2011’s ‘perfect storm’ for stripe rust hits PNW wheat fields

Club wheats like Cara and Chukar, as well as some soon-to-be-released experimentals, topped other varieties in yields in 2010 in 16- to 20-inch rainfall zones at Washington State University Extension test sites.

The reason, says WSU wheat breeder Steven Guy, is their high performance in the face of stripe rust resistance.

Chukar and Cara posted 140- to 148-bushel-per-acre average yields, and three test clubs averaged 134- to 137-bushel yields during a period that Guy calls the “perfect storm” for stripe rust conditions.

Key Points

Club varieties of wheat did better against stripe rust.

“Perfect storm” conditions led to persistent stripe rust in the last two years.

Researchers are concerned with new races of the disease developing.

Resistance to rust in the clubs revealed nearly zero symptoms of the disease. The experimentals — ARS 970075-3C, 970163-4C and 970071-3C — are among new high-resistance varieties expected to be released soon from WSU wheat breeder Kim Campbell’s research program.

2010 a tough year, too

Without rust’s impact last year, Xerpha probably would have been a top contender in the yield comparisons, says Guy. But it posted 110-bushel-per-acre average performance.

“This shows what kind of impact rust can have,” he told growers attending a WSU research plot tour near Reardan, Wash.

Even Chukar at some of the worst infestation locations did demonstrate some signs of rust, noted Guy.

There was such an “incredible amount” of stripe rust spore load present in the last two years, said Guy, that even resistant varieties like Chukar would have proven economically viable to have been sprayed with fungicide.

“The epidemic situation with stripe rust this year has been such that even resistant varieties have become overwhelmed,” he added.

WSU spring wheat breeder Mike Humphrey said the current stripe rusts are “new, exotic incursions” and “not your grand-dad’s stripe rust.”

Super strains

The current strains are “more adaptive and more aggressive” than those experienced by previous generations, Humphrey explained. “They create spores at higher temperature, and produce more spores even under lower temperatures,” he added. “These new races that started in 2001 are not the ones you have dealt with in the past.”

A new “highly aggressive” strain spread across North America in 2001, he said. “A lot of management decisions we made historically kind of have to be thrown out of the window, or at least fine-tuned. These are not typical rusts.”

Overwintering a problem

In Washington, in particular, a constant green bridge provides good overwintering for the pathogen, helping to evolve new races much quicker, said Humphrey.

“We have a nasty population of stripe rust here, which makes it difficult in wheat breeding,” he says.

“There are only two genes we have now that protect against all of the races of stripe rust, and there are reports of these two genes going down [becoming infected] in other parts of the world,” Humphrey warned. Even the club wheats are not bullet-proof, he added.

Both adult plant and seedling resistance to the disease are important to package together to fight the current strains of stripe rust, Humphrey said. Even if a mutation creates a new strain, these plants should exhibit a “reasonable level” of protection, he believes.

“We have tools and increasingly we have the resources to address this problem,” he says, noting that new federal funding to augment backing from local wheat commissions and other support organizations has helped in the fight against stripe rust.

A characterization of the fight is that in the Pullman, Wash., area stripe rust continued to be present throughout the winter, a very unusual situation for the region.

“Conditions remained for a stripe rust blow up all the way from the Sacramento Valley of California to Canada,” Humphrey said.

“You are dealing with the perfect storm for stripe rust for two years in a row of cool, wet weather, abundant inoculum, and a nasty and aggressive strain.”


RAMPANT RUST: Wheat stripe rust continued to be a battle for grain growers in the Pacific Northwest this year, while some of the most popular varieties fell victim with reduced yields, says WSU wheat breeder Mike Humphrey.

This article published in the August, 2011 edition of WESTERN FARMER-STOCKMAN.

All rights reserved. Copyright Farm Progress Cos. 2011.