Potato Review Group

Contents

Background

Symptoms of Verticillium wilt

Alternative hosts

Soil test for Verticillium

Control of Verticillium

Further information:

Verticillium wilt notes

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Background

  1. The disease may be caused by two species of fungi:
    • Verticillium albo-atrum
    •  Verticillium dahliae
  2. Verticillium wilt may reduce tuber yield by as much as 70 %. More …
  3. Verticillium wilt may occur in crops showing patches of early senescence.
  4. Propagules may occur in soil as microsclerotia of V. dahliae or resting mycelium of V. albo-atrum.
  5. Propagules may be moved within fields or between fields by:
    •  soil on machinery
    •  blowing dust
    •  irrigation water
  6.  Propagules may be introduced in soil on seed tubers but mycelium within infected seed tubers is considered to be of relatively minor importance.
  7. Propagules may remain viable for several years.

More …

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Symptoms of Verticillium wilt

  1. Verticillium infects through the roots, hyphae grow into the vascular system and leaf area of infected stems may be restricted.
  2.  As the disease develops, lower leaves wilt, become chlorotic and finally necrotic. Symptoms progress up the stem until the stem becomes desiccated and dies.
  3.  One or more stems on a plant may be infected while other stems on the same plant show no symptoms.
  4. Symptoms may occur on only one side of a stem or leaf.
  5.  If infected stems are peeled or cut at a sharp angle at ground level, tan or light brown coloration of the xylem may be seen.
  6.  Severe infection may result in premature crop senescence.
  7. Tubers on infected plants may show signs of vascular browning.
  8. The symptoms may be confused with those of the following diseases, which may also be confused with each other:
    • stem canker (Rhizoctonia)
    • Fusarium wilt
    •  pink rot (Phytophthora erythroseptica)
    •  black leg (Pectobacterium)
    •  ring rot (Cornynebacterium)
    •  brown rot (Ralstonia solanacearum)
  9.  Positive identification may require isolation of the fungus.

More …

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Alternative hosts

  1. Agricultural and horticultural crops including:
    • linseed
    • cotton
    • tomatoes
    • aubergines
    • strawberries
    • raspberries
  2.  Weeds including:
    • Chenopodium album
    • Capsella bursa-pastoris
    • Taraxacum spp.
    • Equisetum arvense
  3.  Many species of trees.
  4. Non-susceptible crops include:
    • cereals
    • grasses
  5. It is often suggested that Verticillium wilt is exacerbated by nematode infection (free-living and potato cyst nematodes).

More …

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Soil test for Verticillium

  1. There is a test for V. dahliae available which was developed for the strawberry industry and is performed by FERA.
  2.  A 2 kg soil sample, comprising 50 sub-samples, should be taken with uniform distribution from an area of 1 ha.
  3. There is circumstantial evidence that crops may be at risk of early senescence if soil contains > 4 propagules / g soil.

More …

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Control of Verticillium

  1. Experiments with soil applied chemicals have resulted in only small reductions in infection. More …
  2. Plants which are infected with Verticillium may be more susceptible to black dot.
  3. Application of azoxystrobin (“Amistar”) to soil has been shown to reduce black dot while having little affect on Verticillium infection.
  4. Other experiments have shown some reductions in Verticillium after soil amendment with organic materials. More … and more …
  5. Flaming of potato haulm has also been shown to result in some reductions in Verticillium populations.
  6. Long rotations with non-host crops and good control of weeds can help to minimise build up of Verticillium in soil.

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Further information

Verticillium wilt notes

Verticillium wilt 2017 (Symptoms; biology; alternative hosts; influence of soil conditions; soil test)

Verticillium wilt 2005 (Population change during crop growth; experiments on chemical applications to soil)

Verticillium wilt 2001 (Verticillium species; yield loss; effects of soil amendments)

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