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Researchers study verticillium yield losses

Canola industry leaders have been worried about verticillium stripe and its impact on crop yields for several years.

Reports out of Europe suggest the fungal disease could cause losses of 10 to 50 percent on oilseed rape. However, extreme losses are usually confined to a small number of fields in England and northern Europe.

University of Alberta scientists will soon publish a Canadian estimate to nail down what verticillium means for yield.

“We were the ones who gave the blackleg yield loss model … and the clubroot yield loss model,” said Sheau-Fang Hwang, a plant pathologist with the U of A. “So, everyone expects we will … (provide) the verticillium yield loss model.”

Hwang and her colleagues hoped to release their results this year, but publication will be delayed until 2024.

Verticillium stripe is a relatively new disease for canola growers in Western Canada. It was first discovered in 2014 near Winnipeg.

The fungus, Verticillium longisporum, infects canola and produces tiny, pepper-like sclerotia on or inside the stem of the plant. The sclerotia fall on the soil and into crop stubble after harvest. The small particles move with wind and water to other locations. Farmers can also pick up the fungus on their equipment and boots and transport it to other fields.

The infection interferes with the uptake of water and nutrients. Symptoms include early ripening, plant stunting and leaf chlorosis and shredding or striping of the stem tissue. The symptoms usually appear later in the growing season.

“Looking for verticillium, you have to slough off that outer stem wall … to reveal the micro-sclerotia. That’s a really key (part) of diagnosis,” said Justine Cornelsen, agronomic and regulatory services manager with BrettYoung Seeds and a former agronomist with the Canola Council of Canada.

On the Prairies, verticillium is most common in Manitoba, where it appeared in 40 percent of canola fields in 2022.

“In Manitoba, we don’t talk much about clubroot. We talk about verticillium,” said Cornelsen, who lives near Virden, Man.

The disease is also spreading across Saskatchewan. It was detected in dozens of eastern Saskatchewan fields in 2022 and in other regions this summer.

Earlier this year, Hwang authored a paper saying verticillium is a significant threat to canola production in Canada. When verticillium and blackleg are present in the same field, the two fungal diseases seem to join forces.

“(When) inoculated together in field and greenhouse experiments, blackleg severity and yield losses increased relative to when (the blackleg pathogen) was applied on its own. The severity of verticillium stripe also tended to increase,” says the 2023 paper, published in Plants.

“The results suggest that the interaction between (blackleg and verticillium) may cause more severe losses in canola.”

Cornelsen has been keeping a close eye on verticillium since it first appeared in Manitoba a decade ago.

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