Improving the biocontrol efficacy of Meyerozyma guilliermondii Y-1 with melatonin against postharvest gray mold in apple fruit

Abstract Apple gray mold caused by Botrytis cinerea can reduce postharvest shelf-life and quality of apple produce, and thus causes serious economic losses. In this study, we investigated the biocontrol efficacy of Meyerozyma guilliermondii Y-1 with and without its combination with melatonin (MLT) against B. cinerea in the postharvest apple fruit, and the underlying physiological and molecular mechanisms. Our results showed that the combination of M. guilliermondii Y-1 (1 × 108 cells/mL) and MLT (100 μmol/L) synergistically and significantly reduced the decay incidence and lesion diameter. MLT improved the ability of strain Y-1 to colonize in apple fruit wounds and surface whether at 22 or 4 °C. Moreover, M. guilliermondii Y-1 and MLT treatment markedly increased the defense-related enzyme activities, including catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), phenylalanine ammonia-lyase (PAL), and polyphenol oxidase (PPO), as well as the total antioxidant capacity (T-AOC), total phenolics and lignin contents. As expected, the expression levels of four pathogenesis-related (PR) genes (MdPR1, MdPR5, MdGLU, and MdCHI) and two jasmonic acid (JA) signaling pathway related genes (MdPDF1.2 and MdCOI1) were significantly increased in response to strain Y-1 and MLT treatment. Furthermore, the most pronounced and/or rapid increase was observed in the combined than individual treatments of either strain Y-1 or MLT. Our results suggest that the effective combination of strain Y-1 and MLT might be a reliable alternative against B. cinerea postharvest infection in apple fruit.