Grain weight is one of the important traits in rice for it determines grain yield and affects appearance quality in some degree. Grain weight is controlled by quantitative trait loci (QTLs) and determined by grain width, length, thickness and plumpness. To date, many QTLs have been identified, however only two QTLs have been fine mapped. It is urgent for identifying more QTLs expressed in different environments and genetic backgrounds so that they could be used in further fine mapping and breeding applications. So a chromosome segment substitution line (CSSL) population consisting of 65 lines, derived from Asominori and IR24 cross with the genetic background of Asominori, were grown in different environments to detect grain-weight related QTLs based on the stepwise regression of the traits and markers. The phenotypic values for milled rice weight (MRW) and brown rice weight ( BRW) showed a continuous distribution and some transgressive lines were also observed in the CSSLs population. A total of six QTLs for grain weight were detected in five environments, which located on the chromosomes 1, 6, 7, 8, and explained 13%–35% of phenotypic variance. The qMRW-1a and qPRW-1 could express stably in all experiment environments, both being in the same chromosome location of nearest marker XNpb113 on chromosome 1. Thus the markers could be used for marker assisted selection (MAS) of rice grain weight. MRW and PRW differed significantly between the CSSLs harboring the QTL allele and Asominori. In comparision with previous studies, they were found to be expressed in various genetic populations, and also had the similar chromosomal location with the gene for sucrose phosphate synthase. Therefore we deduced the QTL was associated with rice starch metabolism. qMRW-1a and qPRW-1, which had highly stable expression characteristic, should be used for fine mapping to elucidate the genetic basis of the rice grain weight.
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