Comparative evaluation of biological control agents and chemical fungicides for managing gray mold and bacterial speck of tomato

Abstract The extensive use of chemical fungicides for the management of Botrytis cinerea and Pseudomonas syringae pv. tomato (Pst) in tomato crops has contributed to the emergence of resistant pathogen populations, potentially limiting the long-term effectiveness of conventional control strategies. Consequently, alternative and sustainable disease management approaches are being actively explored. In this study, we evaluated the efficacy of the biological control agents (BCAs) Bacillus velezensis K165 and Rhodotorula glutinis Y44 against B. cinerea and Pst in tomato plants. The BCAs were applied individually and in combination as root and foliar treatments, respectively. Application of K165 and Y44 reduced disease severity caused by B. cinerea compared with untreated controls, with levels of protection comparable to those achieved with a commercial fungicide (active ingredients: cyprodinil and fludioxonil). Similarly, treatments with K165 and Y44 were associated with reductions in disease severity and bacterial populations of Pst on tomato leaves relative to the untreated control, with effects that were comparable to or, in certain cases, lower than those observed with a copper-based fungicide. Notably, the combined application of K165 as a root treatment and Y44 as a foliar spray resulted in more consistent and, in several cases, enhanced disease suppression compared with the individual BCA applications against both pathogens. Molecular analyses further indicated that both BCAs were associated with the induction of the defense-related genes PR1 and PIN2 following pathogen challenge, suggesting activation of plant defense responses.