Grapevine resistance induced by protein hydrolysates against mildews

Powdery (Erysiphe necator) and downy (Plasmopara viticola) mildew are two of the most important diseases of grapevine worldwide, which need intense application of synthetic chemical fungicides to be satisfactorily controlled. However, the appearance of pathogens’ strains resistant to pesticides and the concerns about the negative effects on environment and human health have sparked interest in developing alternative methods. Induction of grapevine resistance is a promising alternative to chemical fungicides, but the full potential of resistance inducers has yet to be recognized. Our aim was to further develop innovative methods for mildew control, based on a better understanding of the resistance mechanisms induced by a specific protein hydrolysate in grapevine. Treatments with a protein hydrolysate named SCNB2 significantly reduced powdery and downy mildew symptoms under greenhouse conditions. SCNB2 reduced powdery mildew infections under field conditions in three consecutive years having different weather conditions, and it was able to limit downy mildew infections at the beginning of the season in cases of low infection pressure. SCNB2 showed direct toxic effect against P. viticola sporangia, but not against E. necator conidia suggesting different antifungal properties. Gene expression analysis revealed that SCNB2 induced the expression of defence-related genes encoding pathogenesis-related (PR) proteins before pathogen inoculation. Moreover, the expression of PR genes was greater in SCNB2-treated than in control plants at one day post inoculation with E. necator or P. viticola, suggesting limitation of pathogen diffusion at the early stages of infection. SCNB2 is a promising resistance inducer with broad spectrum activity against grapevine mildews and based on the relatively low cost of its composition it may offer an additional tool to reduce susceptibility of grapevine against its key diseases.