CHEMICAL CONTROL OF GROWTH AND FLOWERING IN MANGIFERA INDICA L.

During the last few years a group of growth suppressing chemicals, commonly known as growth retardants have been introduced as foliar sprays (12) and ornamental horticulturists are presently using them with considerable success (2). Of the growth retardants tried so far on fruit trees, the most promising ones are B-Nine (N-dimethylaminosuccinamic acid) and Cycocel (2-chloroethyl trimethylammonium chloride) which show a number of particularly striking effects on apples, pears and cherries. Effects associated with their use include suppression of vegetative growth and promotion of flowering, regardation of fruit growth, reduction in pre-harvest drop, improvement of colour of fruits and their storage life (1, 4, 6, 10, 13, 15).

Reports on the effects of these chemicals on tropical fruits are very few. A preliminary experiment carried out during 1967-68 indicated a beneficial effect of B-Nine and Cycocel on flowering of a biennial mango tree (9). This paper deals with the effects of these two chemicals on growth and flowering of young as well as mature trees of the varieties (intensively alternate bearing) and Baramasia (perpetual flowering).

Between the two chemicals, B-Nine and Cycocel, the latter had a remarkably suppressing effect on growth, irrespective of varieties and age of plants (tables 1 and 2). B-Nine, on the other hand, behaved differentially in this respect. It significantly reduced linear extension of shoots when applied to the mature Langra trees but failed to do so when given to the young Langra plants which were more vigorous in growth than mature ones. In case of young Baramasia mango plants, B-Nine showed a promotion, instead of inhibition, in linear extension of shoots in all the three concentrations tried, though this promotion in linear extension did not reach the significant level (table 2). Cycocel significantly retarded linear increase of shoots in young as well as mature Langra and in young Baramasia mango. Growth reducing effect of Cycocel was more pronounced in mature trees than in young ones. Further, retardation in linear extension of shoots of young as well as mature mango trees was more at higher concentrations of Cycocel and the most significant reduction in linear extension was noted at 2000 ppm in case of mature Langra and at 4000 ppm in case of young plants of Langra and Baramasia. The efficacy of Cycocel over B-Nine can be explained in the light of Luckwill's hypothesis based on his own observations on young apple trees (8) and other observations (5, 16) that Cycocel brings about a reduction in gibberellin production in young leaves which in turn results in a reduced output of auxin from the apical meristem and consequent