FRUIT-BUD DIFFERENTIATION IN MANGO 'ALPHONSO' AND 'TOTAPURI' UNDER MILD TROPICAL RAINY CONDITIONS

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1 Scientia Hortieulturae, 10 (1979) Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands FRUT-BUD DFFERENTATON N MANGO 'ALPHONSO' AND 'TOTAPUR' UNDER MLD TROPCAL RANY CONDTONS H. RAVSHANKAR ~, M.M. RAO and K.M. BOJAPPA College of Agriculture, Dharwad, Karnataka State (ndia) Present address: ndian nstitute of Horticultural Research, Bangalore (ndia) (First received 31 March 1978; in revised form 21 July 1978) ABSTRACT Ravishankar, H., Rao, M.M. and Bojappa, K.M., Fruit-bud differentiation in mango 'Alphonso' and 'Totapuri' under mild tropical rainy conditions. Scientia Hortic., 10: Fruit-bud differentiation in 'Alphonso' mango (Mangifera indica L), a biennial-bearing cultivar grown under the mild tropical rainy climate of Dharwad (ndia), was initiated in early October and reached a peak by mid-november. Based on the morphological and histological changes, the developmental process could broadly be divided into 4 stages. The marked drop in the night temperature and relative humidity appeared to be favourable for fruit-bud differentiation. n 'Totapuri', a regular-bearing cultivar, these stages occurred slightly earlier. NTRODUCTON in ndia, the time of flowering in mango varies in different regions. The temperature appears to be the decisive factor since flowering is earlier in South ndia, with a tropical climate, than in North ndia. t is not clear whether any difference exists with regard to the time of fruit-bud differentiation. The available reports are conflicting (Singh, 1958; Khan, 1960). The process of fruit-bud differentiation and the panicle expansion is said to be continuous without any intervening period of dormancy (Singh, 1958). Recently, sprays of 2-chloroethyl phosphonic acid (CEPA, syn. ethephon, ethrel) have been applied during the period of fruit-bud differentiation to promote flowering in trees which are expected to remain "off" due to a bien. nial-bearing rhythm (Pandey et al., 1973; Chacko et al., 1974). This calls for determining the period of fruit-bud differentiation for different cultivars in different regions. n the present paper, studies on the period and the process of fruit-bud differentiation in 2 cultivars are reported. MATERALS AND METHODS Twenty-five-year old 'Alphonso' and 'Totapuri' mango trees, grown in the

2 96 college orchard at Dharwad, were used. Dharwad has a mild tropical rainy climate with mild dry winters (savannah climate). Both fruited shoot terminals of the previous season and mature past-season shoots that are expected to differentiate fruit-buds, were tagged on 1 August 1975 for collecing samples of buds periodically for microscopical study of fruit-bud differentiation. The term "fruited shoots" referred to those which had borne flower panicles in the 1975 fruiting-season (Jam--June) and were not expected to differentiate fruit-buds for the following season (1976) due to biennial bearing. The shoot apices were softened and fixed in 0.2% potassium hydroxide for h. The material was given 3 washings with 50% ethanol, each lasting 30 min. t was dehydrated by tertiary-butyl-alcohol (Johanson, 1940) and embedded in paraffin wax after infiltration. For microscopical examination of stages of bud development, the schedule suggested by Maheswari (1940) was followed. RESULTS Time of fruit-bud differentiation and flowering. -- Fruit-bud initiation in dissected buds of 'Alphonso' mango shoots, which were expected to flower, started during the 1st week of October The initiation and differentiation progressively increased and reached a peak in mid-november 1975 (Fig. 1). By 15 December, the differentiation reached the advanced "bud burst" stage, as evidenced by the presence of primary and secondary branches of flower panicles. n 'Totapuri', the regular-bearing cultivar, the time of fruit-bud initiation and differentiation were about a fortnight earlier. From perusal of the meteorological data, it may be surmised that the peak of fruit-bud differen- 2.~_ 13 "6 t # # i t,,, X V i.o E i i i i i NO i ~ i t~au6 ts~ ~SSEP toot :5OCT ~ V ~SNOV ~OEC tsoec Fig.. Time of fruit-bud differentiation in 'Alphonso' mango.

3 97 tiation in mid-november coincided with the onset of winter, especially regarding a marked drop in night temperature (from 19.8 to 15.2 C) and relative humidity (from 79.5 to 56.5%). The "bud burst" stage was accompanied by the lowest night temperature (11.6 C). Thus, low night temperature and dry atmosphere are probably favourable for fruit-bud differentiation in mango. Sen and Mallik (1941) have already stated that the advent of cold and dry weather appeared to be the determining factor for fruit-bud differentiation in mango. Under the coastal climate of Konkan, Gunjate et al. (1977) observed maximum fruit-bud differentiation in 'Alphonso' in September-October, but did not associate it with any specific climate. The flowering in Dharwad occurs in early- to mid-january, when the temperatures start rising. Thus, there appears to be a slight time lag between fruit-bud differentiation and inflorescence expansion. This may be due to a slow rate of axis expansion due to low temperatures during the latter half of December. Morphological and histological changes associated with fruit-bud differentiation. -- n August 1975, the terminal buds on the shoots which were expected to differentiate fruit buds, were small, green, partially covered with dried scales with brownish tips and inactive. Prior to floral-bud differentiation, the main axis in the apical bud was rounded off to a dome shape with broadening scales (Fig. 2, numbers 1 and 2; Fig. 3a). The fruit-bud differentiation in 'Alphonso' could then be divided into 4 stages. Fig. 2. Morphological stages of development of apical bud of 'Alphonso' mango shoot.

4 98 Fig. 3. Longitudinal sections showing the histological stages of development of the apical bud of 'Alphonso' mango shoot differentiating into a fruit bud. (a) The bud before differentiation (X 30). (b) nitial stage showing meristematic protrusions (x 30). (c) Later stage showing distinct initiation ~f secondary branches of panicle (x 20). (d) Advanced stage (bud burst) showing lohing of secondary branches and formation of flower primordium (x 20). The letters on the photographs mean: S ffi Scale; OS = Outer Scale; S= inner scale; G = growing tip; mp ffi meristematic protrusion; ma ffi main axis; Sb = secondary branch; FP = flower primordinm.

5 99 Stage. High meristematic activity (early October, 1975), marked by the origin of broad conical protruberances in the axils of scales. This is the sign of fruit-bud differentiation (Singh, 1958). Morphologically, the buds appear as shown in Fig. 2, numbers 1 and 2. Stage. The buds become plump by the 2nd week of November, getting conically protruded (Fig. 2, numbers 5 and 6) and the growing-tip gets protruded out of the scales. The main axis elongates and becomes multilobed due to the development of the primary branches of the flower panicle (Fig. 3b). Some of the side protuberances also get multilobed due to the primordia of secondary branches. Stage. The flower bud gets conical and plump and emerges out of the scales (Fig. 2, number 7). The main axis elongates, while the primary and secondary branches show lobing, indicating the formation of a flower cluster (Fig. 3c). Stage V. By the last week of December, the scales start loosening, indicating the "bud break" stage (Fig. 2, numbers 9--12). Further elongation of the axis and loosening of scales (Fig. 3d) makes the bud enter the "bud-burst" stage which is the most advanced stage of fruit-bud differentiation. The stages of bud development in 'Totapuri' were the same as in 'Alphonso', except that they occurred a fortnight earlier. These were similar to those noted for 'Dashehari' and 'Langra' cultivars by Singh (1958). However, the duration of the fruit-bud differentiation in the present cultivars was shor~r as compared to the ones studied by Singh under Saharanpur (subtropical) conditions. This shorter duration may be due to the existence of a shorter cold period at Dharwad. ACKNOWLEDGEMENT The authors are grateful to Dr. B.N. Viswanath for taking the microphotographs. REFERENCES Chacko, E.K., Kohli, R.R. and Randhawa, G.S., nvestigations on the use of (2- chloroethyl) phosphonic acid (ethephon, CEPA) for the control of biennial bearing in mango. Scientia Hortic. 2: Gunjate, R.T., Rajputh, J.C. and Limaye, V.P., Fruit-bud differentiation in 'Alphonso' mango under Konkan conditions. J. M.A.U., 2 (2): Johanson, D.A., Plant Micro-technique. McGraw Hill, New York, London. Khan, A.A., Deblossoming in relation to biennial bearing in mango. Punjab Fruit J., 25: Maheswari, P., Recent advances in micro-technique.. The paraffin method in plant cytology. Cytologia, 10: Pandey, R.M., Singh, R.N. and Sihha, G.C., Usefulness of ethrel in regulating flower bearing in mango. Sci. Cult., 39 (3): Sen, P.K. and Mallik, P.C., The time of differentiation of flower buds in mango. ndian J. Agric. Sei., 11: Singh, R.N., Studies on differentiation and development of fruit buds in mango.. Morphological and histological changes. Hortic. Adv., 5: