Series of Advanced Backcross Populations Uncovers Diversity and Complexity in Genetic Control of Grain Length and Grain Width in Asian Cultivated Rice

The use of genetic variations in Asian cultivated rice is essential for crop improvement. Advanced technologies and accumulated genome information support this effort to ensure sustainable production under changing environmental conditions. Grain length and grain width are important agronomic traits in rice. Extensive studies have revealed their complex genetic control. To further clarify the genetic basis of grain length and grain width in rice, we constructed a comprehensive catalog of QTLs for these traits based on QTL analysis of advanced backcross populations from crosses between a japonica rice cultivar 'Koshihikari' and 12 diverse donor cultivars. It comprised 469 QTLs (average 39.1 QTLs per donor) and provided estimates of allelic effects within a uniform japonica genetic background. To validate and delimit QTLs, we used sub-CSSLs-a set of plant materials with one or no segregating regions from these donors in a homogeneous genetic background. New QTLs were validated by genetic mapping in three chromosomal regions previously unreported in other mapping populations. Our results underscore the diversity and complexity of genetic control of grain length and grain width in Asian cultivated rice, and these insights will facilitate more precise genetic improvement of rice grain traits.