Antifungal activities of polyhexamethylene biguanide and polyhexamethylene guanide against the citrus sour rot pathogen Geotrichum citri-aurantii in vitro and in vivo

Polyhexamethylene biguanide (PHMB) and polyhexamethylene guanide (PHMG) are broad-spectrum antibacterial agents. Experiments were conducted to investigate the antifungal activities of PHMB and PHMG against a major citrus sour rot pathogen Geotrichum citri-aurantii both in vitro and in vivo. PHMG and PHMB treatments significantly inhibited arthroconidia germination and mycelial growth of G. citri-aurantii in vitro. PHMG and PHMB at 5 mg/L inhibited 97.8% and 95.8% of the germination of G. citri-aurantii arthroconidia, respectively. Observations by light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) further showed ultrastructural alterations caused by PHMG or PHMB treatments, including distortion, deformation and concave collapse in hyphae, plasma membrane disruption in both hyphae and arthroconidia, and cell wall damage in arthroconidia. Use of PHMG and PHMB significantly (P < 0.05) reduced sour rot development on artificially inoculated ‘Shatang’ mandarin fruit. Overall, PHMG and PHMB could be alternative means for control of postharvest sour rot of citrus fruit.

► Antifungal activities of PHMG and PHMB against the major pathogen Geotrichum citri-aurantii were studied.
► PHMG and PHMB effectively inhibited growth of G. citri-aurantii in vitro.
► Application of PHMG and PHMB significantly reduced postharvest decay of ‘Shatang’ mandarins caused by G. citri-aurantii.
► PHMG and PHMB might provide an alternative means to control postharvest sour rot of citrus fruit.