Efficient marker-assisted breeding for clubroot resistance in elite Pol-CMS rapeseed varieties by updating the PbBa8.1 locus

Abstract Clubroot disease poses a severe threat to rapeseed (Brassica napus) production worldwide and has recently been spreading across China at an unprecedented pace. Breeding and cultivation of resistant varieties constitute a promising and environment-friendly approach to mitigating this threat. In this study, the clubroot resistance locus PbBa8.1 was successfully transferred into SC4, a shared paternal line of three elite varieties in five generations by recurrent selection. Specific KASP markers of clubroot resistance gene PbBa8.1 and its linked high erucic acid gene (FAE1) were designed and applied for foreground selection, while a 1000 + SNPs were selected and used for the background selection. This breeding strategy resulted recombinants had the highest recovery ratio of the recurrent parent genome (> 95%) at BC2F2, while breaking the linkage with FAE1 during the selection. An updated version of the paternal line (SC4R) was generated at BC2F3, showing significantly improved clubroot resistance at seedling stage by artificial inoculation and was comparable to that of the donor parent. Field trials of the three elite varieties and their updated versions in five environments indicated similar agronomic appearance and final yield. The introduced breeding strategy precisely pyramiding the PbBa8.1 and FAE1 loci with the assistants of technical markers in a shorter period and could be applied to other desirable traits for directional improvement in the future.