Screening of Ampelomyces quisqualis Isolates Hyperparasite on the Tobacco Powdery Mildew Fungus

12 isolates of Ampelomyces quisqualis from different sources were in vitro inoculated to the center of the powdery mildew colonies on the diseased tobacco leaves, and two parameter values of pathogenicity scales and virulence of Ampelomyces isolates were obtained by counting the numbers of pycnidia and by measuring mycoparasited area on powdery mildew colonies, furthermore relative pathogenicity of Ampelomyces isolates were got by calculating the two parameters, five isolates of Ampelomyces mycoparasite were found to have the potential to control tobacco powdery mildew.