Effect of blue light treatments on Geotrichum citri-aurantii and the corresponding physiological mechanisms of citrus

Sour rot caused by Geotrichum citri-aurantii is one of the main diseases of postharvest citrus fruit. Blue light irradiation (455 nm) in citrus infected by G. citri-aurantii, as well as the associated physiological mechanisms of blue light in citrus during postharvest storage were investigated in this study. The results showed that blue light induced pigments (carotenoids) generation and ultraviolet (UV) resistance of G. citri-aurantii at a light intensity of 50 μmol m−2 s−1. When blue light intensity was 150 μmol m−2 s−1, morphological and ultra-structural alterations were observed. The cell staining results showed that lipid droplets (LDs) production and reactive oxygen species (ROS) burst were accelerated. The expression levels of genes related to carotenoid synthesis, redox, and LDs synthesis were upregulated by blue light treatment. In addition, sour rot decay occurrences of Citrus unshiu, Citrus sinensis L. Osbeck and Citrus reticulata Blanco cv. Ponkan under 200 μmol m−2 s−1 were reduced to 0%, 3.33% and 41.67%, respectively. The activities of antioxidant enzymes and defense-related enzymes were significantly boosted by blue light irradiation. Furthermore, the titratable acid (TA) and hardness were significantly higher in citrus under blue light treatment. These findings strongly indicated that blue light played an important function in reducing pathogen fungus growth and could be used to effectively control citrus postharvest diseases.