Looking for new genes for resistance to wheat stem sawflies

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Scientists discovered some 70 years ago that they could fight wheat stem sawfly by growing a new type of wheat. The wheat had a solid stem instead of a hollow one, making it harder for females to lay eggs and leaving less room for larvae to grow.

Montana wheat farmers still benefit from that breakthrough, and Montana State University now has a new grant that could add weapons to their arsenal, said MSU wheat breeder Luther Talbert.

With a five-year $500,000 grant from the USDA’s National Institute of Food and Agriculture, Talbert and his colleagues will screen 4,000 to 5,000 varieties of wheat that originated in areas of the world where wheat stem sawflies are a problem. The scientists will look for resistant traits that may be present in the wheat and then try to identify the genes associated with that resistance. New resistance genes will be incorporated into new varieties of wheat.

“I’m very excited. I have wanted to do this for several years,” said Talbert, a professor in MSU’s Department of Plant Sciences and Plant Pathology. “It’s good that the USDA will give us the opportunity to do this. It’s good that our colleagues in the wheat breeding community are willing to help out.”

Peggy Lamb, an agronomist at MSU’s Northern Agricultural Research Center in Havre, said, “Any steps that can be taken to better understand, select and breed wheat that will help growers in the sawfly-infested regions of Montana and the U.S. is huge. Funding from this grant will definitely bolster the wheat stem sawfly resistance research that Luther and his spring wheat breeding program have been working on for several years.”

In addition to Lamb, Talbert’s team on the new project includes MSU entomologist David Weaver; MSU molecular biologist Jamie Sherman; Terry McKeever, a farmer near Loma; Shiaoman Chao, a molecular geneticist at the USDA’s Agricultural Research Service in Fargo, N.D.; and researchers at four international wheat breeding companies: Bayer CropScience, Limagrain Cereal Seeds, Westbred (Monsanto), and Agripro (Syngenta).

Lamb finds farms that have sawfly problems, then lays out an area for field trials, plants the seed that Talbert’s group has packed, and maintains the plots. The field crews of Talbert and Weaver will collect field data from the sites. Weaver and his laboratory staff will process samples to identify any potential new mechanism by dissecting stems. Sherman’s crew will help with genetic studies to identify the new genes for resistance. Syngenta will provide an observation nursery in western North Dakota to help the researchers screen and identify potentially new sources of sawfly resistance.

“Current resistance based on solid stem doesn’t always hold up,” said Syngenta Northern Plains Wheat Breeder Joe Smith. “Syngenta feels additional sources of resistance would be useful. This kind of research is good for Montana growers, but also could be useful for growers in neighboring states that are experiencing sawfly problems.”

Lyle McKeever of Loma said MSU researchers have conducted wheat stem sawfly research on his farm for about 10 years. His son, Terry, will be involved in the upcoming study by letting the scientists grow test plots of wheat on his farm.

“This area has some of the worst sawfly pressure in the state,” said the younger McKeever.

Not sure why, Terry McKeever said climate, temperature and elevation could play a role. At any rate, wheat stem sawflies have invaded the family’s farms since the 1970s. What started out as a nuisance has turned into major losses of yield.

“Solid stem helps a lot but those varieties don’t have the yield potential that some of the hollow stem varieties have,” Terry McKeever said.

Lyle McKeever said he reduced his problem by planting two varieties of solid stem wheat and planting spring wheat instead of winter wheat, but solid stem wheat isn’t totally effective. In fact, he calls it semi-solid wheat because some wheat stem sawflies still make their way into the stems. Spraying isn’t the answer either.

“You can spray for wheat stem sawfly,” Lyle McKeever said. “But you have to spray about every other day each week because it keeps hatching.”

Weaver said Montana growers estimate that wheat stem sawflies cause approximately $75-100 million damage a year in Montana, making this insect the most destructive wheat pest in the state. Overall losses to this pest have been estimated at $350 million for the entire Northern Great Plains.

Talbert added that, “Montana is the epicenter for wheat stem sawflies in our part of the world, so it’s a bigger deal for us than most people.”

Unless their life cycle is interrupted, adult female sawflies lay their eggs in the spring inside the wheat stem. During the summer, the larvae eat the inside of the wheat plant, disrupting the movement of sugar and water, weakening the plant and reducing yields. At the end of the summer, the larvae cut the wheat stems at the base so it can emerge the next year.

“That certainly appears to be the worst thing it does,” Talbert said.

Weaver suggested that losses in grain weight due to feeding by the larvae might be quite a bit greater.

“It is certainly more insidious because growers can’t see how much of the crop’s potential has been stolen, whereas stems on the ground are very obvious,” Weaver said.

The larvae live inside the wheat stubble during the fall and winter. In the spring, adults emerge from the stem, and the cycle continues.

Finding new resistant genes will be harder than detecting the gene tied to solid stems, but with new advances in molecular genetics, the outlook is promising, Talbert said. Weaver added that the new resistance targets for wheat stem sawfly should include everything from influencing female choices in laying eggs through compounds that kill the growing larvae.

Whatever the outcome, Talbert said he hoped the new project will have the same long-lasting impact as its predecessor.

“The previous wheat breeding community’s discovery of solid stems has saved growers many millions of dollars over the past several decades,” Talbert said. “It’s our goal to leave a similar legacy – identify new genes for resistance that will be equally useful in the future.”




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