Mapping and genetic analysis of two fertility restorer loci in the wild-abortive cytoplasmic male sterility system of rice (Oryza sativa L.)

Hybrid varieties developed by making use of the wild abortive cytoplasmic male sterility system account for 90% of hybrid rice produced. Previous inheritance studies have established that the fertility restoration in this system is controlled by two major loci, but the chromosomal locations of the fertility restorer (Rf) loci have yet to be resolved. In this study we determined the genomic locations of the two Rf loci by their linkage to molecular markers. The Rf gene containing regions were identified by surveying two bulks, made of 30 highly fertile and 46 highly sterile plants from a large F2 population of the cross between Zhenshan 97A and Minghui 63, with RFLP markers covering the entire rice genome. The survey identified two likely Rf gene containing regions, located on chromosomes 1 and 10 respectively. This was confirmed by ANOVA using a large random sample from the same F2 population and also with a genome-wide QTL analysis of a test-cross population. The results also showed that both loci have major effects of almost complete dominance on fertility restoration and the effect of the locus on chromosome 10 is larger than the one on chromosome 1. The two loci acted as a pair of classical duplicate genes; a single dominant allele at one of the two loci would suffice to restore the fertility to normal or nearly normal. Closely linked markers identified in this study may be used for marker assisted selection in hybrid rice breeding programs.