Characterisation of pectobacterium wasabiae causing blackleg and soft rot diseases in South Africa

Abstract

Pectolytic bacteria were isolated from potato tubers and stems showing tuber soft rot and blackleg symptoms. Approximately half (52 %) of the isolates could grow at both 27 and 37 °C while another half (48 %) failed to grow at 37 °C. All isolates could be amplified with primers specific to the pectate lyase (pel) gene. Carbon utilisation profiles could not conclusively identify these isolates. PCR amplification using primers specific for Pectobacterium carotovorum subsp. brasiliensis was positive for all isolates that grew at 37 °C. However, the group that did not grow at 37 °C failed to amplify with P. atrosepticum specific primers. To characterise this group of isolates, the intergenic transcribed spacer region (ITS) was amplified and PCR products digested with two restriction enzymes (RsaI and CfoI) to generate ITS-PCRRFLP profiles. The profiles of these new isolates were compared to those of the type strains of other pectolytic bacteria. Profiles of five of the selected atypical strains generated with the enzyme CfoI appeared to be most similar to those of P. wasabiae type strain. Phylogenetic analysis using concatenated partial gene sequences of housekeeping genes mdh and gapA clustered these isolates together with those of P. wasabiae reference strains thus confirming their identity. These strains were virulent on potato tubers and stems but did not elicit hypersensitive response on tobacco plants. This is the first report of P. wasabiae causing soft rot and blackleg of potatoes in South Africa.