Impact of arbuscular mycorrhiza to soil microbial communities and biocontrol of soil-borne pathogens

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Evidences of microbial population shifts in the mycorrhizosphere have been reported but the mechanisms regulating these changes and their impact on plant health are poorly known. Arbuscular mycorrhizal fungi (AMF) have coevolved in intimate relationship with land plants for at least 400 M yr and most plant species are adapted to the environment in close relationship with these fungal symbionts. AMF directly influence the plant nutrition metabolism and the release of photosynthates in the root environment, hence the microbial community living in the rhizosphere. AM fungi are key-factors in the rhizosphere and would contribute to make more complex and stable the rhizosphere microbial community, lowering the impact of soilborne plant pathogens. A better knowledge of microbial dynamics in AM systems will favor the use or manipulation of the AM symbiosis in horticulture and agrosystems, lowering the use of chemicals to control root diseases. The general goal of this research program is to understand how the AM fungi influence the rhizosphere microbial communities and lower the pathogenic pressure on host plants. Specific goals are : 1) To analyze the functional relationships between Fusarium, AM fungi and bacterial communities as related with plant health in the field; 2) To analyze the intraspecific and spatial variability in the AMF-Fusarium interaction in the AM rhizosphere in controlled soil microcosms; and 3) To characterize the physical interaction between hyphosphere bacteria and AMF mycelium, and the role of biofilm-forming communities in biocontrol. Various molecular, biochemical, microbiological and microscopical approaches will be used to test the effects of AM fungal and bacterial communities on Fusarium community structure and virulence. This research program will provide novel insight in the mechanisms leading to microbial competitive interactions in the mycorrhizosphere and to the lower disease development in mycorrhizal plants, significantly enhancing our capability to manage this symbiosis in a sustainable agricultural approach.