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First detection of Pythium aphanidermatum crown rot of industrial hemp in Nevada

Shouhua Wang: Nevada Department of Agriculture

<div>Industrial hemp (<em>Cannabis sativa</em> L.) is a regulated crop in Nevada. In July 2017, approximately 5-10% of industrial hemp plants (var. Cherry Wine) observed in a production field exhibited symptoms of crown rot, leaf yellowing, extensive wilt, and eventual death of entire plants. White-colored mold on the crown area was frequently observed when a plant was pulled from the ground. To identify the causative agent of the disease, pieces of stem tissue were cut from the margin of the crown rot, surface sterilized, placed onto potato dextrose agar amended with streptomycin sulfate (PDA+strep) and corn meal agar-PARP (CMA-PARP), and incubated at 22ºC in the dark. Tissue plated on PDA+strep did not yield growth of any pathogens. On CMA-PARP, a fast-growing <em>Pythium</em> was obtained from all pieces of stem tissue plated. The isolate produced oogonia, antheridia, and sporangia on CMA, and morphologically resembled <em>P. aphanidermatum</em>. To further investigate its identity, DNA was extracted from 4 representative isolates followed by PCR using primers ITS1/ITS4 to amplify the ITS region of rDNA. PCR products were purified and sequenced directly. A consensus DNA sequence of 866 bp was obtained and a BLASTn search confirmed that the species was <em>P. aphanidermatum</em>. Hemp crown and root rot caused by <em>P. aphanidermatum</em> was first reported in a research plot in Indiana in 2017. This is the first detection of <em>P. aphanidermatum</em> in a commercially grown industrial hemp crop in Nevada.</div>