Genetic bases of appearance quality of rice grains in Shanyou 63, an eliterice hybrid

Appearance quality of the rice grain represents a major problem of rice pro duction in many rice-producing areas of the world, especially in hybrid ric e production in China. In this study, we conducted a molecular marker-based genetic analysis of the traits that are determinants of the appearance qua lity of rice grains, including traits specifying grain shape and endosperm opacity. The materials used in the analysis included an F-2:3 population an d an F-10 recombinant inbred line population from a cross between the paren ts of Shanyou 63, the most widely grown rice hybrid in China. Molecular mar ker-based QTL (quantitative trait locus) analyses revealed that grain lengt h and grain width were each controlled by a major QTL accounting for a very large proportion of the genetic variation, plus one or two minor QTLs each explaining a small proportion of the genetic variation. The major QTLs can be detected in both the F-2:3 and recombinant inbred line population using both paddy rice and brown rice, whereas the minor QTLs were detected only occasionally. The QTL located in the interval of RG393-C1087 on chromosome 3 is the major locus for grain length, and the one in the interval RG360-C7 34a on chromosome 5 plays a major role in determining grain width. Similarl y, white belly, which largely determines the opacity of the endosperm, is a lmost entirely controlled by a major locus on chromosome 5, located in the same genomic region as the major QTL for grain width. The implications of t he results with respect to hybrid rice improvement were discussed.