Western Canadian farmers face two cereal diseases that have the potential to be more damaging than they presently are: stripe rust on wheat and fusarium head blight on wheat, barley and oats.
At the recent Agronomy Update in Lethbridge, Agriculture Canada plant pathologist Denis Gaudet said stripe rust is endemic to Asia and has been in North America for at least 100 years.
“Stripe rust has always been a problem, to a small extent, in cereal crops in southern Alberta. Where we’ve seen it the most is in the soft white wheat, because it matures later and the irrigation provides a higher moisture situation, which is conducive for stripe rust development,” Gaudet said.
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“If we look at our spring wheat varieties across all different classes, we see most are susceptible and some are highly susceptible.”
The fungus that causes stripe rust is Puccinia striiformis, a member of the family that cause leaf and stem rusts. It has several biological types for wheat, barley and other grass species.
“The stripe rust fungus traditionally likes cool infection temperatures, unlike stem and leaf rusts that are typically warm temperature rusts,” he said.
The spores need to germinate in a film of water and then penetrate the plant to infect. It’s not a hot weather rust.
It occurs as individual pustules on younger leaves and seedlings. It affects the leaves and the heads and grows systemically in the plant before breaking out on the surface in big rust pustules. As the plant develops, the disease produces prominent striping of the leaves.
“When the spores break loose, they’ll fly around, reinfect plants and you get a secondary cycle happening during the summer,” said Ron Howard, a plant pathologist with Alberta Agriculture.
“There are reports of significant yield losses with this rust, especially if it strikes the crops early – up to 75 percent in terms of yield and downgrading losses, mostly from shriveled kernels because this rust goes right up onto the heads.”
Gaudet said the stripe rust fungus is interesting because it doesn’t require much moisture for infection.
“All it requires is three hours of continuous moisture, which usually is provided by morning dew. Rain and rainfall patterns don’t necessarily affect this fungus,” he said.
“What is important is the temperatures for germination. Its optimum temperature for germination was around 12 C.”
Gaudet said soft white wheat breeders had successfully incorporated stripe rust resistance into local lines, and farmers usually didn’t see the disease. However, soft white wheat began to show less resistance to the disease in the late 1990s.
“In 2000, researchers started seeing a new set of races, with a higher germination temperature capability. Their optimum temperature for germination is around 18 C. And they have a shorter latency,” Gaudet said.
“It’s for this reason we’ve started to see this fungus moving out of the traditional area of the Pacific Northwest where it’s cool, to the Mississippi flyway and the central wheat production belt in North America.”
Howard said the biggest risk with stripe rust is the spore showers that come into Alberta, mostly from the Pacific Northwest.
“Every year, we seem to see stripe rust moving farther north. It used to be mainly a problem in irrigated soft white wheat, occasionally in hard red wheats in southern Alberta. Now it’s not unusual to see stripe rust as far north as Edmonton,” Howard said.
“Stripe rust spores mostly blow up from the U.S. Our biggest concern is rust spores coming out of Oregon and Washington. But stripe rust also occurs in northern California and it is possible it moves up from there. There’s another pathway for stripe rust out of Texas, straight up to Western Canada.
There’s also been a question as to whether the disease can overwinter in Western Canada, and Gaudet said the weather must stay warm for that to happen. Temperatures below –10 C will kill the fungus, so it generally overwinters where temperatures are milder.
“But (in 2006) we saw stripe rust develop in southern Alberta, where there was a lot of the seeding of the winter wheat variety Bellatrix. Around June 20, we started hearing reports of stripe rust around Medicine Hat. When we looked at it, all the Bellatrix was heavily infested and we were seeing major losses – 15 to 30 percent loss,” Gaudet said.
“We had mild conditions that winter, so we immediately suspected the fungus had overwintered in the area, moved from the fall infected winter wheat onto the spring growth, then moved to the spring crops.”
Reports from Montana indicated a stripe rust epidemic in late May and early June and wind pattern records showed prevailing winds favoured the spread to southern Alberta and Saskatchewan. That means both overwintered spores and an infection from across the border could have played a role in the outbreak.
Gaudet said researchers are in the process of setting up a stripe rust nursery in Lethbridge to establish an inventory of races to monitor what’s going on with the disease.
Fusarium head blight affects wheat, barley, oats, corn, rye and certain grasses. Howard said it’s a disease much favoured by warm weather, especially during heading.
“When you get warm, wet weather occurring, that creates the ideal conditions for fusarium,” he said.
“This fungus also causes root rots and stem rots, so it can be a fairly nasty problem.”
Symptoms include bleached florets, which Howard said are what farmers are looking for when they scout their crops in June and July.
“If you have a hand lens, you can see salmon coloured spores that form along the infected florets. The spores blow off crop residues and debris, up into the florets during flowering. The result is fusarium damaged kernels,” he said.
“In corn, it causes stalk rots and ear rots. In Ontario they have a tremendous problem with it. As time goes on and our corn acreage expands, we can expect to see fusarium ear and stalk rot as a problem in our corn.”
Fusarium head blight affects wheat’s yield, grade and quality.
Mycotoxin contamination caused by the fungus has implications for animal and human health. Once fusarium head blight gets into an area, Howard said it’s impossible to eradicate.
“Historically, fusarium head blight has been most destructive in the eastern Prairies, with millions of dollars lost in Manitoba and eastern Saskatchewan because of fusarium head blight in their wheat and barley crops,” Howard said.
“We know fusarium graminearum and the other fusarium strains that cause head blight are steadily moving west. It seems there’s an evolution of more aggressive strains of this fungus now and as they move west they’re going to have a greater impact.”
Howard said the biggest concern with fusarium is the production of toxins in the grain, particularly deoxynivalenol, or DON.
“When DON exceeds certain levels, the grain may be unfit for cattle. It causes them to go off their feed and can induce spontaneous abortions.”
Howard said scientists who work with fusarium have noticed changes in the fungus to types producing more DON.
“And these species seem to be more pathogenic on cereal crops. In Manitoba, where fusarium used to be just an issue on wheat, now it’s becoming a serious problem on barley and oats. In Ontario it’s a serious problem on corn and we do see it on corn occasionally in Alberta.”
