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Population dynamics of the late blight pathogen in Canada for 2017.

Rick Peters: Agriculture and Agri-Food Canada

<div>Late blight was once again an important disease issue for both potato and tomato crops in Canada in 2017. Plant tissue samples infected with the late blight pathogen were received from several potato and tomato production regions in Canada. Using established protocols, <em>Phytophthora infestans</em> was isolated from these samples and assessed to determine genotype, mating type and metalaxyl-m sensitivity. Pathogen isolates collected from British Columbia potatoes were identified as the US-11 genotype, which is an A1 mating type and highly resistant to metalaxyl-m. Samples received from all other production regions, including Alberta, Manitoba, Ontario and New Brunswick yielded isolates of the US-23 genotype, which is an A1 mating type and sensitive to metalaxyl-m. Although isolates of US-23 were often sensitive to metalaxyl-m early in the season, increased resistance to this chemical pesticide was documented as the season progressed. Greenhouse/storage trials revealed that US-23 was less aggressive on potato foliage than US-8 or US-24, but equally aggressive as the other genotypes on potato tubers. The US-23 genotype has become the predominant genotype in most growing regions across Canada in recent years. However, every year there are fluctuations in the genotypes found, which underscores the importance of continuous population monitoring. The epidemiology of late blight has completely changed in Canada with the distribution and spread of new pathogenic strains.</div>