Abstract:
Potato blackleg and soft rot cause major losses
and are caused by two bacterial genera, Pectobacterium
and Dickeya. Species affecting potatoes are
Pectobacterium atrosepticum (Pba), Pectobacterium
carotovorum subsp. carotovorum (Pcc), Pectobacterium
carotovorum subsp. brasiliense (Pcb), Pectobacterium
wasabiae (Pwa), Dickeya dadantii (Dda) and Dickeya
solani (Dso). Pathogenicity of these species is dependent
on temperature, with each species having its own optimal
temperature and temperature range for growth, leading to
varying degrees of losses. Pectobacterium atrosepticum,
a temperature sensitive species, mainly occurs in temperate
climates, Pcc in temperate to tropical, and Dickeya
spp. in subtropical environments. The aim of this study
was to determine the cardinal growth temperatures for the
species responsible for blackleg and soft rot in vitro.
Bacterial isolates were incubated in a temperature gradient
shaking incubator at 30 different temperatures ranging
from ±5 °C to ±56 °C, and growth measured at two set time intervals. Results were statistically analysed
using the Gaussian function. The optimal temperature
of 31 °C and temperature range of 20 °C to 38 °C for
Pectobacterium carotovorum subsp. brasiliense, was
similar to those recorded for Pcc. Pectobacterium
wasabiae grew at an optimal temperature of 29 °C and
range of 20 °C to 34 °C. Higher optimal temperatures of
32 °Cand 34 °C,with ranges of 21 °C to 38 °Cand 23 °C
to 41 °C were recorded for Dda and Dso, respectively.
The minimal variation in optimal temperatures between
different species might be an indication that temperature
ranges, rather than optimal temperature, play an important
role in disease development. Results for Dso, which
has not yet been reported in South Africa, are especially
important in light of prevailing temperatures in South
African potato production regions.
