Inhibitory Mechanism of Geraniol against Geotrichum citri-aurantii in Citrus

In order to study the antifungal mechanism of geraniol on Geotrichum citri-aurantii, the effects of different concentrations of geraniol on the spores and mycelia of G. citri-aurantii were investigated by physicochemical analysis and microstructural observation. The results showed that the minimum inhibitory concentration (MIC) and minimum fugicide concentration (MFC) of geraniol against G. citri-aurantii were both 0.500 g/L. The spore germination rate of G. citri-aurantii treated with geraniol at MIC for 12 h was only (3.28 ± 1.28)%, which was significantly lower than that (92.17 ± 1.88)% in the control group (P < 0.05). Transmission rlectron microscope (TEM) showed that geraniol treatment destroyed the integrity of G. citri-aurantii cells, and led to separation between the cell wall and membrane, the organelles were indistinguishable, and the cells were vacuollated. The membrane permeability was altered, alkaline phosphatase (AKP) and nucleic acid was leaked out from the cells, the relative conductivity was increased, membrane lipid peroxidation was enhanced, and reactive oxygen species (ROS) were accumulated. In conclusion, geraniol affects the normal physiological function of G. citri-aurantii by inhibiting the spore germination and mycelial growth, disrupting the cellular structures, and promoting the accumulation of membrane lipid peroxidation and ROS, which provides a new idea for the effective control of G. citri-aurantii in citrus.