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Population structure, virulence and resistance to mefenoxam of Phytophthora capsici in Michigan

Yufang Guo: Michigan State University

<div>The oomycete plant pathogen <em>Phytophthora capsici </em>is highly dynamic and destructive with a broad host range. In Michigan, it causes economic losses to many important vegetable crops. The objectives of this study were to investigate the population structure and characterize the virulence and mefenoxam sensitivity for nine <em>P</em>.<em> capsici </em>populations collected from six counties between 2003 and 2016 in Michigan. Simple sequence repeats (SSR) markers from intergenic regions and effectors/surrounding regions were developed to study the population structure and the potential linkage with virulence parameters. Analysis of molecular variance revealed moderate to high degree of genetic difference among the populations. Significant differentiation (F<sub>ST</sub>) was identified in over 60% of the pairwise comparisons among populations, indicating the high genetic diversity of <em>P</em>. <em>capsici</em> in Michigan. Bayesian clustering showed some population structure when isolates were grouped by host. Significant difference was detected in mefenoxam resistance among populations. <em>In vitro inoculation indicated significant difference in virulence-related parameters among the populations. General linear model</em> (GLM) and <em>mixed linear model</em> (MLM) based association analyses identified some markers significantly associated with at least one of the virulence parameters. These results expand the understanding of the genetic base of this important pathogen.</div>