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Emerging pathogens of wasabi (Wasabia japonica) in British Columbia, Canada.

Emily Betz: Simon Fraser University

<div>Wasabi is grown semi-hydroponically in polyethylene greenhouses under humid conditions to simulate the natural riverbed conditions where it is found. Surveys of five greenhouses in the Lower Mainland and on Vancouver Island of British Columbia were conducted during the summers of 2016 and 2017 to identify the major pathogens of this crop. Symptoms observed included wilt, petiole blight, leaf spot, powdery mildew, white rust and root/rhizome rot. Diseased tissues (except for mildew and white rust) were sterilized with 0.4% bleach and 70% ethanol and plated onto V8 juice and potato dextrose agars with 100 mg/L streptomycin. Isolates were first identified by morphology and further confirmed by PCR of the ITS region. In total, 10 fungi/oomycetes were observed on diseased tissues, notably <em>Verticillium isaacii</em> (wilt), <em>Leptosphaeria biglobosa</em> (Phoma leaf spot), <em>Erysiphe cruciferarum </em>(powdery mildew), <em>Albugo candida</em> (white rust), <em>Botrytis cinerea </em>(gray mold), and <em>Fusarium/Pythium</em> (rhizome rot). <em>Verticillium</em> <em>isaacii</em> is previously unreported from wasabi and detached leaf, petiole, and rhizome inoculations were conducted to test pathogenicity. Mycelium was grown for 3 weeks in potato dextrose broth then blended and used to inoculate wounded wasabi tissues. Symptoms of chlorosis, necrosis, and blackening appeared after 7 days. Emerging diseases of wasabi continue to be a threat to commercial production, and management of pathogens is paramount to the success of wasabi farms.</div>