Abstract: The occurrence of diseases and changes in activities of the three protective enzymes , phenylalanine ammonialyase (PAL) 、peroxidase ( POD) and superoxide dismutase ( SOD) in leaves of Cymbidium sinense,were studied after inoculating Colletotrichum gloeosporioides. The results showed that the activities of PAL increased significantly after 36 h inoculation with C. gloeosporioide , and reached the highest activities at 84 h. POD activities appeared two peaks at 12 h and 60 h , respectively , after inoculation. The first peak surpassed the second peak. SOD activities rose quickly after inoculation with C. gloeosporioide , and reached the highest level at 12 h ,
then fell . The increase in the activities of PAL , POD and SOD showed that these three enzymes play an important role in resisting the infection of C. gloeosporioide.

Key words: Cymbidium sinense, Colletotrichum gloeosporioide, Protective enzymes activities