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A Host-Pathogen Interaction Paradigm: Is Leptosphaeria maculans’s New Races Adopting Rapidly to Canadian Canola in Western Canada?
D. FERNANDO (1), S. Liban (2), X. Zhang (2), G. Peng (3), D. Cross (4). (1) Univ of Manitoba, Winnipeg, MB, Canada; (2) University of Manitoba, Winnipeg, MB, Canada; (3) Agriculture and Agri-Food Canada, Saskatoon, Saskatoon, SK, Canada; (4) Agriculture and Agri-Food Canada, Melfort, Melfort, SK, Canada

Blackleg caused by <i>Leptosphaeria maculans</i> is the most destructive disease affecting Canola (<i>Brassica napus</i> L.). Genetic resistance has proven to be an effective means of disease control in western Canada. However, this pathogen has appeared on cultivars rated as resistant. Information on genetic variability in the population is essential in developing an effective control strategy. Race structure was assessed on avirulence alleles <i>AvrLm1, AvrLm2, AvrLm3, AvrLm4, AvrLm6, AvrLm7, AvrLm9, LepR1, LepR2</i>, and <i>AvrlmS</i>. Overall, certain alleles were more prevalent in the pathogen population with AvrLm6 and Avrlm7 present in >90% of isolates and <i>AvrLm3, Avrlm9</i>, and <i>AvrLepR2</i> present in <10% of isolates. The latter 3 alleles have changed to the virulent forms affecting the majority of the Canadian canola cultivars which carry the corresponding Rlm genes (i.e. <i>Rlm3, Rlm2</i>). However, some loci differed greatly across geographic locations. For example, <i>AvrLm2</i> ranged from 86% in Vegreville, Alberta to 38% in Plum Coulee, Manitoba. Selection pressure from different race-specific resistance genes in commercial canola cultivars (i.e. <i>Rlm3</i>) is postulated as the most significant factor influencing the variation in the emergence of ‘newer’ virulence forms observed. The presentation will address some of the innovative measures undertaken by the researchers and industry to address this change in race structure and mitigate blackleg spread across the Prairie Provinces.

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