Phyllosphere microbiome-based biocontrol solution against 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. Consequently, the phyllosphere microbiota can differ strongly from root-associated communities. We hypothesize that the grapevine phyllosphere is a valuable source of biocontrol bacteria, whose adaptation to the aerial plant environment may enable them to reach their full protective potential against foliar pathogens. In previous work, we isolated phyllosphere bacteria and showed that many strains were very effective against such pathogens in vitro, inhibiting their mycelial and spore development. This work investigates the biocontrol ability of these phyllosphere bacteria in leaf disc assays against two foliar pathogens: Botrytis cinerea (gray mold) and Plasmopara viticola (downy mildew). Our results show that 40 strains out of 46 affected at least one pathogen by altering their spore physiology and/or reducing disease progression. Among these strains, 27 strains could impact both pathogens and 20 were also capable of stimulating plant defenses. Because bacterial consortia might perform better than single strains, we also compared the protection conferred by individual bacteria and associations of up to three strains. When combined, bacteria showed improved efficacy in vitro against B. cinerea and in planta against P. viticola, 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 winegrowers manage grapevine diseases by providing an effective and sustainable protection of their crops.