Friday, September 11, 2009

Nonvirus Leafroll

Potato leaves roll upward for several reasons, not necessarily because of virus leafroll.
Varietal response to environmental factors—especially inadequate nutrition or intense light and long days—causes relatively uniform leafrolling throughout a field or a portion of it, in both symptom severity and time of onset.

Leafroll may also be due to genetic factors influencing the response of certain clones, and can cause variability in potato populations grown from true seed.

Rolling caused by improper plant nutrition is not fully understood. Mineral deficiencies involving minor elements and nitrogen toxicity are important.

Aphid populations on the plant can cause toproll in the absence of the leafroll virus.
Nonvirus leafroll is not infectious and leafrolled plants usually yield well.
Proper diagnosis of leafrolling is particularly important in potatoes seed programs.

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Potato Yellow Vein Disease

Potato Yellow Vein Disease is common in some countries in South America. It is apparently caused by a virus transmitted by the whitefly Trialeurodes vaporariorum.

Symptoms of Potato Yellow Vein Disease

Soon after infection, bright yellowing of minor veins (tertiary) is evident.
As potatoes disease progresses, secondary veins and leaf lamina become yellow, usually leaving primary veins green.
Stunting or weakness of the plants have not been detected, but tuber yield can be reduced by 50%.
Secondarily affected potatoes plants show vein yellowing right after emergence.


Attempts to control the vector by pesticide applications have led to an increase in disease incidence because populations of natural biological control are affected.

Elimination of infected potato plants in and around fields, as well as weeds such as Solanum nigrum and Lycopersicon sp., reduces sources of infection.

The practice of interplanting beans with potatoes should be avoided because populations of the vector increase in beans.

Planting seed potatoes produced in areas where the disease does not occur also prevents having sources of infection for the potato crop.

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Thursday, September 10, 2009

Fusarium and Verticillium Wilts of Potato

Crop of potato may be infected by the fungi that cause Fusarium wilt and Verticillium wilt.
The wilt organisms usually enter the potatoes plants through young roots and then grow into and up the water conducting vessels of the roots and stem.
As the vessels are plugged and collapse, the water supply to the leaves is blocked. With a limited water supply, leaves of plants begin to wilt on sunny days and recover at night.
Wilting may first appear in the top of thepotatoes plants or in the lower leaves.
The process may continue until the entire plant is wilted, stunted, or dead. Although potato plants may recover but are they become usually weak, unthrifty, and produce fruit of low quality.

Symptoms Fusarium Wilt

Fusarium wilt symptoms in potato as slight vein clearing on outer leaflets and drooping of leaf petioles.
Potato tubers may show browning of the vascular ring as well as browning at the stem end and decay where stolons are attached.

Verticillium Wilt

Verticillium wilt symptoms on potato are similar to those of Fusarium wilt. Often no symptoms are seen until the plant is bearing heavily or a dry period occurs.
The bottom leaves become pale, then tips and edges die and leaves finally die and drop off. V-shaped lesions at leaf tips are typical of Verticillium wilt of tomato. Infected plants
usually survive the season but are somewhat stunted and both yields and fruits may be small depending on severity of attack.
In potatoes the pathogen may be part of a complex that includes, among others, the root lesion nematode and the bacterial soft rot organism, resulting in premature plant death (“potato early dying disease”).
Tubers from Verticillium infected plants may show light brown vascular discoloration, usually restricted to the stem end.
Brown streaks in the vascular tissue can be observed well up into the plant, which rapidly collapses and dies.

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Thecaphora Smut potato disease

(Cased by Thecaphora (Angiosorus) solani )

Potato smut is restricted to the tropical regions of the America. It occurs in cool highlands and irrigated coastal deserts, where it may cause serious problems.
Little is known about its biology. Extreme care must be taken to avoid spreading the disease. Therefore, do not move infected tubers or infested soil to disease-free areas. Occurrence of this disease should be carefully recorded.

Symptoms of Thecaphora Smut

Symptoms are tuber-like outgrowths of stems and stolons that contain numerous small cavities filled with brown to black spores.
Potatoes tubers may contain small, inconspicuous superficial pustules with a few sporefilled cavities or large protuberances.
Single potato plants and even single stolons may carry tuber-like outgrowths as well as healthy-appearing tubers.
After maturity, diseased outgrowths disintegrate rapidly into masses of brown spores.
Certain potato cultivars such as Antarqui show protuberant lesions 3-10 mm in diameter on the tuber surface.

After 2-3 months of potatoes storage, these lesions become sunken and subsequently hypertrophied tissues develop in the new sprouts or close to them. Datura stramonium (jimson weed) is a sensitive and propagative host.


Dissemination is probably by infected or contaminated seed and soil. Resistant or tolerant varieties exist.
Crop rotations are useful although the fungus persists in fields for many years. Strict quarantine should be enforced to prevent spreading the disease to new areas.
Fumigation of infested soil, complemented with the use of healthy potato seed tubers of resistant potato cultivars, can eliminate the disease.
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