Abstract

Cannabis (Cannabis sativa L., marijuana) plants with symptoms of crown rot, root decay, wilting and plant death were sampled during 2018 and 2019 from seven licensed production greenhouses. Affected tissues from 140 diseased plants were surface-sterilized and plated onto potato dextrose agar. Ninety-five isolates morphologically resembling Pythium species were subcultured and subjected to PCR of the ITS1-5.8-ITS2 region of ribosomal DNA. The following species were identified based on >99% sequence identity to reference isolates in GenBank: P. myriotylum (43 isolates), P. dissotocum (35 isolates), P. aphanidermatum (3 isolates) and Globisporangium ultimum (syn. P. ultimum) (2 isolates). A fifth species – P. catenulatum (12 isolates), was distinguished from P. rhizo-oryzae using the cytochrome oxidase c subunit I (COI) sequence. Cannabis licensed production facilities in British Columbia had all five species present, while P. dissotocum was found in two facilities in Ontario, and P. myriotylum was present in one facility in northern California. Isolates selected to represent each Pythium species were grown on potato dextrose agar at 25°C and they all showed comparable colony growth after 6 days. The same isolates caused root browning, decay and stunting of cannabis plants grown in a coco: perlite potting medium. Plant mortality was similar after 21 days but rates of disease progression varied depending on the isolate tested. Wounding of roots and prolonged periods of saturation enhanced disease development. These results demonstrate for the first time that crown and root rot on greenhouse-grown cannabis plants can be caused by up to five Pythium species.

摘要

2018 年和 2019 年期间，从七个许可的生产温室中对具有树冠腐烂、根腐烂、萎蔫和植物死亡症状的大麻 ( Cannabis sativa L., marijuana) 植物进行了取样。对来自 140 株患病植物的受感染组织进行表面灭菌并接种到马铃薯葡萄糖琼脂上。对 95 个形态上类似于腐霉物种的分离物进行传代培养，并对核糖体 DNA 的 ITS1-5.8-ITS2 区域进行 PCR。根据与 GenBank 中参考分离株 >99% 的序列同一性鉴定了以下物种：P. myriotylum（43 个分离株）、P. dissotocum（35 个分离株） 、 P . aphanidermatum （3 个分离株）和Globisporangium ultimum（syn.P. ultimum ) (2 株)。第五个物种 - P. catenulatum （12 个分离株）使用细胞色素氧化酶c亚基 I (COI) 序列与P. rhizo-oryzae区分开来。不列颠哥伦比亚省的大麻许可生产设施有所有五种，而安大略省的两个设施中发现了P. dissotocum，加利福尼亚北部的一个设施中发现了 P. myriotylum。选择代表每个腐霉的分离株物种在 25°C 的马铃薯葡萄糖琼脂上生长，6 天后它们都显示出相当的菌落生长。相同的分离物导致种植在可可：珍珠岩盆栽培养基中的大麻植物的根部褐变、腐烂和发育迟缓。21 天后植物死亡率相似，但疾病进展率因所测试的分离株而异。根部受伤和长时间的饱和会促进疾病的发展。这些结果首次表明，温室种植的大麻植物的冠腐病和根腐病可由多达五种腐霉属物种引起。