Agriculture Reference
In-Depth Information
growth, warm temperatures, high humidity and the
anaerobic conditions that develop during infection, infected
tubers rapidly break down and spread bacteria to adjacent
tubers (Plate 16.2) The pathogen can invade healthy tubers,
primarily through lenticels particularly when they have
swollen in response to moist or wet conditions, or tubers
already infected with other diseases. This can result in
localized pockets of rot. Infected potatoes generate heat
further increasing the rotting process and which can result
in an extremely rapid disease progression. A runaway
infection can lead to the breakdown of an entire store in
days. Other bacterial species, typically of the genera
Clostridium, Pseudomonas
, and
Bacillus
, can be associ-
ated with tuber soft rot.
Control measures are to avoid harvesting during wet
conditions and minimizing potato damage during harvest
and handling. Remove damaged potatoes before loading in
clean stores. If harvested when wet, ventilate continually
until the potatoes are dry and provide good air circulation
in storage. Check the pile temperature at regular intervals
and if temperatures are elevated consider additional
ventilation or unloading the store.
Figure 16.2
Brown rot of potato. Crown copyright.
Brown rot
Brown rot or bacterial wilt is caused by the bacterium
Ralstonia solanacearum
. Tubers symptoms include vascu-
lar rotting and pitted lesions (Figure 16.2). In the former a
distinct, greyish brown discoloration of the tuber surface
covers water-soaked tissues. Gray-white droplets seep out
when tubers are cut open. Lesions on tubers are produced
because of infection through lenticels.
Ring rot
Ring rot is caused by the bacterium
Clavibacter michiganen-
sis
subsp.
sepedonicus
and is one of the most damaging dis-
eases of the potato industry. It can be identified from a very
characteristic soft cream cheese-like rotting of the vascular
ring (Figure 16.3). Some external swellings and cracking
may also be visible on infected tubers. Infected tubers of sus-
ceptible cultivars almost always rot during storage, as once
established the bacteria multiply rapidly and a small initial
infection of tubers may result in the total loss of the crop.
Figure 16.3
Ring rot of potato. Crown copyright.
or on plant debris and initiate infection in the crop. Lesions
on infected potato plants produce spores that spread to
healthy plants and cause infection, particularly under
warmer growing conditions.
Dry rot
Dry rot is caused by four different
Fusarium
spp.,
F. avena-
ceum, F. coeruleum, F. culmorum
and
F. sulphureum,
the
latter being the most virulent. A characteristic pattern of
concentric, circular wrinkles can often be seen radiating
around the initial entry wound and later obvious white
mycelial growth. There are differences in the early
symptoms of infection by the different species but typically
infection progresses to a dry and crumbly tuber decay in
which tissue shrinks and collapses. It is often laced with
Fungal rots
Early blight
Early blight is caused by fungal species of the genus
Alternaria
, principally by
A. solani
and
A. alternata
.
Symptoms are characterised by shallow, gray to black, dry
pit-like lesions. Early blight in tubers is often associated
with wounding. The fungus can survive over winter in soil
