Virulence of isolates of Albugo Candida from western Canada to Brassica species

Abstract

Isolates of Albugo Candida, collected from different geographical locations in western Canada, were tested for virulence on a set of differentials from Brassica species to determine the variability and distribution of different races and pathotypes. Most isolates were classified as race 7 based on virulence to Brassica rapa accessions and these could be subdivided broadly into two pathotypes, 7A or 7V, on the basis of their virulence to B. rapa cvs. Torch and Reward. Some isolates were classified as race 2 based on virulence to Brassica juncea and these could also be subdivided into pathotypes, 2A or 2V, based on their virulence to B. juncea cvs. Burgonde and Cutlass. The predominant pathotype was 7V. Two isolates of race 7, 28-7 and 29-1, appeared to be less virulent as they were avirulent on all of the differentials except rapid-cycling B. rapa accession CrGCl-18. Race 7 was most prevalent in collections from Alberta and Manitoba. In British Columbia, pathotypes 2A, 2V, 7A, and 7V were commonly observed and about 50% of the sample collections were mixtures of races 2 and 7. A few single pustule isolates from the Peace River region of Alberta and British Columbia appear to be hybrid pathotypes combining virulence characteristics of pathotypes 2A or 2V with 7A or 7V. These isolates are pathogenic on both B. juncea and B. rapa cultivars.