Toxin levels in fusariuminfected Manitoba wheat have been increasing rapidly relative to the number of fusarium-damaged kernels (FDK).
But this crop year, the levels of the toxin DON (deoxynivalenol) are closer to the old one-to-one ratio with FDK, says Canadian Wheat Board (CWB) agronomist Mike Grenier.
“The DON levels aren’t as high (relative to FDK) as the last couple of years, but I’m not sure why,” Grenier said.
Tom Graefenhan, the Canadian Grain Commission’s (CGC) program manager for microbiology isn’t sure either.
“There are a lot of factors that play into this that we don’t understand yet,” he said.
It could be an anomaly, or a combination of factors ranging from the weather during the 2010 growing season, to the varieties of wheat grown.
It’s also possible the recent shift within the disease itself to a potentially more toxic chemotype has slowed or even reversed.
In North America the F. graminearum chemotype traditionally responsible for fusarium head blight is known as 15 acetyl-deoxynivalenol (15 ADON), according to information at the CGC’s website.
But a second chemotype – 3 acetyl-deoxynivalenol (3 ADON) has been on the increase in Manitoba and North Dakota. It’s potentially more toxic than 15 ADON.
In 1998, the 3 ADON chemotype accounted for 10 per cent of the DON in infected Manitoba wheat, but by 2008 it had risen to 70 per cent, Graefenhan said.
Given the rapid shift, it’s natural to assume it will continue unabated, he said.
“But we shouldn’t take that for granted and we shouldn’t expect the trend to continuously follow one direction,” Graefenhan said.
In 2009, Graefenhan’s predecessor, Randy Clear, found 3 ADON had decl ined in Ontario.” The bottom line is we see changes and it can go up and it can go down.”
An analysis of infected Manitoba wheat later this year could shed light on whether 3 ADON has plateaued in Mani toba, increased or retreated.
The increase in DON, relative to FDK, prompted the CGC to tighten FDK tolerances in the top grades of wheat to ensure customers don’t get unacceptable levels of DON, also referred to as vomitoxin.
DON, while toxic to humans and livestock at certain levels, is less toxic than many other toxins produced by fungi.
Every year Agriculture and Agri-Food Canada surveys Manitoba fields of spring and winter wheat, barley and oats
for fusarium. Often winter wheat, which flowers earlier than spring wheat, avoids infection, but not this year, said Ag Canada plant pathologist Andy Tekauz. The average winter wheat DON level in 2010 was 10 parts per million (ppm).
“That’s very high,” he said.
But Tekauz stressed since his samples were hand picked, levels might be higher than in crops that were combined. The more heavily infected, and therefore shrivelled seeds, will pass through the combine and not be collected, resulting in lower DON levels.
The spring wheat, barley and oats tested by Agriculture Canada had DON levels of 4.0, 1.8 and 1.9 ppm, respectively.
“High DON levels in the winter wheat shows the value of having a higher level of resistance in a crop in a year when you get a lot of infection (like 2010),” Tekauz said.
Only one winter wheat, CDC
Buteo, is rated “I” (Intermediate) for fusarium resistance and the rest, including CDC Falcon, the favourite of Manitoba farmers, is rated “S” (Susceptible).
In contrast three Canada Western Red Spring wheats are rated “MR” (Moderately Resistant) and 10 are rated “I.”
“Where we are now, we’ve made strides but you shouldn’t rely on a single strategy to get effective control of fusarium,” Tekauz said. “You have to use everything available to you from variety selection, to fungicide use, to rotation.”
Fusarium hasn’t traditionally been a problem west of eastern Saskatchewan, but a wet season saw a big jump in infections last year in Saskatchewan and Alberta, Graefenhan said.
“We’ve never seen so many samples affected by FDK from those provinces,” he said.
“But I don’t want to spread panic. It’s nowhere near what we see in Manitoba.”
About 1,500 samples of fusarium-infected grain were collected from Saskatchewan and Alberta, he said.
“If something doesn’t show up this year, it’s probably not there because the conditions were so favourable for a lot of fungi,” he said. “We thought this would be a good year to do a thorough monitoring of areas where we haven’t seen much fusarium graminearum.”
Weather in 2011 could have a big impact on whether fusarium infections farther west increase or retreat. A drier year could see less of the disease, but if it’s wet, fusarium could be back in areas where traditionally it has not been a big problem, Graefenhan said. [email protected]
“HighDONlevelsinthewinterwheat showsthevalueofhavingahigherlevel ofresistanceinacropinayearwhenyou getalotofinfection(like2010).”
– Andy Tekauz