Mode of action of ethephon as a chemical thinner on Japanese pear [Pyrus pyrifolia] flower
2006
Ohkawa, K.(Chiba Univ., Matsudo (Japan). Faculty of Horticulture) | Shiraishi, N. | Ohara, H. | Matsui, H.
The mechanism of flower thinning by ethephon treatment was investigated in the Japanese pear "Hosui". Ethephon at 250 ppm was applied to flower clusters 7 days before full bloom (DBFB). After ethephon treatment, the proportion of flowers in which the abscission layer was formed at the juncture between peduncle and inflorescence axis was increased from 1 DBFB to 2 days after full bloom (DAFB). In contrast, there was no abscission layer formed at this juncture in control flowers at 2 DAFB. Ethylene evolution from the ethephon-treated flower clusters was increased markedly. Abscisic acid (ABA) and 1-aminocyclopropane- 1-carboxylic acid (ACC) concentrations in inflorescence axis, peduncle or flower were also increased by ethephon treatment. However, there were no differences in the indoleacetic acid (IAA) content between ethephon-treated flower clusters and control flower clusters before 1 DBFB. When ethephon at 250 ppm was applied to flower clusters at 12 or 4 DBFB, or 2 DAFB, ethylene evolution from the flower or fruit clusters was found to differ with the treatment time. The fruit set percentage at 23 DAFB tended to decrease with increasing ethylene evolution following ethephon treatment. Together, the results suggest that ethephon treatment exerts a thinning effect by promoting the formation of the abscission layer through increased ethylene evolution, and that the thinning effect depends on the ethylene evolution following ethephon treatment.
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