Transferring of clubroot-resistant locus CRd from Chinese cabbage (Brassica rapa) to canola (Brassica napus) through interspecific hybridization

Clubfoot, caused by Plasmodiophora brassicae is one of the most severe threats to brassica species in China and worldwide. Breeding for clubroot resistant varieties is one of the best ways to overcome this disease. In this study, we introduced clubroot resistance (CR) gene CRd from Chinese cabbage (85-74) into elite Brassica napus inbred line Zhongshuang 11 through interspecific hybridization and subsequent backcrossing with whole-genome molecular marker-assisted selection (MAS). The resistant test of CRd to P. brassicae isolates was evaluated in the greenhouse as well as in field conditions. Close linkage markers and the wholechromosome background marker selection approach improved the recovery rate from 78.3% in BC1 to 100% in BC3F1 . The improved clubroot-resistant variety, Zhongshuang 11R, was successfully selected in the BC3F2 generation. The greenhouse and field resistant tests revealed that Zhongshuang 11R was resistant to P. brassicae pathotypes. The agronomic characteristics of Zhongshuang 11R were similar to those of its recurrent parental line, including oil content, composition of fatty acid, plant height, primary effective branches, grain yield per plant and thousand-seed weight. In addition, the oil quality could satisfy the quality requirements for commercial rapeseed oil. Our results will enrich the resistant resources of canola and will certainly accelerate clubroot resistance breeding programs in B. napus.