The use of growth regulators to increase precocity in apple trees

Abstract

SummarySprays of 500 or 1000 ppm daminozide, 250 or 500 ppm paclobutrazol (PP333), or 250 ppm ethephon were applied to cvs Bramley, Discovery and Cox’s Orange Pippin apples on M.9 and MM. 106 rootstocks as single, double or triple applications during June, July or August (3, 7 and 11 weeks after petal-fall). Each growth regulator reduced final fruit set on Cox’s Orange Pippin but only paclobutrazol decreased set on Bramley. Paclobutrazol applications which included a spray at 3 weeks after petal-fall reduced the number of Cox fruit and yield per tree at harvest. The June application reduced extension shoot growth on Bramley, Cox and Discovery, but failed to increase spur or axillary fruit bud formation in the following year. For both Bramley and Cox the application of250 ppm ethephon in July, or June and August, induced more spur buds to form without affecting shoot growth. These results are discussed with reference to maximizing vegetative growth and fruiting on young trees. In a second experiment spraying young Cox’s Orange Pippin and cv Crispin trees on M.9 rootstock once during bloom with 200 ppm triadimefon increased final fruit set on spur and terminal clusters and total number of fruit per tree at harvest. Total yield was unchanged while mean fruit weight was decreased. Initial fruit set on axillary clusters was increased in both Cox and Crispin on MM.106 but not on M.9. Putrescine at 16 or 160 ppm, amino-oxyacetic acid (AOA) at 500 or 1000 ppm, both applied once during bloom or one week after petal-fall, or 50 ppm Promalin (GA4+7+ BA), applied before June drop, were without effect.