Prevalence of pathogenicity groups ofLeptosphaeria maculansin western Canada and North Dakota, USA

Blackleg, caused by Leptosphaeria maculans, is an economically important disease of canola (Brassica napus). Little is known about the current distribution of pathogenicity groups (PGs) of L. maculans in Canada and the United States. Four hundred and eighty-nine isolates of L. maculans or Leptosphaeria biglobosa from western Canada and North Dakota, United States, were placed in five PGs (PG-1 recognized as L. biglobosa since 2001, PG-2, PG-3, PG-4, and PGT) on the basis of a series of inoculations on canola cultivars ('Westar', 'Glacier', and 'Quinta'). Only PG-1 and PG-2 were observed in populations from a 1984 to 2001 collection. All five PGs were observed in populations collected between 2002 and 2004. New, more aggressive strains of L. maculans may pose a significant threat to the canola industry in Canada and the United States.