Effects of Plant Growth Regulators on Fruit Set and Fruit Shape of Parthenocarpic Apple Fruits

We applied auxin, cytokinin, gibberellins, and gibberellin synthetic inhibitor to flowers of 'Ohrin', which is parthenocarpic, and 'Fuji', which is non-parthenocarpic, to elucidate the relationship between plant growth regulators and parthenocarpy in apple. The percentage of fruit set in gibberellin A(3) (GA(3)) was about 60% in 'Ohrin' and about 7% in 'Fuji'. Forchlorfenuron (CPPU) combined with GA(3) treatment increased the fruit retention rate more than 14 days after treatment (DAT) than GA(3) alone. Dichlorprop (2,4-DP) combined with GA(3) slightly enhanced the gibberellin effect of inducing parthenocarpy. In 'Ohrin', GA(3) and gibberellin A(4+7) (GA(4+7)) showed a higher fruit retention rate before flowering than after. Parthenocarpic fruits were induced even when uniconazole (UCZ) was sprayed after flowering, but not before flowering. The calyx end was large in GA(4+7), and in GA(3) and CPPU singly, and GA(3) and CPPU combined treatments, which increased the percentage of fruit set. These results suggest that gibberellins before flowering trigger parthenocarpic apple fruits. Subsequent fruit growth requires cytokinins and auxin.