A new scenario of pathogen-microbiota interactions involving the oomycete Plasmopara viticola.

A key question in microbial ecology is how the microbiota regulates host invasion by pathogens. Several ecological theories link the diversity, abundance and assembly processes of the microbiota with its resistance to invasion, but the specific properties of microbial communities that confer protection to the host are poorly understood. We addressed this question for the oomycete Plasmopara viticola, the causal agent of grapevine downy mildew. Using state-of-the-art microbial ecology methods, we compared microbial communities associated with asymptomatic and symptomatic leaf tissues to elucidate pathogen-microbiota interactions. Despite visible symptoms, P. viticola infection induced only subtle changes in microbial community composition. Symptomatic tissues showed enrichment in basidiomycete yeasts and Bacillus species, both known for their biocontrol activity, and exhibited a higher degree of determinism in community assembly processes. Asymptomatic tissues hosted more diverse microbiota, but lacked consistent associations with known biocontrol agents. Instead, they were often associated with other airborne grapevine pathogens. These findings suggest a novel interaction scenario: upon infection, P. viticola reshapes locally the leaf microbiota, excluding other pathogens and selecting for beneficial microbes. Although further studies are needed to uncover the underlying mechanisms, these findings underscore the relevance of targeting disease lesions in the search for protective microbial consortia.