Broad Spectrum Antimicrobial Activity of Bacteria Isolated from Vitis vinifera Leaves

It is known that plant-associated microorganisms must be considered as key drivers for plant health, productivity, community composition, and ecosystem functioning. Much attention has been paid to the exploration of the plant-associated microbiome in search of new microorganisms with antagonistic activity against various phytopathogens. P. viticola represents one of the main fungal agents of grape yield losses during the pre-harvest stage. To date, the use of chemical pesticides is the main method to control downy mildew infection in vineyards. In recent years, innovative and more environmentally suitable control strategies, such as Biological Control Agents (BCAs), have been greatly improved. In this study, 16 new bacterial strains, isolated from the leaves of three table grape cultivars, were tested for their in vivo effectiveness against downy mildew of grape, resulting in one B. velenzensis (‘BLG_B4), one P. pleuroti (‘BLG_B5), one P. psychrotolerans (‘BLG_B1.3’) and one B. subtilis (‘BLG_B1.1.1’) bacterial strains that were marked as good BCAs. As possible mechanisms of action, a genetic analysis was performed to evaluate the ability of selected bacterial strains to reduce the expression of two P. viticola effectors. Finally, their effectiveness against a wide range of fungal pathogens and their safety for human health was also evaluated.