Peptide analogs of a Trichoderma peptaibol effectively control downy mildew in leaf disc assay and vineyard

Grapevine (Vitis vinifera) is one of the main crops worldwide. Plasmopara viticola, the causal agent of downy mildew, causes enormous economic damage in terms of yield, quality and productivity to this crop. Although the disease control is largely based on the use of synthetic fungicides, the European Union (UE) policies promote the reduction of the reliance on synthetic plant protection products (PPPs) and the implementation of integrated approaches to crop protection. Biocontrol agents (BCA) constitute a great resource for the development of biopesticides. The fungal genus Trichoderma includes different species commonly used as BCAs against several crop pathogens and among their antifungal strategies, there are secondary metabolites such as peptaibols. The promise of peptaibols as agrochemicals is, however, hampered by their poor water solubility, preventing an efficient delivery for practical use in crop protection. Some water-soluble trichogin analogs with Gly to Lys substitutions were synthesized and analyzed for their antimicrobial activity against P. viticola. Among the peptides that proved effective in inhibiting the oomycete sporulation on leaf discs assay, the peptide 4r was selected for a two-year field trial experiment. In comparison with the untreated control, the protection level was comparable to that obtained with a cupric fungicide. The peptide did not show any phytotoxic effect and reduced downy mildew incidence and severity on leaves and bunches. Since it was demonstrated active also against the fungal pathogen Botrytis cinerea, the peptide 4r may be a candidate broad-spectrum fungicide whose biological properties deserve further investigations.