Faculté des sciences

Assessing the importance of specific volatile organic compounds in multitrophic interactions

D'Alessandro, Marco ; Turlings, Théodoor (Dir.)

Thèse de doctorat : Université de Neuchâtel, 2006 ; 1910.

Plants interact with a multitude of beneficial and harmful organisms of different trophic levels and it is generally accepted that such multitrophic interactions are highly relevant for various defence responses in plants. One of the most intriguing responses in plants is induced by herbivore feeding and results in the release of large amounts of volatile organic compounds (VOCs). These... Plus

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    Summary
    Plants interact with a multitude of beneficial and harmful organisms of different trophic levels and it is generally accepted that such multitrophic interactions are highly relevant for various defence responses in plants. One of the most intriguing responses in plants is induced by herbivore feeding and results in the release of large amounts of volatile organic compounds (VOCs). These herbivore-induced plant volatiles (HIPVs) may serve as indirect defence signals by attracting natural enemies of herbivorous arthropods, but also function as key regulators of plant physiological changes. Some HIPVs even trigger defence responses in neighbouring plants or prime these plants to respond faster to subsequent herbivore attacks. However, the function of individual compounds within complex blends of HIPVs has largely remained uninvestigated. The current thesis aimed to understand the role of specific VOCs in multitrophic interactions from the perspective of plant defence responses. In a first part (Chapters II and III), we focused on indirect defence responses by maize seedlings (Zea mays var. Delprim). We developed two new methods that allowed us to study the importance of various HIPVs for the attraction of Cotesia marginiventris and Microplitis rufiventris, two parasitoids that attack larvae of various Spodoptera moths. It was found that some major HIPVs were not important in the attraction of these parasitoids, whereas several minor compounds seemed to be essential and highly attractive. Moreover, the two parasitoid species were differently attracted towards these HIPVs and their responses strongly depended on previous experiences with specific HIPVs. In a second part (Chapter IV), we investigated the role of soil-born micro-organisms in defence responses by maize seedlings and we found that they too affected the attraction of the parasitoids. Analyses of VOC-blends revealed that seedlings grown in soil with micro-organisms released additional compounds, mainly isomers of 2,3-butanediol, and these compounds were produced by the γ-proteobacterium Enterobacter aerogenes that we isolated from maize seeds. Both bacteria and synthetic versions of the bacteria-derived VOCs induced systemic resistance in maize seedlings against the fungal pathogen Setosphaeria turcica, but not against the herbivore Spodoptera littoralis. Molecular tools were employed to study possible mechanisms of induction. The results of these studies not only revealed novel roles that organisms and VOCs play in plant defence responses, but also present new methodological approaches that can be used to identify key compounds affecting multitrophic interactions. The advances and challenges in the identification of such key compounds are reviewed in Chapter V. Overall, this work aims to contribute to a better understanding of the role of specific VOCs in interactions between plants and other organisms, which seems a fundamental first step towards the application of VOCs in alternative crop protection strategies against agricultural pests.