COMPARISON OF GROEL SEQUENCES, 16S-23S RDNA SPACERS, AND PEA29-TYPE PLASMIDS FROM ERWINIA AMYLOVORA AND E.PYRIFOLIAE
Strains of Erwinia amylovora were compared with strains of E. pyrifoliae in a series of molecular tests. E. pyrifoliae strains form a PCR-ribotype group unlike the four PCR-ribotype groups of E. amylovora. Analysis of the 16S-23S rDNA-spacer region indicated multiple spacers that differ in length and tRNA genes explaining the ribotype groupings. When six of the seven spacers from E. amylovora and E. pyrifoliae were characterized by sequence analysis, each contained four spacers with tRNAGlu genes and two spacers with tandem tRNAIle and tRNAAla genes. Three tRNAGlu spacers found in E. amylovora were not present in E. pyrifoliae, but a fourth tRNAGlu spacer in E. amylovora was present in E. pyrifoliae. Overall, the spacers in Rubus strains of E. amylovora and in E. pyrifoliae were more closely related than the spacers in tree fruit strains of E. amylovora and E. pyrifoliae. The genetic makeup of plasmid pEA29 from E. amylovora and the large plasmid from E. pyrifoliae was found to be similar in some regions. The absence of sequence in E. pyrifoliae corresponding to the forward primer used to identify pEA29 in E. amylovora explains the failure of the E. amylovora primer set to amplify the large E. pyrifoliae plasmid. A comparison of partial groEL sequence from Erwinia strains yielded a phylogeny which shows that strains of E. pyrifoliae from Asian pear are classified in a subgroup distinct from the subgroup for E. amylovora and for E. persicinia, E. cypripedii, and E. aphidicola. Phage sensitivity tests added to the molecular evidence supporting the view that the Asian pear strains represent a distinct species.
Schnabel, E.L., McGhee, G.C. and Jones, A.L. (2002). COMPARISON OF GROEL SEQUENCES, 16S-23S RDNA SPACERS, AND PEA29-TYPE PLASMIDS FROM ERWINIA AMYLOVORA AND E.PYRIFOLIAE. Acta Hortic. 590, 429-439