Elucidating the Chemical Ecology of Belowground Plant-Plant Communication

Aphids, i.e. greenflies and blackflies, comprise the major agricultural pests in Western and Northern Europe. Control currently involves the use of insecticides that kill. Alternative sustainable approaches are required which minimise insecticide use. One way is to use naturally-occurring attractive chemicals that enhance the performance of beneficial insects in crops. However, as deployment of these chemicals is expensive and difficult to maintain, causing the plant to release these attractants represents a more sustainable prospect. We have shown that bean plants infested with pea aphids increase the attractiveness of neighbouring bean plants towards parasitic wasps that attack aphids, and that this is mediated by belowground communication. Our further studies show that aphid feeding aboveground causes release of chemicals by the same plant belowground. We propose that the released chemicals are responsible for the observed belowground communication. The aim of this project is to exploit this discovery, by identifying the released chemicals and determining their effect upon neighbouring plants. We will (i) determine the conditions under which aphid-feeding related signals are transferred from roots to their surrounding environment (ii) isolate the chemical signals produced and released by roots using newly developed isolation techniques (iii) identify isolated signals using sophisticated analytical chemistry approaches (iv) measure the behavioural response of parasitic wasps to plants exposed to the identified signals and (v) identify the induced volatile organic compounds (VOCs) collected from recipient bean plants exposed to the chemical signals, using volatile collection techniques, and electrical recordings from parasitic wasp antennae. This project will contribute towards an understanding of plant-plant communication belowground, and represents an exciting opportunity to provide an entirely new class of chemical signal tools that can be used to control insect pests on major world crops.

Bean plants, Vicia faba, infested with pea aphids, Acyrthosiphon pisum, induce indirect defence in neighbouring uninfested V. faba plants by increasing their attractiveness to the aphid parasitoid, Aphidius ervi. Our preliminary data show that this induction of attractiveness is mediated by belowground signal transfer and that A. pisum feeding aboveground causes belowground release of small lipophilic molecules. We hypothesize that these induce defence in neighbouring plants. This project will elucidate fully the chemical basis of the observed plant-plant signalling in V. faba following A. pisum feeding, and define the impact of identified elicitors upon the attraction of A. ervi towards recipient plants. Specifically, we will (1) determine the dynamic for the emission of aphid-feeding related signals between roots of hydroponically-grown plants, using wind-tunnel behavioural bioassays and A. ervi (2) demonstrate the biological activity of hydroponic solution extracts, collected by solid-phase extraction (SPE), using wind-tunnel behavioural bioassays and A. ervi (3) characterise the chemical signals in hydroponic solution extracts using sophisticated analytical chemistry techniques, including GC and coupled GC-MS (4) demonstrate the biological activity of identified elicitors by addition to hydroponic solution containing intact V. faba plants, and measuring the response of A. ervi to these plants using wind-tunnel assays, and (5) characterise the extent and impact of the identified chemical signals upon defence in recipient V. faba plants, by collecting induced volatile organic compounds (VOCs) using dynamic head-space collection and vapour-phase extraction (VPE) techniques, and coupled GC-electrophysiology (GC-EAG, GC-SSR) using A. ervi antennae.