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Verticillium dahliae from asymptomatic hosts likely emerged from sympatric potato crops in the Columbia Basin of Washington

David Wheeler: Washington State University

<div><em>Verticillium dahliae </em>is a pathogen and an endophyte. The relatedness of isolates from asymptomatic and symptomatic hosts and the contribution of inoculum from asymptomatic hosts is unknown. We tested the hypotheses that: (i) isolates from asymptomatic hosts are genotypically and phenotypically different from isolates from symptomatic hosts; and (ii) there is migration from the former to the latter. <em>V. dahliae</em> from symptomatic potato and mint hosts and asymptomatic mustard and grass hosts were genotyped with 10 microsatellite markers. Genotypic diversity and evenness was generally greater among isolates from asymptomatic hosts than symptomatic hosts. Population differentiation, as assessed with discriminant analysis of principal components and analysis of molecular variance, was detected among isolates from asymptomatic hosts and mint (<em>P </em>≤ 0.01) but not potato (<em>P </em>≥ 0.07)<sub>. </sub>Multilocus genotypes from potato were also detected from asymptomatic hosts and unidirectional migration of <em>V. dahliae </em>from potato to asymptomatic hosts was more likely than competing scenarios. <em>V. dahliae</em> isolates from asymptomatic hosts caused wilt and produced microsclerotia on potato but produced microsclerotia without causing wilt on brown mustard and barley. The origin of <em>V. dahliae</em> isolates from asymptomatic hosts in the Columbia Basin of WA is likely potato. The stability, prevalence, and impact of asymptomatic infections needs to be determined to inform disease management strategies.</div>