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Identification of Pythium spp. associated with diseased cucurbits in South Carolina

Sean Toporek: Coastal Research and Education Center, Clemson University

<div>Root rot and damping-off of cucurbits is commonly caused by <em>Pythium </em>spp., but little is known about their diversity and abundance in this crop group. A survey was conducted in South Carolina to identify <em>Pythium</em> species associated with diseased cucurbits. Four common cucurbit crops, bottlegourd, cucumber, Hubbard squash, and watermelon, were transplanted into four different fields, two managed organically and two managed conventionally, in May, July, and September 2017. Of 960 transplants, 236 had symptoms of root and stem rot. A total of 165 <em>Pythium</em> isolates was recovered from diseased root and stem tissues. Isolates were identified to species level by sequencing the ribosomal internal transcribed spacer region and the mitochondrial cytochrome oxidase I region. <em>P.</em> <em>aphanidermatum</em> (40.0%) and <em>P. myriotylum</em> (39.4%) were the most commonly identified species. Six additional species were detected at much lower frequencies (20.6% total). Planting date and host significantly influenced the abundance of <em>P. aphanidermatum </em>recovered, with a significantly higher recovery rate in July compared to May and September and a significantly higher recovery rate in watermelon and cucumber than in squash and bottlegourd. Results of this survey will help manage the economically important <em>Pythium </em>species affecting cucurbit production. To the best of our knowledge, this is the first survey of <em>Pythium </em>spp. associated with root rot and damping-off in cucurbits in the United States.</div>