Abstract: In order to explore the inhibitory effect of pyropheophorbide-a（PPa）on plant pathogens，and to find a new agent with low toxicity and high efficiency against the cucumber Fusarium wilt（CFW），Fusarium oxysporium f. sp. cucumerinum H46 5 strain and cucumber cultivar‘Changchun Mici’were used as materials，and the effect of different concentrations of PPa on the mycelial growth of H46 5 pathogen was deteced. The area of infected cucumber leaves，the malondialdehyde（MDA）content，the free proline content were measured. The activities of peroxidase（POD），catalase（CAT）and superoxide dismutase（SOD）were determined after PPa treatment under different lighting condition. The reactive oxygen species（ROS）including H2O2 content and superoxide anion production rate was estimated using 3,3′-diaminobenzidine（DAB）staining and nitro-blue tetrazolium（NBT）staining. The results showed that PPa had a significant inhibitory effect on H46 5，and its inhibitory effect was positively correlated with its concentration. The optimal inhibitory concentration of PPa was 2 g • L-1. PPa treatment also significantly reduced the level of CFW disease and MDA content of the plant，and increased the proline content and antioxidant capacity of the plant，and maintained the ROS balance of the plant. Although the inhibitory ability of PPa was limited by the effects of light intensity and light duration，and the results proved that PPa had a good effect on inhibiting the disease of CFW.

Key words: cucumber, Fusarium wilt, pyropheophorbide-a, reactive oxygen species, disease resistance