The R-PDA medium was made by adding 400ug/ml rifimpicin to common PDA medium and used for isolating 5 species of tobacco pathogenic fungi. With R-PDA studying, the 63. 8% of detected frequency of different pathogens was obtained with no contamination by bacteria and as less as 7.5% contamination by nonpathogenic fungi. While the PDA medium as a control gave only 25% detected frequency for pathogens with 89. 4% contamination by bacteria. This selective isolation method could make the isolating procedures sim...