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 ~ 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.