In order to determine the relationship between the defense gene of PAL and resistance of Cucurbita pepo to watermelon mosaic virus (WMV),we determined and analyzed changes of PAL gene expression in different resistant varieties of C.pepo tissue by the methods of indoor inoculation and real-time PCR after inoculated with the pathogen of WMV.(1)In vitro,the results showed that the incidence and disease index of disease-resistant variety of GBRV-8 (15.6% and 14.2) were significantly lower than that of the susceptible variety of Guangban (91.1% and 65.9).(2)Real-time PCR results showed that the relative expression of PAL gene was increased after inoculated with the pathogen of WMV in different tissues and different resistant varieties of C.pepo at initial stage,but decreased later.Also,the relative expression of PAL gene in the leaves of different disease-resistant varieties of C.pepo was significantly higher than that in petioles and stems after inoculated with WMV.(3)The relative expression of PAL gene in five different varieties was significantly different from the control after determined at different days,and the relative expression of PAL gene in resistant varieties and middle-resistant varieties were higher than that in susceptible varieties.The relative expression of PAL gene in resistant varieties of GBRV-8 was the highest and susceptible varieties of Guangban was the lowest.Therefore,the relative expression of PAL gene had a positive correlation to the disease resistance of varieties.