Plant flour-based protein hydrolysates enhance table grape toleranceto Botrytis cinerea

Protein hydrolysates (PHs) are emerging as sustainable biostimulants capable of enhancing plant tolerance to biotic andabiotic stresses. In this study, PHs were produced in-house from soybean and pea flours through enzymatic hydrolysisusing two proteolytic enzymes, alcalase and papain, yielding four hydrolysates (PH1–PH4). The resulting PHs were char-acterized in terms of protein content, degree of hydrolysis, and peptide composition. The efficacy of the PHs in protectingtable grape berries against Botrytis cinerea, the causal agent of grey mould, was then evaluated on two cultivars, RedGlobe and Italia. The soybean hydrolysate obtained with alcalase (PH1), applied at 3.2 mg/mL, was the most effectivetreatment in both cultivars, reducing disease incidence by up to 90% compared with untreated controls, with Red Globeshowing the greatest responsiveness. In parallel, in vitro assays demonstrated that hydrolysates did not inhibit conidialgermination, and only PH2 and PH4 exerted a limited formulation-specific reduction in mycelial growth; overall, theseresults suggested that their protective effect was largely mediated through indirect mechanisms associated with plantdefence responses. Although further large-scale trials are needed, these findings indicate that flour-derived protein hydro-lysates represent a promising, low-cost, and environmentally sustainable strategy for enhancing table grape resistance toB. cinerea and reducing reliance on synthetic plant protection products.