Story Posted: July 21, 2009

Test Results Confirm Trace Levels of the Clubroot Pathogen

Saskatoon... SaskCanola Research Manager, Pat Flaten, today confirmed that the retesting of a soil sample from a randomly-selected field in west-central Saskatchewan, using a DNA diagnostic test and a canola plant bioassay, has confirmed trace levels of the clubroot pathogen (Plasmodiophora brassicae).

The results of the testing undertaken and confirmed by pathologists from Agriculture and Agri-Food Canada (AAFC) and staff for the Ministry of Agriculture were provided to SaskCanola.

"Re-testing of the soil sample over the past 2 months confirms that it is possible for the clubroot pathogen to exist in Saskatchewan, even in the absence of disease symptoms in the field. Therefore, we want to ensure that proper measures are being taken by the agricultural community and associated stakeholders to prevent even trace levels of the pathogen from developing into a disease issue," Flaten stated.

Confirmation of clubroot requires observation of disease symptoms in a susceptible crop in addition to detection of the pathogen's DNA in a plant or soil sample. In this case, clubroot DNA was detected in the soil sample, and although clubroot symptoms were not observed in the crop when it was surveyed, the positive bioassay (canola plants grown in a sample of the soil in a greenhouse under favourable disease conditions) indicates that there were viable clubroot spores in the soil sample tested; however, the spore levels appeared low.

"Plant pathologists will work together to develop a management strategy for the affected field," Faye Dokken, Provincial Plant Disease Specialist with the Ministry of Agriculture stated. "Recently, clubroot was declared a pest in Saskatchewan under The Pest Control Act, which will facilitate increased clubroot surveillance and disease prevention and management in the province."

Under the right conditions - warm, moist, low pH soils - infection could take place and lead to disease, which has the potential to increase the spore levels under each rotation involving a cruciferous crop or even cruciferous weeds. While it is possible that the clubroot pathogen may be present in the soil, with or without causing disease, proper crop rotation will prevent heavy infestations from developing within a field.

"It is important that farmers scout their crops as they head into the 2009 harvest. Any unusual wilting, stunting, or yellowing should be further investigated by pulling up plants and checking the roots - the characteristic clubroot galls will appear as swellings and malformations on the roots, cutting off the plant's ability to take up water and nutrients. Farmers are also reminded to be vigilant as to their best practices regarding cleaning of field equipment, in order to prevent clubroot movement to and within Saskatchewan," Flaten concluded.

"Plant pathologists from AAFC and the Ministry conduct an annual survey of canola crops in Saskatchewan to identify and quantify new and common diseases of canola. More intensive surveillance of canola crops and soil testing for clubroot in the province is warranted for 2009," Dokken said. "The annual canola disease survey will be conducted as usual in August, and soil samples will be tested from an additional 60 fields in 2009."

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