Regulation of Fruit Set in the Grape Vine

Abstract

Defoliation reduces fruit set in the grape vine, but the mechanism of this effect is the subject of controversy. Effects of leaf removal on set have been attributed either to reduction in supply of organic nutrients to the developing bunch or to reduction in supply of fruit· setting factors. In the experiments reported here, small immature fruits developed on defoliated and decapitated vine cuttings, on cuttings in which leaves, apices, and roots were removed as they appeared, and on inflorescences which were cultured in the light in vitro on a medium devoid of exogenous growth substances. These results indicate that fruit set is regulated by supply of organic nutrients rather than by specific hormonal stimuli originating from organs external to the developing bunch.