The effect of GA3-application on growth and flowering of liatris

Scientia Horticulturae, 19 (1983) 343--348

343

Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

THE EFFECT OF GA3-APPLICATION ON GROWTH AND FLOWERING OF LIATRIS

L.W. WANJAO' and KIMANI WAITHAKA

Department of Crop Science, Faculty of Agriculture, University of Nairobi (Kenya) Present address: Horticultural Crops Development Authority, Uniafric House, P.O. Box 42601, Nairobi, Kenya (Accepted for publication 22 March 1982)

ABSTRACT Wanjao, L.W. and Waithaka, K., 1983. The effect of GA3-application on growth and flowering of liatris. Scientia Hortic., 19: 343--348. The effect of gibberellic acid (GA3) on breaking corm-dormancy, growth and flowering of Liatris spicata L. cultivar 'Gloriosa' (gay-feather) was investigated. GA3 could be substituted for the cold requirement in breaking corm-dormancy and promoting earlier flowering, but it did not promote the elongation of the floral stalks. The combined effect of GA 3 and cold treatment led to earlier flowering and more inflorescences than either treatment given alone. GA3-application after the corms had received the cold treatment resulted in fewer, but more marketable infloreseences than when the application was done before the cold treatment.

INTRODUCTION

Liatris corms require chilling for dormancy release, shoot growth and early flowering. Dry storage of the corms at 3--5°C for 8 or more weeks and then forcing them outdoors at 21--25°C led to rapid flowering, more uniformedsized flowers and acceptably long floral stalks (Waithaka and Wanjao, 1982). Similar findings have been reported for tulip, hyacinth and gladiolus (Tsukamoto, 1954; Rees, 1969; Lin and Wilkins, 1975). Van Bragt and Zijlstra (1971) found that gibberellins injected into dry bulbs at planting reduced the time to flowering, an effect similar to that of cold treatment. They also found that gibbereUins did n o t compensate for reduced scape elongation resulting from unsatisfactory low-temperature treatment. Cocozza and Caputo (1980) also found that the combined effect of cold treatment and GA3 induced earlier flowering than could be obtained by cold treatment alone. With the increasing demand for liatris cut flowers in Kenya, this study was conducted to investigate the effect of GA3 on the breaking of corm-dormancy, shoot growth and flowering.

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© 1983 Elsevier Science Publishers B.V.

344 MATERIAL AND METHODS Uniform-sized liatris corms, 3 cm in diameter, of 'Gloriosa' were selected. The previous season's daughter corms split from the old m o t h e r corms were washed and soaked in b e n o m y l solution (1.5 g 1-1) for 30 min. They were then allowed to drip dry at room temperature for 4 days. Commercial GA3 (90%) was first dissolved in 3 ml of 80% ethanol, and then made up to the required concentrations of 5 0 , 1 0 0 , 2 5 0 and 500 mg 1-1 with water. The corms receiving GA3 treatment were soaked in GA3 solutions for 15 h at room temperature (23°C). Some corms were treated with 250 mg 1-I, either before or after cold treatment, to investigate the influence of the time of GA3 application on growth and flowering. Those corms receiving cold treatment were dry-stored in polythene bags in a cold chamber at 3--5°C for 4 or 8 weeks. All the corms were removed from the low temperature and planted outdoors on the same date. Control corms were neither subjected to low-temperature treatment nor were they GA3-treated. The corms were planted at a spacing of 25 cm between rows and 10 cm within rows. Experimental plots measured 1.00 × 1.25 m. Factorial experiments were laid o u t in a randomized complete block design. Every treatment combination was replicated 3 times. Sixty corms were used for every treatment. Data were collected from 30 corms and the rest served as guard rows. RESULTS growth. - - GA3-application to chilled and unchilled dormant corms prom o t e d complete shoot emergence at all levels. The time of GA3 application at 250 mg 1-1 (before or after cold treatment) did n o t affect the % shoot emergence (Table I). GA3-application on chilled and unchilled corms p r o m o t e d early and high shoot emergence irrespective of the time of application. GA3-application on unchilled d o r m a n t corms substituted for cold treatment in promoting the production of vegetative shoots. The combined effect of GA3-application and cold treatment p r o m o t e d more vegetative shoots than the number produced b y either treatment alone (Table II). GA3 applied to the corms before cold treatment p r o m o t e d greater production of shoots than when the application was done after cold treatment (Table I).

Shoot

- - GA3-application alone p r o m o t e d flowering at all concentrations (Table II). The number of inflorescences increased with increasing duration of cold treatment and GA3 concentration (Table II). The combined effect of GA 3 and cold treatment on the production of inflorescences was even greater than either of the treatments given alone (Table II). GA3-application to the corms before cold treatment resulted in production of more inflorescences than when the application was done after cold treatment (Table I). Increasing GA3 concentration did n o t increase the % o f marketable inflorescences (i.e. those above 30 cm) (Table II). GA3-application did not substitute for cold

Flowering.

345 TABLEI The influence of the time of GA 3 application on shoot emergence, flowering, marketability of the inflorescences, and the period from corm planting to flower-cutting time (days) of liatris; percentages transformed to arcsin. Mean separation within comparable means for every parameter by Duncan's multiple range test, 5% level Parameters

Period of cold treatment (weeks)

No GA3

Time of GA3 application (250 mg 1-l) Before cold After cold treatment treatment

% sprouted corms

4 8

56.8 a 90.0 b

90.0 b 90.0 b

90.0 b 90.0 b

Total number of shoots out of 30 corms

4 8

43.3 a 65.3 b

84.3 d 112.7 e

63.3 b 75.7 c

% corms with flowering shoots

4 8

37.3 a 90.0 b

90.0 b 90.0 b

90.0 b 90.0 b

Total number of inflorescences out of 30 corms

4 8

16.0 a 52.3 b

76.3 d 98.0 e

56.7 b 69.0 c

% marketable inflorescences

4 8

61.3 b 83.5 c

42.0 a 55.2 b

56.1 b 81.4 c

Average length of marketable inflorescences (cm)

4 8

44.4 b 50.1 c

38.6 a 42.4 b

43.4 b 51.5 c

Period from corm planting to flower-cutting time (days)

4 8

80 76

94 86

104 98

f e

b a

d c

t r e a t m e n t in p r o m o t i n g floral stalk e l o n g a t i o n because t h e l e n g t h o f m a r k e t able inflorescences decreased w i t h increasing GA3 c o n c e n t r a t i o n (Table II). GA3-application t o t h e c o r m s after cold t r e a t m e n t p r o m o t e d p r o d u c t i o n o f m o r e and l o n g e r inflorescences t h a n w h e n t h e a p p l i c a t i o n was d o n e b e f o r e cold t r e a t m e n t (Table I). GA3 also r e d u c e d t h e p e r i o d f r o m c o r m p l a n t i n g t o f l o w e r - c u t t i n g t i m e (Table II). DISCUSSION D o r m a n c y o f m a n y resting organs is t e r m i n a t e d b y t r e a t m e n t with chillingt e m p e r a t u r e s o f 3 - - 5 ° C (Vegis, 1 9 6 4 ) . A d e q u a t e l o w - t e m p e r a t u r e t r e a t m e n t released liatris c o r m s f r o m d o r m a n c y and p r o m o t e d earlier and h i g h e r s h o o t e m e r g e n c e ( W a i t h a k a and Wanjao, 1 9 8 2 ) . Vegis ( 1 9 6 4 ) suggested t h a t active b u d g r o w t h was p r e v e n t e d b y either a d e f i c i e n c y o f e n d o g e n o u s g r o w t h prom o t e t s or by t h e p r e s e n c e o f inhibitors. GA3-application o n unchilled lily, tulip a n d h y a c i n t h b u l b s and gladiolus c o r m s was r e p o r t e d t o b r e a k b u d d o t -

346 TABLE II The effect of cold treatment and GA3 on the total number of shoots and inflorescences out of 30 corms, the % marketable inflorescences (percentages transformed to arcsin), the average length of marketable inflorescences (cm) and the period from corm planting to flower-cutting time (days) of liatris. Mean separation within comparable means for every parameter b y Duncan's multiple range test, 5% level Period o f cold treatment (weeks)

GA 3 concentration (mg 1-1 ) 0

50

100

250

500

Total number of shoots out of 30 corms 0 4 8

5.3 a 45.7 c 73.3 fg

30.7 b 67.7 e 74.3 fg

55.0 d 78.0 g 90.0 i

71.7 ef 86.3 hi 104.0 j

82.7 gh 88.7 i 106.7 j

Number of inflorescences out of 30 corms 0 4 8

0.0 a 11.6 b 53.0 e

11.7 b 40.7 d 54.0 e

28.7 c 60.3 f 78.7 h

55.7 e 73.0 gh 96.3 i

69.7 g 78.0 h 102.0 j

21.1 b 42.4 d 55.5 fg

21.0 b 39.0 d 53.2 f

% marketable inflorescences 0 4 8

0.0 a 57.4 g 79.8 i

28.8 c 47.3 e 68.4 h

24.6 b 49.0 e 59.7 g

Average length of marketable inflorescences (cm) 0 4 8

0.0 a 39.4 cde 39.0 cde 43.4 gh 42.6 fg 41.8 efg 50.1 j 46.6 i 45.8 hi

37.9 bcd 40.4 def 44.4 ghi

36.2 b 36.9 bc 40.3 def

Period from corm planting to flower-cutting time (days) 0 4 8

-109 98

g f

98 95 90

f e d

94 90 86

e d c

89 85 81

cd c b

82 80 76

b b a

mancy and promote shoot emergence, while abscisic acid inhibits shoot emerg e n c e i n c h i l l e d l i l y b u l b s ( T s u k a m o t o a n d K o n o s h i m a , 1 9 7 2 ; L i n e t al., 1 9 7 5 ; V a n B r a g t a n d V a n A s t , 1 9 7 6 ; S a n i e w s k i e t al., 1 9 7 7 ) . O u r f i n d i n g s t h a t G A 3 application on unchilled liatris corms promoted the breaking of bud dormancy and shoot emergence are in agreement with earlier reports on other bulbous and cormous plants. A combination of cold treatment and GA3-application promoted even earlier and greater shoot emergence than either treatment alone. The requirement of low-temperature treatment by bulbous and cormous

347 plants for floral induction and development has been reported by various workers (Gill et al., 1957; Rees, 1969; Lin and Walkins, 1975; Waithaka and Wanjao, 1982). In some plant species, the cold requirement for flower induction and initiation can be replaced by exogenously applied GA (Lang, 1957). Van Bragt and Zijlstra (1971) similarly reported t h a t gibberellins injected into dry non-chilled tulip bulbs p r o m o t e d flower development and early flowering. Similar findings were reported by Saniewski et al. (1977) and Van Bragt and Van Ast (1976). These workers also demonstrated t h a t GA3 partially substituted for the chilling-requirement because of the production of shorter floral stems. GA3 substituted for cold requirement in flower initiation in liatris, but only partially in the elongation of the floral stems. It follows that flower initiation and growth of the floral shoots are independent processes which both require low-temperature treatment. The combined effect of cold treatment and GA3-application induced greater and earlier flowering t h a n cold t r e a t m e n t alone, but the inflorescences were still n o t as long as those produced when the corms had received 8 weeks of cold treatment alone. This resulted in production of m a n y unmarketable inflorescences and the marketable ones were of the lowest grade. GA3 enhanced earlier flowering and the inflorescences were ready for cutting before they had grown fully to a marketable size. Probably GA3-application before cold treatment or treating unchilled corms with GA3 interferes with or retards the synthesis and build-up of other growth-promoting substances or their precursors, which are directly triggered by adequate cold treatment. Since GA3-application after cold t r e a t m e n t p r o m o t e d production of inflorescences more than cold treatment alone, it would mean that there are more marketable inflorescences produced when the corms are GA3-treated after cold treatment. ACKNOWLEDGEMENTS The authors wish to acknowledge the Agricultural Development Corporation, Kenya, for supplying them with the experimental site and the plant material. Their gratitude and appreciation is extended to Mr. G.N. Kamau and Mr. G.N. Macharia for their technical assistance. REFERENCES Cocozza, T.M. and Caputo, V., 1980. A research on the possibility of using gibbereUin for tulip forcing. Acta Hortic., 109: 163--167. Gill, D.L., Beijer, J.J., Stuart, N.W. and Gould, C.J., 1957. Some effects of bulb storage temperatures and planting conditions on production of tulip flowers in the greenhouse and outside in southern Georgia. Proc. Am. Soc. Hortic. Sci., 70: 451--460. Lang, A., 1957. The effect of gibberellin upon flower formation. Proc. Natl. Acad. Sci., U.S.A., 43: 709--717. Lin, W.C. and Wilkins, H.F., 1975. Influence of bulb harvest dates and temperature treatments on the growth and flowering of Lilium longiflorum Thumb. cv. 'Nellie White'. J. Am. Soc. Hortic. Sci., 100: 6--9. 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.

348 Rees, A.R., 1969. Effects of duration of cold treatment on the subsequent flowering of tulips. J. Hortic. Sci., 44: 27--36. Saniewski, M., Nowak, J. and Rudnicki, R.M., 1977. The physiology of hyacinth bulbs. XI. The effect of gibberellic acid on the growth and flowering of variously chilled bulbs. Scientia Hortic., 7 : 179--184. Tsukamoto, Y., 1954. Dormancy of gladiolus. I. Temperature treatment for the breaking of dormant gladiolus corms and its reaction to tetrazolium. J. Hortic. Assoc. Jpn., 23: 16--20 (in Japanese with English summary). Tsukamoto, Y. and Konoshima, H., 1972. Changes in endogenous growth regulators in gladiolus corm during dormancy. Physiol. Plant., 26: 244--249. Van Bragt, J. and Van Ast, K.J., 1976. Substitution of the cold requirement of tulip cv. 'Apeldoorn' by GA 3. Scientia Hortic., 4: 117--122. Van Bragt, J. and Zijlstra, F.A., 1971. Effects of gibberellins on flowering of tulip cv. 'Apeldoorn'. Z. Pflanzenphysiol., 64: 139--144. Vegis, A., 1964. Dormancy in higher plants. Annu. Rev. Plant Physiol., 15: 185--224. Waithaka, K. and Wanjao, L.W., 1982. The effect of duration of cold treatment on growth and flowering of liatris. Scientia Hortic., 18: 153--158.