Elusive resistance

Not all wheat varieties live up to their official fusarium resistance ratings

Farmers need to take fusarium head blight resistance ratings with a grain of salt, according to research out of Manitoba Agriculture.

The research shows that varieties can perform much differently in the real world than they did in the variety registration trials where they received the official rating that is published in the provincial seed guides.

Some varieties with intermediate or even susceptible ratings performed better than many that received moderately resistant ratings.

“It’s one more thing to take into account when you’re looking for information on variety selection,” said study author Holly Dirksen, field crop pathologist with Manitoba Agriculture.

Samples of 72 spring wheat varieties from 14 Manitoba locations were collected and tested for fusarium damaged kernels (FDK) and deoxynivalenol (DON) accumulation between 2009 and 2015.

“Basically what we just found is results are variable,” she said.

Some moderately resistant varieties performed poorly, while a couple in the intermediate category had the best results of all 72 varieties.

The researchers produced a bar chart showing the level of FDK and DON for all 72 varieties in a continuum ranging from moderately resistant varieties on the left to susceptible varieties on the right.

“You would expect your bars to be the lowest on the far left and have a straight gradient to the highest on the far right, which is not what we see,” said Derksen.

The bars go up and down like a bumpy road.

That does not mean the seed guide ratings should be discounted. The Manitoba Agriculture research should be thought of as supplemental information when choosing a variety.

Derksen said the research is also applicable to growers in Saskatchewan and Alberta because all provinces have the same strains of the pathogen.

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Levi Wood, president of the Western Canadian Wheat Growers Association, was pleased to hear about the research findings.

“This is actually really interesting, especially when everybody that’s growing wheat all across the (Prairies are) talking about fusarium more than anything else right now,” he said.

Wood said fusarium is rampant in durum crops where he farms near Regina.

“The risk of fusarium at this point is seriously, seriously impacting our ability to successfully grow durum wheat,” he said.

The disease is having a “massive downgrading impact” on his durum crop and affecting his farm’s profitability.

“It’s tens if not hundreds of thousands of dollars on our farm alone,” said Wood.

Farmers in his area are contemplating switching from durum to winter wheat or spring wheat, and any new source of information that can help in variety selection is welcome.

“I definitely will check that out for sure,” he said.

Canterra Seeds pounced on the results of the seven-year study, issuing a news release drawing attention to the findings.

AAC Cameron VB marketed by Canterra had the lowest mean FDK and DON levels compared to all other CWRS varieties tested despite receiving an intermediate rating at registration.

“We are encouraged by these research results,” Rick Love, pedigreed seed business manager for Canterra, said in the release.

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“It shows the importance of comparing multiple years of data when making a variety selection for your farm.”

Derksen stressed that the official rating can’t be discounted because in some ways the research is more thorough.

A misting technique is used during the registration trials to get even infection levels in all plots, while infection levels in the Manitoba Agriculture study are highly variable.

Also, the sample size is bigger in the registration trials because varieties are grown in three repetitions and each repetition is tested individually, while the Manitoba Agriculture study used a composite sample to save money.

The other major finding of the study is that it appears there is not a one-to-one relationship between FDK and DON as was once thought.

“Now we know that relationship is quite variable,” she said.

The relationship can be very inconsistent in some years, and 2016 is a good case in point. The FDK levels are not that high in last year’s spring wheat crop, but the DON levels are.

Derksen said that’s because the infection occurred late in the growing season, so there was little visual evidence of fusarium, but buyers are looking at high DON levels in the crop.

Researchers are still crunching the numbers for the 2016 crop, and it’s possible it may change the results of the long-running study because it was a year with a lot of fusarium damage.

In the meantime, she encouraged growers to consult with neighbours about their experience with certain varieties as well as local retailers who may have conducted variety trials in their area because those are two other good sources of information.

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