Phyllosphere microbiome-based biocontrol solution against the filamentous pathogens Botrytis cinerea and Plasmopara viticola in grapevine

Plants harbor different microbial communities in their different organs. This difference is due to the various conditions to which the different parts of the plant are subjected. As a result, the phyllosphere microbiome may be drastically different than the root microbiome. Since each microbiome is supposed to be well adapted to its environment, we hypothesize that bacterial communities from the leaves should be more effective in protecting the plants against the pathogen attacking the aerial part of the plant than the ones from the soil commonly used as biocontrol agents. In a previous study, we demonstrated that many phyllosphere bacteria isolated from the grapevine phyllosphere were indeed very effective against such plant pathogens under in vitro conditions, inhibiting their mycelial and spore development. In this project, we investigated the biocontrol ability of these phyllosphere bacteria in planta against two filamentous pathogens colonizing the aerial part of the plant: Botrytis cinerea, the ascomycete responsible for gray mold and Plasmopara viticola the oomycete responsible for downy mildew. Our results show that more than 40 strains were able to inhibit at least one pathogen in their spore physiology or infection progress. Among these strains, 27 strains were able to impact both pathogens and 20 were also capable of stimulating plant defenses and. Finally, when used in consortia, bacteria showed synergistic effects, resulting in a much stronger protection than that obtained by the application of the strains alone. These data suggest that phyllosphere bacteria could be a promising tool to help wine grower to fight against grapevine diseases by providing a strong long-lasting protection on their crops.