Induction of Defense Responses and Partial Control of Powdery Mildew and Gray Mold in Vitis vinifera cv. Chardonnay by Pseudomonas protegens-Based Formulations

Grapevine (Vitis vinifera L.) is an economically important fruit crop cultivated worldwide. However, its production and fruit quality are severely constrained by powdery mildew (Erysiphe necator) and Botrytis bunch rot (Botrytis cinerea) diseases. Increasing concerns regarding chemical fungicide resistance and environmental sustainability highlight the urgent need to develop alternative and more sustainable disease management strategies. This study assessed the field efficacy of Pseudomonas protegens-based formulations (TANIRI® WP at 1 g·L−1 and MaxGrowth at 1 mL·L−1) within an integrated disease management program in cv. Chardonnay. Defense-related gene expression analysis revealed that biological treatments predominantly up-regulated pr1, pr2, and pr10 in both leaves and berries. In contrast, the chemical inducer acibenzolar-S-methyl (ASM) triggered earlier but less consistent induction of pr1 and pr2, alongside transient activation of pal and lox9. Repeated field applications of P. protegens formulations moderately reduced the severity of Botrytis bunch rot (20.89%) and powdery mildew (6.14%), though control levels remained below conventional sulfur/Bacillus subtilis-based treatments (30.04% and 13.56%, respectively). Overall, these findings suggest that biological inducers could complement conventional management practices for grapevine health. In particular, P. protegens may act mainly by systemically inducing host defense responses and partially suppressing pathogen development under field conditions.