Abstract
Influence of high temperature conditions during the ripening period of paddy rice on husked rice quality was examined. The incidences of white-back kernel and white-based kernel were high when average temperatures during the 20-day period after heading was 27°C or higher . Almost no such incidence was apparent below that temperature. Because the husked rice was thicker and the protein content was lower in white-back kernel than in milky white kernel, it is presumed that the effect of white-back kernel on taste deterioration would be less than that of milky white kernel. The grain weight tended to be lighter in the condition with average temperatures of 26°C or higher during the 30-day period after heading, whereas the whole grain ratio tended to decrease at 27°C or higher temperatures. Concerning the husked-rice quality, the temperature suitable for ripening was 24°C, at which temperature the maximum grain weight was observed. Differences among cultivars were found in the ratio of imperfect rice incidence, showing the cultivar difference in the pattern and severity of the incidence. Especially, cultivar differences were marked in the incidence of white-back and white-based kernel. Cultivars with “weak” ripening capability at high temperatures include Hinohikari, Koganebare, Hatsuboshi, and Mineasahi. They are all derived from Kiho, which has inferior ripening capability at high temperatures, suggesting that the ripening capability at high temperature was genetically controlled.
