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.