Flies breaking into resistant wheat

Soft wheat growers have gradually inched planting dates ahead of long-established Hessian-fly-free dates. Giving fly-resistant varieties a few extra days of warm growing weather helps the cover crop soak up more nitrogen and reduce erosion losses.

But USDA researchers recently confirmed that these tiny, fast-reproducing flies have found their way around single-gene plant resistance. Of 21 resistant genes evaluated, only five would provide effective protection of wheat from Hessian fly in the Southeast: H12, H18, H24, H25 and H26.

None of the released genes, from 20 different locations, were effective at all locations.

That’s bad news for the Mid-Atlantic as well.

Key Points

Single-gene plant resistance trait is losing its effectiveness against Hessian flies.

Early-planted wheat may have provided a window for resistance .

Gene stacking may be the best option for the future.

Sue Cambron, a USDA Agricultural Research Service scientist, evaluated flies from Alabama, Georgia, North Carolina, South Carolina and Louisiana.

The study didn’t include all of the 33 named resistance genes, but even those genetic lines considered the most effective are allowing wheat to become susceptible to the fly larvae. Even some newer genes that haven’t been deployed in commercial cultivars weren’t too effective.

The genes recognize avirulent Hessian flies and activate a defense response that kills the fly larvae attacking the plant. However, she explains, this leads to fly strains that can overcome resistant wheat, much like insects becoming resistant to pesticides.

Resistance breakdown may be hastened by fly cross-breeding with those from other cereal crops, such as rye, suggests Brandi Schemerhorn, a USDA ARS entomologist and an assistant professor at Purdue University.

She suspects a certain number of flies in any population survive to overcome any wheat resistance gene. Then, those survivors eventually establish a population that renders the gene ineffective.“What we have to do is slow down that adaptation or virulence,” Schemerhorn adds.

Stacking genes in wheat cultivars may be the best solution. Only a few resistant genes haven’t been deployed. Combining two of them would be the best option.The scientists agree that releasing wheat lines with only one resistance gene is no longer a good idea.

Schemerhorn is working to combine two of the unreleased genes — H24 and H26 — for testing.

This article published in the March, 2011 edition of AMERICAN AGRICULTURIST.

All rights reserved. Copyright Farm Progress Cos. 2011.