Comparative evaluation of VOCs emitted by Achillea collina infested by aphids and mechanically damaged

Plants along the centuries evolved wide range of mechanisms to cope with biotic and abiotic stresses, including the emission of induced volatile organic compounds (VOCs), whose production is trigged by mechanical damage or pathogen infestation of plant tissues, providing them defensive tools (Arimura et al. 2005). This study focuses on VOCs emitted by Achillea collina Becker ex Rchb. as a results of aphid infestation and mechanical damages. In particular it takes account of differences between compounds induced by the generalist Myzus persicae (Sulzer), the specialist Macrosiphoniella millefolii DeGeer aphid species infestation and two different types of mechanical injury (pin shoot and extended pressure). Headspace Solid-Phase-Microexctraction-Gas Chromatography-Mass Spectrometry (HS-SPME-GC/MS) “in vivo” method was used to evaluate A. collina VOCs. We observe, in both aphids infestation a decrease of trans-2-hexenal associate with an increase of 2-hexen-1-ol and 1-hexanol, suggesting the activation of the methabolic pathway that leads to production of green leaf volatile compounds (Gatehouse 2002). The same result was recorded in mechanically induced damages suggesting that in A. collina the production of these compounds is a non specific response to induced both by mechanically and aphids provoked injuries. Furthermore a decrease of some terpenes (β and γ-pinene) and the increase of others (α-phellandrene and isocaryophyllene) were recorded. The involvement of significantly varying compounds in tritrophic interaction mechanisms is also discussed.