Pathogenic diversity of Didymella rabiei isolates from southern Alberta, Canada

Sixty-three isolates of Didymella rabiei collected from Southern Alberta were analyzed for pathogenic variability using six differential chickpea genotypes. Although all isolates were pathogenic on all of the differentials, they varied in virulence. The reaction of host genotypes was classified as resistant or susceptible based on the severity of disease symptoms, and isolates were grouped into 25 pathotypes, suggesting a very high level of diversity in the population of D. rabiei. The predominant pathotypes were XV and XVI, each comprising 14% of the total number of isolates tested. Pathotypes VII and XXV each represented 8% of the isolates tested, while pathotypes III, IV and XIX each represented 6%. The rest of the pathotypes each represented 2-3% of the total isolates. Cluster analysis generated two main groups, at an average distance of 1.0 between the clusters. Fourteen sub-groups were identified among the isolates at an average distance between isolates and within sub-groups of 0.5. No associations were found between geographical origins, pathotypes, cluster groupings, parts of the plants or the host varieties from which the isolates were obtained.