Effect of shading and girdling on physiological fruit drop of Japanese persimmon ‘Akiou’

‘Akiou’ is a nonaploid (2n=9x=135) seedless pollination constant, and non-astringent (PCNA) type of Japanese persimmon cultivar developed at the Fukuoka Agricultural Research Center in 2012. The cultivar was selected for embryo culture of imperfect seeds derived from a cross between ‘Fuyu’ and ‘Taishuu’, both of which are hexaploid (2n=6x=90) PCNA cultivars. This cultivar has a large fruit size, high sugar content, and excellent taste, and has been introduced to many regions. However, owing to it being seedless and low parthenocarpy, physiological fruit drop is frequent, and fruit set is unstable. In this study, we investigated the effects of shading on the fruit set of ‘Akiou.’ For the shading treatment, the whole tree was covered with cheesecloth from day 1 to 78 after full bloom. Under 50% shading and 45 days after full bloom, the fruit set was low at 20%, while that of unshaded control trees was 68%. In addition, the effect of girdling on the fruit set rate was investigated for three years. The girdling treatment was applied to the trunk 20 days after full bloom. After 70 days of full bloom, the fruit set rate in the girdling treatment group (58-73%) was significantly higher than that in the untreated group (15-32%). These results indicated that shading promoted physiological fruit drop of ‘Akiou’ and that girdling suppressed physiological fruit drop. This suggests that insufficient supply of assimilation product due to reduced solar radiation is a factor causing physiological fruit drop of ‘Akiou,’ and that girdling, which increases the distribution of assimilation product to the fruit, is an effective preventive measure.