Selection of chromosome segment substitution lines with reduced grain chalkiness without yield penalty in rice

Grain chalkiness decreases the appearance quality (APQ) of rice (<i>Oryza sativa</i> L.) grains and reduces consumer satisfaction. Improving APQ is a crucial issue for both marketing and breeding. Here, we screened chromosome segment substitution lines (CSSLs) with higher APQ to find promising genetic resources. These CSSLs harbor chromosome segments derived from multiple donors in the genetic background of 'Koshihikari', a leading <i>japonica</i> rice cultivar in Japan. Three CSSLs had an increased percentage of perfect grains without panicle weight loss under field conditions across 3 years in Tsukuba city, Ibaraki prefecture, Japan. The positions of reduced chalkiness in grains differed among CSSLs, suggesting the different contribution of the harbored chromosome segments to APQ improvement. There were no significant differences in days to heading, culm length, panicle length, or panicle number in all three CSSLs, but 1000-grain weight was reduced in one. These results identify two promising genetic resources for further improvement of APQ in current <i>japonica</i> cultivars with reduced chalkiness but unaltered heading date and yield traits.