Abstract

Plants of the cannabis (Cannabis sativa L., marijuana) strain ‘Chronic Ryder’, grown outdoors in the Fraser Valley of British Columbia (BC), displayed symptoms of powdery mildew in late July 2019. The disease progressed rapidly under cool, wet conditions to infect leaves, stems, shoot tips and inflorescences by early September. To identify the pathogen, DNA was extracted from healthy and diseased leaves and subjected to PCR using eukaryotic universal primers that amplified the ITS1-5.8S-ITS2 region of rDNA. A 650 bp band present only in the diseased plants, showed 99.45% sequence homology to Podosphaeria macularis, the powdery mildew pathogen that infects hop plants. In greenhouse-grown cannabis infected with the powdery mildew pathogen Golovinomyces ambrosiae, a 700 bp size band was present. Conidial morphology also distinguished the two pathogens – P. macularis produced ovoid-oval conidia with fibrosin bodies, while G. ambrosiae produced cylindrical-oblong conidia with no fibrosin bodies. A survey of powdery mildew-infected hop fields and indoor cannabis growing facilities in different geographical locations in BC, showed that plants were infected exclusively by either P. macularis or G. ambrosiae, respectively. Inoculations using P. macularis-infected leaf segments placed on cannabis ‘Pink Kush’ leaves under high humidity at 22–26°C gave rise to small mildew colonies after 24–35 days, confirmed to be P. macularis by PCR. Development of P. macularis in cannabis plants was slower compared with G. ambrosiae. To date, only one outdoor location for cannabis has been confirmed to have P. macularis; the potential for spread to other sites or to indoor cultivation facilities is unknown.

摘要

2019 年 7 月下旬，在不列颠哥伦比亚省 (BC) 的弗雷泽河谷户外种植的大麻 ( Cannabis sativa L., marijuana) 菌株“慢性莱德”出现白粉病症状。该病在凉爽潮湿的条件下迅速发展到 9 月初感染叶、茎、芽尖和花序。为了鉴定病原体，从健康和患病的叶子中提取 DNA，并使用扩增 rDNA 的 ITS1-5.8S-ITS2 区域的真核通用引物进行 PCR。仅存在于病株中的 650 bp 条带与感染酒花植物的白粉病病原体Podosphaeria macularis显示出 99.45% 的序列同源性。在感染白粉病病原体Golovinomyces ambrosiae的温室种植的大麻中，存在 700 bp 大小的条带。分生孢子形态也区分了两种病原体 - P. macularis产生带有纤维蛋白体的卵圆形 - 椭圆形分生孢子，而G. ambrosiae产生没有纤维蛋白体的圆柱形长圆形分生孢子。对 BC 省不同地理位置的受白粉病感染的啤酒花田和室内大麻种植设施的调查表明，植物分别仅被P. macularis或G. ambrosiae感染。在 22-26°C 的高湿度条件下，用受黄斑假单胞菌感染的叶段接种，在 24-35 天后产生小霉菌菌落，证实为黄斑假单胞菌通过 PCR。与G. ambrosiae相比，大麻植物中P. macularis的发育较慢。迄今为止，只有一处户外大麻场所被证实有黄斑假单胞菌；传播到其他地点或室内种植设施的可能性尚不清楚。