SHOOT GROWTH, FLOWER INITIATION AND DORMANCY OF APPLE IN THE TROPICS

The bi-annual and continuous cropping of apples in Indonesia offers a unique opportunity to study growth regulation in this plant. Bud burst and flower emergence are induced at any time of the year by hand defoliation. At the time of defoliation there are high levels of gibberellins and cytokinins in the apices and ABA and other inhibitors in the subtending leaves. Cessation of shoot growth by terminal bud formation depends on competition between a large number of growing points. Flower initiation follows terminal bud formation but subsequent flower development is slow until after harvest and defoliation. Daminozide hastens terminal bud formation and flower initiation. GA₃ delays these by promoting leaf emergence. Physiological dormancy of terminal buds is avoided by defoliation within a month of harvest. No chilling requirement is apparent; no chilling temperatures occur. Dormancy of most lateral buds is not broken by defoliation. Burst of lateral buds is increased dramatically by bud slicing, partially by branch bending and, under some conditions, by ethephon treatment. There is no evidence for growth control mechanisms which differ from those known in the temperate zone.