Abstract
Differences in ripening capability at high temperatures were examined for Koshihikari and Hitomebore in farmers' fields in Fukushima prefecture. Mean daily average temperatures during 20 days, mean daily lowest temperatures during 20 days and cumulative temperatures above 30 °C for daily highest temperature during 10 days around heading were calculated and the effects of temperature on rice grain qualities were analyzed. The average incidence of milky white kernel, white-back & white-belly kernel and white-based kernel for the two cultivars was 8.2%, 4.6% and 1.2%, respectively. The incidences of white-back & white-belly kernels and white-based kernel were significantly higher in Koshihikari than in Hitomebore. The incidence of white-back & white-belly kernel was significantly and positively correlated with mean daily average temperatures in Koshihikari and the correlation was highest with the average temperature during 8 to 27 days after heading. The average temperatures during this period were similar in Koshihikari and Hitomebore, which indicated that ripening capability at high temperatures was higher in Hitomebore than in Koshihikari.
