Several growth regulators such as B-9, Gibberellic acid and so on, were applied to increase berry setting by preventing shot berry, with raises considerable problem in growing ´Kyoho´ grapes and their effects examined for 2 years from 1974 to 1975. The results were as follows.
1. The most pronounced increase in the seeded berry setting was brought about by the foliar application of 0.5% B-9 at G-7 leafing. The application of FC-907, which was developed most recently was also effective, but less than that of B-9.
2. The application of GA increased the setting of seedless berry remarkably, and the seedless berry weighed 6.5-7.5g, and rather large for seedless ones, thus promising a high marketability. 4-CPA treatment increased number of set berry, but not practical and recommendable to the growers due to small berry size.
3. The shoot extension was inhibited by application of B-9 and FC-907, but more markedly by the latter. The other regulators had no effect. FC-907 tended to decrease leaf number.
4. In the first growth stage only, GA application caused a rapid berry growth, resulting in larger size than seeded berry applied with B-9. However, the later growth slowed down after hard seed stage, and the berry shape was similar to oblong, while the typical double sigmoid curve was shown in that of B-9 application.
5. GA application exhibited a significant increase in berry setting ratio regardless of tree vigor, while the effect of B-9 application was lowered in vigorous shoot.
6. The best time for GA application proved to be two days after full bloom, and GA can be commercially sprayed during 6 days from 50% bloom stage to 4 days after full bloom.
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