STUDIES ON THE PHYSIOLOGY OF FLOWERING AND FRUIT GROWTH IN MANGIFERA INDICA L. VI. - HORMONAL CONTROL OF FRUIT DEVELOPMENT AND ITS POSSIBLE SIGNIFICANCE TO BIENNIAL BEARING

The problem of biennial bearing in mango centres around the process of fruit development and the inhibitory influence of the developing fruits on the mango tree. This phenomenon can be understood only, if we have a knowledge regarding the endogenous growth factors involved in fruit setting and development. It is the purpose of this paper to present the results of our studies on the hormonal control of fruit development in Dashehari mango and to discuss its possible significance to biennial bearing.

Fruits for these studies were collected from 14 years old trees of the variety Dashehari. The age of fruits was determined from a fruit growth curve obtained from the growth measurements of fruits resulting from hand pollination. Fruit samples were collected at various intervals till maturity. After recording the measurements, the fruit and seed samples were frozen to -23°C for the extraction of growth substances. Auxins, inhibitors and gibberellin-like substances were extracted from whole fruit or its components viz. pericarp and seed with cold methanol under low temperature. The mathanolic extract was concentrated to dryness in a flash evaporator. The flash evaporated residue was partitioned into acidic, neutral and acqueous fractions with peroxide-free diethyl ether for auxins and inhibitors, and with ethyl acetate for gibberellin-like substances following standard procedures (8, 9, 10, 21, 25). The various fractions were further purified by descending paper chromatography using isopropanol-ammonia-water (10:1:1 v/v) as the solvent system. The chromatographic behaviour of the growth substances from mango fruits were compared with that of suspected synthetic compounds. Also, the acidic, ethyl acetate fraction of seed extract containing gibberellin-like substances was fractionated further by column chromatography on charcol/celite mixture (8).

The developed chromatograms were tested for the presence of auxins and inhibitors by Avena first internode, and Avena and wheat coleoptile straight growth tests and cress seed germination test (1, 18). The gibberellin-like substances were tested by D5 dwarf maize bioassay and lettuce hybocotyl test (2, 20).

The developed chromatograms of plant extracts were also viewed under UV light and later sprayed with various chromogenic reagents for the detection and chemical identification of auxins and gibberellins (9, 21).