エスレル散布によるカキの薬剤摘果

Abstract

As a clue in elucidating the mechanism of flower or fruit thinning of Japanese persimmon (Diospyros Kaki Linn. f. cv. Fuyu) by the ethrel (2-chloroethylphosphonic acid) application, the influence of ethrel on their abscission layer formation was investigated in 1975. About 50 year-old mature trees at flower bud stage (at about 10 days before bloom) or young fruit stage (at 18 days after full bloom) were sprayed with 75 or 150ppm ethrel solution.1. The drop rate of flowers or fruits up to 14 days after application was about 23% and 71% with 75ppm and 150ppm ethrel application, respectively, at flower bud stage, while the natural drop was about 6% in this period. On the other hand, the drop rate of young fruit was about 11% and 23% with 75ppm and 150ppm application, respectively, at young fruit stage, while the natural drop was about 4%.2. Flowers or fruits dropped by the application at flower bud stage or naturally abscissed at their juncture between calyx and peduncle or fruit stalk. The abscission layer formation in this juncture was observed under the microscope. On the other hand, fruits dropped by the application at young fruit stage or naturally abscessed at their juncture between calyx and fruit. No specific cell of the abscission layer in this juncture was observed under the microscope.3. At 10 days before bloom it was observed that (a) formation of flower abscission layer cells in the controls had begun at the rim in the juncture between calyx and peduncle, (b) at 1 day before bloom they had not yet formed in the central part of the juncture, and (c) at 16 days after full bloom they were formed in the entire juncture.In the case of flower to which ethrel was applied, the abscission layer was formed by the same process as the control, but the layer was complete 1 day before bloom.No difference between the controls and the treated ones was observed in the morphological changes of abscission layer tissue, although it was obvious that the formation of the abscission layer was somewhat accelerated by ethrel application. Also, no difference in effect on the abscission layer formation was observed between the two ethrel concentrations.4. At the base of the petiol of mature leaves, the abscission layer had already been formed conpletely 10 days before bloom when it was first observed. Furthermore, no changes in the abscission layer were observed in either the controls or the ethrel-treated trees.5. In regard to the development of abscission layer tissue, most abscission layer cells in the control fruit at 18 days after bloom were loosened, and small, irregular crevices had formed everywhere around the abscission zone. In contrast, in ethreltreated flowers, 3 days before bloom a continuous crevice was formed as cells detached from each other along the middle part of the abscission zone. No cell loosening was found among all the other cells, which were tightly combined.