Garlic and peppermint essential oils induce defensive responses on sweet peppers

Abstract: Plant essential oils (EOs) are a promising tool for the sustainable control of
agricultural pests, however, their impact on plants and the associated trophic networks has been scarcely investigated. We studied in the laboratory whether different nanoformulated EOs can induce defences on sweet pepper, Capsicum annuum, by foliar application. Firstly, through a dual choice test, based on the olfactory response of the model parasitoid Encarsia formosa, garlic and peppermint EOs were selected among different plant extracts over four botanical families (i. e., Apiaceae, Asteraceae, Liliaceae and Lamiaceae). The behavioural responses of the herbivores Bemisia tabaci, Frankliniella occidentalis and the predators Orius laevigatus and Nesidiocoris tenuis to EO induced plant volatiles were thus investigated. The expression level of defence-related genes in plant tissues and the phytotoxic impact in the whole plant were measured in response to EO foliar applications in sweet pepper. Garlic and peppermint EOsprayed plants at different concentrations triggered different behavioural responses on both pests and natural enemies in olfactory trials. Gene expression analysis highlighted activated defence signalling pathways in EO sprayed sweet pepper plants, while a variable phytotoxic effect was recorded. Our results suggest that EOs may have an impact on sweet pepper and the associated trophic network. These findings could serve as a basis for future development of plant protection strategies in the framework of Integrated Pest Management.