Mechanism of the Thinning Action of NAA in Japanese Persimmon (Kaki) Fruits

The ethylene production and abscission of Japanese persimmon fruits following NAA and ethephon applications as affected by seed number per fruit and exogenous gibberellin were investigated in 1976 and 1977.1) The application of either NAA or ethephon at 50ppm 20 days after full bloom induced the ethylene production and abscission more distinctively in the open-pollinated fruits (mean seed number per fruit; 1.9) than in the hand-pollinated fruits (mean seed number per fruit; 5.6). Further, the effect of seed number on the ethylene production was more pronounced in the case of ethephon application, where very low level of ethylene was released from the hand-pollinated fruits.2) NAA spray about 10 days after full bloom with the application of GA3 at 500ppm 15 hrs prior to the NAA spray accelerated the ethylene evolution and abscission of fruits to a greater degree than the NAA spray alone. On the contrary, the pre-application of GA3 depressed the ethylene evolution caused by the ethephon spray and completely eliminated its thinning action.3) The application of GA3 at 200ppm 48, 24 or 6hrs prior to the NAA spray slightly increased the NAA-induced ethylene production, but all the treatments, particularly those applied 48 and 6hrs prior to the NAA spray decreased the cumulative fruit drop to the level almost similar with that of control. Eventhough the application of GA3 at 200ppm 20hrs after the NAA spray had hardly any effect on the NAA-induced ethylene production, the resultant fruit drop was completely restrained by the supplementary GA3 application.