Abstract: Changes of phenylalanine ammonialyase and chlorophyll in muskmelon cultivars of different resistance to cucumber mosaic virus-XJ (CMV-XJ) were investigated.Compared with healthy control,the enzyme activity increased in all infected muskmelon plants,but the increase in enzyme activity for resistant cultivar “Xinyu” was two times of that for susceptible cultivar “Wangwenxiang” and the peak of enzyme activity for “Xinyu” appeared 12 days earlier,that is bigger increase range of enzyme activity and earlier enzyme activity peak for resistant cultivar.But the change of chlorophyll was negatively related with the resistance to the virus;after infection by CMV-XJ,the chlorophyll content of resistant cultivar “Xinyu” is not different significantly from that of the healthy control,but the chlorophyll content of susceptible cultivar “Wangwenxiang” decreased  by 62.9% compared with the healthy control.There is regular relation between resistance of the muskmelon cultivar and changes of phenylalanine ammonilyase and chlorophyll after infection by CMV-XJ.The regularity can be used as the biological criterion for the determination of susceptibility and resistance to CMV-XJ for muskmelon cultivars.

Key words: cucumber mosaic virus-XJ, muskmelon, phenylalanine ammonialyase, chlorophyll