Hormonal control of parthenocarpic fruit set in 'Rojo Brillante' persimmon (Diospyros kaki Thunb.).

In persimmon (Diospyros kaki Thunb.), one to three waves of fruit abscission can occur. The parthenocarpic cv. Rojo Brillante may abscise close to 50% of flowers, which implies a major economic losses. In order to study this process, 700 flowers were labelled, 600 had the lobes of the calyx removed at three stages to promote abscission. Half of them were also treated with gibberellic acid (GA3; 10 mg l-1) to counteract the effect, and 100 were used as control. In the second year, GA3 (25 mg l-1) was applied to whole trees. Calyx lobe removal (CLR) reduced fruit growth rates and advanced and increased fruitlet abscission, whereas GA3 counteracted this effect. Furthermore, when GA3 was applied to the whole tree, fruit set was increased. The time-course of fruit abscission paralleled a decreased in hormonal and carbohydrate contents. Control fruit showed a peak of gibberellin (GA1 and GA4) and IAA concentration at anthesis. Hexose concentrations remained almost constant from flower bud to fruit set, whereas that of sucrose diminished with time. A peak in ethylene production occurred at anthesis, which increased when CLR was performed prior to or at anthesis, but not when performed at fruit set, when ethylene was markedly smaller. GA3 also counteracted it. Accordingly, we suggest that fruit set depends on the induction of gibberellin (GA) and IAA responses in the persimmon, and since there is no shortage of hormones or carbohydrates at anthesis, ethylene production at anthesis seems the most plausible cause of the physiological fruitlet abscission.