Saskatchewan’s first cases of clubroot in canola fields may have continued to sit undetected for who knows how long, had it not been for the fields’ use as seed trial sites for Cargill.

The two cases, reported early last month in separate fields in the province’s north-central region, had shown no above-ground symptoms, the agrifood company said last week. Rather, they were discovered only because Cargill plant scientists had pulled the canola trial plants right out of the ground as part of a routine whole-plant observation.

Plasmodiophora brassicae, the soil-borne pathogen that causes clubroot in canola crops, creates deformed roots in canola and other brassica plants and can thus sit undetected until the clubroot galls interfere with the plants’ water uptake.

During the usual evaluations, the company’s staff spotted nodules on the roots of certain plants, which were then sent for tissue and soil testing at an independent lab, Cargill said in a release last week.

Plant tissue analysis and DNA testing confirmed the presence of the clubroot pathogen, the company said.

The finding was a surprise as the plants otherwise appeared normal and the nodules almost weren’t spotted, Lorin DeBonte, assistant vice-president of research and development for Cargill Specialty Canola, said last week in an interview.

Cargill then put restrictions on access to the farmers’ fields where the affected plants were found, as per the province’s Pest Control Act, the company said.

"Upon discovering the presence of clubroot, we notified grain growers and owners of lands around the disease observation nurseries and provided them with the guidance and resources they required to manage the issue in a timely and cautious manner," DeBonte said in the release.

The Winnipeg-based Canadian arm of the U.S. agrifood giant said it’s now working with the fields’ owners, producers, the Canola Council of Canada and the provincial ag ministry to manage the confirmed sites as per the province’s clubroot management plan.

Within Canada, clubroot is established mainly in vegetable-producing regions of British Columbia, Quebec, Ontario and Atlantic Canada, and turned up in canola in Quebec in 1997.

Even after several decades of large-scale canola production in Western Canada, the disease didn’t hit Prairie canola until it showed up in spots near Edmonton in 2003 and began moving east.

Cargill’s plants this fall were the first in Saskatchewan to show symptoms, although soil samples from a random field in the west-central region of the province turned up positive for the pathogen back in 2009.

Warm soils, high soil moisture and low soil pH favour the spores’ germination, infection and development. Once the microbe infects a host plant, it alters hormone balance and speeds up cell division and growth in the roots, creating deformed galls.

Related stories:

Clubroot confirmed in Saskatchewan, Oct. 4, 2011

Traces of clubroot confirmed in Sask. field, July 22, 2009