Showing posts with label Diseases. Show all posts
Showing posts with label Diseases. Show all posts

Friday, September 11, 2009

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.

Management

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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