Fusarium is Becoming the Fungus Among Us

by | Sep 6, 2022

There’s reason to believe Fusarium could become a negligible problem.

It’s been two years since an important reform was made in the fight against disease in Alberta. Fusarium was officially removed from the province’s Pest and Nuisance Control Regulation on June 2, 2020.

The big change it created was an environment which called for management of the disease, as opposed to former policy of zero tolerance. The majority consensus of the agriculture industry agreed that focusing on zero tolerance was no longer a feasible strategy, especially since the pathogen has airborne spread and has been found in crop production areas of Alberta.

The change brought Alberta in harmony with other provinces in how they mitigate it. For farmers, the fight still rages on against a fungal pathogen with multiple known pathotypes, the worst offender being Fusarium graminearum, responsible for Fusarium head blight (FHB).

Thankfully, it’s classified as a priority one disease in wheat, meaning plant breeders are firmly locked into the fight.

Prior to the early 1990s, FHB was thought of as an eastern Canadian issue, not one farmers out West would have to worry about. Which was true until it wasn’t, when an epidemic of the disease hit the Red River Valley in Manitoba in 1993.

“This really galvanized opinion that it can happen in Western Canada and could become a real problem,” says Rob Graf, recently retired Agriculture and Agri-Food Canada (AAFC) wheat breeder.

Rob Graf

Rob Graf, recently retired Agriculture and Agri-Food Canada (AAFC) wheat breeder. Photo: AAFC

Graf has the distinction of breeding the only winter wheat variety, Emerson, that carries an resistant (R) rating against FHB. As with many breakthroughs in science, this was at least in part, by accident. Graf didn’t specifically breed Emerson for the excellent resistance it expresses at the outset but that’s exactly what happened.

Over the past couple of decades, research scientists have focused their efforts to create higher yielding wheat varieties of semidwarf stature and increased disease resistance. FHB resistance has gradually been incorporated and improved over the years, in addition to all these and many other factors.

“It’s been a situation of continual improvement,” he says. “If you look at the adoption of varieties, particularly CWRS but other classes as well, farmers have been very willing to adopt varieties that have better resistance, especially for Fusarium head blight.”

He also pointed to the improvements in durum, where the first varieties with Intermediate resistance are now being registered.

“We’ve moved from a time when a majority of wheat varieties were Moderately Susceptible to Susceptible; now, the majority that are grown carry an MR [moderate resistance] rating. I have no doubt that trend will continue.”

Graf continues to be optimistic about the battle against Fusarium. He believes that in 10 to 15 years, there’ll be continued improvement in varieties, perhaps to the point that R ratings will stop being dubbed as rarities.

“We know a lot more than we did even five years ago,” he says of the collective effort against Fusarium. “With genomic analysis, important regions and more genes that influence resistance have been identified, and this will help to take us to that next level.”

A wheat breeder and director of the Crop Development Centre in Saskatoon, Sask., Curtis Pozniak says “significant progress” has been made with varietal development in the fight against Fusarium. From his vantage point, he sees no reason to think that won’t continue what he calls “the most challenging” disease farmers fight in the field.

Breeding against Fusarium is extremely difficult, but Pozniak is a fan of genetic stacking, whereby crossing parents with small yet effective Fusarium resistance can result in a strong commercially viable variety with an MR or even R rating.

“It wasn’t that many years ago when most wheat varieties were in the Susceptible to Moderately Susceptible category. So, there has been significant progress made, but it has been a slow slog. It is a real challenge to pull together all the genes that control resistance, given that each one of them can have a very small effect. You really have to pile them together, so they’re complementary to one another to build the resistance in sort of a stepwise fashion.”

Two big challenges for finding a strong variety are the complex genetics of resistance, and the impact of environmental growing conditions on resistance. The environment can make things challenging, because a variety may look great in a certain environment in one year, but lousy the next, or vice-versa. To layer on more complexity, there are several types of Fusarium resistance. For example, Type 1 resistance is simply if the plant itself prevents infection whereas Type 2 is that the plant is infected, but to what extent. Type 5 resistance is when the plant limits the ability of the Fusarium fungus from producing harmful mycotoxins.

Curtis Pozniak

Curtis Pozniak, wheat breeder and director of the Crop Development Centre. Photo: Crop Development Centre

“What makes it so challenging is that there are different genes controlling each of those components of resistance,” he says. “So, you put all of that together — the lack of immunity, large number of genes, strong environmental influence, the fact that resistance is made up of these individual components — that starts to give you a sense as to the challenge that we as plant breeders face with improving Fusarium tolerance.”

Another issue breeders such as Pozniak face is that many farmers want shorter varieties to deal with less straw going through their combine. Perhaps an unintended consequence is the fact that the plant is simply that much closer to the ground. As a result, there is more opportunity for Fusarium inoculant to move from the ground to infect the plant spike at the optimum time.

“That sort of inter-trait relationship also adds a level of complexity because if we’re trying to breeder shorter types for growers, it can have an impact on the amount of Fusarium that we might see. You put all that together, and it’s pretty complex,” says Pozniak.

Despite this, though, it’s plain to see in Prairie Fusarium screening nurseries the strong varieties with solid resistance prove themselves year over year with “substantial improvement.”

“But that improvement isn’t consistent across all wheat classes,” he says, citing the obvious need to continue improvement, especially in durum wheat.

Beyond that, varieties must be marketable, too. Pozniak notes just because a variety was made that will perform well agronomically, it doesn’t mean it will be wanted by processors or millers.

At Results Driven Agricultural Research, Alberta’s funding arm for on-farm research, the future is exciting with what’s being done to combat Fusarium.

Fusarium head blight in wheat

Fusarium head blight in wheat, identified by the salmon pink sporulation and brownish discolouration. Photo: Kelly Turkington, AAFC

Its research director Clint Dobson says the organization is sponsoring two projects totalling $360,000 to “pyramid” different genes to create more advanced varieties in conjunction with the federal government. The second initiative focuses on straight genetic improvements for FHB resistance.

Dobson says a toolbox full of options is critical, even during peace time, because when it hits, it’s often hard and fast.

“It’s significant challenge,” he admits. “It’s not every year but it’s about being prepared for the years where there is significant challenges and economic impacts on-farm.”

From RDAR’s perspective, a multi-pronged approach is required.

“It will result in long-term return from those research investments on how to manage and it and potentially avoid it through better varieties,” he says. “Breeding is a continuous improvement to having wheat seed early in the toolbox to get ahead of it. Also, it’s looking at multiple tools to even be responsive so you can make better management decisions and in-crop treatments. Definitely the varieties are the focus, that way producers don’t have that challenge and we have the resistance up front.”

Similarly, the Alberta Barley and Wheat commissions are committed to serious, long-term funding for Fusarium as part of their respective research programs.

The commissions are currently sponsoring more than 20 projects totalling more than $2 million through research clusters and its own programs.

“The long-term strategy is developing resistant varieties,” says David Simbo, the commissions’ former research program manager. “If you look at the wheat and barley cluster, a number of projects would be devoted toward that in addition towards the breeding programs. Generally, they are breeding varieties that would be resistant to Fusarium head blight. There are also a number of ongoing genetic studies with results that will feed into the breeding program so the breeders will use results of genetic studies to promote resistant varieties.”

Simbo notes, though, that just because a variety carries a strong resistance towards Fusarium, it must be good all around with a strong agronomic package or else farmers won’t grow them. For crops that have specific end-use markets, such as malting barley, the variety must be able to perform well in the malthouse. A relatively new malting barley variety, Lowe, does well against Fusarium but has poor uptake because it’s not preferred by maltsters and brewers.

“It didn’t take off and become the variety that farmers are growing because, in addition to Fusarium resistance, there might be other parameters they are looking for such as lodging and yield. If a farmer doesn’t have Fusarium on the fields, he may not look at resistance as the big thing.”

Header photo — Closeup of Fusarium graminearium. Photo: 20/20 Seed Labs

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