Abstract
To investigate the effects of gibberellic acid (GA) on the suppression of physiological fruit drop, experimental GA treatment (dipping fruit in 50 ppm GA3 aqueous solution) combined with seed injury (SI) treatment were conducted using ‘Shimizu Hakuto’ peach. In experimental GA treatment (Exp. 1) 30 (G30) and 50 (G50) days after full bloom (DAFB), enlargement of fruit thickness was enhanced and rates of split-pit fruit were higher in G50 compared with G30. Suppression of embryo growth and browning of the seed coat, which were not observed in G30, occurred in G50. However, fruit drop was decreased in both G30 and G50 compared with that in the control. Next, SI was performed at 55 (SI55) and 65 (SI65) DAFB for fruit treated by G30 or G50, and control (Exp. 2). Fruit drop was delayed in G30 + SI55 and G50 + SI65 but was not decreased in G30 + SI65 or G50 + SI55 compared to control + SI55 or control + SI65. Furthermore, SI was performed at 70 (SI70) DAFB, and GA treatments were performed one day (SI70 + G71) and three days (SI70 + G73) after SI treatment (Exp. 3). Fruit drop were temporarily decreased by both GA treatments and the effect was obviously higher in SI70 + G73 than in SI70 + G71. Activation of GA content in flesh was higher in SI70 + G73 than in SI70 + G71 but there was no difference in the GA content of seed between these two treatment groups. Results of Exp. 3 indicate that GA contents of flesh might rapidly disappear following SI treatment and retention of fruit on the tree was not maintained. Based on the above results, GA3 treatment during Stage 1 of fruit growth effectively decreases physiological fruit drop.
