Abstract: Objective: The dynamic response of physiological metabolism in postharvest citrus to toxin from Colletotrichum gloeosporioides was studied to obtain a better understanding of the interaction between citrus and C. gloeosporioides. Methods: The crude toxin was isolated by organic solvent extraction, and its bioassay was performed by the acupuncture method in postharvest citrus. Moreover, the dynamic effects of the crude toxin and pathogenic bacteria on physiological metabolism of citrus fruits in terms of the contents of phenols, flavonoids, and malondialdehyde (MDA), cell wall components in citrus peel and the activities of polyphenol oxidase (PPO), peroxidase (POD), superoxide dismutase (SOD), phenylalanine ammonialyase (PAL), and β-1,3-glucanase (GLU) were analyzed. Results: Typical lesion caused by the toxin was observed, and the content of MDA was significantly increased, while the content of cell wall compounds was decreased. Upon treatment with the crude toixn at a low concentration, there was a positive correlation of lesion diameter with the content of flavonoids, lignin and the activities of PPO and POD, whereas a negative correlation existed between cell wall compounds and lesion diameter. However, the defense enzyme system and citrus fruits were damaged by the crude toxin at a high concentration, causing a dramatic decrease in the enzyme activities. Conclusion: Physiological metabolism of citrus fruits can be influenced by the crude toxin of C. gloeosporioides , and thus it plays an important role in the pathogenicity of C. gloeosporioides.

Key words: Colletotrichum gloeosporioides, toxin, physiological metabolism, citrus