Characterization of the Race Structure of Causing Blackleg of Winter Canola in Oklahoma and Kansas.

Blackleg, caused by the fungus , is a widespread disease of winter canola () in Oklahoma and Kansas. Deployment of genetic resistance is the primary strategy for managing blackleg. Resistance genes () in canola interact with avirulence genes in the fungus () in a gene-for-gene manner. Little is known about the diversity and frequency of avirulence genes and the race structure in the region. Isolates of spp. were collected from diseased leaves in nine counties in Oklahoma and one county in Kansas from 2009 to 2013. Based on pathogenicity and PCR amplification of mating type and species-specific internal transcribed spacer loci, most isolates ( = 90) were The presence of avirulence genes was evaluated using phenotypic interactions on cotyledons of differential cultivars with , , , and and amplification of , , and by PCR. The avirulence alleles and were present in the entire population. was found in 34% of the population, in 4%, and in only 1%. A total of five races, defined as combinations of avirulence alleles, were identified that included , , , , and . Races virulent on the most genes, at 32% and at 62%, were predominant. Defining the avirulence allele frequency and race structure of should be useful for the identification and development of resistant cultivars and hybrids for blackleg management in the region. The results suggest that and would be effective, although their deployment should be integrated with quantitative resistance and cultural practices, such as crop rotation, that limit selection pressure on genes.