Pectobacterium spp. Associated with Bacterial Stem Rot Syndrome of Potato in Canada

Pectobacterium atrosepticum, P carotovorum subsp. brasiliensis, P. carotovorum subsp. carotovorum, and P wasabiae were detected in potato stems with blackleg symptoms using species- and subspecies-specific polymerase chain reaction (PCR). The tests included a new assay for P. wasabiae based on the phytase gene sequence. Identification of isolates from diseased stems by biochemical or physiological characterization. PCR, and multi-locus sequence typing (MLST) largely confirmed the PCR detection of Pectobacterium spp. in stem samples. P. atrosep-ticum was most commonly present but was the sole Pectobacterium sp. detected in only 52% of the diseased stems. P wasabiae was most frequently present in combination with P atrosepticum and was the sole Pectobacterium sp. detected in 13% of diseased stems. Pathogenicity of P. wasabiae on potato and its capacity to cause blackleg disease were demonstrated by stem inoculation and its isolation as the sole Pectobacterium sp. from field-grown diseased plants produced from inoculated seed tubers. Incidence of P carotovorum subsp. brasiliensis was low in diseased stems, and the ability of Canadian strains to cause blackleg in plants grown from inoculated tubers was not confirmed. Canadian isolates of P carotovorum subsp. brasiliensis differed from Brazilian isolates in diagnostic biochemical tests but conformed to the subspecies in PCR specificity and typing by MLST.