Effects of gibberellins and benzylandenine on dormancy and flowering of Lilium speciosum

Scientia Horticulturae, 10 (1979) 255--260 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

255

EFFECTS OF GIBBERELLINS AND BENZYLADENINE ON DORMANCY AND FLOWERING OF LILIUM SPECIOSUM KIYOSHI OHKAWA

Kanagawa Horticultural Experimental Station, Ninomiya, Nakagun, Kanagawa 259--01 (Japan) (First received 17 July 1978; in revised form 1 November 1978)

ABSTRACT Ohkawa, K., 1979. Effects of gibberellins and benzyladenine on dormancy and flowering of Lilium speciosum. Scientia Hortic., 10: 255--260. G A 4 +7 (I000 rag/l), alone or in combination with B A (100 mg/l), was found to induce shoot emergence and flowering in dormant bulbs of L. speciosum, while GA3, alone or in combination with BA, had no effect. B A had a significant influence on increasing flower numbers, particularly when combined with G A 4 +7.

INTRODUCTION

Previous work has established that Lilium speciosum bulbs require low temperatures for the induction of shoot emergence and flowering (Ohkawa, 1976, 1977 and others). Shoots from bulbs exposed to temperatures above 21°C do not emerge and the bulbs are, therefore, considered to be dormant. It is possible to separate the shoot-emergence response from the floweringresponse by a combination of low temperature and photoperiod. Bulbs exposed to an insufficient duration of low temperature will produce shoots but no flowers when grown under less than 14 h photoperiod (short day = SD) conditions. If the same shoots are exposed to more than 14 h photoperiod (long day = LD), 100% flowering occurs. These studies suggest that photoperiod (LD) can substitute for the low-temperature requirements for flowering, at least partly. Similar behaviour was found in Lilium longiflorum (Wilkins et al., 1967). The unique system of controlling shoot emergence and flowering by manipulating storage temperature and photoperiod provides a useful method of studying factors controlling shoot emergence and flowering in Lilium speciosum. In the present study the relationship of gibberellins and cytokinins on shoot emergence and flowering was investigated.

256 MATERIALS AND METHODS

Two hundred and forty (74 g) bulbs of Lilium speciosum cultivar 'Uchida' were obtained from a grower in Atsugi, Kanagawa on 10 October and immediately packed in moistened sawdust and stored for 0, 30 or 60 days at 5°C. After the storage treatment, 10 bulbs were soaked for 48 h in each of the following solutions: (1) water (control); (2) gibberellic acid (GA3) 2000 mg/l; (3) GA3 100 mg/1; (4) gibberelin (GA4÷7) 1000 rag/l; (5) GA4.7 100 mg/1; (6) benzyladenine (BA) 100 rag/l; (7) GA 3 100 mg/l + BA 100 mg/1; (8) GA4 ÷7 100 mg/l + BA 100 mg/1. The solutions were aerated with an air pump throughout the treatment period. After treatment, 10 bulbs were planted in a 40 × 30 × 9 cm polyethylene container and grown in a greenhouse maintained at 22 + I°C and 8 h photoperiod. GA3, GA4 ÷7, and BA were supplied from Takeda Chemical Co., Abbott Laboratories and Kumiai Chemical Co., respectively. RESULTS The duration of storage at 5°C had a significant influence on shoot emergence and flowering in L. speciosum (Table 1). In the water controls, the non- and 5°C 3(~days storage treatments did not produce stem elongation, although in all treatments continuous differentiation of leaf primordia occurred. All the growth regulators studied had an effect on shoot emergence at either one or more of the storage treatments (Table 1). Generally, this effectiveness of some treatments became apparent only after storage at 5° C. At non-storage, GA4 *7 1000 mg/1 and GA4 +7 100 mg/1 + BA 100 mg/1 were the only'treatments affecting shoot emergence. Although the shoots emerged rather rapidly, the final length of the shoot was very short. At the other storage conditions, treatments containing GA4,7 also had the greatest influence on shoot emergence. Generally, the shoots emerged quicker than after the other treatments. After 30 days of storage, the GA4 +7 treatments stimulated 100% shoot emergence, and 100% stem elongation. In addition, the GA4 +7 1000 mg/1 and GA4 *7 100 mg/1 + BA 100 mg/1 treatments were the only treatments effective in stimulating flower differentiation. After 60 days of storage, the only noticeable effect with bulbs treated with GA4 +7, other than speed of shoot emergence, was in hastening flowering. The other gibberellin, GA3, also stimulated shoot emergence, although generally the effect was less than that observed with GA4.7 (Figs. 1 and 2). Comparable effectiveness in stimulating early shoot emergence and flowering was noticed only after 60 days storage at 2000 mg]l. The effect of BA on time of shoot emergence at the 30- and 60-day storage treatment was improved when combined with GA4 +7 or GA 3 , with the rate being faster in the former treatment. BA, alone and when combined

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258

Fig. 1. Plants grown from bulbs stored at 5°C for 30 days and then soaked in GA4,7 1000 mg/1 solution for 48 h. Note that 7 plants out of 10 differentiated and flowered normally, 3 of which had already been harvested.

Fig. 2. Same treatment as Fig. 1, except that GA4÷v was replaced by G A 3 2000 mg/l. Note that 8 bulbs emerged and elongated, but no flower differentiation occurred.

259 with GA4 +7, also stimulated earlier flowering and more floral buds as compared to other treatments. In combination with both GA treatments, stem length was reduced by BA. DISCUSSION Results presented here support the findings of Ohkawa {1976, 1977) and others that low-temperature storage of bulbs is required to break dormancy and induce flowering in Lilium speciosum. The mechanism of overcoming dormancy and of floral induction by low-temperature storage is not known. A hormonal relationship has been proposed by others. In Lilium longiflorum, Laiche and Box (1970, 1973) and Lin et al. (1975) reported that treatment of bulbs with GA3 (1000 mg/1) partially substituted for low temperature. Bulbs that were partially dormant (untreated controls emerged) responded to GA3 application by producing shoots at a faster rate than the controls. GA3 shortened the time to reach anthesis. Results presented here suggest that completely and partially dormant bulbs of £ilium speciosum may be stimulated by GA4 *7 and GA4 ÷7 + BA to overcome dormancy and induce flowering. GA3 and BA alone were effective only with partially chilled bulbs, thus supporting the work of the others. The fact that differences in response to the different GA treatments occurred, indicates that several GA's may be involved in overcoming dormancy and inducing flowering in Lilium spp. Either one or more specific GA's are sufficient to trigger the entire sequence of events, or possibly several GA's are involved and required in a sequential order to overcome dormancy and stimulate flowering. Research on floral induction in other plants supports the findings that several GA's are involved in promoting flowering under non-inductive conditions. This response varies among the various plant species (Michniewicz and Lang, 1962). In Myosotis, flower formation was obtained with GA7 and GA1 only, the latter being less effective. In Silene, flowering was induced by GA 7 only, and in Bryophyllum GA3, GA4 and GA 7 were the most effective. The interaction of GA and BA in stimulating flowering in Litium spp. has not been reported previously. In chrysanthemums, Pharis (1972) showed that GAs and BA combinations were most effective in inducing flowering. Combination with GA3 was not as effective. The production of more floral buds by BA application may have practical significance. Although my studies are still preliminary, they suggest that BA may be involved in stimulating floral production. ACKNOWLEDGEMENTS I thank Dr. H. Suge, Associate Professor of Tohhoku University, and Dr. L.H. Fuchigami, Associate Professor of Oregon State University, for helpful comments on the manuscript.

260 REFERENCES Laiche, A.J. and Box, C.O., 1970. Response of Easter lily to bulb treatments of precooling packing media, moisture, and gibberellin. HortScience, 5: 396--397. Laiche, A.J. and Box, C.O., 1973. Response of lilies to gibberellic acid. MAFES Res. Highlights, 36(6): 8. Lin, W.C., Wilkins, H.F. and Angell, M., 1975. Exogenous gibberellins and abscisic acid effects on growth and development of Lilium longiflorum. J. Am. Soc. Hortic. Sci., 100: 9--16. Michniewicz, M. and Lang, A., 1962. Effect of nine different gibberellins on stem elongation and flower formation in cold-requiring and photoperiodic plants grown under non-inductive conditions. Planta, 58: 549--563. Ohkawa, K., 1976. The role of gibberellins in shoot emergence and elongation, flower differentiation and development of Lilium speciosum rubrum. J. Jpn. Soc. Hortic. Sci., 45: 289--299. Ohkawa, K., 1977. Studies on the physiology and control of flowering in Lilium speciosum rubrum. Kanagawa Hortic. Exp. Stn. Special Bull., 73 pp. Pharis, R.P., 1972. Flowering of chrysanthemum under non-inductive long days by gibberellins and N6-Benzyladenine. Planta, 105: 205--212. Wilkins, H.F., Waters, W.E. and Widmer, R.E., 1967. Influence of temperature and photoperiod on growth and flowering of Easter lilies(Lilium longiflorum 'Georgia', 'Ace' and 'Nellie White'). Proc. Am. Soc. Hortic. Sci., 93: 640---649.