potato disease

موضوع: potato disease الثلاثاء مارس 29, 2011 2:18 pm

[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط]

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Soft, watery rotting of the stem, usually beginning at a point of breakage, which spreads throughout the stem and leaves. The rot quickly develops into death of the plant. Infestation can spread to daughter-tubers, which begin to rot either in the field or later during storage (see: [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط])
Damage

Severe infestation leads to plant death and a consequent loss of yield. Tubers can spoil if conditions for storage and shipping are less than optimal.
Conditions for Development

The disease is transmitted in the field by droplets (from rain or irrigation) and the passage of mechanical tools. Disease development is intensified by dense foliage and high humidity.
Control

Pesticides: Spraying with copper agents can lessen the severity of infection.

Management: Increasing the intervals between irrigation in affected fields

Black Dot

Pathogen: Colletotrichum coccodes
Symptoms

[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط]
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Foliage - Brown spots on leaflets, petioles and stems. Yellowing, wilting and early death. Small black sclerotia develop at the base of the stem, on the stolons and roots.
Tubers - Grayish-brown lesions with sclerotia. Symptoms on the tubers resemble those of silver scurf.
In the field - The wilting and early death are similar to those that occur with Verticillium wilt.
Damage

When infestation is severe, plants collapse and there can be a severe decrease in yield. Tuber quality is also damaged by the development of silvery blemishes and black dots (sclerotia). Latently infected seed tubers can transmit the disease.
Conditions for Development

The fungus can survive for long periods in the form of sclerotia on and within the tubers, and also in vegetative remains. Other solani spps can serve as hosts for the disease. Colletotrichum is considered a weak pathogen that attacks plants under stress conditions, often accompanied by one or more other pathogens. The disease is more severe in light sandy soils, with minimal nitrogen, poor drainage, and high temperatures. When infested tubers are planted in fumigated soil, there can be more severe expression of disease.
Control

Varieties: There can be differences in susceptibility.
Pesticides: Seed treatments and soil treatments.
Management: Use of disease-free planting tubers, crop rotation, appropriate irrigation and fertilization.

Black Scurf, Rhizoctonia Canker

Pathogen: Rhizoctonia solani
Symptoms

Irregularly shaped black sclerotia, which cannot be removed by washing, develop on the tubers. There can be additional symptoms: cracks, malformation and depressions. Necroses at the ends of the buds cause delayed budding, misshapen stems, and weak plants. Brown cankers develop at the base and belowground portion of the stem, and cause collapse of the stem, stunting, the appearance of aboveground tubers, and, occasionally, severe chlorosis of the top of the plant. A light-colored promycelium develops at the base of the stem (the sexual stage of the fungus).
Damage

Severe decreases in tuber quality and yield. The surface of the tuber becomes covered with sclerotia in a variety of sizes and shapes. There are occasionally cracks, depressions and malformations of the tubers.

Conditions for Development

The fungus is maintained and transmitted by sclerotia on the tubers and within the soil or plant residues. With optimal conditions - 18^oC - the sclerotia germinate and penetrate stems, roots and stolons. Development of sclerotia on tubers is pronounced in poorly drained soils. Sclerotia development is accelerated from the time of foliage destruction until harvest.

Control

Varieties: There are no resistant varieties.
Pesticides: Soil sterilization with metham-sodium and methyl bromide, and tuber disinfestation (with rizolex, benzymidazol, etc.).
Management: Using clean manure and disease-free seed tubers, and limiting the amount of time the tubers are left in the soil after defoliation.

Early Blight

Pathogen: Alternaria solani
Symptoms

The disease first becomes evident in senescent leaves, causing dark necrotic lesions in a characteristic concentric pattern. Contamination of the tubers is manifested by dry, dark, round depressions on the peel.
Damage

Severe infestation results in loss of yield, due to early leaf death. Dry rot develops on the tubers during storage.
Conditions for Development

Initial infestation is by wind-borne conidia that penetrate through superficial wounds in the epidermis (such as those resulting from sand storms or insect damage). Infestation of the tuber begins during harvest when foliage comes in contact with the tubers.

Control

Varieties: Most of the early varieties are susceptible; there are some tolerant varieties.

Pesticides: Use of fungicides protects against the disease or eliminates it in the field. Recently, systemic chemicals have been developed.

Management: Avoid irrigating during the hottest hours and immediately after storms. Avoid harvesting non-mature tubers. Protect against insect infestations.

Deep Pitted Scab

Pathogen: Streptomyces spp
Symptoms

Deep (up to 15mm), irregularly shaped scabs on the tuber, accompanied by cracks at the edges of the wounds.
Damage

Sharply decreased quality, infestation of soil and propagation material. The same pathogen can infest peanut, which makes it inadvisable to use these two crops in rotation.
Conditions for Development

The scabs begin to develop within 50 days of planting; they spread and grow as the tuber develops. Soil moisture has no effect on disease severity.
Control

Varieties: Some (e.g. Agria and Desiree) are more susceptible than others (e.g. Alpha and Nicola).

Pesticides: Soil fumigation with methyl bromide or formalin. (Use of methyl sodium is not effective.)

Leak

Pathogen: Pythium ultimum and other spp.s
Symptoms

Dark lesions that spread on and within the tuber and quickly turn to soft rot. A foul odor becomes apparent as other microorganisms begin to develop.
Damage

Complete rotting of the tuber during harvest and storage. Tubers are unusable for propagation. Soil contamination.
Conditions for Development

The pathogen becomes established in the soil by means of oospores (viable on plant residues), and inoculates by directly penetrating into wounds. Most inoculation occurs during the growing season, harvest and grading. Pathogen populations are transmitted in the soil by a variety of hosts (e.g. carrot, pea, peanut, etc.).
Control

Pesticides: Systemic chemicals for control of late blight are generally also effective against leak. If there has been no treatment administered for late blight, systemic fungicides may be applied at the end of the growing season. Soil fumigation may eradicate the pathogen in the soil.
Management: Proper drainage in the field, preventing delay of harvest, taking care not to wound tubers, keeping the storage area well ventilated

Potato Virus X (PVX)

Pathogen: Potato Virus X (PVX)
Symptoms

[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط]

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Chlorotic veins, decrease in size of the leaves, mosaic in the leaves and necrotic lesions in tubers.
Damage

Yield reduction and decrease in tuber quality. Tubers are unusable for propagation.
Conditions for Development

The virus is transmitted by tubers and dispersed by wind, animals, mechanical devices, cutting blades, contact between plants or plant roots, etc. A combination of PVX, PVY and PVA can cause more severe symptoms.
Control

Varieties: There are resistant and tolerant varieties.

Management: Use of disease-free seed tubers, burning infested plants, and restricting movement in infested fields.

Potato Virus Y (PVY)

Pathogen: Potato Virus Y (PVY)
Symptoms

[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط]

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Shortening of the stem internodes, spotting and severe malformation of the upper leaves, defoliation, and early plant death.
Damage

Yield reduction. Affected tubers are unusable for propagation.
Conditions for Development

The virus is transmitted by affected tubers, and is dispersed by aphids from infested plants (potato and other solanaceae spp.); it is also spread by contact. The most severe symptoms result from a combination of [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط] and PVY (streak).
Control

Varieties: Use of resistant and tolerant cultivars.

Pesticides: Control of aphids, high-pressure spraying of oils.

Management: Use of disease-free seed tubers, and burning infested plants

Verticillium Wilt

Pathogen:Verticillium dahliae
Symptoms

The disease causes stunting, wilting, early senescence and total plant death. There is chlorosis on one side of the leaf between the main veins, which develops into necrosis at the edges, causing the leaf to die. Occurrence is usually noticed on one side of the plant. Brown discoloration becomes apparent in the vascular bundles of the stem and tubers. Small dark sclerotia are formed on desiccated stems and roots.
Damage

A considerable decrease in yield, but without damage to visual quality. Seed tubers carry the pathogen in their vascular bundles and can transmit the disease. Infested potato plants that have dried out infest the soil with micro-sclerotia, which can survive for long periods (10-14 years).

Conditions for Development

The fungus penetrates through plant roots, becomes established in the vascular bundles, and spreads systemically. Disease severity can be enhanced by the presence of free nematodes (Pratylenchus) in the soil or of Erwinia (the pathogen responsible for black foot disease) in the mother tubers, or by irrigating with saline water. The disease is most severe during autumn-winter.

Control

Varieties: Tolerant varieties exist.

Pesticides: Soil fumigation with high concentrations of metham-sodium or methyl-bromide eradicates the fungus. Treatment with low dosages of nematicides can also be partially effective.

Management: Use of disease-free seed tubers; crop rotation; use of disease-free manure.

PLRV, Potato Leafroll Virus

Pathogen: Potato Leafroll Virus (PLRV)
Symptoms

[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط]

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Primary symptoms: inward curling of the upper leaves, accompanied by faded color. The curling effect sometimes extends to the lower leaves as well.

Secondary symptoms: plant stunting, stiffening of the leaves (characterized by a rustling sound) and a loss of color intensity. Affected tubers sometimes exhibit necrotic lesions that can spread during storage.
Damage

Yield reduction. Affected tubers are unusable for propagation.
Conditions for Development

The virus is transmitted by affected tubers, and is dispersed by aphids from infested plants (potato and other solanaceae spp., including wild plants). Inoculation is efficient, and is particularly harmful during the plant's early development.
Control

Varieties: Few varieties are resistant to PLRV.

Pesticides: Control of aphids via spraying, soil treatment with systemic chemicals, and high-pressure spraying of oils.

Management: Use of disease-free seed tubers, and burning infested plants

Blackleg and Tuber Soft Rot

Pathogen: Erwinia carotovora var. atroseptica, E. carotovora var. carotovora
Symptoms

Blackening and rotting at the base of the stem; hollowing above the blackened area; stunting and yellowing of the foliage, and upward curling of leaflets. As the disease progresses, the plant wilts and dies. In the tubers, soft black rot begins to develop, usually from the stolon, and develops until the tuber disintegrates. The ability of the tuber to bud is impaired. There is a characteristic foul odor. Rot may also develop on the sides of the tuber lenticels and wounds.
Damage

Plant death and substantial yield loss. Rotting develops in the soil or during storage. Infestation may be latent, and be expressed after planting or during storage.

Conditions for Development

The mother-tuber is the main source of contamination. Cutting of infested seed-tubers can intensify the distribution of the disease in the field. The bacteria survive in plant residues remaining in the soil, are transmitted by free water, and can contaminate neighboring plants. The disease penetrates through cracks in the tubers and lenticels. The disease in the daughter tubers continues to develop in the soil, under conditions of high humidity, and in poorly-ventilated storage areas.
Control

Management: Optimal drainage and aeration of the soil; avoidance of over-watering; removing affected plants from the field and burning them; control of seed production. Sterilization of tools, sorting machinery, etc. Well ventilated storage, and thorough drying of tubers after washing
Potato Diseases - Common Scab

[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط]

Common scab (Streptomyces scabies) is an unsightly disease of potatoes that has very little affect on storability. The blemish is caused by a bacteria-like organism called an actinomycete. Lesions may be circular or angular and may coalesce into large irregular areas. Severity can range from sparse colourless, corky lenticels to dark brown, raised or pitted scabs covering the tuber surface.

The disease is promoted by light free draining soils and dry weather in June/July, when rapid tuberisation takes place.

Common scab might easily be confused with [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط]. However, powdery scabs tend to have a more round character and when coalescing they tend to merge as discrete eruptions rather than one large scab.[/hide]

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