Effect of Temperature and Daylength on Flowering of Early Flowering Gladiolus

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1 Effect of Temperature and Daylength on Flowering of Early Flowering Gladiolus Hideo Imanishi, Yukiko Imae, Eiichi Kaneko and Shigeyuki Sonoda College of Agriculture Osaka Prefecture University 1-1, Gakuen-cho, Sakai, Osaka Japan Keywords: Chilling, cultivars with different pedigrees, daylength, early (spring) flowering gladiolus, flowering Abstract Early flowering gladiolus initiates flower buds when the first leaf has expanded after planting. In Bride, Robinetta, Impressive, Charming Beauty and Elvira flowering was accelerated and number of leaves at flowering was decreased by exposing corms to chilling at 6-10 C for 6 weeks under dry or wet conditions. In Elvira and Charming Beauty days to flowering after planting was decreased by chilling corms before planting, but actual flowering date was advanced by planting corms earlier without chilling. Long day treatment by extending natural daylight to 16 hours accelerated flowering in Bride, Robinetta and Impressive, especially when applied to chilled corms of Bride and Robinetta. However, the promotive effect was not observed in Elvira, Charming Beauty and Comet. Early flowering gladiolus cultivars with different pedigrees were classified into 3 groups by their response to temperature and daylength. INTRODUCTION Early (spring) flowering gladioli are semi-hardy cormous plants. They are planted in the fall, bloom in the spring, and rest in the summer. They have been given botanical names such as G. x colvillei, G. x nanus etc. If cited from International Checklist for Hyacinths and Miscellaneous Bulbs (1991), G. x collvillei hybrids were produced in England in 1823 by hybridizing G. cardinalis and G. tristis. G. x ramosus was produced before 1839, by hybridization of (G. cardinalis x G. carneus) x G. oppositiflorus. Anderton and Park (1989) showed another possibility that G. x ramosus is obtained by crossing of G. cardinalis with G. blandus (= G. carneus). G. x tubergenii is a listed name of no botanical standing for a hybrid of (G. carneus x G. oppositiflorus) x G. liliaceus. G. x nanus has been retained as a garden name for a group of dwarf growing early flowering cultivars. This nanus hybrids are known to be produced in the middle of the 19 th century by hybridizing G. cardinalis and G. scullyi, and later further hybridizing with G. tristis and G. carneus (Everett, 1981). G. x Herald is derived from hybridization between G. x nanus and G. x childsii (summer flowering type) (Le Nard and de Hertogh, 1993). The aim of this study was to test the response to chilling and daylength of several cultivars with different pedigrees and to compare their response. MATERIALS AND METHODS Cultivars used for this study were as follows: Bride (G. x colvillei), Robinetta (G. x ramosus), Amanda Mahy and Impressive (G. x nanus), Charming Beauty (G. x tubergenii), Comet (G. x Herald) and Elvira. Elvira was produced by hybridization of Nymph (G. x nanus) and G. x Herald seedling. Exp. 1. Progress of Flower Bud Formation Corms of Bride (2-4g) and four other cultivars (Robinetta, Amanda Mahy, Elvira, Charming Beauty) were planted on 22 September in an unheated plastic house. Eight to ten plants of Bride were sampled at 4 weeks intervals to determine the development of flower Proc. 8th Int. Symp. on Flowerbulbs Eds. G. Littlejohn et al. Acta Hort. 570, ISHS

2 buds by dissection under the microscope. On 18 December, plants of all cultivars were sampled. Exp.2. Effects of Growing Temperature on Flowering On 17 September, corms of Bride (3-6g) and Elvira (8-12g) were planted 4 each in 21 cm pot. After sprouting, they were moved to growth chambers maintained at C, C and C and grown under 50% shade of natural daylight. Flowering data were taken when the first floret showed color. Data were recorded for flowering date, length of cut flower and leaf, and number of florets per spike and leaves. Exp.3. Effects of Chilling and Daylength on Flowering 3.1 Corms of Bride were exposed to chilling at 1, 6, or 10 C for 6 weeks under wet or dry conditions. They were planted in a pot on 29 October and moved to a glasshouse maintained at minimum 13 C. In another experiment, corms of Elvira were exposed to chilling at 10 C for 0, 2, 4, and 6 weeks under dry condition and planted on 5 September in a house maintained at minimum 5 C. 3.2 Corms of Elvira and Bride were planted on 17 September in a bed of an unheated plastic house ( 3-25ºC) and those chilled at 10ºC for 6 weeks under wet condition were planted on 29 October. Half of the chilled and non-chilled plants were kept under natural short day (ND) conditions of the winter ( hours) and other half received long day (LD) conditions. Long day treatment started on 1 December and was given by extending natural daylength to 16 hours with incandescent lamps giving 100 lux or more at plant level. 3.3 Chilled or non-chilled corms of Comet, Charming Beauty, Robinetta and Impressive were planted in a pot on 20 October. Chilling was given at 10 C dry for 6 weeks. Plants were moved to a glasshouse maintained at min. 10ºC. Half of the plants were subjected to long day conditions as described in Experiment 3.2. RESULTS Exp.1. Progress of Flower Bud Formation Eight to ten plants sampled were divided into 2 groups according to their shoot growth for presentation of observed results in Fig. 1. All plants of Bride were vegetative on 20 November, when they had just emerged. New leaves had not expanded till early February of the next year. On 18 December, apical meristem was enlarged in the plants having the first leaf of 10 to 20 cm in length. Two to three florets initiated and bracts of the first floret were visible in the plants having the first leaf of 20 to 30 cm. The primordia of the outer and inner tepals of the first floret appeared on 14 January and carpel primordia were formed on 10 February. The pollen mother cells were formed on 13 March and the pollen became mature and functional on 18 April. The plants bloomed on 8 May. The initiation and development of flower buds was faster in Elvira and Charming Beauty than in Robinetta, Bride and Amanda Mahy when compared on 18 December ( Fig. 2). Charming Beauty and Elvira bloomed in mid-april, whereas other cultivars bloomed in early to mid May. Exp.2 Effects of Growing Temperature on Flowering In Bride, flowering occurred on 26 April at C, but flowering time was delayed and more leaves were formed at C as compared to the plants grown in an unheated plastic house (Table 1). At C flower buds were not initiated. Elvira flowered at any temperature and earlier when grown at C. Exp.3. Effects of Chilling and Daylength on Flowering 3.1 Chilling at 6 and 10 C for 6 weeks under wet or dry conditions caused an earlier flowering, but chilling at 1 C had no promotive effects (Table 2). Difference of cut flower quality was not observed among lots, though the number of leaves decreased in the chilled lots. In Elvira flowering was accelerated and number of leaves decreased with increasing duration of chilling at 10 C (Fig. 3). 438

3 3.2 In Bride chilling at 10 C wet for 6 weeks resulted in earlier flowering also under unheated growing conditions (Table 3). Long day caused a little earlier flowering. In Elvira chilling reduced days from planting to flowering and number of leaves, but earlier planting resulted in earlier actual flowering date. Long day did not affect flowering time but increased flowering percentage a little. 3.3 Chilling at 10 C dry for 6 weeks caused earlier flowering and reduced number of leaves in Charming Beauty, Robinetta and Impressive (Table 4). On the contrary, in Comet chilling did not advance flowering and reduced flowering percentage under natural short daylength. Chilling caused a decrease in number of florets except for Impressive. Long day accelerated flowering in Robinetta and Impressive. Especially in the chilled corms of Robinetta, a strong accelerating effect was obtained. Flowering of Charming Beauty was not affected by daylength in the non-chilled corms, but long day delayed flowering time in the chilled corms. In Comet, long day treatment increased flowering percentage and delayed flowering time. DISCUSSION Initiation of flower buds occurred in late fall to early winter after planting as in Dutch iris (Sano, 1961) and freesia (Kosugi, 1953). In Elvira and Charming Beauty flower buds initiated earlier than in Bride, Robinetta and Amanda Mahy as shown in Fig. 2. Elvira flowered at 25-25ºC and Comet or Charming Beauty flowered at 30-25ºC (Hosoki et al, 1986a). From these results it is concluded that these three cultivars do not require low temperature for flower bud initiation. In Elvira earlier planting advanced actual flowering date and similar results were obtained in Charming Beauty (data are not shown) and Comet (Hida, 1970). On the contrary, Bride flowered at 20-17ºC or 20-20ºC (Hosoki et al, 1986a) and Robinetta flowered at 20-20C (Hosoki et al, 1986a). However, flowering time was delayed by 46 days at 20-17ºC as compared with plants grown at 15-12ºC. In G. tristis, one of the parents of Bride, corms stored at 5ºC for 3 or 6 weeks flowered 20 and 11 days, respectively, before the controls (Gonzalez et al, 1998). These results suggest that flowering of Bride occurs without low temperature but is accelerated by exposing to low temperature. This suggestion was supported by exposing corms to low temperature before planting (chilling). Chilling at 6-10ºC for 6 weeks under wet or dry conditions was effective for accelerating flowering in all cultivars except for Comet. Hosoki et al (1986a) reported that flower bud initiation and development of Charm, Robinetta and Bride were promoted by chilling, whereas those of Elvira and Comet were not. Only Elvira showed different results, though the planting conditions were not comparable. In summer flowering gladiolus, long day treatment by supplemental low intensity illumination greatly reduces the incidence of flower bud blasting in winter and improve flower quality although flowering time is delayed (Shillo et al, 1981; Imanishi and Imae, 1990). Almost the same results were obtained in Comet. In Charming Beauty and Elvira the effect of long day was hardly observed. In Charm and Rose charm, similar results were obtained (Shillo et al, 1981). On the contrary, long day was apparently effective for advancing flowering in Bride, Robinetta and Impressive. This was contrary to the result that most of G. x nanus cultivars including Elvira and Nymph were not sensitive to photoperiod (Halevy et al, 1984). Elvira is grouped into G. x nanus. It seems likely that response to daylength differs among cultivars belonging to G. x nanus. The results obtained were summarized in Table 5. Comet (G. x Herald) showed almost the same responses to low temperature and daylength as summer-flowering gladiolus probably because G. x Herald was produced by crossing with G. x childsii which is one of the summer-flowering strains. Elvira which was produced by hybridizing Nymph (G. nanus) and G. x Herald showed responses close to Comet, but flowering was accelerated by chilling. The promoting effect of chilling was probably derived from Nymph, because Impressive (G. x nanus) was sensitive to chilling. Charming Beauty (G. x tubergenii) was very close to Elvira in the response to chilling and daylength, although their genetical background differs. Bride (G x colvillei), Robinetta (G. x ramosus) and Impressive (G x nanus) were very similar in their 439

4 responses to temperature and daylength and differed from other three cultivars. Only a relatively small number of species was involved in the development of the early 19th century hybrids, G. x colvillei, G. x robinetta and G. x nanus and all of the species involved are endemic to the Cape region of South Africa with Mediterranean climate (Goldblatt and Manning, 1998). However, G. x tubergenii Charming Beauty differed from the early 19th century hybrids in the response to temperature and daylength, though all species involved in the development of this pedigree are also endemic to Cape region. This might be an indication that the parental species of G.x tubergenii are different from those shown in International Checklist for Hyacinthus and Miscellaneous Bulbs (1991). It was described that G. x tubergenii was derived from a crossing of G. x Herald with G. tristis var. concolor (Hosaka, 1950) or from a crossing of G. x ramosus with G. x Herald (Geelhaar and Tornier, 1967). These parentages correspond better with the observed results. In conclusion, early (spring) flowering gladioli could be classified into 3 groups by their response to temperature and daylength: a typical spring flowering type, Bride (G. x colvillei), Robinetta (G. x ramosus) and Impressive (G. x nanus), an intermediate type, Charming Beauty (G. x tubergenii) and Elvira (G. x nanus x G. x Herald), and a summer flowering type, Comet (G. x Herald). This grouping is similar to the grouping based on morphological, ecological and biochemical data by Hosoki et al (1986a, b), though the grouping of Elvira differs. Literature Cited Anderton, E.W. and Park, R Growing Gladioli, pp Timber Press, USA. Everett, T.H The New York Botanical Garden Illustrated Encyclopedia of Horticulture. Vol. 5, pp Garland Pub., N.Y. Geelhaar, H. and Tornier, I Die Gladiole - Kultur, Züchtung, Pflanzenschutz, pp VEB Deutscher Landwirtschaftsverlag, Berlin. Goldblatt, P. and Manning, J Gladiolus in South Africa. pp Fernwood Press, Vlaeberg. González, A., Bañón, S., Fernández, J.A., Franco, J.A., Casas, J. L. and Ochoa, J Flowering response of Gladiolus tristis (L.) after exposing to cold treatment. Scientia Hortic. 74: Halevy, A.H., Kofranek, A.M., and Besemer, S.T Photoperiodic response of miniature gladiolus cultivars. HortScience 19: Hida, K Cultivation of autumn planting (spring flowering) gladiolus. Nogyo oyobi Engei 45: (In Japanese). Hosaka, H Gladiolus. In: Y. Ishii, ed., Encyclopedia of Horticulture vol. 2, pp Seibunndo-shinkousha, Tokyo. (in Japanese) Hosoki, T., Terabayashi, S., and Asahira, T. 1986a. Ecological classification of spring-flowering gladiolus. J. Japan. Soc. Hort. Sci. 55: (in Japanese with English summary). Hosoki, T., Terabayashi S., and Asahira T. 1986b. Morphological and biochemical classification of spring-flowering gladiolus and the relationship between major cultivars. J. Japan. Soc. Hort. Sci. 55: (in Japanese with English summary). Imanishi, H., and Imae, Y Effects of low light intensity and low temperature given at different developmental stages on flowering of gladiolus. Acta Hort. 266: Kosugi, K Studies on the flower bud differentiation and development in the freesia I.. On the time of flower bud differentiation and process of flower bud development. J. Japan Soc. Hort. Sci. 22: (in Japanese) Le Nard, M., and De Hertogh, A.A Plant breeding and genetics. In: M. Le Nard and A.A. De Hertogh, eds., The Physiology of flower bulbs, pp. Elsevier, London. Sano, Y., Hayashi, Y., Takatsuki, K., and Osada, K On the flower bud differentiation and development of bulbous iris in Japan. Tech. Bull. Fac. Agri., Kagawa Univ. 13: (in Japanese with English summary) Shillo, R., Valis, G. and Halevy, A.H Promotion of flowering by photoperiodic lighting in winter-grown gladiolus planted at high densities. Scientia Hortic. 14: Van Scheepen, J. (ed.) International Checklist for Hyacinths and Miscellaneous Bulbs, pp. 440

5 Tables Royal General Bulbgrowers Association, Hillegom, The Netherlands. Table 1. Effect of growing temperature on flowering of Bride and Elvira. Cultivars Day-night Flowering Date of Days to Length of No. of temp. flowering flowering cut flower leaf leaves florets ( C) (%) (cm) (cm) Bride Apr Jun Elvira Mar Jan Feb Corms were planted on 17 Sept. and grown under 50% shade. Table 2. Effects of temperature and moisture during chilling on flowering of Bride. Chilling Flowering Days to Length of No. of moisture temperature (%) flowering cut flower leaf florets leaves flowered ( C) (cm) (cm) inflorescences wet dry wet room (cont.) Corms were planted on 29 Oct. and grown at min. 13 C. 441

6 Table 3. Effects of chilling and daylength on flowering of Bride and Elvira. Cultivars Chilling Date of Day Flowering Length of No. of Planting length percent date cut flower leaf leaves florets flowered (cm) (cm) inflorescences Bride No Sep. 17 ND 100 May No Sep. 17 LD 100 May Yes Oct. 29 ND 100 May Yes Oct. 29 LD 100 Apr Elvira No Sep. 17 ND 81 Mar No Sep. 17 LD 94 Mar Yes Oct. 29 ND 80 Mar Yes Oct. 29 LD 100 Mar Corms were chilled wet at 10 C for 6 weeks. Plants were grown in an unheated plastic house. Long day (LD) treatment starting on 1 Dec. was given by extending natural daylength (ND) to 16 hr. Table 4. Difference in response to chilling and day-length among four cultivars. Cultivars Chilling Daylength Flowering Days to No. of No. of (%) flowering leaves florets Comet No ND (x Herald) Yes ND No LD Yes LD Charming No ND Beauty Yes ND (x tubergenii) No LD Yes LD Robinetta No ND (x ramosus) Yes ND No LD Yes LD Impressive No ND (x nanus) Yes ND No LD Corms were chilled dry at 10 C for 6 weeks. Corms were planted on 20 Oct. and grown at min. 442

7 10 C. Long day (LD) was given by extending natural daylength (ND) to 16 hr. 443

8 Table 5. Summary of the results obtained by authors and other researchers (Hosoki et al. 1986). Pedigrees Cultivar Flowering Advanced Accelerated Accelerated above flowering flowering flowering 25 C by early by chilling by long day planting G. x Herald Comet Yes Yes No No G. x nanus Nymph Elvira Yes Yes Yes No x G. x Herald G. x tubergenii Charming Yes Yes Yes No Beauty G. x ramosus Robinetta No No Yes Yes G. x nanus Impressive No No Yes Yes G. x colvillei Bride No No Yes Yes Figurese (see next pages) Fig. 1. developmental stages of flower buds of Bride plants grown in an unheated plastic house. Corms were planted on 22 Oct. The dots indicate the number of plants at each stage. Flower bud stage : I, vegetative stage; II, apical meristem enlarging; III, bract differentiation; IV, three-primordia stage of the first floret; V, outer tepal and stamen differentiation; VI, inner tepal differentiation; VII, three carpel differentiation, VII, mother cell of pollen formed; IX, pollen become mature and functional. Fig. 2. Difference of flower bud formation among cultivars. Corms were planted on 22 Oct. and grown in an unheated plastic house. Ten plants were used for observation on 18 Dec. The dots indicate the number of plants at each stage. Flower bud stage: see Figure 1. Fig. 3. Effects of chilling duration on flowering of Elvira. Corms were chilled at 10 C under dry condition and planted on 5 Sep. in a house maintained at min. 5.?, Days to flowering;?, Number of leaves. 444

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