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Effect of gibberellic acid on growth and flowering of Henckelia humboldtianus Gardner (Ceylon Rock Primrose)
Scientia Horticulturae 159 (2013) 29–32
Contents lists available at SciVerse ScienceDirect
Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti
Short communication
Effect of gibberellic acid on growth and flowering of Henckelia humboldtianus Gardner (Ceylon Rock Primrose) H. Sumanasiri a , S.A. Krishnarajah b , J.P. Eeswara a,∗ a b
Department of Crop Science, Faculty of Agriculture, University of Peradeniya, Sri Lanka Royal Botanic Garden, Peradeniya, Sri Lanka
a r t i c l e
i n f o
Article history: Received 8 October 2012 Received in revised form 20 April 2013 Accepted 23 April 2013 Keywords: Henckelia humboldtianus Gibberellins (GA3 ) Regulation of growth and flowering
a b s t r a c t Henckelia humboldtianus Gardner (Ceylon Rock Primrose), an endemic species to Sri Lanka, is a potential new flowering potted plant. This study investigated the role of gibberellins (GA3 ) in controlling vegetative growth and flowering of H. humboldtianus plants. H. humboldtianus plantlets, micropropagated using leaf pieces, were treated with 25 ml of GA3 (0, 50, 100, or 200 mg l−1 ) four weeks and six weeks after transplanting to pots containing a soil mix of sand, top soil and coir dust at a 1:1:1 ratio. GA3 treatment resulted in a progressive decrease in the time to flowering with increase concentration. Plants treated with 200 mg l−1 GA3 exhibited early flowering (10.0 ± 0.5 days), highest number of inflorescences per plant (10.9 ± 1.8) and highest number of flowers per inflorescence (24.0 ± 0.5) compared to all the other treatments. All GA3 treatments increased the peduncle length, plant height and petiole length providing a better appearance as a potted plant compared to the untreated plants. Results suggest that GA3 can be used to improve the flowering behavior and enhance the appearance of H. humboldtianus for the marketing process as a newly introduced species. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Henckelia humboldtianus (Gardner) A. Weber and B.L. Burtt (Webber et al., 2000) (Synonym Didymocarpus humboldtianus Gardner, Ceylon Rock Primrose, Dassanayake and Forseberg, 1981), belongs to the family Gesneriaceae, is a new species with potential as a flowering potted plant. Earlier, this species was described in the genus Didymocarpus, a large genus comprising at least 70 species, distributed from NW India eastwards through Nepal, Bhutan, NE India, Burma, South China, South Vietnam, Thailand, Malay Peninsula and Sumatra. Later it was categorized under the re-established genus Henckelia Spreng (Webber et al., 2000). H. humboldtianus is an endemic species, which is commonly found in the montane forests at elevation of 1700 m in the Knuckles range in Sri Lanka. This species is a perennial herb, has numerous velvety crinkled, pale green leaves which are arranged very near to the soil surface at the base of the plant making a rosette and produce several inflorescences per plant. Flowers are bell shaped with five unequal petals and color varies from pale violet to almost white with yellow in the throat (Dassanayake and Forseberg, 1981). Fruits, consisting of a linear capsule, dehisce along one side, contain small elliptical seeds. In natural habitats H. humboldtianus regenerates
∗ Corresponding author. Tel.: +94 812395103; fax: +94 812395110; mobile: +94 718095100. E-mail addresses: [email protected], [email protected] (J.P. Eeswara). 0304-4238/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scienta.2013.04.021
mainly by seed. Flowering shoots are annual (monocarpic) or seasonal and die after fruiting or during unfavorable environmental conditions. At the same time initiation of the next year’s flowering shoots appear with few young leaves at the base of the plant. When favorable conditions return, shoots and leaves expand producing inflorescences in leaf axils. In order to make this species as an attractive flowering potted plant, it is essential to control vegetative growth, elongate petioles, peduncles and regulate flowering according to the market requirements. Therefore, a better understanding of control of growth and flowering in H. humboldtianus is needed. Gibberellins have been reported to promote flowering in long day ornamental plants such as Philodendron (Chen et al., 2003), Zantedeschia (Kozlowska et al., 2007) and facultative long day plant, Brunonia (Wahyuni et al., 2011). It has also been reported that gibberellins can stimulate flower transition in ornamental plants, which are photoperiodically neutral and do not respond to cold (Halvey, 1990). GA has been used in species of Hyacinthus, Liatris, Muscari, Iris, Lilium, Tulipa and Zantedeschia to replace low temperature treatment required for flowering (De Hertogh and Lenard, 1993). In cold requiring species flower bud dormancy is controlled by a period of low temperature and gibberellins can partly substitute the cold requirement (Chang and Sung, 2000; Song et al., 2003). GA-dependent signaling appears to be a key regulator of recurrent flowering character of roses (Remay et al., 2009) and has been suggested to be a pathway that promote flowering in the absence of external floral-inductive stimuli (Blazquez et al., 1998).
30
H. Sumanasiri et al. / Scientia Horticulturae 159 (2013) 29–32
The objective of this study was to determine if GA3 can be used to promote flowering and vegetative growth of H. humboldtianus plants with the aim of introducing it as an attractive flowering potted plant to the floriculture industry.
were analyzed using categorical data analysis with the help of the SAS computer package.
2. Materials and methods
All GA3 treated H. humboldtianus plants produced flowers and application of GA3 significantly reduced the time to flowering (P < 0.05). Furthermore, growth and flowering responses of plants to GA3 were similar in both seasons. Therefore, data obtained during two seasons were pooled and presented in Table 1. Plants treated with 200 mg l−1 GA3 initiated flowers within 10.0 days of the second GA3 treatment and this was significantly different (P < 0.05) from all the other treatments (Table 1) The application of GA3 also increased the number of inflorescences per plant (Table 1). The highest number of inflorescences was observed at 7 weeks after second GA3 treatment in plants treated either with 100 or 200 mg l−1 GA3 concentration (11.0 ± 2.4 and 10.9 ± 1.8, respectively) (Table 1). The lowest GA3 concentration (50 mg l−1 ) did not increase the number of inflorescences compared to that of untreated plants. Furthermore, application of GA3 increased the number of flowers per inflorescence (P < 0.05) and the highest number of flowers per inflorescence was observed at 200 mg l−1 concentration (24.0 ± 0.5) (Table 1). Application of GA3 affected not only reproductive growth, but also vegetative growth of H. humboldtianus. The untreated plants were shorter (2.5 ± 0.3 cm) compared to that of treated plants and the tallest plants were obtained at 50 mg l−1 (4.1 ± 0.6 cm) GA3 concentration. However, no significant differences between 50, 100 and 200 mg l−1 GA3 concentrations were observed (Table 1). With increased GA3 concentration petiole and peduncle lengths were also increased. The tallest inflorescences were observed in plants treated with 200 mg l−1 GA3 concentration (15.3 ± 1.2) which was significantly different compared to that of untreated plants (10.2 ± 1.3 cm) while longest petioles were observed at 100 mg l−1 GA3 concentration which was significantly different compared to the untreated plants. However, no significant differences were observed for petiole length as well as peduncle length between the GA3 treatments (Table 1).
2.1. Plant materials H. humboldtianus leaf pieces were cultured on 1/2 MS medium supplemented with 1 mg l−1 BAP and regenerated shoots were multiplied on the same medium at 6 week intervals. Eighteen weeks after establishing the cultures, multiplied plants were acclimatized in a soil mix containing sand and coir dust at 1:1 ratio. Eight weeks old acclimatized, H. humboldtianus plants (approximately 6 months from culture establishment) were transplanted to individual 100 mm (0.5 l) diameter plastic pots containing soil mix of sand:top soil:coir dust (1:1:1 ratio) and kept in a green house (28 ± 2 ◦ C, 60-70% RH and 12 h light/12 h dark). Plants were fertilized with 25 ml of diluted (2.5 ml l−l ) solution of Crop Master® (Unipower Pvt (Ltd.), Sri Sadaham Mawatha, Colombo 10, Sri Lanka) per plant at two weeks interval throughout the experimental period. 2.2. GA3 treatments Plants were treated with four concentrations (0, 50, 100 and 200 mg l−1 ) of gibberellic acid (GA3 67545-1G, Sigma–Aldrich Inc., USA) at two weeks after planting. Approximately 25 ml of GA3 solution was sprayed onto leaves of each plant. Thereafter 4 weeks after planting (two weeks after the first treatment) plants were again treated with the same concentration of GA3 . Thus, the total amounts of GA3 applied per plant in four different concentrations were 0, 2.5, 5.0 and 10 mg, respectively. The experiment was laid out as a randomized complete block design with 3 blocks. Blocking was done according to the plant size. Each treatment in each block consisted of 12 plants. Treated plants were observed every 2 days and number of days to first visible bud was recorded. The number of flowers per inflorescence, number of inflorescences per plant, plant height, petiole length and peduncle length was measured at weekly intervals until the plant reached the flower shedding stage. The experiment was repeated twice in two seasons: viz. main season (Maha season: October–March) and minor season (Yala season April–September), demarcated based on the two distinctive rainfall peaks occur in the year. 2.3. Statistical analysis The parametric data obtained (plant height, petiole length, and inflorescence length) were statistically analyzed using Analysis of Variance Procedure (ANOVA) and non parametric data (number of flowers per inflorescence, and number of inflorescences per plant)
3. Results
4. Discussion Application of GA3 to H. humboldtianus promoted earlier flowering, increased the number of inflorescences per plant, number of flowers per inflorescence and improved the vegetative growth producing an attractive flowering potted plant (Fig. 1). Results of the present study agrees with previous studies including, GA3 promoted earlier flowering and anthesis in facultative long day plant Brunonia during short days (Wahyuni et al., 2011), Helleborus niger L. and the hybrid Helleborus x erucsmithii M. Mathew (Christiaens et al., 2012). Scanning electron microscopic examination of, Streptocarpus × hybridus cultivar (hybrid Delta), treated with gibberellins (GA4+7 ) at 1 cm leaf length stage showed floral initiation and development within 1 week of gibberellins treatment
Table 1 Effect of GA3 on vegetative growth and flowering of H. humboldtianus. GA3 concentration (mg l−1 )a Total amount of GA3 applied (mg/plant) Days to flower Plant height (cm) Petiole length (cm) Peduncle length (cm) Number of inflorescences per plant Number of flowers per plant
0 0 18.7 ± 0.5 a 2.5 ± 0.3 b 3.2 ± 0.3 b 10.2 ± 1.3 b 6.0 ± 1.4 b 14.0 ± 0.3 c
a GA3 was applied twice at 2nd and 4th weeks after planting. Values followed by a common letter in a row are not significant (P < 0.05). All the data except days to flower are 7 weeks after second GA3 treatment.
50 2.5 17.8 ± 0.7 a 4.1 ± 0.6 a 6.8 ± 0.8 a 13.8 ± 1.7 a 5.5 ± 1.5 b 15.0 ± 0.5 c
100 5.0 13.0 ± 0.5 b 3.9 ± 0.4 a 7.0 ± 0.9 a 14.1 ± 0.9 a 11.0 ± 2.4 a 18.0 ± 0.6 b
200 10.0 10.0 ± 0.5 b 3.7 ± 0.5 a 6.2 ± 0.9 a 15.3 ± 1.2 a 10.9 ± 1.8 a 24.0 ± 0.5 a
H. Sumanasiri et al. / Scientia Horticulturae 159 (2013) 29–32
31
Fig. 1. Effect of GA3 on growth and flowering of Henckelia humboldtianus.
while no evidence of floral initiation was observed in untreated plants. Furthermore, when plants were treated with GA4+7 at 23 cm leaf length stage more advanced stage of flower development compared to untreated pants was observed (Lyons et al., 1985; Orvos et al., 1989). The promotive effects of gibberellins on flowering have been reported for cold requiring plants and rosette long day plants (LDP) growing under sub-optimal environmental conditions (Chen et al., 2003; Galoch et al., 1995; Gulewska et al., 2000; King et al., 1987; Ogawa, 1981; Zeevart, 2006). Exposure to low temperature may increase GA biosynthesis in plant species which requires chilling to induce flowering and application of GA may substitute chilling requirement (Hazebroek et al., 1993; Pharis and King, 1985; Zanewich and Rood, 1995). It has been reported that short day chrysanthemum cultivars which required chilling for flowering also required GA while cultivars which did not require GA showed no chilling requirement (Sumitomo et al., 2009). Gibberellin promotes elongation of intact plants of many species, especially dwarf biennials in the rosette form (Lyons and Meyers, 1983; Lyons et al., 1985; Orvos et al., 1989). It has been reported that plant height, number of leaves, leaf width, inflorescence length, flower length, flower number and rhizome weight of Bleamcanda chinensis can be increased and the time required for flowering can be reduced by applying 100 ppm GA3 (Bhuj et al., 1998). These observations agree with the results of the present study which showed an increase in peduncle length, petiole length and plant height of H. humboldtianus. H. humboldtianus is a shade loving rosette plant which grows naturally in shade rock cavities and small pockets of soil on rock surfaces of Knuckles range, Sri Lanka, where the RH is around 70-80% and the day and night temperatures are about 20 ± 2 ◦ C and 15 ± 2 ◦ C, respectively during April to September (Yala season) while night temperature drops to 10-12 ◦ C during December–January (Maha season) (Somasiri and Nayakekorala, 1999; Punyawardena, 2005). This area receives moderately high mean annual rainfall over 2500 mm without pronounced dry period and highest rainfall occurs during October–November months (Punyawardena, 2010). Even though, flowering of H. humboldtianus occurs intermittently throughout the year (Dassanayake and Forseberg, 1981), April–May is the major flowering season. In the present study micropropgated plants were maintained in a green house (28 ± 1 ◦ C, 60-70% RH and 12 h light/12 h dark) of the Royal Botanic Garden, Peradeniya, Sri Lanka where environmental conditions may not be conducive as in the natural habitats. Thus, it may be possible that gibberellins may promote flowering of H. humboldtianus plants under unfavorable environmental conditions replacing the low temperature requirement needed for flowering. In natural habitats leaves of H. humboldtianus grow very near to
soil surface and condensed at the base making the appearance unsuitable as a potted plant. As a result of the increase in vegetative and reproductive growth achieved by applying GA3 overall appearance of the plants were improved (Fig. 1) showing potential of commercializing H. humboldtianus as a flowering potted plant. 5. Conclusion Application of GA3 promoted early flowering in H. humboldtianus plants. Considering both flower yield and appearance of the plants 200 ppm GA3 can be recommended as most suitable to improve the uniformity of flowering and the appearance of H. humboldtianus plants. References Blazquez, M.A., Green, R., Nilsson, O., Sussman, M.R., Weigel, D., 1998. Gibberellins promote flowering of Arabidopsis by activating LEAFY promoter. Plant Cell 19, 791–800. Bhuj, B.D., Chaturvedi, O.P., Diwedi, S.K., 1998. Effect of GA3 and IAA on the vegetative growth, flowering and rhizome production in Belamcacanada chinensis (L.). CAB abstract 19 (3), 356–358. Chang, Y.S., Sung, F.H., 2000. Effect of gibberellic acid and dormancy breaking chemicals on flower development of Rhododendron pulchrum Sweet and R. Scabrum Don. Sci. Hortic. 83, 331–337. Chen, J.R.J., Henny, D.B., Mc Connell, D.B., Caldwell, R.D., 2003. Gibberellic acid affects growth and flowering of Philodendron ‘Black Cardinal’. Plant Growth Regul. 41, 1–6. Christiaens, A., Dhooghe, E., Pinxteren, D., Van Labeke, M.C., 2012. Flower development and effects of a cold treatment and a supplemental gibberellic acid application on flowering of Helleborus niger and Helleborus × ericsmithii. Sci. Hortic. 136, 145–151. Dassanayake, M.D., Forseberg, F.R., 1981. Didymocarpus. In: Dassanayake, M.D., Fosberg (Eds.), A Revised Handbook to the Flora of Ceylon. Amerind Publishing Co. Pvt. Ltd., New Delhi, pp. 83–88. De Hertogh, A.A., Lenard, M., 1993. The Physiology of Flower Bulbs. Elsevier Science, Amsterdam, p. 512. Galoch, E., Czaplewska, J., Kopcewicz, J., 1995. Flower promoting activity of gibberellins (GA3 ) in Pharbitis nil apex cultures exposed to various photoperiods. Acta Physiol. Plant. 17, 71–76. Gulewska, H.K., Majewska, M., Kopcewiczet, J., 2000. Gibberellins in the control of photoperiodic flower transition in Pharbitis nil. Physiol. Plant. 108, 202–207. Halvey, A.H., 1990. Recent advances in control of flowering in horticultural crops. In: XXIII International Horticultural Congress Plenary Lectures, Firenze, Italy, 27th August–1st September 1990, pp. 39–49. Hazebroek, J.P., Metzger, J.D., Mansager, E.R., 1993. Thermoinductive regulation of gibberellins metabolism in Thlaspi arvense L. (II. Cold induction of enzymes in gibberellin biosynthesis). Plant Physiol. 102, 547–552. King, R.W., Pharis, R.P., Mander, Z.N., 1987. Gibberellins in relation to growth and flowering in Pharbitis nil Chois. Plant Physiol. 84, 1126–1131. Kozlowska, M., Zajac, M.R., Stachowiak, J., Janowska, B., 2007. Changes in carbohydrate contents of Zantedeschia leaves under gibberellins-stimulated flowering. Acta Physiol. Plant. 29, 27–32.
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Lyons, R.E., Meyers, P., 1983. Effects of GA4+7 and NAA on several aspects of flowering in Streptocarpus. Hortic. Sci. 18, 457–458. Lyons, R.E., Veilleus, R.E., Booze-Daniels, J.N., 1985. Relationship between GA application and phyllomorph length in Streptocarpus. J. Am. Soc. Hortic. Sci. 110, 647–650. Ogawa, Y., 1981. Simulation of the flowering of Pharbitis nil Chois by gibberellins (GA3 ): time dependent action at the apex. Plant Cell Physiol. 22, 675–681. Orvos, A.R., Lyons, R.E., Grayson, R.L., 1989. Effect of GA4+7 on flower initiation and vegetative growth of Streptocarpus × hybridus Voss. ‘Hybrid Delta’. Sci. Hortic. 41, 131–140. Pharis, R.P., King, R.W., 1985. Gibberellins and reproductive development in seed plants. Ann. Rev. Plant Physiol. 36, 517–568. Punyawardena, B.V.R., 2005. Climate of the intermediate zone of Sri Lanka. In: Mapa, R.B., Dassanayake, A.R., Nayakekorale (Eds.), Soils of the intermediate zone of Sri Lanka. Special Publication No. 4, Soil Science Society of Sri Lanka, 6–18. Punyawardena, B.V.R., 2010. Climate of the dry zone of Sri Lanka. In: Mapa, R.B., Somasiri S., Dassanayake, A.R. (Eds.), Soils of the Dry zone of Sri Lanka. Special Publication No. 7 Soil Science Society of Sri Lanka, 9–26.
Remay, A., Lalanne, D., Thouroude, T., Le Couviour, F., Hibrand-Saint, O.L., Foucher, F., 2009. A survey of flowering genes reveals the role of gibberellins in floral control in rose. Theory Appl. Genet. 119 (5), 767–781. Somasiri, S., Nayakekorala, 1999. Climate. In: Mapa R.B., Somasiri, S., Nagarajah, S. (Eds.), Soils of the Wet zone of Sri Lanka. Special Publication No. 1 Soil Science Society of Sri Lanka, 5–13. Song, J.S., Bang, C.S., Chang, Y.D., Jang, H.T., 2003. Effect of cold and GA3 treatment on flowering of eight perennials native to Korea. Acta Hortic. 620, 267–272. Sumitomo, K., Li, T., Hisamatsu, T., 2009. Gibberellin promotes flowering of chrysanthemum by upregulating CmFL a chrysanthemum FLORICAULA/LEAFY homologous gene. Plant Sci. 176, 643–649. Wahyuni, S., Krisantini, S., Johnston, M., 2011. Plant growth regulators and flowering of Brunonia and Calandrinia sp. Sci. Hortic. 128, 141–145. Webber, A., Burtt, B.L., Vitek, E., 2000. Material for a revision of Didimocarpus (Gesneriaceae). Ann. Naturhist. Mus. Wien. 102B, 441–475 www.biologiezentrum Zanewich, K.P., Rood, S.B., 1995. Vernalization and gibberellin physiology of winter canola. Endogenous gibberellin (GA) content and metabolism of [3H]GA1 and [3H]GA20. Plant Physiol. 108, 615–621. Zeevart, J.A.D., 2006. Florigen coming of age after 70 years. Plant Cell 18, 1783–1789.
Contents lists available at SciVerse ScienceDirect
Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti
Short communication
Effect of gibberellic acid on growth and flowering of Henckelia humboldtianus Gardner (Ceylon Rock Primrose) H. Sumanasiri a , S.A. Krishnarajah b , J.P. Eeswara a,∗ a b
Department of Crop Science, Faculty of Agriculture, University of Peradeniya, Sri Lanka Royal Botanic Garden, Peradeniya, Sri Lanka
a r t i c l e
i n f o
Article history: Received 8 October 2012 Received in revised form 20 April 2013 Accepted 23 April 2013 Keywords: Henckelia humboldtianus Gibberellins (GA3 ) Regulation of growth and flowering
a b s t r a c t Henckelia humboldtianus Gardner (Ceylon Rock Primrose), an endemic species to Sri Lanka, is a potential new flowering potted plant. This study investigated the role of gibberellins (GA3 ) in controlling vegetative growth and flowering of H. humboldtianus plants. H. humboldtianus plantlets, micropropagated using leaf pieces, were treated with 25 ml of GA3 (0, 50, 100, or 200 mg l−1 ) four weeks and six weeks after transplanting to pots containing a soil mix of sand, top soil and coir dust at a 1:1:1 ratio. GA3 treatment resulted in a progressive decrease in the time to flowering with increase concentration. Plants treated with 200 mg l−1 GA3 exhibited early flowering (10.0 ± 0.5 days), highest number of inflorescences per plant (10.9 ± 1.8) and highest number of flowers per inflorescence (24.0 ± 0.5) compared to all the other treatments. All GA3 treatments increased the peduncle length, plant height and petiole length providing a better appearance as a potted plant compared to the untreated plants. Results suggest that GA3 can be used to improve the flowering behavior and enhance the appearance of H. humboldtianus for the marketing process as a newly introduced species. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Henckelia humboldtianus (Gardner) A. Weber and B.L. Burtt (Webber et al., 2000) (Synonym Didymocarpus humboldtianus Gardner, Ceylon Rock Primrose, Dassanayake and Forseberg, 1981), belongs to the family Gesneriaceae, is a new species with potential as a flowering potted plant. Earlier, this species was described in the genus Didymocarpus, a large genus comprising at least 70 species, distributed from NW India eastwards through Nepal, Bhutan, NE India, Burma, South China, South Vietnam, Thailand, Malay Peninsula and Sumatra. Later it was categorized under the re-established genus Henckelia Spreng (Webber et al., 2000). H. humboldtianus is an endemic species, which is commonly found in the montane forests at elevation of 1700 m in the Knuckles range in Sri Lanka. This species is a perennial herb, has numerous velvety crinkled, pale green leaves which are arranged very near to the soil surface at the base of the plant making a rosette and produce several inflorescences per plant. Flowers are bell shaped with five unequal petals and color varies from pale violet to almost white with yellow in the throat (Dassanayake and Forseberg, 1981). Fruits, consisting of a linear capsule, dehisce along one side, contain small elliptical seeds. In natural habitats H. humboldtianus regenerates
∗ Corresponding author. Tel.: +94 812395103; fax: +94 812395110; mobile: +94 718095100. E-mail addresses: [email protected], [email protected] (J.P. Eeswara). 0304-4238/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scienta.2013.04.021
mainly by seed. Flowering shoots are annual (monocarpic) or seasonal and die after fruiting or during unfavorable environmental conditions. At the same time initiation of the next year’s flowering shoots appear with few young leaves at the base of the plant. When favorable conditions return, shoots and leaves expand producing inflorescences in leaf axils. In order to make this species as an attractive flowering potted plant, it is essential to control vegetative growth, elongate petioles, peduncles and regulate flowering according to the market requirements. Therefore, a better understanding of control of growth and flowering in H. humboldtianus is needed. Gibberellins have been reported to promote flowering in long day ornamental plants such as Philodendron (Chen et al., 2003), Zantedeschia (Kozlowska et al., 2007) and facultative long day plant, Brunonia (Wahyuni et al., 2011). It has also been reported that gibberellins can stimulate flower transition in ornamental plants, which are photoperiodically neutral and do not respond to cold (Halvey, 1990). GA has been used in species of Hyacinthus, Liatris, Muscari, Iris, Lilium, Tulipa and Zantedeschia to replace low temperature treatment required for flowering (De Hertogh and Lenard, 1993). In cold requiring species flower bud dormancy is controlled by a period of low temperature and gibberellins can partly substitute the cold requirement (Chang and Sung, 2000; Song et al., 2003). GA-dependent signaling appears to be a key regulator of recurrent flowering character of roses (Remay et al., 2009) and has been suggested to be a pathway that promote flowering in the absence of external floral-inductive stimuli (Blazquez et al., 1998).
30
H. Sumanasiri et al. / Scientia Horticulturae 159 (2013) 29–32
The objective of this study was to determine if GA3 can be used to promote flowering and vegetative growth of H. humboldtianus plants with the aim of introducing it as an attractive flowering potted plant to the floriculture industry.
were analyzed using categorical data analysis with the help of the SAS computer package.
2. Materials and methods
All GA3 treated H. humboldtianus plants produced flowers and application of GA3 significantly reduced the time to flowering (P < 0.05). Furthermore, growth and flowering responses of plants to GA3 were similar in both seasons. Therefore, data obtained during two seasons were pooled and presented in Table 1. Plants treated with 200 mg l−1 GA3 initiated flowers within 10.0 days of the second GA3 treatment and this was significantly different (P < 0.05) from all the other treatments (Table 1) The application of GA3 also increased the number of inflorescences per plant (Table 1). The highest number of inflorescences was observed at 7 weeks after second GA3 treatment in plants treated either with 100 or 200 mg l−1 GA3 concentration (11.0 ± 2.4 and 10.9 ± 1.8, respectively) (Table 1). The lowest GA3 concentration (50 mg l−1 ) did not increase the number of inflorescences compared to that of untreated plants. Furthermore, application of GA3 increased the number of flowers per inflorescence (P < 0.05) and the highest number of flowers per inflorescence was observed at 200 mg l−1 concentration (24.0 ± 0.5) (Table 1). Application of GA3 affected not only reproductive growth, but also vegetative growth of H. humboldtianus. The untreated plants were shorter (2.5 ± 0.3 cm) compared to that of treated plants and the tallest plants were obtained at 50 mg l−1 (4.1 ± 0.6 cm) GA3 concentration. However, no significant differences between 50, 100 and 200 mg l−1 GA3 concentrations were observed (Table 1). With increased GA3 concentration petiole and peduncle lengths were also increased. The tallest inflorescences were observed in plants treated with 200 mg l−1 GA3 concentration (15.3 ± 1.2) which was significantly different compared to that of untreated plants (10.2 ± 1.3 cm) while longest petioles were observed at 100 mg l−1 GA3 concentration which was significantly different compared to the untreated plants. However, no significant differences were observed for petiole length as well as peduncle length between the GA3 treatments (Table 1).
2.1. Plant materials H. humboldtianus leaf pieces were cultured on 1/2 MS medium supplemented with 1 mg l−1 BAP and regenerated shoots were multiplied on the same medium at 6 week intervals. Eighteen weeks after establishing the cultures, multiplied plants were acclimatized in a soil mix containing sand and coir dust at 1:1 ratio. Eight weeks old acclimatized, H. humboldtianus plants (approximately 6 months from culture establishment) were transplanted to individual 100 mm (0.5 l) diameter plastic pots containing soil mix of sand:top soil:coir dust (1:1:1 ratio) and kept in a green house (28 ± 2 ◦ C, 60-70% RH and 12 h light/12 h dark). Plants were fertilized with 25 ml of diluted (2.5 ml l−l ) solution of Crop Master® (Unipower Pvt (Ltd.), Sri Sadaham Mawatha, Colombo 10, Sri Lanka) per plant at two weeks interval throughout the experimental period. 2.2. GA3 treatments Plants were treated with four concentrations (0, 50, 100 and 200 mg l−1 ) of gibberellic acid (GA3 67545-1G, Sigma–Aldrich Inc., USA) at two weeks after planting. Approximately 25 ml of GA3 solution was sprayed onto leaves of each plant. Thereafter 4 weeks after planting (two weeks after the first treatment) plants were again treated with the same concentration of GA3 . Thus, the total amounts of GA3 applied per plant in four different concentrations were 0, 2.5, 5.0 and 10 mg, respectively. The experiment was laid out as a randomized complete block design with 3 blocks. Blocking was done according to the plant size. Each treatment in each block consisted of 12 plants. Treated plants were observed every 2 days and number of days to first visible bud was recorded. The number of flowers per inflorescence, number of inflorescences per plant, plant height, petiole length and peduncle length was measured at weekly intervals until the plant reached the flower shedding stage. The experiment was repeated twice in two seasons: viz. main season (Maha season: October–March) and minor season (Yala season April–September), demarcated based on the two distinctive rainfall peaks occur in the year. 2.3. Statistical analysis The parametric data obtained (plant height, petiole length, and inflorescence length) were statistically analyzed using Analysis of Variance Procedure (ANOVA) and non parametric data (number of flowers per inflorescence, and number of inflorescences per plant)
3. Results
4. Discussion Application of GA3 to H. humboldtianus promoted earlier flowering, increased the number of inflorescences per plant, number of flowers per inflorescence and improved the vegetative growth producing an attractive flowering potted plant (Fig. 1). Results of the present study agrees with previous studies including, GA3 promoted earlier flowering and anthesis in facultative long day plant Brunonia during short days (Wahyuni et al., 2011), Helleborus niger L. and the hybrid Helleborus x erucsmithii M. Mathew (Christiaens et al., 2012). Scanning electron microscopic examination of, Streptocarpus × hybridus cultivar (hybrid Delta), treated with gibberellins (GA4+7 ) at 1 cm leaf length stage showed floral initiation and development within 1 week of gibberellins treatment
Table 1 Effect of GA3 on vegetative growth and flowering of H. humboldtianus. GA3 concentration (mg l−1 )a Total amount of GA3 applied (mg/plant) Days to flower Plant height (cm) Petiole length (cm) Peduncle length (cm) Number of inflorescences per plant Number of flowers per plant
0 0 18.7 ± 0.5 a 2.5 ± 0.3 b 3.2 ± 0.3 b 10.2 ± 1.3 b 6.0 ± 1.4 b 14.0 ± 0.3 c
a GA3 was applied twice at 2nd and 4th weeks after planting. Values followed by a common letter in a row are not significant (P < 0.05). All the data except days to flower are 7 weeks after second GA3 treatment.
50 2.5 17.8 ± 0.7 a 4.1 ± 0.6 a 6.8 ± 0.8 a 13.8 ± 1.7 a 5.5 ± 1.5 b 15.0 ± 0.5 c
100 5.0 13.0 ± 0.5 b 3.9 ± 0.4 a 7.0 ± 0.9 a 14.1 ± 0.9 a 11.0 ± 2.4 a 18.0 ± 0.6 b
200 10.0 10.0 ± 0.5 b 3.7 ± 0.5 a 6.2 ± 0.9 a 15.3 ± 1.2 a 10.9 ± 1.8 a 24.0 ± 0.5 a
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Fig. 1. Effect of GA3 on growth and flowering of Henckelia humboldtianus.
while no evidence of floral initiation was observed in untreated plants. Furthermore, when plants were treated with GA4+7 at 23 cm leaf length stage more advanced stage of flower development compared to untreated pants was observed (Lyons et al., 1985; Orvos et al., 1989). The promotive effects of gibberellins on flowering have been reported for cold requiring plants and rosette long day plants (LDP) growing under sub-optimal environmental conditions (Chen et al., 2003; Galoch et al., 1995; Gulewska et al., 2000; King et al., 1987; Ogawa, 1981; Zeevart, 2006). Exposure to low temperature may increase GA biosynthesis in plant species which requires chilling to induce flowering and application of GA may substitute chilling requirement (Hazebroek et al., 1993; Pharis and King, 1985; Zanewich and Rood, 1995). It has been reported that short day chrysanthemum cultivars which required chilling for flowering also required GA while cultivars which did not require GA showed no chilling requirement (Sumitomo et al., 2009). Gibberellin promotes elongation of intact plants of many species, especially dwarf biennials in the rosette form (Lyons and Meyers, 1983; Lyons et al., 1985; Orvos et al., 1989). It has been reported that plant height, number of leaves, leaf width, inflorescence length, flower length, flower number and rhizome weight of Bleamcanda chinensis can be increased and the time required for flowering can be reduced by applying 100 ppm GA3 (Bhuj et al., 1998). These observations agree with the results of the present study which showed an increase in peduncle length, petiole length and plant height of H. humboldtianus. H. humboldtianus is a shade loving rosette plant which grows naturally in shade rock cavities and small pockets of soil on rock surfaces of Knuckles range, Sri Lanka, where the RH is around 70-80% and the day and night temperatures are about 20 ± 2 ◦ C and 15 ± 2 ◦ C, respectively during April to September (Yala season) while night temperature drops to 10-12 ◦ C during December–January (Maha season) (Somasiri and Nayakekorala, 1999; Punyawardena, 2005). This area receives moderately high mean annual rainfall over 2500 mm without pronounced dry period and highest rainfall occurs during October–November months (Punyawardena, 2010). Even though, flowering of H. humboldtianus occurs intermittently throughout the year (Dassanayake and Forseberg, 1981), April–May is the major flowering season. In the present study micropropgated plants were maintained in a green house (28 ± 1 ◦ C, 60-70% RH and 12 h light/12 h dark) of the Royal Botanic Garden, Peradeniya, Sri Lanka where environmental conditions may not be conducive as in the natural habitats. Thus, it may be possible that gibberellins may promote flowering of H. humboldtianus plants under unfavorable environmental conditions replacing the low temperature requirement needed for flowering. In natural habitats leaves of H. humboldtianus grow very near to
soil surface and condensed at the base making the appearance unsuitable as a potted plant. As a result of the increase in vegetative and reproductive growth achieved by applying GA3 overall appearance of the plants were improved (Fig. 1) showing potential of commercializing H. humboldtianus as a flowering potted plant. 5. Conclusion Application of GA3 promoted early flowering in H. humboldtianus plants. Considering both flower yield and appearance of the plants 200 ppm GA3 can be recommended as most suitable to improve the uniformity of flowering and the appearance of H. humboldtianus plants. References Blazquez, M.A., Green, R., Nilsson, O., Sussman, M.R., Weigel, D., 1998. Gibberellins promote flowering of Arabidopsis by activating LEAFY promoter. Plant Cell 19, 791–800. Bhuj, B.D., Chaturvedi, O.P., Diwedi, S.K., 1998. Effect of GA3 and IAA on the vegetative growth, flowering and rhizome production in Belamcacanada chinensis (L.). CAB abstract 19 (3), 356–358. Chang, Y.S., Sung, F.H., 2000. Effect of gibberellic acid and dormancy breaking chemicals on flower development of Rhododendron pulchrum Sweet and R. Scabrum Don. Sci. Hortic. 83, 331–337. Chen, J.R.J., Henny, D.B., Mc Connell, D.B., Caldwell, R.D., 2003. Gibberellic acid affects growth and flowering of Philodendron ‘Black Cardinal’. Plant Growth Regul. 41, 1–6. Christiaens, A., Dhooghe, E., Pinxteren, D., Van Labeke, M.C., 2012. Flower development and effects of a cold treatment and a supplemental gibberellic acid application on flowering of Helleborus niger and Helleborus × ericsmithii. Sci. Hortic. 136, 145–151. Dassanayake, M.D., Forseberg, F.R., 1981. Didymocarpus. In: Dassanayake, M.D., Fosberg (Eds.), A Revised Handbook to the Flora of Ceylon. Amerind Publishing Co. Pvt. Ltd., New Delhi, pp. 83–88. De Hertogh, A.A., Lenard, M., 1993. The Physiology of Flower Bulbs. Elsevier Science, Amsterdam, p. 512. Galoch, E., Czaplewska, J., Kopcewicz, J., 1995. Flower promoting activity of gibberellins (GA3 ) in Pharbitis nil apex cultures exposed to various photoperiods. Acta Physiol. Plant. 17, 71–76. Gulewska, H.K., Majewska, M., Kopcewiczet, J., 2000. Gibberellins in the control of photoperiodic flower transition in Pharbitis nil. Physiol. Plant. 108, 202–207. Halvey, A.H., 1990. Recent advances in control of flowering in horticultural crops. In: XXIII International Horticultural Congress Plenary Lectures, Firenze, Italy, 27th August–1st September 1990, pp. 39–49. Hazebroek, J.P., Metzger, J.D., Mansager, E.R., 1993. Thermoinductive regulation of gibberellins metabolism in Thlaspi arvense L. (II. Cold induction of enzymes in gibberellin biosynthesis). Plant Physiol. 102, 547–552. King, R.W., Pharis, R.P., Mander, Z.N., 1987. Gibberellins in relation to growth and flowering in Pharbitis nil Chois. Plant Physiol. 84, 1126–1131. Kozlowska, M., Zajac, M.R., Stachowiak, J., Janowska, B., 2007. Changes in carbohydrate contents of Zantedeschia leaves under gibberellins-stimulated flowering. Acta Physiol. Plant. 29, 27–32.
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