EN
Fire blight caused by Erwinia amylovora is the most destructive disease affecting apple (Malus x domestica Borkh.), pcar (Pyrus communis L.) and number of other plant species mainly of the Rosaceae family. However, the symptoms of various diseases, either of biotic or abiotic origin, might be mistaken for those of fire blight. Therefore, in almost all cases its diagnostics should be based on etiological studies. For this purpose the classical procedure consisting in isolation of bacteria on selective or semi selective media and determination of pathogenicity of bacteria with morphology similar to E. amylovora is most often applicd. Lately, the serological methods, ecspecially ELISA and immunofluorescence, have been introduced to routine use in laboratories of Polish Plant Protection Service (PPS). However, the highest sensitivity and specificity offer the methods based on analysis of genetic material of the bacteria: hybridization of nucleic acids and polymerase chain reaction (PCR). When required, two PPS laboratories use a PCR-based method. The paper reviews research on application of molecular methods for detection of E. amylovora in plant material, its identification and determination of genetic diversity among the strains originating from various plant species and various geographic regions.