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Thecaphora Smut

(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

thecaphora-smutSymptoms 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. A

fter 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.

Management

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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Verticillium Wilt

(Verticillium albo-atrum, V. dahliae)

Verticillium wilts may be a serious problem in tropical and subtropical regions and irrigated deserts where water deficiency may be severe. V. dahliae is more severe during prolonged warm, dry weather in cooler regions of potatoes production.

Symptoms of Verticillium Wilt

This potato disease is characterized by leaf yellowing, which begins at the plant base and may develop unilaterally, restricted to the sides of leaves, the stem, or the plant.
verticillium-wiltLater, the plant may wilt. The vascular system of the lower stem turns brown. Potatoes plants frequently become yellowed and mature early without pronounced wilting (early dying).
Stems wilted by V. albo-atrum are blackened by the presence of a blackish resting mycelium.
However, when V. dahliae causes wilting, the lower portion of the stem becomes grayish because of the presence of microsclerotia.
The vascular ring of tubers may have light brown discoloration extending from the stolon end up to more than halfway through the potato tuber. Larger tubers often have light tan, discolored eyes (pink eye).
These fungi are long-lived in soil or plant debris and have a wide host range, including other solanaceous plants, cotton, and weeds.
Surface-borne inoculum on seed tubers is important in disease spread. Interaction with nematodes (Meloidogyne, Pratylenchus, Globodera), fungi Rhizoctonia, Colletotrichum, Fusarium), and bacteria (Erwinia) can increases damage.

Management

Use crop rotations with nonsusceptible cereals, grasses, or legumes. Resistant or tolerant potato varieties are available.
Treat potatoes seed tubers with disinfectant fungicides to remove soil-borne inoculum. Prevent water stress by irrigation.
Systemic fungicides are useful while growing potatoes.

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Fusarium Dry Rot and Wilt

(Fusarium spp.)

Different Fusarium species distributed worldwide cause various problems. Warm temperatures favours this disease.

Symptoms of Fusarium Dry Rot and Wilt

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Dry rot is one of the most serious potatoes storage problems. Tubers initially have dark, slightly sunken lesions that later expand superficially, leaving internal cavities that may contain different colour mycelia, depending on the species involved.
The margin of the rot is clearly defined.
Concentric rings appear on the potatoes tubers surface and external mycelium is evident.
Potatoes tuber dries and hardens.
Under humid conditions, secondary soft rot develops. Infection originates in surface fusaruim-dry- rot-wiltwounds during harvest and handling.
It can be reduced by initial curing at about 15°C and 95% relative humidity to promote wound suberization, prior to cold storage.
Improperly suberized cut seed decays under adverse soil conditions.
Potato plants may fail to emerge, or be weak and subsequently wilt and die.
Fusarium wilt fungi are soil-borne.
Symptoms are yellowing of lower leaves, chlorotic mottle of upper leaves, and subsequent wilting.
Vascular tissues of stems and tubers become discolored.
Potatoes tubers show several types of internal and external discoloration such as brown sunken necrosis at the stolon attachment or eyes, and circular brown rotted areas.
Warm weather enhances wilt. Some Fusarium strains become systemic and are seed transmitted.

Management

Use disease-free potatoes seed, good water management, and crop rotation. Treat cut seed with chemical protectants.


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