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RESEARCH PRODUCT

Services provided by soil microorganisms to improve plant phosphate nutrition

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Since the first Green Revolution, agricultural practices have been based on the massive use of synthetic fertilisers and plant protection products. Since then, global consumption of phosphate fertilisers has more than tripled, reaching 47 million tonnes in 2019. Current projections estimate that phosphate rock stocks (natural phosphorus resources for fertiliser production) could be depleted within the next century, leading us to change our agricultural practices. In soils, P is mainly present in complexed forms that are not easily accessible to plants. To reduce the use of phosphate fertilisers, it is necessary to make this complexed phosphate accessible to plants. This can be done by beneficial microorganisms such as arbuscular mycorrhizal fungi (AMF) and plant growth promoting rhizobacteria (PGPR). These soil microorganisms are of increasing interest as agro-ecosystem service providers that can maintain crop productivity and quality while reducing synthetic fertiliser inputs. The main objective of the thesis was to study, using potato as the agronomic plant of interest, the potential valorisation of AMF and PGPR associations for plant growth and nutrition while limiting P inputs. As a first step, we developed biotests to characterise and select bacteria with plant growth stimulating capacities that can interact with AMF. We tested these biotests on a Premier Tech collection of 26 bacterial isolates. Based on these tests, we developed a bacterial consortium from the above- mentioned collection that we inoculated in the greenhouse on potatoes planted in pots containing agricultural soil. We observed that inoculation of the consortium improved the phosphate nutrition and tuber yield of the plant as well as the rate of colonisation by native AMF. In parallel, we conducted a field trial in which we tested the effect of AMF inoculation on different potato cultivars. Our results suggest that the contribution of inoculation is highly dependent on the cultivar. It should be noted that inoculation, whether performed in the field or under controlled conditions, did not alter the native microbial communities.