I.  REVISIONS TO THE INTERNATIONAL STANDARDS FOR NAMING PATHOVARS OF PHYTOPATHOGENIC BACTERIA

from:  April 1991, Review of Plant Pathology vol. 70

(a) Standard 5. Definition pathovar

The present standard reads:
'The term pathovar is used to refer to a strain or set of strains with the same or similar characteristics, differentiated at infrasubspecific level from other strains of the same species or subspecies on the basis of distinctive pathogenicity to one or more plant hosts. Classification of a taxon as a pathovar does not exclude recognition of differences in biochemical, serological, or other non-pathogenic characters between that and other pathovars of the same species or subspecies, but implies that at infrasubspecific level other differences are considered to have less taxonomic significance in comparison to differences in pathogenicity.'

    Add:
'Usually pathovars are distinguished in terms of proved differences in host range.   However, clear differences in symptomatology on the same plant species (e.g. Xanthomonas campestris pv. oryzae and X. campestris pv. oryzicola) can warrant different pathovar designations.

   This definition allows alternative division of pathogenic species or pathovars into races.  A race of a bacterium is a collection of strains which differ from others within a bacterial species or pathovar in their host specialization to cultivars or other germplasm.  Races are identified through the use of plant host differentials which may be cultivars or other identifieable germplasm.  Races have no nomenclatural standing.  A race should be designated with letters or numbers.
   The term pathogenic group may be useful to designate informally a set of organisms having certain characteristics in common, it it is used with care and exact definition to avoid ambiguity (Lapage et al., 1975, p. 127)  The term is an informal one which has no nomenclatural standing and is not a substitute term for race.
  The term 'forma specialis' (syn. special form), is not a substitute for pathovar or race for phytopathogenic bacteria.  It is applied only to pathogens which are specific for a particular host.  The term is defined by Lapage et al. (1975, p. 126).

(b) Standard 6.  Naming of Pathovars

The present standard reads:
'Pathovar names must be treated as Latin.  The name of a pathovar is a ternary or quaternary combination, consisting of the name of genus followed by a specific epithet, and where appropriate a subspecific epithet preceded by the abbreviation 'subsp.' and finally by the pathovar epithet preceded by the abbreviation 'pv.' (pathovar).
   Note:  The first time a name is used in a publication, it should be given in full with its authority.  Subsequently where there is no risk of confusion, the examples below offer acceptable abbreviations.  Example:  Pseudomonas syringae pv. lachrymans abbreviated to: 1) P.s. pv. lachrymans; 2) P.s. lachrymans; 3) pv. lachrymans.'