Characterization of Plasmodiophora brassicae populations from Alberta, Canada

Abstract

Clubroot, caused by Plasmodiophora brassicae, was identified in a number of canola (Brassica napus) fields in central Alberta in 2003. To characterize the virulence of the pathogen in the province, field populations from a number of locations in the Edmonton region were tested on the two most widely used sets of differential hosts, those of P.H. Williams and the European Clubroot Differential (ECD) series. Populations from British Columbia and Ontario were included for comparison. While the reaction of some hosts could be clearly defined as either resistant or susceptible, others showed intermediate disease index scores. If disease indices of 0%–49% and 50%–100% were regarded as resistant and susceptible, respectively, then populations from Alberta were classified as ECD 16/15/12 and 16/15/0 on the ECD set, or pathotypes 3 and 5, respectively, on the hosts of Williams. The population from British Columbia was classified as ECD 16/2/12 or pathotype 6, and the Ontario population was classified as ECD 16/0/14 or pathotype 6. The Alberta populations were more virulent on the B. napus hosts than those from other provinces, perhaps a reflection of their canola origin. In addition, 48 canola cultivars included in the 2004 Prairie Canola Variety Trials were screened for resistance to a local population of the pathogen, and all appeared to be highly susceptible. If clubroot were to become more widely established in western Canada, it could have a major negative impact on yields.