Effects of Rf-1, Rf-3 and Rf-6(t) genes on fertility restoration in rice (Oryza sativa L.) with WA- and BT-type cytoplasmic male sterility

Genes involved in the fertility restoration (Rf) of wild-abortive (WA)-type cytoplasmic male sterility (CMS) in rice have not been clearly identified, because of the inconsistency of their number and map position. Although the Rf-1 genes, which restore Chinsurah Boro (BT)-type CMS, have been recently isolated, their effects on WA-type CMS are still unclear. In the present study, near-isogenic lines (NILs) of japonica rice, differing at Rf loci, were developed using marker-assisted selection (MAS) to determine the effect of each R gene on WA- or BT-cytoplasm in a japonica background. The NILs were crossed with a japonica CMS line, then the pollen and seed fertility of the hybrid plants was analyzed. The Rf-1 locus consisting of two R genes from IR36 was sufficient to restore fertility in the hybrids with BT-type CMS but conferred very little fertility to those with WA-type CMS. Rf-3 on chromosome 1, a weak Rf gene, and Rf-6(t) on chromosome 10 were unable to confer seed fertility to plants with BT-type or WA-type CMS. Both Rf genes, however, could accelate the development of abortive pollen in the case of WA-type CMS and their effect was additive. Crossing of CMS rice with chromosome segment substitution lines carrying Rf loci from IR24 resulted in similar pollen development and seed fertility.