Field Performance of the Yeast Biocontrol Agent Papiliotrema Terrestris Strain PT22AV Against Rice Blast in Northern Italy: Evidence from Two-year Multi-site Trials

Abstract Rice blast, caused by Pyricularia oryzae , is one of the most destructive fungal diseases of rice worldwide and remains a major constraint in temperate production systems such as Northern Italy. Current management relies largely on synthetic fungicides, particularly strobilurins such as azoxystrobin and pyraclostrobin, whose long-term sustainability is increasingly challenged by regulatory restrictions, environmental concerns, and the risk of resistance development. In this context, integrating biological control agents into disease management programs represents a promising strategy. In this study, four field trials conducted over the 2023 and 2024 growing seasons evaluated the performance of the biofungicide YSY®, based on the yeast Papiliotrema terrestris strain PT22AV, against rice blast. Treatments were compared with biological and chemical standards. Disease incidence and severity on flag leaves and panicles, as well as grain yield, were assessed. Across trials, YSY® consistently reduced disease incidence and severity under moderate pressure, with efficacy ranging from 50–80%, depending on dose, site, and cultivar. The yeast outperformed the Bacillus subtilis biological reference in all experiments and showed no phytotoxic effects under field conditions. In integrated programs, disease control was comparable to that achieved with two chemical applications, indicating that the yeast strain PT22AV can contribute to reduce fungicide inputs by up to 50% without compromising efficacy. Yield responses were consistent evident alongside disease control, with increases of up to 25%. These results further support the role of PT22AV as a sustainable tool for rice blast management, representing an example of biological control strategies that align with the principles of integrated and environmentally sustainable crop protection, including the evolving European regulatory context such as the 10th Omnibus Package on plant protection products.