Nine isolates ofErwinia chrysanthemifrom rotting potato tubers were compared with six type or reference strains of this species. Phenotypic properties of the potato isolates closely agreed with those ofErw. chrysanthemipv.zeaeand with the characteristics proposed for Dickey's infrasubspecific subdivision IV (1979) and Samson&Nassan‐Agha's biovar 3 (1978), whereZea mayswas among the most common host species. Pathogenicity tests on 20 ornamental and agricultural species showed onlyCyclamensp. andZ. maysto be susceptible. In Ouchterlony double diffusion tests, antisera to whole live cells of one potato strain reacted with four of the six pathovars ofErw. chrysanthemi.Tuber isolates did not produce blackleg symptoms in inoculated stems. The rationale of intensive pathogenicity testing is discusse