Bacterial wilt, scab and soft rot of potato

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Bacterial wilt, scab and soft rot of potato
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Bacterial Wilt or brown spot (Ralstonia
solanacearum)

• Symptoms
• The disease affects both above and underground
  parts of the plant.
• Infected plants show sudden wilting and complete
  collapse of plants.
• Vascular browning is the characteristic symptom
  of the disease.

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• Bacterial mass ooze out from the cut ends of the
  stem.
• Infected tubers are the main source of infection
  from one place to another.
• Bacteria spread from plant to plant by root
  contact or through water films.
• Increase in the temperature enhances wilting and
  high soil moisture favours survival of pathogens
  in soil.

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Epidemiology

• Infected tubers are the main source of infection
  from one place to another
• Bacteria spread from plant to plant by root
  contact or through water films
• Increase in the temperature enhances the wilting
  and high soil moisture favours survival in soil

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Management (Bacterial wilt)

• Use of disease free tubers for planting.
• Crop rotation with non host crop plants
• (maize, sorghum, garlic, onion, cabbage etc)
• Avoid injuries to the tubers during intercultural
  operation.
• Seed tuber treatment with bio control agents
• ( Bacillus subtilis, Pseudomonas florescens)

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Potato scab (Streptomyces scabies)

• It is caused by a soil borne pathogen. The same
  organism also attacks many other root crops like
  beet, radish, turnip and carrot.
• Symptoms
• Two phases of scab viz. shallow and deep scab are
  found.
• Shallow scab consists of a superficial rough area
  on the skin of tubers.
• Deep scab consists of lesions which are 1-3mm or
  more deep and darker than the shallow lesions.
• The tissues of the pits are corky in both the
  phases.

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Epidemiology

• Pathogen introduce into the soil through infected
  tubers and survives indefinitely once soil is
  contaminated
• Survive on decaying plant debris

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Management

• Use disease free seeds
• Green manuring before planting will reduce
  infection
• Irrigate the land at regular intervals for
  keeping the soil moist from the time of
  tuberization. This will check the disease
  incidence

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Soft rot black leg (Erwinia carotovora)

• Symptoms
• It occurs in two phases viz., black leg of shoots
  and soft rot of tubers. In black leg phase, black
  lesions appear at base of the stem followed by
  yellowing, rolling of top leaves
• Tuber develops water soaked areas which rot and
  emit an offensive odor in the soft rot phase
• Small sunken areas develop on tuber surface

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Epidemiology

• Moisture and temperature are factors affecting
  soft rots
• Infection occurs at 94 100 Relative Humidity
  and temperature of 21-29 0C
• Immature tubers are more susceptible

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Management

• Cut and injured tubers should be discarded
• Avoid prolonged wetting of tubers
• Store and transport the tubers under well
  ventilated conditions.