Relationship between an Air Temperature Drop in Summer and Autumn and Fruit Skin Coloring in ‘Fuyu’ Persimmon

Abstract

Ambient temperatures affect many important traits of tree crops, including persimmon (Diospyros kaki Thunb.). Recent effects of global warming have adversely influenced persimmon fruit in terms of softening and inferior coloration. This study presents insights into air temperature effects on the coloration and harvest time of ‘Fuyu’ persimmon fruit over the last 20 years (1993–2012). The monthly mean air temperature in September and October had a significantly negative correlation with fruit coloration on November 25. The fruit apex coloration on November 25 (7.8), measured with Yamazaki and Suzuki’s color chart (CC), was significantly higher by around CC1.5 in cool years when September and October had a monthly mean air temperature of less than 21°C, than in years with 21°C or more. The date when the daily mean air temperature first decreased to a given temperature after mid-August, was negatively correlated with the fruit skin color on both October 25 and November 25. The date when the daily mean air temperature first decreased to 23°C or less showed the most significant correlation coefficient: r = −0.59** and −0.60** for October 25 and November 25 fruit skin color, respectively. These results indicate that fruit skin coloration is markedly influenced by the air temperature during September and October, and by encountering a given low temperature before the start of coloration.