3. HISTORY
The symptoms of Blackleg of Potato were first described in Germany
between 1878 and 1900.
But the descriptions were incomplete and cannot definitively be linked to
the particular disease.
Investigations between 1918 and 1958 confirmed that these bacteria were of
a single species, and were officially appointed the name Pectobacterium
carotovorum.
A variety of Pectobacterium (P. carotovorum var. atrosepticum, which
includes B. melanogenes and B. phytophthorus) can be differentiated from
the rest, although it is considered the same species of bacteria.
4. SYMPTOMS
They are characterized by stunted, yellowish foliage that has stiff, upright
habit.
The lower part of the below ground stem of such plants is dark brown to
black in color and extensively decayed.
When infected, the pith region of the stem is particularly susceptible to decay
and may extend upward in the stem far beyond the tissue with externally
visible symptoms.
Young plants affected by blackleg are particularly susceptible, typically
dying after a halt in some cases of early disease development, mature stems
may turn yellow and wilt even before black decay is evident development.
7. PATHOGEN DESCRIPTION
Blackleg of potato caused by pectolytic bacteria.
It is a gram-negative, non sporulating, facultative
anaerobe that is also associated with soft rot of
potatoes.
8. DISEASE CYCLE
A contaminated tuber can infect growing stems, or
move into the vascular bundles of mature stems.
The pathogen will often survive in the infected tubers
until the following planting season.
The disease also spread through insect vector is seed
corn maggot (Hylemya platura and H. florilega).
9. FAVOURABLE CONDITION
The pathogen P. atrosepticum thrives in moist, cool
conditions, typically causing symptoms at temperatures
below 25°C.
It is vulnerable to temperatures above 36°C and dry
conditions, and thus survives best in potato tuber tissues,
although it is known to survive in other plant tissues.
Unlike other pectolytic bacteria, evidence shows that P.
atrosepticum does not survive well in soil outside its host
tissue.
10. MANAGEMENT
Cultural practices
Blackleg of potato has been successfully managed
primarily using cultural techniques.
These techniques generally rely on sterile propagation
techniques, using knowledge P. atrosepticum’s narrow
environmental range to control planting timing,
removing infected tissues and plants during the
growing season, reducing tuber harvest damage, and
proper storage.
11. STERILE PROPAGATION
Clean seed potato stocks established using tissue cultures have
been very successful in breaking the cycle of carrying disease
forward from year to year.
Buildup of tuber contamination is limited by reducing the
number of field generations of these seed potatoes to 5 to 7
years.
If healthy seed potatoes are to be cut, they should be first
warmed to 12-15 °C, cut, stored for 2 days at 12-15 °C in a
humid environment with good air flow.
This warming and storing period ensures proper tuberization of
the tissue, which forms a barrier from P. atrosepticum
infestation.
13. REFERENCES
Ali HF, Ahmad M, Junaid M, Bibi A, Ali A, Sharif M, Ali B,
Nawab K, Sadozai A. 2012. Inoculum Sources, Disease
Incidence and Severity of Bacterial Blackleg and Soft Rot of
Potato. Pakistan Journal of botany
Bain B,A, Perombelon MCM. 1990. Blackleg Development
and Tuber Yield in Relation to Numbers of Erwinia-
carotovora Sub sp. atroseptica on Seed Potatoes. Plant
Pathol.
