Isolates Reveal Their Allele Frequency in Western Canada.

Blackleg, caused by , is a major disease of canola in Canada, Australia, and Europe. For effective deployment of resistant varieties and disease management, it is crucial to understand the population structure of . In this study, we analyzed isolates from commercial fields in western Canada from 2014 to 2016 for the presence and frequency of avirulence () genes. A total of 1,584 isolates were examined for the presence of genes , , , , , , , , , and via a set of differential host genotypes carrying known resistance genes and a PCR assay. Several genes showed a higher frequency in the pathogen population, such as and , which were present in >90% of isolates, whereas , , and showed frequencies of <10%. A total of 189 races (different combinations of genes) were detected, with , , and as the three predominant races. When the effect of crop rotation was assessed, only a 3-year rotation showed a significantly higher frequency of relative to shorter rotations. This study provides the information for producers to select effective canola varieties for blackleg management and for breeders to deploy new genes in disease resistance breeding in western Canada.