Varietal Difference in the Occurrence of Milky White Kernels in Response to Assimilate Supply in Rice Plants (Oryza sativa L.)

Abstract

We examined the association of assimilate supply in the occurrence of milky white kernels in three cultivars with different percentages of milky white kernels in the field condition: ‘Hatsuboshi’, ‘Koshiibuki’ and ‘Koshihikari’. Five days after heading, the plants were placed in four controlled-environment chambers with either a high or low night temperature and elevated or normal [CO₂] supply. Plants in each chamber were either defoliated with only flag leaf remaining, flag leaf and second leaf remaining or left intact (control). The percentage of each type of chalky kernel was examined. The percentage of milky white kernels was increased by defoliation and decreased by elevated [CO₂], associated with assimilate supply. No association was observed between assimilate supply and white back or basal white kernels. The percentage of milky white kernels was negatively correlated with assimilate supply at a high night temperature in all cultivars. At a low night temperature, there was a clear threshold of assimilate supply, over which the percentage of milky white kernels was nearly zero. Cultivar differences were observed in the relation between the percentage of milky white kernels and assimilate supply. In conclusion, we found a varietal difference in the occurrence of milky white kernels in response to assimilate supply. In the cultivars used in this study, ‘Hatsuboshi’ was more sensitive to the low assimilate supply than ‘Koshihikari’.