Scientists in southern Alberta are trying to gain an edge in the fight against a persistent disease that destroys up to 10 per cent of Canadian wheat crops each year and costs farmers millions of dollars.
It’s called tan spot disease, a fungal infection named for the small, brown lesions it creates on green wheat leaves. While it may not threaten to wipe out entire fields like others, its persistence makes it a regular headache for growers.
Dr. Reem Aboukhaddour, head of the Agriculture and Agri-Food Canada research laboratory in Lethbridge, Alberta, is leading a global collaboration to better understand how the disease works.
“[Tan spot] it’s not necessarily the most harmful… but it’s common, that’s for sure. In the commercial sector, I can always find a tan spot, no matter what,” Aboukhaddour said.
“So it’s up to you how you look at it. Do we have the privilege of ignoring the damage of five to ten percent every year?”
The damage caused by the disease can accumulate quickly.
In 2022, wheat was produced over 50 billion dollars in revenue in Western Canada, according to Cereals Canada, and is responsible for thousands of jobs. Saskatchewan is the largest producer, followed by Alberta and Manitoba.
Like any cultivated crop, wheat is susceptible to blight. Although sunspot disease may be obscure, it causes millions of dollars in losses each year.
Aboukhaddour’s lab in Lethbridge has made new research breakthroughs in recent years that could help shed more light on how the disease spreads and infects plants. These findings, Aboukhaddour says, will hopefully help develop more disease-resistant wheat varieties.
“The fundamental question for us hasn’t changed, which is how do we protect our food. That’s what this all comes down to for me,” she said.
“To build effective genetic resistance, you need to build tolerance to the pathogen itself.”
Understanding How a Tan Works
The tools a pathogen uses to evade or hijack a plant’s defense system are known in the scientific community as the “virulence factors” of the disease.
Aboukhaddour says there is not much knowledge about the virulence factors of the brown spot, but there are a few things that are known for sure.
Brown spot spreads by spores and can survive winter in crop stubble—wheat, but also barley. That means it is more of a threat to growers who practice monoculture, or repeated cultivation of the same crop in the same field.
Aboukhaddour also knows that brown spot occurs in moderately humid climates, especially in early spring and in fields where irrigation systems are used.
Scientists also know full well that brown spot is a resistant disease and occurs everywhere in the world where wheat is grown.
Aboukhaddour’s team found evidence of this when they sequenced the disease’s genome from a large collection of tan spot samples from around the world, collected by Agriculture and Agri-Food Canada.
“[We were able to] “This fungus has been shown to have the ability to have a very dynamic and flexible genome,” she said.
“[It has] have evolved and adapted over time to share the same weapons to kill the plant.”
Another thing that affects the farmer’s financial result
Tan spot disease was discovered about 50 years ago, which in scientific terminology means that it appeared relatively recently.
Aboukhaddour says that losses from tan spot disease were particularly high in the 1970s, before farmers in Canada began routinely using fungicides.
Dr. Kelly Turkington is a phytopathologist at the AAFC Research Laboratory in Lacombe, Alberta. She has collaborated with Aboukhaddour’s team on various projects.
He says brown leaf spot is part of a group of diseases called the “leaf spot complex,” which are major crop stealers for wheat farmers.
Brown spot can be difficult for producers to manage, Turkington said, not only because the disease can survive the winter, but also because there is little information about wheat varieties that are less susceptible to it.
This virus is known to attack all major varieties of wheat grown in Canada, including durum wheat.
Crop rotation is an effective way to control leaf spot, Turkington said, but there are many factors to consider when deciding where to plant a crop. Disease control is one of them.
Other aspects such as commodity prices and knowledge of alternative crops are also taken into account.
Another tool farmers have in their toolbox is fungicides. Depending on the size of the farm, Turkington says it can cost producers thousands to hundreds of thousands of dollars.
Stephen Vandervalk, a farmer and vice-president of the Alberta Wheat Growers Association, told CBC News that the impact of wheat spot disease on farmers in the province varies from year to year.
“Because it’s so volatile, one year it’ll be bad — and it could be three years before you see it again,” Vandervalk said. “When it’s bad, it can be absolutely devastating.”
He added that farmers often use fungicides as a catch-all approach to combating diseases such as opal spot. But there is a better way to prevent the blight he hopes will develop.
“The best way to do that is to put that into the genetics so it’s resistant to brown spot right out of the box.”
While Aboukhaddour believes it is important to use fungicides, he says it may have given farmers the impression that sunburn is less harmful than it actually is. He also worries that the disease will become resistant to some fungicides.
Turkington says he doesn’t see brown spot as something that could outsmart fungicides, but he wants the scientific and agricultural communities to remain vigilant.
“It is very important to be prepared to deal with specific issues that are starting to arise at an earlier stage, rather than allowing the situation to get so far that it becomes harder to deal with effectively.” [them].”
