Prairie grain growers may soon have access to four new spring wheat varieties that are resistant to wheat midge.
Agriculture Canada wheat breeders developed the new varieties with support from the Western Grains Research Foundation.
According to the foundation, old soft red winter wheat varieties from the United States were the source of the resistance trait. Part of winter wheat’s natural resistance to wheat midge comes from two naturally occurring compounds within the wheat kernels: ferrulic acid and p-comaric acid.
These chemical compounds prevent the wheat midge larvae from developing when they feed on immature kernels. The acids dissipate by the time the crop has matured.
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It took plant breeders more than 15 years to move this one, isolated trait into spring wheat varieties that maintain acceptable yield and agronomic traits. Researchers know of only one gene that creates midge resistance, making it essential to protect it.
Interspersed refuge is the scientific term for the technique researchers employ to prevent wheat midge from adapting to the trait that has been transferred to spring wheat. They do this by mixing a small percentage of a susceptible wheat variety into the new resistant varieties.
Stephen Fox, an Agriculture Canada wheat breeder in Winnipeg and one of the lead researchers in the wheat midge program, said it is only a matter of time before a pest will adapt to new conditions when varieties are bred to mitigate damage caused by that pest.
“The basic premise of interspersed refuge is that we provide a safe place for a few of the midge to survive in a field,” he said.
“We can develop varieties to eliminate all food sources which a pest requires, but if you successfully accomplish that, you force the pest to adapt. You force it to find the next easiest food source, which is probably the new variety you have just developed.
“With interspersed refuge, we actually aim to have a small number of viable plants remain in the plant population to give the wheat midge parasites a host. We deliberately allow some insects to survive, thereby reducing the selection pressure for a resistant strain of midge. We’re not pushing the insect to adapt to a new food source.”
Fox said this is the first time interspersed refuge has been tried in a wheat breeding program. If it works as planned, he added, it will mean new wheat varieties bred to battle specific enemies will have a much longer lifespan before those enemies catch up to them.
“All the players in the seed industry in Canada are working to sort out the mechanics of how we make interspersed refuge work for us.”
Fox said the resistance trait brought over from winter wheat is only part of what winter wheat has to offer in the defence against midge. The other contribution is winter wheat’s timing of flowering.
“If you grow winter wheat, it won’t flower at the right time for the midge to successfully lay eggs. Winter wheat typically escapes because it flowers too early,” he said.
“With spring wheat as well, you can avoid wheat midge damage if you plant really early so you get early flowering, but the escape window for early-seeded spring wheat is not very big. You might have to go as early as the first week of May and that’s not always feasible.”
Fox said that on many farms there may be other crops that should be seeded in early May for better agronomic reasons.
The new wheat midge resistant varieties will probably be available within the next four years. Three are in the Canada Western Red Spring wheat class and one is in the Canada Western Extra Strong wheat class.
The varieties were recommended for registration at the variety registration meetings in Saskatoon this winter.
Wheat midge has been a sporadic problem since it was first identified on the Prairies in 1984, causing dramatic yield and grade losses.
In 2006 the insect caused significant economic losses in parts of Manitoba and Saskatchewan.
The affected area is expected to expand this year.
Once wheat midge is in a field, the only immediate defense is a pesticide application.
However, producers have difficulty knowing which fields have wheat midge levels high enough to warrant spraying, which is compounded by a short application window. Insecticide applications need to occur just as the crop is heading to be effective.
