Inheritance and molecular mapping of Rf6 locus with pollen fertility restoration ability on A1 and A2 cytoplasms in sorghum

Of the several male sterility cytoplasms available as an alternative to the widely exploited A1 (milo) cytoplasm in sorghum, A2 is more suitable for commercial exploitation. Diversification of genetic and cytoplasmic base of hybrids involving A2 cytoplasm necessitates mapping of fertility restorer (Rf) genes for use in marker-assisted restorer development. We mapped a major male fertility restoration locus on sorghum chromosome 4 tightly linked with SSR markers, SB2387 and SB2388. This new fertility locus, Rf6, was able to restore male fertility on both A1 and A2 cytoplasms. Analysis of the genomic region around the Rf6 locus identified six genes including a pentatricopeptide repeat (PPR) gene, Sobic.004G004100. With its similar restoration ability to Rf1, Rf2 and Rf5 loci in sorghum, it is most likely that the Rf6 is a member of the PPR gene family, and the PPR gene Sobic.004G004100 could be a candidate for fertility restoration on A1 and A2 cytoplasms.