New clubroot pathotype | Agronomists discovered the resistant strain in central Alberta last year
It didn’t take long for clubroot to overcome the resistance bred into canola varieties.
A new pathotype has been found near Edmonton that can attack all the resistant lines that have been sold in Canada since the first one hit the market in 2009.
“I don’t think it’s widespread yet,” said Stephen Strelkov, professor of plant pathology at the University of Alberta. “We’ve only found it at the core of the clubroot outbreak in central Alberta.”
The Canola Council of Canada will be co-ordinating a survey in the Edmonton region to get a better read on the pathogen’s prevalence and distribution in the area.
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Strelkov said the new pathotype was probably residing in the soil at low levels and then became more pronounced with the increased use of resistant varieties.
“In some ways, it’s not surprising that the first cases are here in central Alberta, where the clubroot infestation is the heaviest and where there has probably been resistant varieties grown for the longest amount of time,” he said.
Dave Harwood, technical services manager for DuPont Pioneer Canada, said growers can count on the new strain to spread beyond the Edmonton area.
Clubroot has been detected in more than 1,000 fields in Alberta since it was first discovered in a canola field in that province in 2003. It is expanding its reach at a rate of 20 to 25 kilometres per year. It has also appeared at low levels in Saskatchewan and Manitoba.
Harwood isn’t surprised that it took only five years for the resistance to break down based on what he has witnessed with rust resistant wheat lines.
“I have developed a healthy respect for plant pathogens,” said Harwood.
The new strain was discovered when canola council agronomists noticed something unusual in an Edmonton field while conducting a disease survey last year.
Disease levels were much higher than they should have been, given that the farmer was growing a resistant variety.
Laboratory tests later confirmed that seven commercially available clubroot resistant cultivars were all susceptible.
In some cases 80 to 90 percent of the plants were infected.
Clubroot is a nasty disease that can cause up to 80 percent yield loss in an infected field.
“Once you get an infestation in a field, it becomes a management issue in perpetuity,” said Strelkov.
“Other diseases come and go.”
The canola council says growers now need to be extra vigilant in adhering to stewardship.
“We are advising that growers practice good sanitation on their equipment, especially during spraying under wet conditions,” Curtis Rempel of the canola council, said in a news release.
“This applies to equipment moving between all fields, not just those currently growing canola, since clubroot spores remain in the soil for years.”
The level of required sanitation depends on the level of clubroot risk in the area, varying from knocking off clumps of soil to pressure washing and disinfecting equipment.
Farmers in clubroot areas should plant canola only once every four years.
Growers are being asked to scout resistant varieties with extra vigilance this year. Producers should contact their council agronomist or seed company representative if levels are higher than expected and are in defined patches in the field.
Other stewardship measures in-clude controlling volunteer canola, wild mustard and stinkweed in years when canola is not planted, minimizing tillage in clubroot regions and avoiding the use of seed, straw, hay, green feed, silage and manure from infected or suspected areas.
Strelkov said the good news is that he has identified genes that are resistant to the new pathotype.
Harwood said it would be nice if those genes were found in canola or rapeseed rather than more distantly related crops. All of the existing sources of resistance on the market came from winter rapeseed crops in Europe.
“The transference of that to spring canola in the Prairies is a relatively straightforward breeding exercise,” he said.
“Moving a trait from a related species is not so straightforward.”
DuPont Pioneer has been screening lines for additional sources of clubroot resistance since it released its first line in 2009. It’s possible that some of those sources will be resistant to the new pathotype.
