CHANGES IN ENDOGENOUS GROWTH REGULATING SUBSTANCES IN THE MANGIFERA INDICA L. SHOOT IN RELATION TO GROWTH AND DEVELOPMENT

Studies of the role of season changes in endogenous growth substances (2, 7) added a new concept in the understanding of the physiology of growth of woody plants. Hatcher (2) observed that auxin content in apple twigs rose in spring as growth began and subsequently declined through the growing season until autumn. Phillips and Wareing (7) and Kawase (3) showed clear relationship of growth inhibitors to the growth and dormancy of the buds of Sycamore (Acerpseudoplatanus) and Betula (Betula pubescenes), respectively. They have reported that extracts of the apical region showed greatest activity in early winter and least when growth was taking place in spring-summer. Little is known about the changes of endogenous growth regulators in mango shoots. In mango, flowering in the variety Langra is preceded by a prolonged growth cessation phase of the shoot but in another variety Baramasia there is no marked growth cessation phase and flowering takes place almost throughout the year on shoots which are green and young. Studies on endogenous changes in growth substances are of special interest in these materials for understanding the nature of varietal difference in growth and bearing habit.

Well established trees of Langra (biennial) and Baramasia (perpetual) were selected for this study. The experiment was conducted during the years 1967–68 and 1968–69. The first sample of 1967–68 was taken in April when the first flush of spring growth in Langra came to a cessation and a second sample in June when there was no further flush of growth. The third, fourth and fifth samples were collected from ringed (ringing in June) and non ringed branches in October, November and December, respectively to cover the period of floral differentiation. In the following spring 60 per cent of shoots on ringed branches and only 3.3 per cent on non ringed branches produced flowers. Samples of Baramasia were taken on the same dates as in Langra. There was no ringing treatment in Baramasia. In this variety 50 per cent of terminal spring shoots flowered in May and 90 per cent of laterals appearing on the shoots which flowered in May, bore flowers through autumn-winter.

In 1968–69 current years growth was sampled during the period from March to January in both the varieties. With the view to suppressing growth and inducing flowering, Langra shoots were ringed in the second week of April, 1968. In this year also no such ringing operation was done in Baramasia as this variety normally flowers freely.

In Langra samples were collected in March, April, August, October,