Changes in the range and virulence ofPlasmodiophora brassicaeacross Canada

Plasmodiophora brassicae causes clubroot on Brassica vegetables and canola around the world. A diverse assemblage of new pathotypes have been identified on canola in the Canadian province of Alberta since 2012, but the pathotypes present in the rest of Canada have not been assessed in detail in recent years. Brassica vegetable and canola fields in Ontario were surveyed for clubroot in 2017-2019. The pathotype of isolates collected was determined using the Williams differential set. Clubroot samples or soil from six other Canadian provinces were also assessed. Clubroot appears to be spreading on canola in Ontario. Pathotype 6 was found only on vegetables and pathotype 2 was predominant on canola; pathotypes 2X and 3X were also identified on canola. The 'X' indicates collections that were virulent on the first generation of clubroot-resistant canola cultivars in Canada. Prior to 2012, the pathotypes in eastern Canada were 1, 2, 3, 4, 5, and 6 and the pathotypes in western Canada were 3, 5, and 8 with 6 found on vegetables in British Columbia. Additional virulent pathotypes 2X, 3X, and 5X were identified in eastern Canada and pathotype 9 was found in Manitoba. Two instances of rapid shifts in pathotype at research sites were demonstrated, one in Ontario (pathotype 6 to 2) and one in Quebec (pathotypes 2 and 5 to 2X and 5X).

Automated summary

In recent years, new pathotypes of Plasmodiophora brassicae have been identified on canola and Brassica vegetables in Canada, with differences observed in pathotype distribution among provinces. The study shows that the situation of clubroot in eastern Canada differs from that in the west, with an increasing threat posed by virulent pathotypes to clubroot-resistant canola cultivars.