Antifungal Activity and Possible Mechanism of Bacillus amyloliquefaciens FX2 Against the Postharvest Apple Ring Rot Pathogen

induced apple ring rot is one of the most serious postharvest diseases in apple production. In our preliminary work, we isolated a bacterial strain (FX2) from an infested apple orchard. Here, we confirmed the strong antifungal activity of FX2 on . Through phylogenetic analysis and morphological observations, we identified FX2 as a strain. We also found that 10% cell-free supernatant (CFS) of FX2 significantly affected mycelial growth and morphology and almost completely inhibited spore germination and germ tube elongation in . Furthermore, 10% CFS damaged the cell ultrastructure, resulting in a remarkable increase in cellular leakage in mycelia. Thus, CFS has the potential to effectively reduce in vivo infection, reduced lesion diameters to 64.7% compared with the control group, and reduced disease incidence by 15%. Finally, ultrafiltration, desalting chromatography, and anion exchange chromatography showed that the antifungal constituents in CFS are composed mainly of antifungal proteins. We further characterized these potential antifungal proteins via liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Herein, we provide novel insights into the antifungal mechanisms of FX2, and we highlight its potential as a novel biocontrol agent for controlling postharvest apple ring rot.