Isolation and characterization of Verticillium longisporum from canola in Alberta, Canada

Verticillium stripe, caused by Verticillium longisporum, is an emerging disease of canola (Brassica napus) in Canada. It was initially reported in the province of Manitoba, but pathogen DNA has since been detected in British Columbia, Saskatchewan, Ontario and Quebec. Although V. longisporum DNA has also been found in canola samples from Alberta, the fungus itself has not been characterized from the province. In 2023, canola field surveys in Alberta, Manitoba and Saskatchewan identified plants with symptoms and signs consistent with Verticillium stripe, including vascular discolouration and necrosis, stem shredding and the presence of microsclerotia. Nine fungal isolates (six from Alberta and three from Manitoba) were recovered in culture and identified as V. longisporum based on colony morphology, microscopy and species-specific PCR primers. Both simplex and multiplex PCR assays confirmed that all nine isolates belonged to the A1/D1 lineage of V. longisporum. In addition, one isolate of V. dahliae was recovered from Manitoba during the study. The aggressiveness of the six Alberta isolates was evaluated in vitro and in greenhouse experiments using a susceptible canola cultivar, revealing significant differences among isolates. Further characterization of V. longisporum populations from western Canada will be necessary to support effective management of Verticillium stripe in canola.