Abstract: Resistance of the clones and hybrids in genus Paulownia were evaltiated by field investigation and DAPI staining fluorescence microscopy for MLO detection,Restilts showed that four types of symptoms were usually occurred in adult diseased trees,i.e. I.witches' broom(WB),Ⅱ.yellowing(Y),Ⅲ.witches' broom & yellowing(WB+Y),and Ⅳ.witches' broom &Phyllody,(WB+P).Symptom expression of diseased trees are directlyrelevant to the MLO concentration within the sieve tubes of vascular tissues.In general,the MLO concentration varies from high to low in order as follows:phyllody,witches'broom,yellowing and healthy-like parts.However,MLO population in the roots of all the cloneswere indistinguishable by means of DAPI staining fluorescence microscopy. There wereapparent differences in the resistances of various clones and hybrids to MLOs. According tothe types of symptoms,disease index and MLO detection results,the testing material can bedivided into three categories:high-resistant,middle-resistant and susceptible. Several goodclones and hybrids with high resistance and ideal growth character were screened.