Spot blotch, caused by Bipolaris sorokiniana, is a damaging disease of barley in Canada, especially in the prairie region (Manitoba, Saskatchewan, and Alberta) where most of Canadian crops are produced. Considerable interaction between isolates of the pathogen and barley genotypes necessitates the evaluation of the virulence diversity in the B. sorokiniana population in order to deploy effective resistance against the pathogen. The virulence diversity of 127 B. sorokiniana isolates from Canada and other countries was evaluated on 12 barley genotypes. Different virulence patterns were detected across B. sorokiniana isolates and eight virulence groups were identified using qualitative analysis of the virulence data. Results indicate broader virulence diversity in the pathogen population in the eastern prairie region of Canada, especially in Manitoba, compared with that previously reported. One group of isolates collected from Manitoba displayed a virulence pattern which had not been reported previously. This group was moderately virulent on most differential lines, including American six-rowed barley genotypes considered to possess durable resistance against B. sorokiniana. Although the classical method of pathotype identification can be exploited to analyze interactions in the barley-B. sorokiniana pathosystem, the continuous range of infection phenotypes found suggests that a quantitative analysis of the complex interactions occurring may be warranted.
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