An extensive phenotypic description and an improved classification and nomenclature of the genus are presented. A total of 266 strains obtained from different geographical areas, including representative strains of all species of the genus and most pathovars of , as well as strains which might be genetically related to the genus , were examined for 295 morphological, biochemical, and physiological features. Similarities among the strains were expressed numerically by using the coefficient of Sokal and Michener. Clustering was performed by using the unweighted average pair group method. The conclusions described below were reached. (i) The genus comprises at least the following eight phena: Swings et al. 1990, and pv. graminis Egli and Schmidt 1982 [not pv. graminis (Egli et al. 1975) ISPP List 1980]. (ii) (Ridé 1958) Ridé and Ridé 1978 is a separate species. (iii) Swings et al. 1983 forms a separate species. (iv) pv. oryzae ISPP List 1980 can no longer be regarded as pathovar of , and its recent reclassification as a new species, (Swings et al., Int. J. Syst. Bacteriol. 40:309-311, 1990), is supported. (v) pv. graminis Egli and Schmidt 1982 [not pv. graminis (Egli et al. 1975) ISPP List 1980] seems to form a separate complex of highly related pathovars obtained from members of the Poaceae; the taxonomic implications of this are discussed. (vi) Strains of nearly all pathovars cluster together in the phenon. Within this species we were able to differentiate some entities on phenotypic grounds; these groups sometimes corresponded to named pathovars (e.g., pv. manihotis, pv. cassavae, pv. phlei). In several other cases, pathovars were found to be heterogeneous. (vii) A number of dubious species were identified as members of or as being close to species. Both and are synonyms of . We also confirmed that , and belong to . (viii) Forty phenotypic features allow the differentiation of the eight phena. (ix) A number of additional features of the genera and are described.


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