The Conditional Chalky Grain Mutant 'Flo11-2modifier Letter Primeof Rice (Oryza Satival.) Is Sensitive To High Temperature And Useful For Studies On Chalkiness

Chalky grains of rice are increased due to high temperature (HT) during a ripening period. However, the underlying mechanisms of the chalkiness are not well known, seemingly due to the obtuse response of wild type and lack of effective mutants. In this study, we isolated and characterized theflo11-2mutant, which showed higher number of chalky grains than wild type under HT but quite small number of chalkiness under cool temperature as well as similar growth, development, and yield to that of the wild type. Using this high sensitivity of theflo11-2mutant, we identified the most critical meteorological factor and developmental stage affecting chalkiness with 5 days HT treatments over 4 consecutive years. The results demonstrated that daily maximum temperature was more causative than daily mean or minimum temperatures which have been regarded as important factors before this. Besides, the developmental stage around 20 days after flowering (DAF) was most sensitive to HT rather than the early stage up to 15 DAF. In addition, we found that theflo11-2mutant with a high chalky ratio was vulnerable to preharvest sprouting, which has never been reported before for chalky grains, but could cause significant yield and quality loss after extremely hot and dry summers followed by rainy cool autumns. Theflo11-2mutant is, therefore, a useful material for chalky grain research.