Induction Expression of Defense Gene in Different Varieties of Cucurbita pepo by Watermelon Mosaic Virus Infection Purification of a Watermelon mosaic virus Isolate from Shanshan County and Evaluation for the Virus Resistance of Various Melon Cultivars Purification of a Watermelon mosaic virus Isolate from Shanshan County and Evaluation for the Virus Resistance of Various Melon Cultivars Detection of genetic variations among Xinjiang isolates of WMV-2 by PCR-SSCP analysis