Identification of neutral alleles at pollen sterility gene loci of cultivated rice (Oryza sativa L.) from wild rice (O. rufipogon Griff.)

Oryza rufipogon Griff. is the ancestor of Asian cultivated rice (O. sativa L.) and possesses valuable genes for rice breeding. Pollen abortion is one of the major causes of indica-japonica hybrid sterility in rice and it happens due to allelic interaction at the pollen sterility gene loci. A total of six loci (Sa, Sb, Sc, Sd, Se, and Sf) have been found to be associated with F-1 pollen sterility between indica and japonica rice, and five of them (all except Sf) have been mapped. Neutral alleles (S (n) ) at each locus have the potential to overcome the pollen sterility associated with the respective locus. Therefore, exploitation and utilization of neutral alleles have significant importance in overcoming indica-japonica hybrid sterility. In this study, an accession (IRW28) of O. rufipogon, native to China, was selected as paternal to cross with typical japonica (Taichung 65) and indica (Guanglu'ai 4) tester lines, and two F-2 populations were developed. The simple sequence repeat markers tightly linked to five pollen sterility loci were applied for genotyping the F-2 populations. Chi-squared tests were applied to examine the normal segregation/distortion at each locus. The expected and observed pollen sterility for each locus were estimated. As a result, the genotypes at five pollen sterility gene loci for IRW28 were identified as: Sa (i-1)/Sa (i-1), Sb (n) /Sb (n) , Sc (i-2)/Sc (i-2), Sd (n) /Sd (n) and Se (n) /Se (n) . Our results suggest that IRW28 (O. rufipogon) has the neutral alleles for pollen fertility at the Sb, Sd and Se loci, and these alleles have a good affinity with indica and japonica rice. These neutral alleles provide valuable gene resources to overcome the inter-subspecific hybrid pollen sterility in rice.