Molecular mapping of the fertility-restoration gene Rf4 for WA-cytoplasmic male sterility in rice

The wild abortive cytoplasmic male sterility(CMS-WA) system, an ideal typeof sporophyticCMS in indica rice, is used for the large-scale commercial production of hybrid rice. Searching for restorer genes is a good approach when phenotyping is very time-consuming and requires the determination of spikelet sterility in testcross progeny. To establish more precisely the genetical and physical mapsof the Rf4 gene, high-resolution mapping of this locus was carried out using simple sequence repeat (SSR) markers and newly designed markersin a F 2 population. The genetic linkageanalysis indicated that five SSR markers (RM6737, RM304, RM171, RM5841 and RM228) on the long arm of chromosome 10 were linked with the Rf4 gene. Rf4 was flanked by two SSR markers RM171 and RM6737 at distances of 3.2 and 1.6 cM, respectively. Also, within the region between Rf4 gene and RM171, a newly designed primer pair, AB443, produced two sterile-specific markers, AB443-400 and AB443-500, 0.5 and 1.03 cM from the gene. The flanking markers identified give promise for their application in molecular marker-assisted selection(MAS) and they are also suitable for starting chromosome walking to clone Rf4 gene in the near future.