Potato Review Group

Contents

Background

Control

Further information:

Brown rot notes

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Background

  1. Cause
    • Brown rot of potatoes is caused by Pseudomonas solanacearum, a non-spore forming, non-capsulate, Gram negative, aerobic bacterium.
    • Strains vary in the adaptability to the environment and to host species.
  2. Environmental requirements
    • Temperature: optimum 30 to 37 oC, declining at 43 oC, uncommon below 15 oC. Race 3 (race infecting potato), optimum 27 to 28 oC.
    • Moisture: survival and infection favoured by high soil moisture, easily desiccated.
  3. Hosts
    • Members of the Solanaceae including potatoes, tomatoes, tobacco, solanaceous weeds e.g. nightshade.
    • Also a wide range of other crops.
  4. Symptoms
    • Wilting of foliage, leaves become chlorotic and die.
    • Vascular bundles in the stem become infected with bacterial slime, visible as dark streaks on the stem; cut surfaces ooze slime.
    • Tubers develop a brown coloration on the vascular ring, which exudes bacterial slime if compressed.
    • Apical eyes of the tuber exude slime, to which soil particles adhere.
  5. Modes of dispersal and sources of inoculum
    • Inoculum is mainly soil borne, infection is generally introduced through seed tubers and remains in the soil, associated with plant debris and solanaceous weeds.
    • Persistence may be for up to two years although little is known of persistence in cool, temperate conditions.

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Control

  1. Use disease free seed.
  2. Rotation: persistence measured as 2-3 years but circumstantial evidence for 7+ years.
  3. Genetic resistance: related to resistance to infection and heat tolerance of the cultivar.
  4. Soil type: chalky soils may suppress P. solanacearum.
  5. Soil amendment: possible effects of calcium and sulphur; interaction of other nutrient deficiencies with cultivar resistance.
  6. Control of nematode populations: synergistic interaction with root knot nematode.
  7. Chemical control: soil fumigants, some effects of MBC, dinitroaniline herbicides (historical).
  8. Biological vaccination: pre-treatment with avirulent strains of P. solanacearum (experimental)

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Brown rot notes

Brown rot 1996 (Symptoms; biology; control)

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