Biotic Diseases
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Transcript of Biotic Diseases
Biotic Diseases
Fungal diseases
Powdery Scab of Potatoes
caused by Spongospora
subterranea
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 potatoescaused by Synchytrium
endobioticum
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 cruciferscaused by
Plasmodiophora brassica
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 Cruciferscaused by Albugo candida
Causative organism: Albugo candida
Obligate parasite caused white rust disease.
Sporangia (conidia) constitutes the asexual stage. Fertilization is
achieved by club-shaped antheridia and single oospered
oogonium.
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
caused by
Phytophthora infestans
Causative organism: Phytophthora infestans
Phytophthora infestans causes destructive disease of member solanaceae as potato and tomato known as late blight. The asexual units behave as conidia depending as environmental conditions. Sexual reproduction is achieved by oogonium and antheridia
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
caused by Taphrina deformans
Taphrina deformans (Exoascus) caused peach leaf curl.
It composed of septated hyphae consisting of binucleated cells
(dikaryotic hyphae) which bear terminal ascogenous cells
(chlamydospores). Each cell developed into single ascus with
no protective sheath (no peridium).
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.