Orange wheat blossom midge (Sitodiplosis mosellana Géhin) is one of the most damaging pests of wheat in western Canada. This project was undertaken to identify additional wheat genes that can prevent wheat midge damage. Currently, there is a heavy reliance on the wheat midge resistance gene Sm1 in western Canadian wheat varieties, which leaves the crop vulnerable if or when the wheat midge population adapts to or overcomes the Sm1 resistance gene. The specific objectives of this project were to: (1) analyze the genetic basis of oviposition deterrence in the wheat lines Waskada (Canada Western Red Spring), 5602HR (Canada Western Red Spring), and Kahla-47 (durum), and (2) analyze the genetic basis of improved Sm1-based midge resistance in the variety Shaw (Canada Western Red Spring).

Oviposition deterrence is reduced egg-laying of wheat midge females on the spikes of particular breeding lines and varieties. Wheat genetic populations (progeny of specific wheat crosses) were grown in replicated field trials in Manitoba and Saskatchewan in which they were exposed to natural populations of wheat midge. Statistical analyses identified a gene on wheat chromosome 1A that was associated with reduced midge-damaged kernels in the spring wheat line BW278. BW278 inherited this region of chromosome 1A from the Chinese spring wheat Sumai-3, which has been used as a source of Fusarium head blight resistance in Canadian spring wheat breeding programs. The CWRS variety Waskada inherited this chromosome region from BW278. Two additional genes on chromosomes 2D and 5A were identified from 5602HR conferring reduced midge-damaged kernels. In the durum wheat line Kahla-47, a gene on wheat chromosome 1B provided reduced midge damage. Combining these different genes may result in further improvements of oviposition deterrence. For instance, developing wheat lines with the oviposition deterrence genes on chromosomes 1A, 2D, and 5A can be accomplished by crossing Waskada with 5602HR and testing progeny with DNA markers. Such a cross is unlikely to produce a new variety but would determine whether combining these genes has merit for managing wheat midge. This would provide guidance to Canadian wheat breeders.

The project also studied the improved midge resistance in the Sm1 carrier Shaw relative to the Sm1 carrier Goodeve. This genetic analysis revealed that this trait is controlled by numerous genes, each contributing a minor reduction in midge-damaged kernels. The complicated genetics and phenotyping of this trait will likely hinder breeding progress. Additional genetic studies will be needed to validate the findings of the Shaw/Goodeve cross. We suggest that a population developed for a cross of Shaw and Fieldstar would be an appropriate follow up study.

The DNA markers identified in these studies will facilitate selection of improved wheat midge resistance in spring and durum wheat breeding. The findings of this study will be used by wheat breeders and geneticists to improve wheat midge resistance and oviposition deterrence in Canadian wheat varieties. Farmers will benefit from these improved varieties.

Funding from the Saskatchewan Wheat Development Commission, Western Grain Research Foundation, and Saskatchewan Agriculture Development Fund was used to conduct DNA marker analyses and to grow two field trial locations per summer. In the second year, funding from Agriculture and Agri-Food Canada enabled testing of two additional field trial locations per summer.