First report of clubroot (Plasmodiophora brassicae) on canola in Ontario

Clubroot, caused by Plasmodiophora brassicae Woronin, is endemic on Brassica vegetables in many regions of Ontario. It has not been previously reported on canola (Brassica napus L.) in Ontario, possibly because the most common pathotype in Ontario, pathotype 6 (Williams’ system) is not highly aggressive on most canola cultivars. In 2016, clubroot symptoms were observed on roots of canola plants in a field near the town of Verner in northern Ontario. In a follow-up survey, P. brassicae DNA was detected in soil of 11 of 95 fields that had been planted with canola, including seven fields in northern Ontario. Pathotype 2 was identified at the Verner site based on the reaction of Williams’ differential cultivars. Pathotype 2 was previously identified on rutabaga in Ontario in the 1970s, but this is the first report of clubroot on canola and of P. brassicae DNA present in canola fields in Ontario.