Erwinia amylovora, which causes fire blight disease, is one of the biggest threats to pome fruit growing worldwide and is one of the top ten most destructive bacterial pathogens. In this study, the relationships between the genetic diversity and disease severity of E. amylovora strains isolated from pears from different regions of Turkey were revealed by pEA29 plasmid DNA derived from A/B primers, amsG primers responsible for amylovoran production, CRISPR 1, 2 and 3 primers, used to characterize the genetic diversity and some properties of the pathogen. The findings indicated significant regional differences in percent disease severity and indices among pear strains. However, no genetic variation was observed in pEA29 and amylovoran production. Only one strain differed from the others with CRISPR 2 primers, and it was observed that the specific primers used to determine the relationship between regional differences and virulence of the strains were not completely sufficient to reveal the genetic difference. The results of the study indicated that E. amylovora is subject to changing ecological and climatic factors in different hosts, in different countries and regions. This scenario may have induced genetic heterogeneity among the examined strains, implying that variations in virulence could also emerge in strains harboring distinct plasmid DNAs. New perspectives can be developed in the control of the disease with a full understanding of the relationships between the pathogen's pathogenicity levels and genetic structure.