Brassica B-genome resistance to stem rot (Sclerotinia sclerotiorum) in a doubled haploid population of Brassica napus x Brassica carinata

Stem rot (caused by Sclerotinia sclerotiorum) is an important fungal disease of canola (Brassica napus), causing significant yield losses worldwide. Sources of genetic resistance to this disease in B. napus are scarce; however, Brassica species carrying the B-genome have been reported to possess high levels of resistance to stem rot. In order to transfer resistance from B. carinata to B. napus, an interspecific cross of B. napus x B. carinata was carried out and a doubled-haploid (DH) population was developed from BC2S3 plants. Fifty-eight DH lines, of which two carried B-genome linkage groups, and nine accessions of the diploid and amphidiploid Brassica species were screened in a growth chamber for resistance to stem rot. The B. napus parent ('Westar') and all B. rapa and B. oleracea reference lines were susceptible to sclerotinia stem rot, while the B. carinata parent as well as the B. nigra and B. juncea reference lines were resistant to this disease. Significant variation for the response to sclerotinia stem rot was found in the DH lines. The two DH lines carrying B-genome chromosomes showed significant (P 0.01) resistance compared to the species without B-genome chromosomes. However, some of the DH lines, in which no B-genome introgression was apparent, also showed good resistance to this disease. Broad-sense heritability was estimated to be H = 54% for S. sclerotiorum-induced lesion length in this population.