Host relationships of three aphid species on wheat in the genus Triticum: Potential for crop resistance in spring wheat

Aphids are the most cosmopolitan insect pests of common wheat, Triticum aestivum L. and durum wheat, Triticum durum Desf. and occasionally cause serious yield losses. Host plant resistance is a desirable aphid management strategy in regions such as North America, where the crop has a narrow profit margin.;Genetically diverse cultivated and wild wheats were used as tools for investigating the potential of crop resistance in the management of cereal aphids: Rhopalosiphum padi L., Sitobion avenae (Fabricius) and Schizaphis graminum (Rondani) which are pests of adult plants of spring wheat. Because relatively little information is available on resistance to aphids in adult wheat plants, the first step was to determine methods that might be used to investigate this resistance, and then to characterize the level of resistance. The second step was to assess whether the low level of resistance generally observed in modern cultivated wheats can be attributed to domestication. The third step was to focus the search for resistance to S. avenae in adult plants on Triticum monococcum L., because it's genome is one of the smallest in the genus, it is the progenitor of domesticated wheats, and it is suspected of being more resistant to aphids than modern wheats.;Biomass relationships between the aphids and the wheats were quantified to estimate resistance. Degrees of resistance were quantified by plant biomass loss during infestation. The antibiosis component of resistance was measured by comparing aphid biomass gain on susceptible check and test lines. The tolerance component of resistance was estimated as plant biomass loss per unit biomass gained by aphids. Cultivated Canadian Spring wheats (Canadian Western Red Spring, Canadian Prairie Spring and Canadian Western Amber Durum) exhibited low levels of resistance to aphids, although Canadian Western Red Spring was more resistant than the highly susceptible Canadian Prairie Spring wheat. There was no correlation between seedling resistance and adult plant resistance among wheats tested at the two growth stages. Resistance shown by seedling plants was largely antibiosis, and resistance shown by adult plants was largely tolerance. The level of resistance was associated with the degree of domestication, with the frequency of resistant accessions being high in the least domesticated diploid wheats and low in the most domesticated hexaploid wheats. However resistant wheats were identified at all ploidy levels. Resistance in wheats is not general to all the aphid species, but species-specific in different wheats. Several accessions of the diploid T. monococcum have high levels of resistance to S. avenae. Overall, spike biomass more effectively estimated resistance than did foliage biomass. Seedling resistance to aphids cannot be used to predict adult plant resistance. The potential use of wild wheats in screening and plant breeding programs for resistance to aphids is discussed.