Molecular validation of a multiple-allele recessive genic male sterility locus (BnRf) in Brassica napus L.

Abstract

The recessive genic male sterility (RGMS) line 9012AB has been used successfully for rapeseed hybrid production in China. This male sterility was previously thought to be controlled by three independent genes (Bnms3, Bnms4, and BnRf). Here, we initially attempted to locate the BnMs4 locus and develop feasible molecular markers for application in practical rapeseed breeding. However, we found that three sequence characterized amplified region markers and five simple sequence repeat markers identified as linked to BnMs4 were also genetically associated with BnRf, suggesting the possible co-localization of these two loci. Moreover, we proved that four intron-based polymorphism markers tightly linked or co-segregated with BnRf could also be mapped to BnMs4 with a genetic distance ranging from 0.054 to 0.594 cM. Finally, integration of genetic maps around BnRf and BnMs4 allows for the physical restriction of both loci to a DNA fragment of about 50 kb. Systematic genetic tests also provided evidence that the candidate BnMs4 locus was allelic to the BnRf locus. These results confirmed a major modification of the sterility inheritance model in 9012A: specifically, that this male sterility was essentially controlled by two loci (BnMs3 and BnRf), whereas the previously designated BnMs4 locus (hereafter designated as BnRf a ) was just one allele of BnRf in addition to BnRf b (the allele from 9012A) and BnRf c (the allele from temporary maintainer), with a dominance relationship of BnRf a > BnRf b > BnRf c . This inheritance model will simplify the breeding process involved with this RGMS line, especially with the BnRf allele-specific molecular markers identified here.