Molecular mapping of fertility restorer gene of an alloplasmic CMS system in Brassica juncea containing Moricandia arvensis cytoplasm

Cytoplasmic male sterility (CMS) system based on Moricandia arvensis cytoplasm is being used to breed hybrid Brassica juncea varieties. The male fertility restorer gene for this CMS was introgressed into B. juncea from M. arvensis and has been tagged with a dominant SCAR marker. The present study was undertaken to fine map the Rf locus and to assign it to specific B. juncea linkage group. We used information obtained from genome walking, anther transcriptome of the male sterile and the fertility restorer lines and synteny relationship with B. rapa for designing markers for targeted fine mapping. Two BC1F1 populations derived from the cross between CMS and fertility restorer lines were used for mapping. Sequence information obtained through genome walking from the SCAR3 indicated that the Rf gene is located in a genomic region having synteny with B. rapa chromosome A09. Screening of more than 550 SSR markers designed based on B. rapa A09 sequence information identified 12 markers flanking the Rf gene and confirmed its location on B. juncea A09 linkage group. Two (one EST-SSR and one STS) out of 67 markers designed based on differential gene expression between anther transcriptomes were found to be informative and were linked to the Rf gene. The markers were validated in a second BC1F1 population. The closest flanking markers BjESSR01 and BjEST01 were at 0.6 and 1.4 cM from the Rf locus.