Molecular mapping of S-c, an F-1 pollen sterility gene in cultivated rice

Hybrids between indica and japonica rice varieties usually show partial sterility, and are a major limiting factor in the utilization of heterosis at subspecific level. When studying male-gamete (pollen) abortion, a possibly important cause for sterility, six loci ( S-a, S-b, S-c, S-d, S-e and S-f) for F-1 pollen sterility were identified. Here we report genetic and linkage analysis of S-c locus using molecular markers in a cross between Taichung 65, a japonica variety carrying allele S-c, and its isogenic line TISL5, carrying allele S-c. Our results show that pollen sterility occurring in the hybrids is controlled by one locus. We used 208 RFLP markers, as well as 500 RAPD primers, to survey the polymorphism between Taichung 65 and TISL5. Six RFLP markers located on a small region of chromosome 3, detected different RFLP patterns. Co-segregation analysis of fertility and RFLP patterns with 123 F-2 plants confirmed that the markers RG227, RG391, R1420 were completely linked with the S-c locus. The genetic distances between the markers C730, RG166 and RG369 and the S-c locus were 0.5 cM, 3.4 cM, and 3.4 cM respectively. Distorted F-2 ratios were also observed for these 4 RFLP markers in the cross. This result suggests that the `one locus sporo-gametophytic' model could explain F-1 hybrid pollen sterility in cultivated rice. RG227, the completely linked marker, has been converted to STS marker for marker-assisted selection.