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Population structure of Phytophthora plurivora on Rhododendron in Oregon nurseries

Nicholas Carleson: Oregon State University

<div><span><i>Phytophthora plurivora </i></span>is a recently described plant pathogen, separated from the <span><i>Phytophthora citricola </i></span>species complex in 2009. Recent studies of Pacific Northwest nurseries have frequently encountered the pathogen, and it has been shown to be among the most dominant species in <span><i>Phytophthora </i></span>communities, however, not much is known about its population genetics. We characterized the population structure of <span><i>P. plurivora </i></span>(n = 70) in a survey of four Oregon nurseries across three different counties with focus on <span><i>Rhododendron</i></span> hosts. Samples were<span><i> </i></span>identified to the species level using a PCR-RFLP assay of the internal transcribed spacer (ITS) region. We used genotyping-by-sequencing (GBS) by digesting with a <span><i>Pst</i></span>I-<span><i>Msp</i></span>I enzyme combination and sequencing on an Illumina HiSeq 3000. Variants were called <span><i>de novo</i></span> using the Stacks pipeline, resulting in 547 high-quality variants and 69 samples after filtering for low read depth. Based on <span><i>F</i></span><sub>st</sub> and discriminant analysis of principal components (DAPC), populations were moderately differentiated among nurseries. <span><i>P. plurivora </i></span>was previously assumed to primarily reproduce clonally, and the observed low genotypic diversity within nurseries corroborated this hypothesis. These findings provide an initial perspective on <span><i>P. plurivora </i></span>population structure in Pacific Northwest nurseries.</div>