INHIBITION OF FLOWERING INMANGIFERA INDICA L. BY GIBBERELLIC ACID

The biennial bearing habit of most of the commercial varieties of mango is a problem of serious economic consequence to the mango growers. In order to obtain some crop in the 'off' year, deblossoming during the 'on' year has been suggested as one of the means (5). This is, however, quite cumbersome.

Gibberellic acid has been reported to inhibit flower formation in several temperate fruit trees and Citrus (2, 3, 4). Such studies have not been reported in mango so far. However, Chacko (1) observed that during the period of flower induction the content of gibberellin-like substance in the shoots of 'on' year Dashehari mango trees was less than that of 'off' year trees, indicating the possibility that the lower gibberellin level might favour flower induction in mango. Preliminary observations revealed that the application of 400 ppm GA₃ to 'on' year shoots was helpful in inhibiting or delaying flowering by two weeks. Detailed studies were, therefore, undertaken and the results are presented in this paper.

A fourteen year old 'on' year tree of the variety Dashehari was selected for this study. One complete branch was taken as an experimental unit. Five branches including control were selected on the eastern side of the tree. In each branch seventy-five shoots were tagged and the apical buds were treated with one of the following concentrations of gibberellic acid, viz., 10^-1M, 10^-2M, 10^-3M and 10^-4M, prepared in lanolin. The first application was given on October 15 (before flower bud differentiation) and was repeated on November 15, 1968. Another branch in the eastern side of the tree was treated with 10^-2M gibberellic acid after one month of the first set of experiment, i. e., on November 15 and was repeated on December 15, 1968. Seventy five shoots from the control branch were treated with pure lanolin. Observations were recorded after signs of bud break were noticed and were continued till flowering was complete.

For microscopic examination, five buds were collected on December 15, 1968 and January 15, 1969, from the treated and control shoots. The buds were fixed in FAA solution, embedded, sectioned and stained with fast green and safranin for recording the floral primordia development.

The data on inhibition of flowering following application of different concentrations of GA₃ are presented in figure 1.

The control shoots started bud break on January 2, and showed visible signs of panicle emergence as early as January 24, 1969. In the shoots treated with 10^-1M GA₃ there was no indication of bud break even on March 1st and 94 per cent of such shoots burst into vegetative growth on