Soil biodiversity and suppressiveness of soil against plant diseases and insect pests

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Thanks to their particular biotic community, soils vary in their suppressiveness towards root diseases caused by phytopathogenic fungi on crop plants. However, the link between soil biodiversity and suppressiveness and the range of deleterious organisms that are controlled by this mechanism are poorly characterized. This project aims at developing an integrated understanding of the relation between soil biodiversity and crop protection, using soils of contrasting suppressiveness status in several countries, in a context of global change materialized by changes in crops and in pathogen/pest importance. Two approaches will be followed: (i) the comparison of emblematic soils known to be suppressive or conducive (such soils are available in Switzerland and France), and (ii) the comparison of soils under different agricultural management strategies (e.g. with soil organic matter-based management practices aiming at enhancing soil biodiversity, including in long-term experiments), which have the potential to result in different levels of suppressiveness (such conditions have been investigated in Germany). First, current knowledge gaps on suppressiveness will be filled, based on (i) chromatographic profiling of soil (to assess soil organic matter quality, which might represent a potential indicator of suppressiveness), (ii) assessment of disease suppressiveness in relation to crop plant physiology and defense status, (iii) metabarcoding of microbial taxonomic biodiversity, and (iv) molecular monitoring of microbial functional groups under controlled conditions. Second, the significance of suppressiveness under global change will be characterized, by assessing (i) the extent of disease suppressiveness on emerging crops (with a focus on wheat), (ii) the possibility of suppressiveness towards insect pests, and (iii) the contribution of arbuscular mycorrhizal fungi, a symbiotic partner neglected so far in this context, to disease suppressiveness. Third, the applicability of project findings to agronomic field conditions will be determined, based on specific monitoring of (i) phytopathogens and (ii) insect pest populations, (iii) metabolomic profiling of crops, and (iv) the analysis of the rhizosphere microbiota in fields. The project involves a multidisciplinary consortium of 6 partners in 3 countries, ranging from prominent academic research groups to field extension specialists to facilitate outreach to the farming community and other stakeholders. This project is expected to generate new knowledge on phytoprotection and the importance of biodiversity in suppressiveness. This knowledge will be important to develop novel biodiversity indicators of soil quality, and to define management strategies to improve crop health in soils with poor or no suppressiveness properties and facing the challenge of global change.