[Mapping quantitative trait loci associated with rice grain shape based on an indica/japonica backcross population]

Appearance of rice grain represents a major character of rice quality in many rice-producing areas of the world, especially in hybrid rice production in China. In this study, we conducted a molecular marker-based genetic analysis of the traits that are determinants of the appearance quality of rice grains, including grain length, grain width and grain shape (measured as grain length to grain width ratio). Two typical indica/japonica varieties Balilla and Nantehao(NTH) were selected to construct Balilla/NTH//Balilla backcross population containing 142 individuals. In the population, grain length, grain width and grain shape all conform to the normal distribution with certain transgressive segregation. It can be deduced that all of three traits were controlled by some quantitative trait loci (QTLs). In order to explore the QTLs effect, number and location, a linkage map consisting of 108 SSR markers based on the backcross population was constructed, and QTLs mapping was carried out for grain length, grain width and grain shape. A QTL, qGL-12, was detected for grain length at the interval RM101-RM270 on chromosome 12, its additive effect was 0.26 mm, and can explain 16.7% genetic variation. As for grain width trait, two QTLs were found, qGW-2 located at RM154-RM211 interval on chromosome 2, and qGW-3 at interval RM257-RM175 on chromosome 3, accounting for 11.5% and 16.6% genetic variation, respectively. The alleles at qGW-2 and qGW-3 from parent Balilla can increase grain width by 0.10 mm and 0.12 mm. For grain shape, 3 QTLs, qLW-2, qLW-6 and qLW-7 were found, located on chromosome 2, 6, and 7, respectively. qLW-2 and qLW-7 had positive effect, and they can explain 12.7% and 18.3% genetic variation, while qLW-6 had negative effect and contributed 11.5% genetic variation to the backcross population. The prospects of application of linkage relationship between SSR marker and QTLs in marker based selection (MAS) in rice breeding, and the improvement of grain shape and rice appearance quality were discussed.