Identification of Brassica accessions with enhanced resistance to Verticillium longisporum under controlled and field conditions

Verticillium longisporum (VL) is a soil-borne vascular fungal pathogen with host-specificity to cruciferous plants such as oilseed rape, threatening its production particularly in the Northern European countries. In a comprehensive screening conducted under greenhouse conditions, 1348 accessions of Brassica napus as well as the progenitor species B. oleracea and B. rapa (syn. campestris) were tested for their resistance to VL. While most of the tested B. napus accessions showed a susceptible to moderate resistant phenotype and the majority of the B. rapa genotypes were highly susceptible, an elevated level of resistance was found in the B. oleracea pool. Resynthesized oilseed rape lines produced on the basis of these data by interspecific hybridization of B. oleracea and B. rapa also exhibited enhanced resistance to VL. In order to verify the greenhouse data, a subset of B. napus breeding lines was further tested for resistance in the field at different sites in North and Northeast Germany. Overall, there was no statistically significant relationship, neither between greenhouse and field data nor between results of different field sites. However, genotypes highly resistant in the greenhouse generally performed well also in the field. Thus, the combination of resistance tests conducted under controlled as well as field conditions is a powerful and reliable approach in the practical selection of resistant breeding lines.