Effect of biotic and abiotic stimuli on volatile emission of Achillea collina Cv. SPAK grown in the Alps

Volatile compounds from plants play a central role in plant-environment interactions by affecting key life processes such as reproduction, defense and communication. Plants normally produce organic volatile compounds (VOCs) but biotic and abiotic stimuli can influence the biosynthesis of novel compounds, and involving hormone signaling pathways, in particular jasmonic acid, salicylic acid, abscisic acid and ethylene (1). A specific group of VOCs related to herbivores are called herbivore induced plant volatiles (HIPV) or ‘inducible volatile organic compounds’ (IVOCs) and are emitted from plant foliage after herbivore damage (2). Achillea collina Becker ex Rchb., a tetraploid proazulenes-containing species of the Achillea millefolium aggregate (yarrow) cultivated in European alpine areas, was a good source of important bioactive compounds. Yarrow is a host plant for several aphids including the generalist green peach aphid Myzus persicae Sulzer and the specialist aphid Macrosiphoniella millefolii (De Geer). Recent work reported that essential oils from several species of the genus Achillea showed some activity as aphid repellents (3). This study describes the application of Headspace Solid-Phase Microextraction (HS-SPME) to characterize the volatile organic compounds emitted in vivo by Achillea collina in response to Myzus persicae and Macrosiphoniella millefolii infestation, to mechanical damage simulating the aphid’s damage and to jasmonic acid treatment. The volatile emission of Achillea collina, Pisum sativum (L.) and Prunus persica (L. Batsh) infested by Myzus persicae was also compared. In A. collina infested plants and treated with jasmonic acid, we observed a great increase in terpenes fractions. Many authors also found variations in the terpene profile of plants infested by aphids and this result suggested terpenes as a chemical class highly sensitive to this biotic stress (4,5). Several changes among alcohols occurred in response to mechanical damage simulating the aphid’s damage. Among this chemical classes, some author reporting an enhancement of the production of 2-hexen-1-ol and germacrene D after aphid infestation in different crop species, and the last one was suggested to be useful in attracting natural enemies of aphids as well as in having anti-feeding/repellent effects (6). Many volatiles appeared as new compounds after aphids infestation as well as after mechanical damage and jasmonic acid treatment, proposing these compounds as herbivore induced plant volatiles (HIPV). Some of this compounds were common for biotic and abiotic stimuli but the emission of other VOCs was induced only in response to specific stimuli. Finally, the comparison of the volatile emission of A. collina, P. sativum and P. persica in response to M. persicae infestation indicated that there were specie-specific and common new induced volatile organic compounds. The common emissions of same VOCs from different plant species when infested by the same aphid suggest the activation of a common set of biosynthetic pathways shared by different plant families. These compounds were produced as bioactive agents against elicitors associated with aphid’s saliva. In conclusion, this method was useful in evaluating the fingerprints of volatile compounds of A. collina under different physiological conditions. This approach could open new perspective for further studies leading to a better understanding of plant- insect interaction mechanisms providing new insights into crop science and insect pest management.