Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 15, 1997
Publication Date: N/A
Interpretive Summary: Phytopathogenic bacteria have been recently classified into genera, Clavibacter and Rathayibacter. Some species and subspecies in these genera cause serious diseases in various crops. Potato ring rot disease caused by Clavibacter michiganensis susp. sepedonicus, is one such serious disease. Traditionally, differentiation and identification of these pathogens have been based on laborious and time-consuming biochemical tests, and results have been sometimes inconsistent. In this study we have developed a rapid and accurate molecular-based procedure for differentiation and classification of these pathogens. Based on finger printing (RFLP analysis) of 16S rDNA sequences, we have identified species and subspecies that are consistent with grouping based on traditional methods. The classification by this approach is phylogenetically valid. The information and pathogen-identification technology will be of benefit to diagnosticians for conducting further surveys of the distribution of the disease in other regions.
A phylogenetic analysis using parsimony of 16S rRNA gene sequences (16S rDNA) revealed that species and subspecies of Clavibacter and Rathayibacter form a discrete monophyletic clade, paraphyletic to Corynebacterium species. Within the Clavibacter-Rathayibacter clade, four major phylogenetic groups (subclades) with a total of ten distinct taxa were recognized: (I_ species C. michiganensis; (II) species c. xyli (III) species R. iranicus and R. tritici; and (IV) species R. rathayi. The first three groups form a monophyletic cluster, paraphyletic to R. rathayi. On the basis of the phylogeny inferred, reclassification for members of Clavibacter-Rathayibacter group is proposed. A system for classification of taxa in Clavibacter and Rathayibacter was developed based on RFLP analysis of the PCR-amplified 16S rDNA sequences. The groups delineated on the basis of RFLP patterns of 16S rDNA coincided well with the subclades delineated on the basis of phylogeny. In contrast to previous classification systems, which are primarily based on phenotypic properties and are laborious, the RFLP analyses allows for rapid differentiation among species and subspecies in the two genera.