Oligomycin-producing sp. newly isolated from Swiss soils efficiently protect against .

UNLABELLED

is a necrotrophic phytopathogen able to attack more than 200 different plant species causing strong yield losses worldwide. Many synthetic fungicides have been developed to control this disease, resulting in the rise of fungicide-resistance strains. The aim of this study was to identify strains showing antagonistic activity against to contribute to plant protection in an environmentally friendly way. We isolated 15 Actinomycete strains from 9 different Swiss soils. The culture filtrates of three isolates showing antifungal activity inhibited spore germination and delayed mycelial growth of . Infection experiments showed that plants were more resistant to this pathogen after leaf treatment with the filtrates. Bioassay-guided isolation of the active compounds revealed the presence of germicidins A and B as well as of oligomycins A, B, and E. While germicidins were mostly inactive, oligomycin B reduced the mycelial growth of significantly. Moreover, all three oligomycins inhibited this fungus' spore germination, suggesting that these molecules might contribute to the 's ability to protect plants against infection by the broad host-pathogen .

IMPORTANCE

This study reports the isolation of new strains with strong plant-protective potential mediated by their production of specialized metabolites. Using the broad host range pathogenic fungus , we demonstrate that the cell-free filtrate of selected isolates efficiently inhibits different developmental stages of the fungus, including mycelial growth and the epidemiologically relevant spore germination. Beyond experiments, the strains and their metabolites also efficiently protected plants against the disease caused by this pathogen. This work further identifies oligomycins as active compounds involved in the observed antifungal activity of the strains. This work shows that we can harness the natural ability of soil-borne microbes and of their metabolites to efficiently fight other microbes responsible for significant crop losses. This opens the way to the development of environmentally friendly health protection measures for crops of agronomical relevance, based on these newly isolated strains or their metabolic extracts containing oligomycins.