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A decade of midge-tolerant wheat

New varieties are in the pipeline for CWRS and SWS classes

Over the past 10 years, western Canadian farmers have deliberately seeded 27 million acres of wheat susceptible to orange blossom wheat midge — and saved themselves an estimated $1 billion in lost yield and quality.

To be clear, only 10 per cent of the seed on those acres was susceptible to midge, and that’s been the reason for the continued success of the other 90 per cent in keeping the critters at bay. If 100 per cent of the varieties were tolerant, the small percentage of midge that could avoid the resistant trait would survive and reproduce, eventually becoming the dominant population, similar to how weeds become resistant to herbicides.

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This approach is important because there’s only one gene — Sm1 — with the resistant trait. Its continued success depends on growers signing agreements that limit the use of farm-saved seed to one generation past certified.

Todd Hyra, western business manager for SeCan, says the program has been a success because 98 per cent of producers in the system have complied with the agreement. “They see the value, and we want to encourage that continued spirit of co-operation that’s kept this valuable trait in play.”

These agreements recently went digital and are logged in an electronic database, says Mike Espeseth, Western Grains Research Foundation communications manager and co-chair of the Midge Tolerant Wheat Stewardship Committee. The program ensures the products’ built-in portion of “refuge” seed stays at 10 per cent in order to maintain Sm1’s longevity.

Two years ago, when it was discovered that older varieties of soft white spring wheat also contained the Sm1 gene, producers were asked to voluntarily remediate products with a 10 per cent refuge while seed suppliers caught up. These days, all new midge-tolerant wheat (MTW) varieties contain refuge in the bag.

Adding tolerance to more varieties

The proportion of CWRS seeded to MTW has dropped over the last few years due to relatively dry weather which in turn meant lower midge pressure. Last year about eight per cent of total Prairie CWRS acreage was midge tolerant. Hyra says the “real home” of MTW is Saskatchewan, while acres have been lower in Alberta and Manitoba. “Seed customers are getting by on midge and have migrated to other varieties that provide shorter, stronger straw or better fusarium suppression.”

That might change if wet conditions continue this year, and breeders have been working on introducing the Sm1 gene into varieties which also offer higher yield and fusarium resistance.

2020 wheat midge forecast.

“We expect the total percentage of MTW acres to increase again as varieties with short strong straw and improved fusarium tolerance hit the market in 2020 and 2021,” Hyra says.

For example, AAC Alida VB has short straw, low DON accumulation and is midge tolerant, he says.

AAC Warman and AAC LeRoy are two more CWRS varieties that combine midge tolerance with fusarium and lodging resistance, says Santosh Kumar, a wheat breeder at AAFC in Brandon. His program focuses almost entirely on CWRS wheat for Western Canada.

Another new variety, AAC Magnet, is rated moderately resistant to fusarium but is lacking on the midge-tolerance side, but not all producers want both.

Harpinder Randhawa is an AAFC Lethbridge spring wheat and triticale breeder responsible for soft white and Canada Prairie spring classes. He says in recent years his program has focused on providing options that tick as many boxes as possible for producers.

In the CPS class, Randhawa recently registered AC Crossfield and AAC Entice. Both are susceptible to midge but have an intermediate level of fusarium resistance. A third, AAC Castle, has midge tolerance as well as intermediate fusarium resistance and good straw strength.

In the SWS class, he’s currently looking for midge-susceptible varieties to use as refuge for new varieties.

Finding promising candidates for MTW refuge is a key breeding challenge in every wheat class. Kumar says there’s a lot of complexity around finding a refuge variety because it has to look very similar to the MTW variety in maturity, height, yield and test weight.

Both breeding programs try to provide choice to farmers.

“If the farmers want fusarium and midge tolerance combined, there are good varieties to choose from. As public breeders, we want to provide better and appropriate choice to farmers so they don’t have to compromise,” Kumar says.

Randhawa says producers look at the whole agronomic package when making seeding decisions, and midge is just one variable. “In some areas with a lot of midge pressure where there are yield losses you don’t really have a choice (but to plant MTW), but in other areas without much pressure, you can decide.”

How midge tolerance works

Santosh Kumar, a wheat breeder for AAFC’s Brandon Research and Development Centre, says there are two mechanisms for midge tolerance in wheat. The first is Sm1-based resistance, which kills the larvae once they start feeding on the developing wheat kernels. This Sm1-based resistance mechanism is called antibiosis.

The second mechanism involves chemical compounds in wheat that inhibit the female midge from laying eggs on wheat heads. This mechanism is called “oviposition deterrence,” and isn’t as common in wheat breeding. Most programs rely on Sm1-based resistance.

But along with other AAFC, University of Manitoba and CDC Saskatoon scientists, Kumar’s program is working on alternatives and screening germplasm for additional sources of midge tolerance. Recently, a team of scientists discovered a promising gene in germplasm from southern Asia, although it’s too early to confirm its efficacy.

Once an alternative to Sm1 is discovered, Kumar says the plan is to bring additional sources of resistance together in new varieties to make midge tolerance more durable.

About the author

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Julienne Isaacs

Julienne Isaacs is a Winnipeg-based freelance writer and editor. Contact her at [email protected]

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