Studies on the standard of fruit thinning in Japanese persimmon, Diospyros Kaki LINN. f.

Abstract

It has been recommended to thin fruits to one fruit per bearing shoot in early July for controlling biennial bearing in Japanese persimmon. But this common practice has not been able to control biennial bearing habit in our orchard. This study has been carried out to make clear the reason why the common practice failed to control biennial bearing, and to propose a proper standard for fruit thinning as a hypothesis.
The orchard used for this study was composed of 33 trees including four varieties; Jirô and Hiratanenashi were biennial bearers and Mompei and Fuyû were annual bearers during the experiment from 1960 to 1962.
Although fruits were thinned to one fruit per bearing shoot early in July, biennial bearing habit has still been hold in the following years in Jirô and Hiratanenashi. This method left too much fruits in on year and too few fruits in off year. To leave proper number of fruits after thinning seemed to be essential for controlling biennial bearing.
A new standard for fruit thinning was searched to cover the weak point of the previous method. It was found that in spite of on and off years, about 85 percent of harvested fruits were borne on the shoots of 6_??_25cm in length Jirô and Hiratanenashi, and of 11_??_30cm in Mompei and Fuyû. The shoots of this length were tentatively called as the “yield composing shoots”. It was assumed to be reasonable to thin fruits to leave proper number of fruits per 100 yield composing shoots. Estimated desirable quantities of fruits per 100 yield composing shoots were 4.0_??_4.5kg for Jirô and Hiratanenashi, and 7_??_8kg for Mompei and Fuyu in our orchard, where yield of 2, 000kg per 10 ares is expected and leaf area index of trees is from one to two.