Effects of temperature during ripening on amylopectin chain-length distribution of 'Koshihikari' and 'Ichihomare'

Because of global warming, the ripening period of rice (Oryza sativa L.) is becoming hotter in Japan, and there is concern that eating quality will decline as a result. Amylopectin is the largest component of rice endosperm starch and its short-chain content has a considerable effect on the eating quality of cooked rice. Here we investigated the effect of high temperature during ripening on amylopectin chain-length distribution in 'Koshihikari', the leading cultivar in Japan, and in 'Ichihomare', released in 2017 and grown in Fukui prefecture, ripened in paddies over multiple years. The amylopectin short-chain content of degree-of-polymerization (DP) 6-13 of 'Koshihikari' grain ripened at high temperature was 3.03 points lower than that of grain ripened at low temperature. In contrast, that of 'Ichihomare' was only 0.26 points lower. For every 1 degrees C increase in temperature during ripening, the short-chain content of DP 6-13 of 'Koshihikari' decreased linearly by 1.03 points whereas that of 'Ichihomare' did not decrease significantly. These results suggest that the amylopectin chain-length distribution of 'Ichihomare' might be more stable to temperature during ripening than that of 'Koshihikari'. The reason is yet unknown, but this trait will contribute to breeding and production of cultivars with stable good eating quality under high temperatures during ripening.