ISHS Acta Horticulturae 225: Bacterial and Bacteria-like Contaminants of Plant Tissue Cultures
TAXONOMY OF AGROBACTERIUM |
| Author: | B. Holmes |
| Abstract:
Taxonomy has three components: classification, nomenclature and identification. The classification of the genus Agrobacterium is well understood both at the infrageneric and suprageneric levels. Within the genus there are defined by genetic and phenotypic data, two major taxa, plus A. rubi represented by only three authentic strains. Two further strains, NCPPB 1650 and NCPPB 1771, are genetically distinct from each other as well as other authentic agrobacteria. These two strains may form nuclei around which additional species may form. The position of the more recently described biotype 3 strains remains to be determined although they are phenotypically most similar to A. rubi and strains NCPPB 1650 and NCPPB 1771. Unknown strains can be identified by simple biochemical tests to the two major taxa and A. rubi. However, identification is made difficult because many workers still differentiate strains of the two major taxa according to their phytopathogenic effect, which is plasmid-mediated and does not correspond to the division of strains into the two major taxa as defined by genetic and phenotypic data. In addition, the strongest candidates as names for the two major clusters have specific epithets meant to indicate the phytopathogenic effects of strains, since it was on this basis that the species were originally defined; they are A. tumefaciens and A. rhizogenes. The nomenclature to be used for the two principal taxa is the major taxonomic problem still to be resolved in Agrobacterium. The logical and least confusing solution within the rules of nomenclature seems to be to use the epithets radiobacter, rhizogenes and tumefaciens to indicate respectively non-pathogenic, hairy-root forming and crown-gall inducing strains within each of the three species defined according to genetic and phenotypic data. As well as plants, strains of A. tumefaciens occasionally infect humans. | |
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