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-PCR-RFLP 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.

Cardinal temperature differences, determined in vitro, between closely related species and subspecies of pectinolytic bacteria responsible for blackleg and soft rot on potatoes

“…Pectobacterium wasabiae was reported for the first time in SA in 2013 (Moleleki et al 2013). An optimal temperature of +30 o C grouped Pwa together with the Pectobacterium carotovorum group, but the limited growth range and maximum growth temperature of +34°C, it appears that Pwa is relatively temperature sensitive in vitro, similar to Pba.…”

Colonization Patterns of an mCherry-Tagged Pectobacterium carotovorum subsp. brasiliense Strain in Potato Plants

“…The inoculated part of the stem was then sealed with parafilm to prevent desiccation and leakage of inoculum down the stem or into the soil (11). Following inoculation, plants were watered every second day from the bottom of the pots (12,30). To determine the relative susceptibility or resistance level of each cultivar, inoculated plants were evaluated daily for development of blackleg symptoms for 21 days.…”

“…In South Africa, two of these species, P. carotovorum subsp. brasiliense and P. wasabiae, have been identified as the main causal agents of soft rot and black leg diseases of potato (30,39).…”

“…Previous studies have shown P. carotovorum subsp. brasiliense strain 1692 (the strain for which a genome sequence is available) to be highly aggressive and more invasive compared with the well-studied P. atrosepticum (29,30). Genome comparisons of P. carotovorum subsp.…”

Occurrence of Pectobacterium wasabiae in potato field samples

“…Up to 2004 the exchange of plant material between Poland other countries was much more restricted than in recent years. Currently Dickeya spp., are also detected in2011; Nabhan et al 2012a,b;Rahmanifar et al 2012;Moleleki et al 2013). For the first time P. wasabiae has been isolated in the 1980s in Japan from Japanese horseradish (Goto and Matsumoto 1987).…”