Abstract
The effects of high temperature(32°C/23°C max/min;27.5°C, daily mean temperature), which is common in August in Fukuyama city, Japan, on the grain weight and the grain quality of rice plants were examined. Air temperature was controlled artificially in growth chambers. The grain weight at 32°C/23°C was lower than at 28°C/19°C as a control in all primary branches at a panicle. The proportion of normal grains relative to all grains was smaller at 32°C/23°C. Moreover, the grain weight and the proportion of normal grains relative to all grains at 35°C/26°C were smaller than those at 32°C/23°C. The decrease in grain weight at high temperature accompanies the decrease in grain thickness. The proportion of imperfectly ripened grains relative to all grains at 32°C/23°C was higher than that at 28°C/19°C, and the proportion of nonfertilized grains at 35°C/26°C was higher than that at 32°C/23°C. The cultivars for which the ratio of grain weight at 35°C/26°C to that at 28°C/19°C was lower than 90% were Moritawase, Arborio as a large grain, and Akenohoshi, which tended to have a bad ripening performance. In contrast, the cultivars with a ratio higher than 95% were Koganemasari, Lakhi Jhota as a small grain, and Hoshiyutaka, known as a good ripened cultivar.
