Farmers key to wheat midge technology

The orange wheat blossom midge fly is a scourge affecting wheat producers around the planet.

For western Canadian producers, it’s been a pest for roughly 35 years. In the 2006 crop year, midge fly larvae caused downgrades of $20 to $75 per acre, with overall yield loss estimates pegged at $40 million.

Producers need a strategic control method but without the significant input costs associated with traditional insecticides.

For about 15 years, scientists have used traditional plant breeding techniques to move a gene called Sm1, which contains natural resistance to the midge fly, from a U.S. winter wheat variety to Canadian spring wheat varieties.

Adult flies emerge from the soil in late June/early July, and the females lay eggs on the wheat heads.

However, wheat varieties containing the Sm1 gene produce phenolic acids when the larvae starts to feed. The larvae don’t like the taste of the acids, so they stop feeding and eventually starve to death.

You may think that’s problem solved. Producers just have to plant wheat varieties containing the Sm1 gene and the flies will disappear.

I wish nature was that simple. Most of the midge population is susceptible to the effects of the Sm1 gene, but a small percentage will mutate and become virulent, meaning they could feed on Sm1 varieties.

If that happened, this virulent population would grow, overtake and consume the Sm1 crop, rendering the Sm1 gene technology useless within 10 years. The trick is to find ways to manage the technology to minimize midge consumption losses.

Seed and crop producers are using an approach called the interspersed refuge system.

To keep midge consumption at bay while preventing the growth of a virulent population, a mixture of two wheat varieties are blended and grown together: 90 percent seeds of a Sm1 gene variety plus 10 percent of a ‘refuge’ variety (no Sm1 gene). The midge are allowed to feed on the 10 percent refuge or susceptible variety.

The idea is that potential virulent flies mate with non-virulent flies and produce non-virulent offspring. Non-virulence is a dominant trait.

Scientists estimate that this approach will extend the life of midge tolerance (the usefulness of the Sm1 gene) to 90 years or more.

The key to making this work is the Midge Tolerant Wheat Stewardship group, an alliance of seed producers, farmer groups, government institutions and plant breeders.

The group is trying to ensure this technology is used efficiently to maximize investment returns and in ways that ensure the viability of the technology for generations.

Producers are required to sign a Midge Tolerant Wheat Stewardship agreement when they buy seed. The agreement outlines that farm-saved seed from a midge tolerant crop can only be used for one generation past the certified seed class.

Growers who use farm-saved seed for subsequent yearly plantings will deplete the refuge variety amount and so increase the risk of virulent midge flies developing.

SRC Biotechnology Laboratories has been part of the stewardship group from the beginning.

In 2009, it developed a molecular diagnostic test method to determine refuge percentage in producer seed lots to ensure the 10 percent refuge amount is maintained. The producer can then use the test result to attain a verification certificate from the Canadian Seed Growers Association to sell their product.

The economic benefits to producers are proven. About one-third of wheat sown in Western Canada is from a midge varietal blend and many of these are top-yielding varieties.

The Midge Tolerant Wheat initiative has been a resounding success thanks to the Midge Tolerant Wheat Stewardship group and its work to help conserve this technology.

Bruce Mann is the business lead for genomic services in the Saskatchewan Research Council’s biotechnology division.

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