New fusarium chemotype tightens FHB tolerance levels

In Canada, the presence of fusarium damaged kernels (FDK) is used for grading wheat. The level of FDK also provides an indication of mycotoxin contamination resulting from Fusarium graminearum, the main causal agent of fusarium head blight.

Recent research results indicate a new strain of F. graminearum is a more potent producer of toxins. As a result of this new strain and its increased toxin production, the Canadian Grain Commission has now tightened tolerance levels for FDK.

Kelly Turkington, a research scientist with Agriculture and Agri-Food Canada in Lacombe AB, and Randall Clear, a mycologist with the Canadian Grain Commission, were aware of a new chemotype of F. graminearum – 3ADON vs the traditional 15ADON – being detected in western Canada.

They developed a research project, funded by the Western Grains Research Foundation Endowment Fund, to find out how widespread the new chemotype was, establish the extent of reproduction and recombination between the two chemotypes, and see if the new chemotype was more virulent on crops. That included testing to see if it produced more mycotoxins, plus checking growth rate, spore production and fungicide sensitivity.

The research team included researchers from the USDA, Agriculture and Agri-Food Canada in Winnipeg and the Canadian Grain Commission. The researchers looked at more than 4,000 isolates of fusarium from wheat, oat, barley and corn, collected from the 2005 to 2007 harvests across Canada.

“Material came from grain collected through the Canadian Grain Commission’s harvest survey in western Canada, plus from industry groups in eastern Canada,” says Clear.

“We’d remove the FDK kernels, grow them out to see which species of fungus caused the FDK, then take those isolates that were F. graminearum and prepare them into pure cultures. Those were sent to colleagues Todd Ward and Kerry O’Donnell, researchers with the USDA in Peoria, Illinois. They had developed a multi-locus assay for determining species and chemotype, which is similar to a race of the species.”

In Winnipeg, Clear and colleague Tom Nowicki took the isolates that produce 15ADON or 3ADON, grew them out on sterile medium and measured their ability to produce the DON mycotoxin.

“We took the genotypic identification, then grew them out to find which toxins they could produce and how much. When we did that, we realized the 3ADON was producing more DON in culture,” says Clear. “That’s interesting because our grading system is based partly on what level of DON we would expect for specific levels of FDK. So if the level of FDK or DON is changing – up or down – we need to be aware of that so we can adjust the grading tolerances.”

He says the grading tolerances are a way to segregate grain, so when it gets exported to customers who have specifications for DON – and most do now – we can be sure it’s going to be under their limits.

“The last year we collected, in Manitoba just over 2/3 of the isolates were of the 3 type. In Saskatchewan, about 1/3 was the 3 type. Alberta is only 5 to 6 percent of the 3 type. PEI is currently almost 100 percent of the new, 3 type,” says Clear.

Turkington says when looking at the ability of the chemotypes to produce mycotoxins, Clear and Nowicki found the 3ADON produces about twice as much toxin as the 15ADON chemotype in the laboratory.

“For a given disease severity due to the new chemotype, you would expect to see more mycotoxin in the affected grain versus the same level of disease severity caused by the older chemotype,” he says.

Turkington noted that Ward and O’Donnell found significant genetic differences between the two populations of F. graminearum, which indicated limited levels of recombination between the two. This suggests that the genetic makeup of the two chemotypes hadn’t changed substantially.

“It wasn’t a case of the 15ADON changing into the 3ADON. They are two distinct populations of F. graminearum,” he says.

“Overall, we didn’t find any difference between the two chemotypes with regards to fungicide sensitivity in terms of tebuconazole, which is the active ingredient in Folicur. So that’s still a chemical that can be used to reduce the impact of fusarium,” he says.

Clear says the observed trend of higher DON levels for a given level of FDK in western grain over the last few years, likely due in part to the shift in chemotypes, has resulted in a tightening of grading tolerances. The benefit to farmers from this research involves a firming up of grading standards that reflect changes to current pathogen populations.

“We know what our populations are now, so we can watch for changes in the future,” he says.

Turkington adds that the research provides a better understanding of this pathogen.

“It illustrates to pathologists, breeders and farmers that these plant disease issues we deal with are not static. They change from within the population itself, or from new pathogens introduced into our cropping systems. So we need to be vigilant in terms of monitoring our crops, to stay on top of these issues before they hit the farmer in the pocketbook,” he says.

The Endowment Fund, the original core fund of WGRF, has supported more than 200 research projects since 1983. Research Reports on many of these projects are available on the WGRF web site.

For further information, contact:

Kelly Turkington
Research Scientist
Agriculture and Agri-Food Canada
Mike Espeseth
Communications Manager
Western Grains Research Foundation