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Which potential of service plants for ‘multi-pest’ regulation in agroecosystems? An integrative conceptual framework highlighting complementarities in mechanisms and traits
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International audience. Alternatives to synthetic pesticide use are required to increase the sustainability of crop protection strategies. Identifying technical options based on the biological regulation of pests (pathogens, animal pests and weeds) is a promising and complex challenge. Among the options to be developed are ‘service plants’, also called ‘cover plants’, ‘companion plants’ or ‘biocontrol plants’. The principle is to sow these plants, either in association or in rotation with cash crops, to provide different ecosystem services, among which pest regulation. Past studies demonstrated the usefulness of service plants for regulating one category of pest, i.e. either pathogens, animal pests or weeds. However, few of them considered the role of these plants for multi-pest regulation. Yet, meeting the challenge of agroecological transition definitely requires an integrated view of the mechanisms leading to a pest regulation. To what extent can service plants provide a relevant option to promote multi-pest regulation, while limiting potential disservices of these plants, is still an open question? Given the diversity of the academic disciplines concerned and the scarcity of the scientific references, developing a conceptual framework appeared as a prerequisite to address this question. Such a framework allowed to synthesize the mechanisms and traits of the service plants potentially involved in the regulation of each category of pest. Both direct (i.e. directly targeting the pest) and indirect (i.e. targeting the pest through the mediation of natural enemies) mechanisms were considered, involving traits of service plants related to growth, morphology, phenology, biochemistry and immunity. Mechanisms and traits by which service plants can trigger unintended effects (e.g. by competing with cash crops for resources, promoting non-targeted pests, etc.) were also synthetized. This framework allowed to identify optimal ranges of trait values promoting the regulation of each category of pest and limiting negative impacts of service plants. It also highlighted different synergies and antagonisms between the different categories of pests, leading to a comprehensive view of the potential for multi-pest regulation. For most of the traits, we identified synergies. For example, tall service plants with a rapid growth rate can promote weed regulation (by competition for light) as well as aerial pathogens and phytophagous insects (by providing a physical barrier or increasing emission of volatile organic compounds affecting these pests). However, synergies and antagonisms need to be studied in more details for traits related to emission of chemical compounds. Indeed, a given molecule may promote the regulation of different types of pests but also may repel beneficial organisms such as natural enemies.323 As a last step, synergies and antagonisms between overall pest regulation and disservices provided by the service plants were also considered. This framework lays the foundations of a plant-trait-based approach that will be useful to prioritize research actions to identify efficient service plants and their way of use in agroecological contexts. Such framework, in combination with the development of databases, will be crucial to help farmers choose the most efficient and resilient service plant Species/varieties to combine in order to enhance multi-pest regulation. Funding: Métaprogramme SuMCrop of INRAE.
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