readbasket of the World Under Siege” blared the headline on an opening slide in Dilantha Fernando’s PowerPoint presentation.
It was a dramatic way to start a workshop on fusarium head blight. But was it exaggerated?
“It all depends on which year we are talking about,” said Fernando, a University of Manitoba plant pathologist.
It was with some urgency that a recent two-day industry workshop at the Richardson Centre for Functional Foods and Nutraceuticals, organized by Fernando and others, looked at fusarium head blight and its impacts.
The workshop heard the disease is spreading, its effects are significant and ability to prevent it is limited.
When the year is bad, the impact can be devastating. It’s estimated a major epidemic of fusarium head blight (FHB), a fungal disease of wheat and barley, causes $1 billion in lost yield, quality and sales throughout North America.
Here in Manitoba, where wheat is the second-largest cash crop after canola, FHB ranks as the most serious plant disease.
Besides having the ability to harm crops, FHB carries another arrow in its quiver. Fusariumdamaged grain contains toxins which can affect the health of both animals and humans.
Identified in Manitoba in 1923, FHB caused little concern until the mid-1980s. Then it began to spread, aided by unseasonably wet weather, increased conservation tillage, shorter crop rotations and limited resistance in wheat and barley varieties, Fernando said.
The first major outbreak of FHB in Manitoba occurred in 1993, producing severe yield and quality losses. By 1998, FHB had spread from Manitoba into much of Saskatchewan and parts of Alberta, which had previously been disease free.
At first, wheat was FHB’s only victim. But by 1998 FHB was detected in almost every barley field in Manitoba. Now winter wheat has proved susceptible as well. FHB produced more damage in Manitoba winter wheat crops last year than in spring wheat. FHB can infect corn, too.
Also known as scab, FHB is caused by several species of the fungal pathogen known as fusarium. Fusarium-damaged kernels are typically shrivelled, lightweight and with a white or pinkish colour – characteristics giving them the common name of “tombstone kernels.”
These kernels contain toxins (called mycotoxins) which are potentially harmful to animals and humans. The main one is deoxynivalenol, or DON (also known as vomitoxin).
DON in grain affected by FHB can reduce the feed intake of livestock.
Although levels are usually low, it doesn’t take a lot of DON in feed to have an effect.
Pigs, being fussy eaters, are the most vulnerable. Every part per million (ppm) of DON in grain will produce a 7.5 per cent weight reduction in swine, Fernando said.
A recurring slide in several PowerPoint presentations showed two pigs from the same litter side by side. One was fat and the other was scrawny. The thin pig had been fed only grain containing DON. He refused to eat it and was slowly starving as a result.
Another slide graphically showed a pig throwing up after eating DON-infected feed, giving full meaning to the term vomitoxin.
Because DON is toxic, the allowable level in feed for swine, calves and lactating dairy cows is less than one ppm. The allowable level in cattle and poultry feed is two ppm or less.
Mycotoxins such as DON can be a health hazard to humans, too, said David Miller, a Carleton University biochemist.
He said the Canadian Food Inspection Agency once seized organic flour from a New Brunswick mill with enough DON in it to make children sick.
In the U.S., authorities investigating a school lunch program in 1998 found kids throwing up because the soft white wheat flour used to make burritos was full of vomitoxin.
Back home in Canada, the risk to human health of mycotoxins in infected grain is very low, Miller stressed. Food safety programs usually prevent DONinfected grain from coming to market.
Even so, Health Canada is considering lowering the regulatory tolerance levels for DON as a food safety measure, Miller said.
On the rare occasions that mycotoxins get through screening programs, they can affect the baking quality of wheat and the malting and brewing qualities of barley.
Speakers noted mycotoxins affect the ability of protein in grain to function. As a result, the resulting bread is heavy, dense and chewy.
And if a freshly opened can of beer unexpectedly gushes foam and you haven’t shaken it, mycotoxins are the culprit.
In other parts of the world, the effects of mycotoxins can be even more serious.
The workshop heard that Kashin Beck syndrome, an osteoarticular disease causing swollen joints and stunted growth, is known to affect several million people in China. Mycotoxins in stored grain are the suspected cause.
World health officials estimate between 10,000 and 30,000 children in Africa get sick and even die every year from eating grain containing mycotoxins.
Plant breeders have had some success in improving resistance to FHB in wheat and barley. But the development of resistant cultivars has been frustratingly slow, the workshop was told.
After years of research, one winter wheat variety showing resistance to the disease was approved for registration and commercialization last February, but it is still two to three years away from being in farmers’ hands. Researchers are hoping however, it marks the genetic breakthrough they’ve been seeking.
“Until you get really good resistant varieties, it’s still going to be a problem,” Fernando said. [email protected]
– DILANTHA FERNANDO, U OF M