The surprising success of midge-tolerant wheat

by Dallas Carpenter

Thanks to the keen eye of a Winnipeg entomologist in the mid 1980s, Prairie wheat farmers are now saved from an estimated $40-60 million annually in damages from the orange blossom wheat midge.

The orange blossom wheat midge was introduced to Canada in the early 1800s, being brought to Canada from Europe. It was not considered a major pest in Saskatchewan until an outbreak occurred in the northeast part of the province in 1983.

Since then, the wheat midge has moved steadily westward, covering the majority of the grain-producing area in Western Canada. That migration of this pest brought with it significant damage to wheat in terms of reduced yields and downgrading.

Through the late 1980s and into the 2000s, farmers were encouraged to manage their risk through practices such as insecticide application and having a rotation that had a resistant non-wheat crop grown between wheat crops. However, a breakthrough came when midge resistance was discovered by breeders and entomologists at the Cereal Research Centre (CRC) in Winnipeg.

As Dr. Ron DePauw, a former wheat breeder with Agriculture and Agri-Food Canada (AAFC) and current Science Advisor with SeCan, explains, it was the unique shape of some of the winter wheat kernels the CRC was testing for Hessian fly damage that provided the first clue to midge resistance.

“In the wintertime, when they were dissecting and analyzing the spikes, Phil Barker (an entomologist with the CRC) noticed that some of the kernels had an atypical shape. He called them ‘tubby’ – they were distorted, with one end being more flat or blunt.

“From there, this is where the eureka moment comes, they thought, ‘This is a response to something,’ and they could see that something had been eating on the kernel. So, they thought perhaps they should challenge it with the midge. And lo and behold, the wheat that had a tubby kernels were resistant to the orange blossom wheat midge.”

While the CRC knew they had a midge-tolerant variety, they didn’t know why it was tolerant. “They had to find out what the chemical compound was in the wheat that resulted in this antibiotic effect where midge isn’t able to survive,” says DePauw. “In time, they were able to determine genetically that there was one gene that was dominant and responsible, and they named it the Sm1 gene.”

The first varieties of midge-tolerant wheat, which were funded by farmers through the Western Grains Research Foundation, were bred at AAFC’s Cereal Research Centre in Winnipeg, the Swift Current Research and Development Centre and the University of Saskatchewan’s Crop Development Centre. Along the way to commercializing the new varieties, the entomologists and wheat breeders realized two things: The first was that the Sm1 gene was the only form of midge tolerance in wheat. The second was that midge would eventually mutate to overcome the Sm1 gene, rendering the gene ineffective within 10 years.

“Entomologists and others got thinking ‘How can we put together a stewardship plan, whereby we have a refuge to retain a sufficient number of susceptible midge?’” recalls DePauw. “ So when there is a mutant midge, the mutant would be more likely to mate with a susceptible midge than another mutant. That became the basis for the midge stewardship plan, that we need to have an interspersed refuge within the field.”

In 2010, with the seed companies and regulatory agencies supporting the plans for marketing midge-tolerant varietal blends, which contained ten per-cent of a midge-susceptible “refuge” variety, the first varieties were released and the midge stewardship agreement was established. The midge stewardship agreement limits the use of farm-saved seed to one generation past certified seed in order to preserve the Sm1 gene and the susceptibility of the wheat midge.

The adoption of midge-tolerant wheat has been an outstanding success. In less than ten years since it was introduced, an estimated 35 per-cent of all wheat grown in Saskatchewan is a midge-tolerant variety.

“From a Saskatchewan-specific perspective, I’m quite pleased with the uptake,” says Todd Hyra, SeCan Business Manager, Western Canada. “The technology was embraced immediately. Because the pest had been such a major issue for such a long time, Saskatchewan jumped on it right away.”

Recent issues such as fusarium head blight and lodging have caused midge-tolerant adoption to stall as farmers look to address these concerns. However, Hyra feels new varieties currently in the development or registration stage that address yield, midge tolerance, fusarium resistance and straw strength, will cause another surge in adoption rates for midge-tolerant wheat in the near future.

“I think it will take these new products that offer a broader protection to fusarium plus midge protection, to take the next step,” he says. “(With these new varieties) you have all the pieces of the package. There’s no disincentive to growing that product; you’re not giving up anything to have all that protection.”

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