Isolates of Erwinia chrysanthemi from Zantedeschia aethiopica (white-flowered calla lily) induced symptoms of soft rot on inoculated cv. Innocence flower-stem segments. Isolates from Phalaenopsis aphrodite and potato caused mild symptoms, while those from green onion and celery produced no symptoms. In addition to pathogenicity, the isolates were further characterized at the molecular level. A specific oligonucleotide primer set was designed for the detection of the pelZ gene of E. chrysanthemi. All E. chrysanthemi isolates tested contained pelZ as determined by PCR amplification. No amplification was observed with other Erwinia spp. The pelZ of E. chrysanthemi isolate S3-1 from Z. aethiopica was cloned, sequenced and compared with the nucleotide sequence of pelZ in GenBank. A point mutation produced an AhdI restriction site, leading to the development of a PCR-RFLP assay to discriminate white-flowered calla lily isolates from others of E. chrysanthemi. Furthermore, macrorestriction analysis by modifying a pulsed-field gel electrophoresis (PFGE) protocol used by PulseNet revealed the genomic variation within E. chrysanthemi. After digestion with the restriction enzyme XbaI, white-flowered calla lily E. chrysanthemi isolates could be easily distinguished from other isolates. Differences in virulence, combined with PCR-RFLP and PFGE analyses, suggest that white-flowered calla lily E. chrysanthemi isolates are a new strain or pathotype in Taiwan.