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Emerging diseases of Cannabis sativa L (marihuana) in Canada

Zamir Punja: Simon Fraser University

<div>Cultivation of <em>Cannabis sativa</em> plants in Canada has increased the incidence and severity of previously unreported diseases. Cannabis plants were sampled during 2014-2017 to determine the prevalence of root, foliar and flower-infecting pathogens. Following isolation, pathogenicity studies were conducted to establish which microbes could induce disease symptoms. Pathogens were identified by PCR and sequence analysis of the ITS region. The causal agents of browning and rotting of roots were <em>Pythium dissotocum</em> and <em>P. myriotylum</em>. As well, <em>Fusarium oxysporum</em> and <em>F. solani</em> were isolated from symptomatic roots of plants, which upon reinoculation onto healthy plants, caused stunting, yellowing and wilting. A rot of the flower buds was associated with <em>Botrytis cinerea</em>, which caused botrytis bud rot. In addition, <em>Penicillium olsonii</em>, and to a lesser extent, <em>P. copticola</em>, were also recovered from diseased flower buds, and caused penicillium bud rot. A rot of the flower buds was also associated with <em>F. solani </em>and <em>F. oxysporum</em>, causing fusarium bud rot<em>. </em>Powdery mildew was found to be caused by the pathogen <em>Golovinomyces</em> (<em>Erysiphe</em>) <em>cichoracearum</em> which was detected on vegetatively propagated cuttings of cannabis. Scanning electron microscopic studies provided details on spore germination and sporulation. These pathogens have the potential to reduce product quality wherever cannabis is grown and disease management practices need to be established.</div>