Introgression and pyramiding of genetic loci from wild Brassica oleracea into B. napus for improving Sclerotinia resistance of rapeseed

Key message Resistant rapeseed lines pyramided with multiple resistant QTLs derived from Brassica oleracea were developed via a hexaploidy strategy. Rapeseed (Brassica napus L.) suffers heavily from Sclerotinia stem rot, but the breeding of Sclerotinia-resistant rapeseed cultivar has been unsuccessful. During the study, interspecific hexaploids were generated between rapeseed variety 'Zhongshuang 9' and a wild B. oleracea which was highly resistant to S. sclerotiorum, followed by backcrossing with Zhongshuang 9 and successive selfing. By molecular marker-assisted selection, three major resistant QTLs were transferred and pyramided from B. oleracea into two BC1F8 lines which exhibited similar to 35% higher resistance level than Zhongshuang 9 and produced good seed yield and seed quality. It is the first report on successful development of Sclerotinia-resistant rapeseed lines by introducing multiple resistant loci from wild B. oleracea. This study revealed the effectiveness of pyramiding multiple QTLs in improving Sclerotinia resistance in rapeseed and provided a novel breeding strategy on utilization of B. oleracea in rapeseed improvement.