Elucidating the Mechanism of Aphid Resistance in Wheat

Cereal aphids are a major pest of wheat crops worldwide. Yield losses are caused directly by aphid feeding, and indirectly when the aphids transmit a plant virus which negatively affects the growth of the plant. Wheat plants produce secondary metabolites that are used in defence against herbivores. This phenomenon can potentially be exploited in the design of future aphid-resistant wheat that responds effectively to aphid infestation, resulting in enhanced management of pest aphid populations. Previous work has shown that (i) wheat differs in susceptibility to aphids (ii) there are differences in the production of secondary metabolites between wheat plants, and (iii) resistance is associated with difficulties of aphids in phloem feeding. However, the relationship between aphid susceptibility and secondary metabolite production in wheat remains undefined. With better understanding, secondary metabolites from wheat plants could be used to manage pest aphids in conjunction with other pest management strategies. Furthermore, these metabolites could be used in conjunction with volatile defence signals released from smart crop plants that switch on metabolite production in neighbouring wheat plants prior to the arrival of pest aphid populations. This multi-disciplinary project, involving analytical chemistry and aphid / behaviour development will test the hypothesis that the mechanism of defence in aphid-resistant wheat against the main cereal aphid pests, Rhopalosiphum padi and Sitobion avenae, involves secondary metabolite defence chemistry. 1) Causal secondary metabolites responsible for aphid resistance in wheat will be collected by analytical techniques and will be identified, using GC, HPLC, LC-MS and NMR, in a comparative study between resistant and non-resistant varieties, with and without aphid infestation. Phloem samples will be collected as well as whole tissue samples. 2) The biological activity of the identified causal metabolites upon aphid survival will be assessed using assays designed specifically for aphids. This project will generate an understanding of (a) secondary metabolite identity from wheat that differs in susceptibility to aphids, (b) responses of aphids to secondary metabolites. Knowledge of the role of secondary metabolites involved in wheat/aphid interactions will underpin design of future wheat varieties that are resistant to aphids and will underpin future development of smart plants for crop protection, whereby aphid-sensitive wheat releases volatile defence signals that induce aphid defence in smart main crops.