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Biotic Diseases
Fungal diseases
Powdery Scab of Potatoes
Causative organism : Spongospora subterranea
Symptoms
The disease causes severe
blemishes (2-20 mm diameter) on
the tuber. These blemishes contain
dark-colored spore balls.
Symptoms
Powdery scab is more prevalent in
cool, damp growing seasons.
The disease causes severe blemishes
that spread beneath the epidermis and
erupt when the tuber emerges.
In severe cases, the tubers are
malformed
and
covered
with
unattractive secondary growths. Deep
cracks could appear.
Wart disease of potatoes
Causative organism : Synchytrium endobioticum
Symptoms
Tubers, stolons and occasionally leaf stalks affected, but not roots.
Tubers may bear cauliflower-like tumors at the eyes or whole tuber may
become shapeless warted mass. May progress in store even from minute
warts not seen at lifting.
Organism in soil, may remain infective for more than 30 years. Spread on
implements and in dung from stock fed with infected tubers. More severe in
wet seasons.
Club root of crucifers
Causative organism : Plasmodiophora brassica
Symptoms
The first symptom usually observed is a wilting of the foliage especially on hot
days. Wilting is the result of impaired root function which reduces the capacity of
the plant to take up water. The diseased roots are also less able to absorb nutrients
and so the foliage may appear yellowish and the plant may be stunted. Although
these above-ground symptoms could be due to other causes, an abnormal
enlargement of the roots is diagnostic for this disease. The fungus penetrates the
roots directly or through wounds and induces the root cells to enlarge. The
resulting enlarged roots appear spindle-shaped, knobby, spherical, or club-shaped.
All roots including the underground stem may be affected .
White Rust of Crucifers
Causative organism: Albugo candida
Symptoms
The symptoms appear as shiny white postulations on the leaf
and stem due to the formation of sori containing conidiophores.
Late Blight of Potatoes
Causative organism: Phytophthora infestans
Symptoms
The disease strikes down plants like a hard frost in summer. It spreads so fast.
It reduces the foliage to a putrid mass in a few days, and the tubers are affected
to various degrees in a similar way, although they do not rot as rapidly. Wilting
of young leaves are the first symptoms. Leaf margins begin to turn brown and
entire leaves will die.
Peach leaf curl
Causative organism : Taphrina deformans
Symptoms
Taphrina deformans can infect leaves, fruits,
and young twigs. Infected leaves become
distorted, puckered, and thickened, initially with
a distinct reddish or purple coloration.
As infection progresses, affected leaves turn
gray with a powdery appearance as a result of
the production of fungal spores on the leaf
surface. Shortly thereafter these leaves turn
yellow or brown and drop. Fruit, which
becomes infected, tends to drop shortly after
infection occurs. Infected twigs are swollen and
stunted, usually with deformed leaves at their
tips.