SUMMARY

A unified approach to naming bacteria ensures accu-rate communication among scientists, regulators and the public. Rules for nomenclature, set out in the Interna-tional Code of Nomenclature of Bacteria (ICNB), ensure that proposals for new names and combinations follow a logical and standardized progression that maintains the integrity of the established nomenclature while facilitat-ing changes based on scientific inquiry into relationships among organisms. However, these Rules only apply to ranks at the level of subspecies and above and not to lower taxonomic ranks. The pathovar is one infraspecific rank that is widely used in the classification and nomen-clature of plant pathogenic bacteria and is often includ-ed in legislation to provide statutory control of bacterial plant pathogens. Thus, phytobacteriologists must rely on two discontinuous but, complimentary systems: the Rules set forth in ICNB for naming down to subspecies level, and the Standards in the International Standards for Naming Pathovars of Plant Pathogenic Bacteria to name pathovars. A framework for determining the prior-ity of names is provided by the Approved Lists of Bacte-rial Names, which gives genus, species and subspecies names and their corresponding type strains, and subse-quent lists of validly published names appearing in the International Journal of Systematic and Evolutionary Mi-crobiology. For pathovar names priority is based on the date of valid publication of legitimate names. A list of pathovar names and pathotype strains is maintained by the Committee on the Taxonomy of Plant Pathogenic Bacteria of the International Society of Plant Pathology. To help researchers avoid common pitfalls encountered when developing nomenclature for novel classification systems, this manuscript clarifies several key Rules an