Identification of RAPD markers linked to a fertility restorer gene for theOgura radish cytoplasmic male sterility of rapeseed (Brassica napus L.)

Bulked segregant analysis was employed to identify random amplified polymorphic DNA (RAPD) markers linked to the restorer gene (Rfo) used in theOgura radish cytoplasmic male sterility of rapeseed. A total of 138 arbitrary 10-mer oligonucleotide primers were screened on the DNA of three pairs of bulks, each bulk corresponding to homozygous restored and male sterile plants of three segregating populations. Six primers produced repeatable polymorphisms between paired bulks. DNA from individual plants of each bulk was then used as a template for amplification with these six primers. DNA polymorphisms generated by four of these primers were found to be completely linked to the restorer gene with the polymorphic DNA fragments being associated either with the fertility restorer allele or with the sterility maintainer allele. Pairwise cross-hybridization demonstrated that the four polymorphic DNA fragments did not share any homology. Southern hybridization of labelled RAPD fragments on digested genomic DNA from the same three pairs of bulks revealed fragments specific to either the male sterile bulks or to the restored bulks and a few fragments common to all bulks, indicating that the amplified sequences are low copy. The four RAPD fragments that were completely linked to the restorer locus have been cloned and sequenced to develop sequence characterized amplified regions (SCARs). This will facilitate the construction of restorer lines used in breeding programs and is the first step towards map-based cloning of the fertility restorer allele.