The capability of Pectobacterium carotovorum isolates to infect monocotyledonous plants has been previously reported; however, no full consideration was given to characterize the association between such isolates and their monocot hosts. To assess differences in aggressiveness among P. carotovorum ssp. carotovorum isolates originating from monocotyledonous or dicotyledonous plants, we used as model plants two susceptible monocot hosts, the ornamentals Zantedeschia aethiopica and Ornithogalum dubium, as well as two common dicot hosts, Solanum tuberosum and Brassica oleracea. Using virulence assays and different genetic analyses we characterized P. carotovorum ssp. carotovorum isolates from diverse geographical locations which originated from plants belonging to four unrelated orders of monocots and five orders of dicots. Invariably, isolates originating from monocots exhibited higher virulence towards the tested monocot plants than dicot isolates, independently of their geographical source. Moreover, monocot and dicot isolates were clearly differentiated by various genetic analyses, such as 16S rRNA sequence clustering, intergenic transcribed spacer-PCR (ITS-PCR) banding pattern and amplified fragment length polymorphism (AFLP). We propose that the observed relationship between pathogenicity and genetic diversity among P. carotovorum ssp. carotovorum isolates reveals a co-evolutionary specialization trend in the interaction between this pathogen and its hosts.