The conditional chalky grain mutant ’flo11-2ʹ of rice (Oryza sativa L.) is sensitive to high temperature and useful for studies on chalkiness

Abstract

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 the flo11-2 mutant, 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 the flo11-2 mutant, 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 the flo11-2 mutant 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. The flo11-2 mutant is, therefore, a useful material for chalky grain research. Abbreviations: Tmax: Daily maximum temperature; Tmean: Daily mean temperature; Tmin: Daily minimum temperature; DAF: Days after flowering; DAH: Days after heading; Ext30: Excess temperature above 30 ºC; HDT: High day temperature; HNDT: High night and high day temperature; HNT: High night temperature; HT; High temperature; HTR: High temperature resistant; HTS: High temperature susceptible; BW: Basal white; MW: Milky white; WB: White back.