Implication des composés organiques volatils dans la capacité des plantes de service à perturber le comportement et les performances de Myzus êrsicae (sulzer) le puceron vert du verger

Abstract : The search for alternatives to the use of pesticides in horticultural production has become a public health requirement. Thus, the introduction of Companion plants (CP) is an ecological method that can help reduce the use of chemical control against Myzus persicae, the green peach aphid. The interest of some of these CP lies in their ability to disturb the installation of the aphid on its host plant and/or to reduce its performance through the emission of volatile organic compounds (VOCs). However, a major obstacle to their use is that their effectiveness is limited to a limited scope and their olfactory production is sensitive to many biotic and abiotic variables. Identifying the most efficient plants, understanding their mode of action and seeking to optimize their effectiveness is therefore an appropriate approach to promote their use in horticulture. Olfactory environment analysis is a key to assessing and understanding CP-host plant -aphid interactions.In the laboratory, we selected with a Y-olfactometer two CP producing VOC mixtures with a marked repellent effect on M. persicae: basil (Ocimum basilicum) which acts directly on the insect, and french marigold (Tagetes patula) which acts indirectly via the host plant. Thus, the VOCs emitted by T. patula make the host plant (pepper, Capsicum annuum) repellent: during the choice tests, the aphids move towards the peppers alone but avoid the VOCs emitted by peppers previously grown intercropped for 5 days with the french marigold. Two compounds, (E)-β-farnesene (EBF) and eugenol have strong repellent properties against M. persicae.Different factors can affect the repellent effectiveness of these plants (climate, plant management, genetics). We compared the VOCs emitted by species and chemotypes and tested the individual repellent effect of VOCs. This "genotype" effect was examined by studying the olfactory behaviour of M. persicae in the presence of individual VOCs emitted by different clones of Rosemary (Rosmarinus officinalis). Five compounds are repellent, bornyl acetate, camphor, α-terpineol, terpinene-4-ol and geranyl acetone. Only the rosemary clone Voltz Splindler was found to be repellent, while the other clones also contain these 5 repellent compounds in varying proportions. It can therefore be concluded that the presence of these compounds is not sufficient to induce a disturbance of the aphid's olfactory behaviour and that the concentration, proportion or even association of VOCs present in the released olfactory bouquets are at the origin of these contrasting results. By the electropenetrography (EPG) technique, we have demonstrated a second effect of the VOCs emitted by O. basilicum in the vegetative stage and by T. patula in the flowering stage on the aphid. They strongly disrupt its feeding behaviour, in particular by reducing the duration of phloem ingestion, which results in a decrease in nutritional resources and leads to a decrease in its fertility. A fertility monitoring on detached organs has allowed us to highlight the importance of the phenological stage of the CP on the composition and efficacy of the olfactory mixture released. A final step in my work confirmed, under tunnel conditions, the effect of VOCs emitted by these two CP on the demographics of M. persicae due to a decrease in its fertility. In conclusion, this thesis highlighted that VOCs emitted into the environment of a host plant by neighbouring plants can provide a service to crops by reducing the performance of pests such as M. persicae. We have shown that variables such as chemotype or phenological stage of the CP can modify its olfactory message and provide a way to optimize this service. We have thus identified disruptive CP and VOCs repellent to M. persicae, the first step towards the development of the push component of a stimulodissuasive diversion strategy to reduce the use of synthetic pesticides against M. persicae.
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Tarek Dardouri. Implication des composés organiques volatils dans la capacité des plantes de service à perturber le comportement et les performances de Myzus êrsicae (sulzer) le puceron vert du verger. Autre [q-bio.OT]. Université d'Avignon, 2018. Français. ⟨NNT : 2018AVIG0702⟩. ⟨tel-02178970⟩

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