Irpex lacteus and Bacillus velezensis synergistically suppress tomato gray mold by enhancing antioxidant defense and phenylpropanoid metabolism

Abstract

Tomato gray mold caused by Botrytis cinerea is a devastating disease in protected cultivation, and biological control using beneficial microorganisms offers a sustainable alternative to chemical fungicides. However, the synergistic effects and underlying mechanisms of combining Irpex lacteus with Bacillus velezensis against tomato gray mold remain unexplored. In this study, we investigated the individual and combined effects of I. lacteus and B. velezensis on tomato resistance against B. cinerea. Both I. lacteus and B. velezensis effectively suppressed B. cinerea growth in dual culture assays.Individual applications of I. lacteus fermentation broth and B. velezensis cell-free culture filtrate on tomato plants achieved control efficacies of 55.93% and 62.75%, respectively, whereas their combination significantly increased control efficacy to 86.95%. The combined treatment markedly reduced disease severity and pathogen-induced cell death, accompanied by significantly decreased accumulation of malondialdehyde (MDA), hydrogen peroxide (H2O2), and superoxide anion (O2·-) compared with pathogen-only controls. Furthermore, the combined treatment substantially elevated the activities of antioxidant enzymes (SOD, POD, CAT, APX), phenylpropanoid pathway enzymes (PAL, PPO, CAD, CA-POD, CGA-POD), and increased the contents of total phenolics, total flavonoids, chlorogenic acid, and DPPH radical scavenging capacity. In addition, the combined treatment restored photosynthetic performance, as evidenced by increased maximum quantum efficiency of PSII (Fv/Fm), enhanced activities of Calvin-cycle enzymes (Rubisco and FBPase), and upregulation of photosynthesis-related genes (FBPA, TPI, FBPase, and SBPase). These biochemical changes were generally more pronounced in the combined treatment than in single microorganism treatments. Collectively, our results demonstrate that I. lacteus and B. velezensis synergistically protect tomato against B. cinerea by mitigating oxidative stress and activating both antioxidant and phenylpropanoid defense pathways. These findings highlight the potential of combined I. lacteus and B. velezensis application as a sustainable biocontrol strategy against tomato gray mold.