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Research targets 'insurance policy' for sawfly in winter wheat

New research at Agriculture and Agri-Food Canada's (AAFC) Lethbridge Research Centre aims to provide winter wheat growers with a valuable insurance policy against future infestations of the wheat stem sawfly.

Researchers have kicked off a long-term breeding effort to develop winter wheat varieties with genetic resistance to the sawfly, which in recent years has risen to become one of the most destructive insect pests of wheat in Western Canada, says Dr. Rob Graf, winter wheat breeder. Unlike spring wheat, winter wheat has largely escaped sawfly damage thus far, but changes in the sawfly population point to an increasing threat.

"Up until around 1980, winter wheat in Montana was unaffected by the wheat stem sawfly, but changes in one of the localized populations produced a strain that is synchronized with winter wheat development" says Graf. "The wheat stem sawfly has become a major pest in winter wheat just south of the border. By initiating development of winter wheat varieties with sawfly resistance, we hope to have a defense in our back pocket if and when we need it."

Another risk factor is late development of winter wheat in some years, which puts the crop at a similar growth stage and equal sawfly susceptibility to spring wheat, he says. "While to this point we haven't seen any evidence of the virulent Montana strain in Alberta, we did see some cutting in winter wheat last year - this was in situations where the winter wheat was at a growth stage where it resembled a spring type."

Growth in winter wheat acreage is another reason to prepare a sawfly defense, says Graf. Winter wheat is becoming more popular due in part to improved varieties backed by better agronomic practices. It offers unique benefits in soil conservation, cropping flexibility and non-disturbance to waterfowl. Winter wheat is an important component of cropping systems across the Prairies, offering ground cover to reduce soil and water erosion in winter and providing active growth to trap carbon in fall and spring when summer crops are not actively growing.

"Winter wheat is a crop with excellent potential," says Graf. "Acreage has been growing for several years and hopefully will continue to grow significantly. As the acreage grows, the Montana experience demonstrates that we could see the sawfly adapt its life cycle to that which corresponds with winter wheat. We need to start development now if we're going to be ready with a variety that gives producers a good measure of control."

The task of improving sawfly resistance in winter wheat centres on developing varieties with a greater degree of stem solidness, he says. The female sawfly inserts its eggs into the hollow stem of the wheat plant, and the damage is caused by the larvae that develop inside the stem. Wheat with increased stem solidness reduce the sawfly population in several ways - eggs are crushed during egg laying, the larvae have greater difficulty tunneling within solid stems, the larvae have less chance of surviving the winter and females have reduced fertility the following spring.

In spring wheat, AAFC breeders have made recent strides in sawfly resistance with the varieties AC Abbey and the recently supported-for-registration BW776. While not immune, these varieties can reduce the amount of sawfly-toppled wheat by 50 percent or greater compared to susceptible varieties. "There are currently no Canadian winter wheat varieties with sawfly resistance," says Graf. "But the same sources of resistance used in the spring wheat effort can be used for improvements in winter wheat."

The winter wheat team plans to use the traditional 'S615' source of sawfly resistance used in current sawfly resistant spring wheat varieties, as well as a new source recently transferred from Golden Ball durum.

"The first stage of our effort is bringing together various sources of germplasm and looking for the best material to carry forward in the breeding program," says Graf. "We've started evaluating our own germplasm resources, and hope to add germplasm from other breeding programs already working on this problem. Once we've identified some good parents, we'll make appropriate crosses and use doubled haploidy to speed up the breeding process. The idea is to develop a complete package, not just sawfly resistance, but the total agronomic, disease/insect resistance and quality package necessary for a top-performing winter wheat."

Agriculture and Agri-Food Canada's Lethbridge Research Centre has a mandate to promote innovation for growth, maintain security of the food system and protect the health of the environment.

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