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RESEARCH PRODUCT

Are soils suppressive to fungal diseases the sources of biocontrol agents ?

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Soils suppressive to soil-borne diseases are defined by a low disease incidence in spite of the presence of a virulent pathogen and a susceptible plant. In many cases, the inhibition of the disease development relies on the activity of the resident soil microbiome. Suppressiveness can be transmitted to conducive soil by mixing a small amount of suppressive soil into the conducive one. To identify microbial taxons linked to the suppressive phenotype of soils, culture independent-based methods have been employed to analyze and compare microbial diversities in two different soils suppressive (respectively conducive) to either Fusarium wilt of flax or Rhizoctonia diseases of sugar beet. Metagenomic DNA was extracted from the rhizosphere of plants grown in these soils. Fungal and bacterial taxonomic diversity was estimated from ITS and 16S genes by amplicon pyrosequencing. Structural shifts were revealed among rhizosphere fungal communities in suppressive soils in absence and in presence of the pathogen, as well as in conducive soils. Important differences noticed in taxonomic composition between suppressive and conducive soils in each system suggest that different rhizosphere fungal groups are linked with disease suppression in Fusarium wilt and Rhizoctonia diseases. Comparisons of suppressive and conducive soils for a given disease revealed fungal groups that may harbour potential biocontrol agents. Fungal groups most abundant in the mix of soil than in conducive soil were identified for Fusarium wilt and for Rhizoctonia diseases respectively. In both cases, some fungi showed an increase in the suppressive soil in the presence of the pathogen (vs non-inoculated suppressive soil). Similar results were obtained for the bacterial communities. These results suggest the role of suppressive soils as sources of specific more than generalist biocontrol agents.