.J. and Ehlers, J.L. 1998. Flower Initiation and Differentiation in Veltheimia bracteata. Acta Hort. 454:223-228. Payne, R.W. 1993. GenstatTM 5 Release 3 Reference Manual. Oxford University Press, Oxford. van Leeuwen, P.J. and van der Weijden, J.A. 1997. Effects of Storage Temperature and Duration on Dormancy and Flowering of Veltheimia bracteata. Acta Hort. 430:419-425. Jansen van Vuuren, P.J. and Ehlers, J.L. 1998. Flower initiation and differentiation in Veltheimia bracteata. Acta Hort. 454:223-228. van Leeuwen, P.J. and van der Weijden, J.A. 1997. Effects of storage temperature and duration on dormancy and flowering of Veltheimia bracteata. Acta Hort. 430:419-425

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Tables Table 1. Influence of storage temperature on the time of maximum emergence, appearance of the inflorescence and opening of first flowers in weeks of four clones of Veltheimia bracteata after planting. Analysed parameters

Clone A Control

Emergence of first Not observed vegetative growth Emergence of 22,89 inflorescence Opening of the first 30,04 flower Time from Not observed emergence of first growth to emergence of inflorescence Time from 7,15 emergence of inflorescence to opening of first flower

‘Lemon Flame’ Control

Clone R Control

Clone A Defoliated Control

‘Lemon Flame’ Defoliated Control

Clone R Defoliated Control

Clone A storage at 25o C

Clone A storage at 30o C

‘Lemon Flame’ storage at 30o C

‘Lemon Flame’ storage at 15o C 12,59

Clone R storage at 15o C

Clone R storage at 20o C

Not observed

Not observed

9,21

6,93

11,70

5,15

5,28

16,83

15,80

14,45

21,84

20,30

Did not flower

19,09

Did not flower

Did not flower Did not flower Did not flower

26,36

Did not flower Did not flower

30,44

30,70

Did not flower

32,38

Did not flower


34,02


Not observed

Not observed

Did not flower

12,16

Did not flower


13,77


8,60

10,40

Did not flower

13,29

Did not flower


7,66


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