Hormonal interactions during early physiological partenocarpic fruitlet abscission in persimmon (Diospyros Kaki Thunb.) 'Triumph' and 'Shinshu' cultivars

Fruitlet abscission is typical to many fruit trees, including persimmon, (Diopyros kaki Thunb.), and often results in unstable fruit production and yield. We documented massive parthenocarpic fruitlet abscission in the persimmon cultivars 'Triumph' and 'Shinshu', which initiated soon after anthesis and peaked at 45 days post anthesis. In contrast, abscission of mature fruitlets 45-65 days after anthesis was minor. The early parthenocarpic fruitlet abscission in 'Shinshu' and 'Triumph' took place in the abscission zone located at the calyx-pedicel junction. Differentiation of the abscission layer occurred during flower development and preceded fruitlet abscission. Endogenous analysis of gibberellins, cytokinins and auxin levels in the abscission zone of 'Triumph' and 'Shinshu' during the developmental stages preceding abscission revealed a reduction in cytokinin endogenous levels in both cultivars. In addition, a decline in GA3 and IAA levels was found in 'Triumph' and 'Shinsu' respectively during flower development. Gibberellin, auxin and cytokinin application to inhibit early fruitlet abscission were analyzed and gibberellin treatment exhibited the highest and most consistent inhibition effect in 'Triumph' and 'Shinshu'. An increase in endogenous levels of gibberellins, cytokinins and auxin in the flower abscission zone was found following GA application in both cultivars. Our results suggest that gibberellin application inhibits early fruitlet abscission by elevating cytokinins, and auxin levels and that a reduction in gibberellins, cytokinins and auxin levels may induce abscission during parthenocarpic fruitlet development in 'Shinshu' and 'Triumph' cultivars.