Flowering of 'Keitt' Mango in Response to Deblossoming and Gibberellic Acid1

after the trees were transferred to warm, outdoor condi Nunez-Elisea, R. and T. L. Davenport. 1991a. Effect of duration of low tions. Buds which didnot generate flowers (about 20%) temperature treatment on flowering of containerized Tommy Atkins' produced new vegetative shoots. In addition, trees that were mango. (Abstr.) HortScience 26:135. Nunez-Elisea, R. and T. L. Davenport. 1991b. Effect of duration of low stimulated to grow in a control chamber at 30/25° C (day/ temperature treatment on flowering of containerized 'Tommy Atkins' night temperature, 12-h photoperiod) or under warm, out mango. Proc. 18th Ann. Meet. Plant Growth Reg. Soc. Amer. (in press). door conditions only produced new vegetative growth. Nunez-Elisea, R., W. Ferreira, M. L. Caldeira, and T. L. Davenport. 1989. In conclusion, mature experimental mango trees with Marcottage of mango: a useful tool for physiological studies of flower induction. Abstract. 86th Annual Meeting of the Amer. Soc. Hort. Sci. regenerated canopies were produced in 4 to 5 months by p. 115. air-layering and selective pruning. A chilling treatment of Ou, S. K.1982. Temperature effect on differential shoot development 18/10° C day/night for 7 to 8 weeks applied to potted trees ofmango during flowering period. J.Agric. Res. China. 31:209-214. at any time of the year consistently induced flowering. Bud Schaffer, B. and G. O. Gaye. 1989. Gas exchange, chlorophyll and nitrogen meristematic cell division during chilling was necessary for content of mango leaves as influenced by light environment. HortSci ence 24:507-509. differentiation of floral structures. The procedures de Scholefield, P. B., D. R. Oag, and M. Sedgley. 1986. The relationship scribed in this report are currently being used in further between vegetative and reproductive development in the mango in studies of the physiology and developmental aspects of northern Australia. Aust. J. Agric. Res. 37:425-433. mango reproduction. Sedgley, M. 1990. Flowering of deciduous perennial fruit crops. Hort. Rev. 12:223-264. Shu, Z. H and T. F. Sheen. 1987. Floral induction in axillary buds of Literature Cited mango {Mangifera indica L.) as affected by temperature. Scientia Hort. 31:81-87. Bernier, B. 1988. The control of floral evocation and morphogenesis. Singh, R. N. 1958. Studies in the differentiation and development of fruit Ann. Rev. PI. Physiol. 39:175-219. buds in mango (M. indica L.). II. Morphological and histological Chacko, E. K. 1984. Physiology of vegetative and reproductive growth in changes. Hort. Adv. 3:37-43. mango (Mangifera indica L.)In: Proc. First Australian Mango Research Singh, L. B. 1959. Movement of flowering substances in the mango {Man Workshop. Cairns, Qld. pp. 54-70. gifera indica L.) leaves. Hort. Adv. 3:20-27. Chacko, E. K. 1991. Mango flowering - still an enigma. Acta Hort. 29:12- Singh, L. B. 1960. The Mango - Botany, Cultivation, and Utilization. 21. Leonard Hill, London. 439 pp. Evans, L. T. 1969. The nature of flower induction. In: The induction of Southwick, S. and T. L. Davenport. 1986. Characterization of water stress flowering. McMillan and Co. (Aust.) pp. 457-480. and low temperature effects on flower induction in citrus. Plant Physiol. Hackett, W. P. 1985. Juvenility, maturation, and rejuvenation in woody 81:26-29. plants. Hort. Rev. 7:109-155. Wareing, P. F. and I. D. J. Phillips. 1981. Growth and Differentiation in Jackson, D. I. and G. B. Sweet. 1972. Flower initiation in woody temperate Plants. 3rd Edition. Pergamon Press. 343 pp. plants. Hort. Abstr. 42:9-24. Whiley, A. W., T. S. Rasmusen, J. B. Saranah and B. N. Wolstenholme. Lambe, A., R. Nunez-Elisea, and T. L. Davenport. 1990. New develop 1989. Effect of temperature on growth, dry matter production and ments in mango marcotting. Tropical Fruit World 1(3):80-82. starch accumulation in ten mango {Mangifera indica L.) cultivars. J. Mustard, M. J. and S.J. Lynch. 1946. Flower-bud formation and develop Hort. Sci. 64:753-765. ment in Mangifera indica. Bot. Gaz. 108:136-140. Wolstenholme, B. N. and D. Hofmeyr. 1985. Effects of various floral Nunez-Elisea, R. and T. L. Davenport. 1989. Requirement for mature induction treatments on container-grown mango trees. South African leaves during floral induction and floral transition in developing shoots Mango Growers Assoc. Res. Rept. 5:36-38. of mango. 3rd Int. Mango Symp. Abstracts, p. 9. Verheij, E. W. M. 1986. Towards a classification of tropical fruit trees. Acta Hortic 175:137-149.

Proc. Fla. State Hort. Soc. 104:41-43. 1991.

FLOWERING OF 'KEITT' MANGO IN RESPONSE TO DEBLOSSOMING AND GIBBERELLIC ACID1

R. Nunez-Elisea and T. L. Davenport panicles. GA3-treated branches began to grow 3 to 5 weeks Tropical Research &f Education Center later than branches of the controls and formed mainly axillary IFAS, University of Florida panicles. The delay of growth was greater with increasing 18905 SW 280 St. GA3 concentration. The primary effect of GA3 was to delay Homestead, FL 33031 bud initiation, thus preventing formation of both vegetative and panicle buds. Flowering of mango may be indirectly pre Additional index words. Mangifera indica L., floral differenti vented by GA3 application since GA3 can postpone growth ation, growth regulators, axillary buds. beyond the flowering period.

Mango (Mangifera indica L.) panicles are formed during Abstract. Branches of mango trees (Mangifera indica L. cv. the winter on apical buds of the current year's wood in Keitt) were deblossomed and sprayed with 0, 10, 50, or 250 South Florida. Cool weather, with temperatures below 15° mg/liter GA3 in late December to examine the effect of GA3 C, promotes floral differentiation (Wolstenholme and Hof on panicle formation. Growth of non-sprayed branches began meyr, 1985; Shu and Sheen, 1987; Whiley et al., 1989; within 3 weeks. Virtually all new growth consisted of axillary Nunez-Elisea and Davenport, 1991). Apical panicles inhibit growth of axillary buds, which remain non-differentiated 'Florida Agricultural Experiment Station Journal Series No. N-00488. (Reece et al., 1946, 1949). They are activated, however, if This research was supported by USDA-CSRS, CBAG Special Grant No. 88-34135-3615. The senior author acknowledges financial support from the panicle is removed or lost due to natural causes. If this the Mexican government agency, CONACYT. occurs during the flowering season, the activated axillary

Proc. Fla. State Hort. Soc. 104: 1991. 41 buds will differentiate into panicles, but if activated later, Results especially during warm weather, they will most likely form Deblossoming alone resulted in the earliest initiation of axillary vegetative shoots. axillary bud growth. By January 17, 23% of the non-treated Exogenous GA3 can inhibit flowering of mango (Kachru control shoots had differentiated buds, whereas only 2% et al., 1971; Rawash et al., 1983; Tomer, 1984; Andrews or fewer shoots of all the GA3 treatments showed differen and Le Fook, 1985; Galan-Sauco, 1990). It has not been tiated buds (Fig. 1). Only panicle buds had differentiated clarified, however, whether GA3 promotes vegetative by this date. The trend was similar by February 6. GA3 growth during the flowering period. In a recent field trial continued to suppress axillary bud growth, while 46% of with 'Tommy Atkins' and 'Keitt' mango trees, GA3 (two the deblossomed-only shoots already had panicle buds. sprays at 100 ppm applied shortly before the flowering Shoots of this group which had initiated growth early were period) greatly suppressed not only flowering, but also now bearing panicles with open flowers. winter vegetative growth and the summer flush of vegeta There was growth of shoots in all treatments between tive growth (Nunez-Elisea and Davenport, unpublished). February 6 and 25; however, 50 and 250 mg/liter GA3 had These results did not agree with the view that GA3 specif resulted in the smallest proportions of shoots with differen ically inhibited differentiation of floral primordia (Kachru tiated buds (56 and 33%, respectively). At this time, most et al., 1971), and led to a closer examination of the role of deblossomed-only shoots had panicles containing flowers GA3 in mango bud development. The purpose of this study at anthesis. The GA3-treated shoots had mostly swollen was to evaluate the effects of exogenous GA3 on axillary buds and tender panicles. By March 11, 90% of all treated bud initiation and expression (type of growth produced) shoots, except those treated with 250 mg/liter GA3, had in 'Keitt' mango trees. differentiated buds. To this date, only panicles had been produced in all the experimental treatments. By April 18, almost all treated shoots, including those sprayed with 250 Materials and Methods mg/liter GA3, had produced axillary growth, which con sisted primarily of panicles. Each flowering shoot produced The study was conducted in late December of 1990 at between 3 and 5 axillary panicles regardless of treatment the Tropical Research and Education Center. Five 15-yr- (data not shown). Less than 3% of shoots produced new old, flowering 'Keitt' trees were used. Four branches with axillary vegetative shoots during the experiment, and these up to 17 developing apical panicles each were selected per were formed only on shoots treated with 50 or 250 mg/liter tree. The branches were distributed around the canopy. GA3. All apical panicles were manually removed to stimulate growth of the non-differentiated axillary buds. The deblos- somed branches were then sprayed to run-off with aqueous Discussion solutions of 0, 10, 50, or 250 mg/liter GA3 which included Reece et al. (1946, 1949) showed that bud initiation the surfactant, Triton X-100 at 1 ml/liter. (meristematic cell division) in mango is regulated separately The effects of GA3 on axillary bud growth and expres from differentiation into either vegetative or reproductive sion were evaluated from mid-January to mid-April, 1991. structures. It has been speculated that floral differentiation Growing mango buds require about 7 to 10 days, after is directed by a chemical signal arriving from mature leaves, initial swelling, to reach a length of about 1 cm and attain while vegetative shoots are formed in the absence of such bud break. At this stage buds have differentiated either a signal (Reece et al. 1946,1949; Singh, 1959). The environ vegetative or floral primordia (Mustard and Lynch, 1946; mental conditions that prevail during bud initiation influ Scholefieldetal., 1986). Breaking buds were identified mac- ence the type of growth expressed by the initiating bud. roscopically by carefully removing the external scales and For example, temperatures below 15° C promote floral, as inspecting the axils. Vegetative buds contain no axillary primordia under the scales, but they show leaf primordia about 5 mm long towards the interior of the bud. Panicle 100 buds, on the other hand, show a distinct structure beneath the external scales, which corresponds to a primordial pani cle branch bearing numerous individual flower buds (Mus tard and Lynch, 1946; Scholefield et al., 1986). Non-dif ferentiated buds were either flattened and not visually growing, or slightly swollen due to initial meristematic ac tivity. The above morphological bud characteristics were used to classify the deblossomed shoots as: a) shoots with non-dif ferentiated buds; b) shoots with differentiated vegetative buds, or c) shoots with differentiated panicle buds or flow ering shoots. Shoots bearing both differentiated and swelling buds were classified on the basis of the differentiated buds. De- Apr. 18 blossomed shoots were examined and classified on five oc Jan. 17 Feb. 6 Feb. 25 Mar. 11 casions beginning in mid-January and extending over a 13 Fig. 1. Axillary flowering of deblossomed shoots of 'Keitt' mango in week period, until almost all shoots had produced new response to a single spray of gibberellic acid applied on Dec. 27, 1990. growth. Each treatment was applied to > 35 shoots.

42 Proc. Fla. State Hort. Soc. 104: 1991. opposed to vegetative differentiation (Shu and Sheen, Literature Cited 1987; Whiley et al., 1989; Nunez-Elisea and Davenport, 1991). Andrews, L. and U. Le Fook. 1985. Effects of growth regulators on flow ering pattern, flower suppression and fruit set in mango (Mangifera Growth of deblossomed 'Keitt' mango branches was indica L. cv. Julie). Joint Proc. 21st Ann. Meet. Carib. Food Crops Soc. strongly inhibited by GA3 in our study, resulting in a delay & 32nd Ann. Meet. Amer. Soc. Horde. Sci. - Tropical Region. Port of in bloom production of more than four weeks. GA3 applied Spain, Trinidad, pp. 61-65. during the flowering period temporarily suppressed axil Galan-Sauco, V. 1990. Los frutales tropicales en los subtropicos. I. Aguac- ate, mango, litchi y longan. Ediciones Mundi-Prensa. Madrid, pp. 133. lary bud growth with increasing rate applied. GA3 did not Greer, N., J. Saranah and A. Whiley. 1988. Mangos in South East Queens promote formation of vegetative shoots while non-GA3- land. Open Day programme and information papers. Maroochy Hor treated buds were simultaneously forming panicles. Very ticultural Research Station. Section C pp. 1-3. few vegetative shoots formed during the experiment and Kachru, R. B., R. N. Singh and E. K. Chacko. 1971. Inhibition of flowering they were only produced during the last week of the study. in mango (Mangifera indica L.) by gibberellic acid. HortScience 6:140- 141. Vegetative shoots are known to be formed on defoliated Mustard, M. J. and S. J. Lynch. 1946. Flower-bud formation and develop branches during cool weather (Reece et al.,1946, 1949; ment in Mangifera indica. Bot. Gaz. 108:136-140. Nunez-Elisea and Davenport, 1989). Therefore, it is un Nunez-Elisea, R. and T. L. Davenport. 1989. Requirement for mature likely that formation of vegetative shoots was inhibited by leaves during floral induction and floral transition in developing shoots of mango. 3rd Int. Mango Symp. Abstracts, p. 9. low temperatures. Nunez-Elisea, R. and T. L. Davenport. 1991. Effect of duration of low Since all growth was temporarily inhibited by GA3, it is temperature treatment on flowering of containerized 'Tommy Atkins' inferred that this growth regulator temporarily repressed mango. (Abstr.) HortScience 26:135. bud initiation. As a consequence, bud differentiation and Rawash, M. A., A. El Hamady and S. El Nabawy. 1983. Regulation of the formation of both vegetative shoots and panicles was flowering and fruiting in mango trees by using some growth regulators. Ann. Agric. Sci. Univ. of Ain Shams (Egypt) 28:227-240. suspended. This notion differs from that suggested by Kac- Reece, P. C, J. R. Furr and C. W. Cooper. 1946. The inhibiting effect of hru et al. (1971) that GA3 is a specific inhibitor of floral the terminal bud on flower formation in the axillary buds of the 'Haden' differentiation in mango. That GA3 inhibits mango flower mango. Amer. J. Bot. 33:209-210. ing may thus be an imprecise interpretation of the general Reece, P. C, J. R. Furr and C. W. Cooper. 1949. Further studies of floral induction in the 'Haden' mango (Mangifera indica L.). Amer. J. Bot. growth suppression GA3 causes when applied during the 36:734-740. flowering period. Scholefield, P. B., D. R. Oag and M. Sedgley. 1986. The relationship Further experiments are needed to clarify the effects between vegetative and reproductive development in the mango in of GA3 on mango flowering when applied during the period northern Australia. Aust. J. Agric. Res. 37:425-433. of vegetative dormancy. Our preliminary trial showed a Shu, Z. H. and T. F. Sheen. 1987. Floral induction in axillary buds of mango (Mangifera indica L.) as affected by temperature. Scientia Hortic. greater delay in the emergence of new growth when GA3 31:81-87. was sprayed on intact 'Tommy Atkins' and 'Keitt' trees prior Sigler, T., A. Ribenfeld and O. Reuvini. 1981. Flower inhibition in mango to flowering, compared to the post-flowering applications seedlings. Hassadeh 61:247-250. of this study. This may indicate that bud responsiveness to Singh, L. B. 1959. Movement of flowering substances in the mango (Man gifera indica L.) leaves. Hort. Adv. 3:20-27. GA3 varies with season and bud type (apical vs. axillary) in Tomer, E. 1984. Inhibition of flowering in mango by gibberellic acid. addition to rate applied. Scientia Hortic. 24:299-303. GA3 has practical applications in mango management. Whiley, A. W., T. S. Rasmusen, J. B. Saranah and B. N. Wolstenholme. It is applied to nursery trees in Spain (Galan-Sauco, 1990) 1989. Effect of temperature on growth, dry matter production and and Israel (Sigler et al., 1981) to prevent premature flow starch accumulation in ten mango (Mangifera indica L.) cultivars. J. Hort. Sci. 64:753-765. ering due to low temperatures, and is being tested in Au Wolstenholme, B. N. and D. Hofmeyr. 1985. Effects of various floral stralia to delay flowering of the temperature-sensitive 'Ken induction treatments on container-grown mango trees. South African sington Pride' mango (Greer et al., 1988). The present re Mango Growers Assoc. Res. Rept. 5:36-38. sults suggest that GA3 may be useful in delaying mango flowering in South Florida to extend the cropping season.

Proc. Fla. State Hort. Soc. 104: 1991. 43