Grain size is one of the most important factors determining rice yield.Several major QTLs for grain size control have been molecularly characterized,and their roles in the regulation of grain size or weight have been explored but still remained obscure.In this study,240 recombinant inbred lines(RILs),derived from a cross between an extra-large grain Japonica variety TD70 and a small grain Indica variety Kasalath,were genotyped and examined.