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Protect your midge-tolerant wheat

The midge-tolerance gene was found in the majority of SWS wheats in 2017. Refuge seed is required to keep this trait in play

Producers should add refuge seed to most Canada Western Red Spring (CWRS) and Soft White Spring (SWS) wheat varieties in 2018 to prolong the longevity of the midge-tolerance Sm1 gene, says Todd Hyra, western business manager for seed marketing agency SeCan.

Last spring, Canadian researchers discovered Sm1 in most SWS varieties, including AAC Indus, AC Sadash and AAC Chiffon. SWS variety AAC Paramount was confirmed to contain the trait later in the year.

If some non-midge tolerant varieties are not present in a field, there is a risk that wheat midge will adapt to the tolerant varieties, meaning the trait would no longer be effective (see ‘How wheat refuge works’ at bottom).

According to SeCan, midge tolerance saves producers $36 per acre for a total $40 to $60 million per year. There are no other known midge-tolerance genes should Sm1 cease working.

The midge-tolerance trait is also present in CWRS varieties including AC Jatharia, AC Shaw, AC Unity and AC Vesper, and in Canada Prairie Spring Red (CPSR) varieties including AC Foray, says Hyra. A durum wheat variety, AAC Marchwell, and the Canadian Western Special Purpose (CWSP) varieties AAC Awesome and KWS Sparrow VB also contain the trait.

AC Andrew does not contain Sm1, which makes it a suitable refuge for SWS wheats.

Sm1, which was first identified in soft red winter wheat varieties in the 1990s, was deliberately bred into spring wheat varieties released in 2010 by CDC and Agriculture and Agri-Food Canada. Last spring, using a marker linked to Sm1, CDC researchers discovered most SWS varieties already naturally contain the gene in their genetic background.

The discovery was made too late in the spring for producers to add refuge seed in 2017 but SeCan is working with producers to remediate their products for 2018. The agency will require remediation for all products except AC Sadash, which makes up 64 per cent of SWS acreage. Producers can either source seed with refuge added, says Hyra, or add AC Andrew to existing supply.

“This past season some of our members produced a good, high-quality supply of AC Andrew that can be purchased to add as refuge to their varieties,” says Hyra.

Resistance

Pierre Hucl, a CDC wheat breeder, says wheat breeding programs will continue to use the Sm1 gene in new varieties as long as they can, despite the discovery.

“For me personally it’s not going to change anything,” says Hucl. “We’ve known the Sm1 gene has been floating around Europe with no refuge for a long time, so the fact that it’s showing up in Canadian varieties is not necessarily a big shock.”

What’s making experts in the Canadian industry nervous, he says, is the fact that no Sm2 or Sm3 gene has been discovered yet and Sm1 has been deployed in Canada without refuge for 10 years.

Researchers are concerned the midge might behave like the Hessian fly, a major economic pest of wheat that overcame resistance genes in the U.S. after roughly 10 years.

“It’s a concern that the Sm1 gene could (lose efficacy), but we also know that it’s been in existence in pure form without refuge for decades,” says Hucl. “But it’s good to err on the side of caution.”

Hyra says several new wheat products are coming out soon that contain Sm1 for midge resistance plus other necessary traits such as shorter or stronger straw and fusarium tolerance. Refuge will be in the bag for new products, he says.

But for the time being, he urges producers to “do the right thing” by replacing seed or adding a 10 per cent refuge. “Sm1 is our most important tool,” he says.


How wheat refuge works

Midge-tolerant wheat varieties have been sold as a blend of two varieties of seed: 90 per cent is a midge-tolerant variety, and 10 per cent is another variety, or “refuge,” that is not midge-tolerant. The two varieties are interseeded, unlike corn refuge systems in which the refuge is grown in a block within or beside the field.

If only midge-tolerant wheat is planted in a field without a non-tolerant refuge, a small population of “virulent” (resistant) midge may survive and breed, producing offspring that can also feed on midge-tolerant wheat, overcoming the midge-tolerant gene’s effectiveness.

If a small percentage of non-midge tolerant wheat is included, some non-virulent midge will feed on that wheat and survive, mating with virulent midge to produce non-virulent offspring. This gives longevity to the midge-tolerance trait.

Use of farm-saved seed is prohibited beyond one year past certification for midge-tolerant wheat to keep the refuge at the 10 per cent level. Producers are required to sign a stewardship agreement to ensure refuge levels are maintained.

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