Higher-toxicity fusarium moving in on Prairies

The fusarium head blight many Prairie farmers know and loathe is being replaced by a new, more toxic and “more aggressive” form of the crop disease, researchers say.

And the amount of toxin it produces could ultimately lead to even lower tolerances for fusarium-damaged kernels when grain is graded.

Mycologist Randy Clear of the Canadian Grain Commission’s Grain Research Laboratory said on the program Farmscape that the previous chemotype, 15-A DON, is being replaced by the more toxic 3-A DON in Prairie wheat crops.

Since 1998, he said, the prevalence of 3-A DON has risen from about five per cent of infected wheat crops on the Prairies to 40-50 per cent.

DON refers to deoxynivalenol, the toxin produced by fusarium graminearum, the main cause of FHB.

The new chemotype “seems to produce more toxin in the grain that’s infected, so the new chemotype with the same level of fusarium damage tends to show us a little bit more of the toxin,” Clear said on the program, which is sponsored by the Manitoba Pork Council and Sask Pork.

That could pose a problem for the CGC’s grading system, he said, as it’s now tailored to ensure levels of DON in grain aren’t above acceptable levels.

In laboratory tests, the new isolates produce twice as much DON on average compared to the 15-A DON chemotype, he said. In field studies, however, he guessed those levels rose by another 10-15 per cent compared to the controlled studies in the lab.

Adjustment

If a consistent pattern of higher DON levels appears in the same level of fusarium damaged kernels, Clear said, tolerances for damaged kernels may need to be adjusted downward, to make sure toxin levels stay within regulated limits.

Researcher Victoria Gauthier, who’s studying 3-A DON at the University of Manitoba, previously told Farmscape producer Bruce Cochrane that the old and new chemotypes are believed to have a single evolutionary origin.

At one point, she said, there may have been a mutation allowing the 3-A DON chemotype a “fitness advantage” and ability to produce more toxin.

Gauthier’s research is expected to produce recommendations for wheat grading techniques within the next year, Cochrane reported.

Current tolerances for fusarium-damaged wheat kernels at primary grain elevators on the Prairies range from as low as 0.25 per cent for grades such as No. 1 Canada Western Red Spring (CWRS) to as much as five per cent for CW Feed.

Livestock’s tolerance for DON in feed varies. Poultry can take as much as 20 to 50 parts per million (ppm) without going off-feed; weanling hogs are expected to refuse feed if the complete feed product contains DON levels of less than one ppm.

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