First report of the powdery mildew pathogen of hops, Podosphaeria macularis, naturally infecting cannabis (Cannabis sativa L., marijuana) plants under field conditions
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| Authors: | Punja, ZK |
| Year: | 2021 |
| Journal: | Can. J. Plant Pathol. Article Link (DOI) |
| Title: | First report of the powdery mildew pathogen of hops, Podosphaeria macularis, naturally infecting cannabis (Cannabis sativa L., marijuana) plants under field conditions |
| 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 degrees 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. |
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