Zebra chip

Zebra chip is caused by a bacterial plant pathogen (Candidatus Liberibacter solanacearum), which is carried between plants by psyllid insects.

Background

Candidatus Liberibacter solanacearum was found in potatoes in Mexico and central America during the 1990s. This spread to solanaceous crops in the United States and New Zealand.

The disease was found in carrots in Finland in 2010, which spread to France, Germany, Morocco, Norway, Spain and Sweden. It was also detected in celery, parsnips and potatoes in Spain, and in parsley in the United Kingdom.

Zebra chip is an exotic disease not known to occur in Australia. It is a declared pest in SA and must be immediately reported to protect our horticultural industries.

Impacts

Candidatus Liberibacter solanacearum bacteria are grouped into 5 haplotypes, which target different vegetable crops. The following gene groups have been described:

  • haplotypes A and B infect solanaceous crops such as capsicum, eggplant, potato and tomato
  • haplotype C, D and E infect apiaceous plants such as carrots, celery, and parsley, with haplotype E also affecting potatoes.

All haplotypes are transmitted by plant grafting and vegetative propagation. Different strains can also spread by affected seeds and tissue culture.

The disease travels through psyllids that feed on infected plants, or via transmission of the bacteria through their offspring.

Infected psyllids can fly between host plants or be moved as eggs, nymphs or adults on plant material. They also disperse by aircraft, shipping containers, farm machinery and vehicles.

Vectors

Haplotypes A and B are transmitted by the tomato potato psyllid (Bactericera cockerelli), found in central and north America, Australia and New Zealand.

Haplotype C is spread by the carrot psyllid (Trioza apicalis) which lives in northern Europe, with temperate and sub-arctic climates.

Haplotypes D and E are transmitted by the Bactericera trigonica psyllid which inhabits the Mediterranean regions, in temperate and sub-tropical climate zones.

Management

Growers can apply on-farm biosecurity measures to reduce the risk of zebra chip, such as:

  • using pest-free propagation material and seedlings, sourced from a reputable supplier
  • monitoring host crops with sticky traps to detect psyllid insects
  • removing host weeds from crops and adjacent areas to reduce psyllid infestation
  • putting up biosecurity signs to manage farm visitors and teaching hygiene practices to workers
  • reporting unusual sign of pests and diseases.

Identification

Solanaceous crops

General symptoms affecting these plants include:

  • plant stunting
  • erect new foliage
  • upward leaf curling
  • leaf purpling and chlorosis
  • shortened and swollen terminal internodes, resulting in leaf rosettes, enlarged nodes, axillary branches or aerial tubers
  • small, misshapen fruit.

In potato, the below-ground symptoms can affect the entire tuber. These include:

  • collapsed stolons
  • browning of vascular tissue concomitant
  • necrotic flecking of internal tissues
  • streaking of the medullary ray tissues.

Upon frying, these symptoms become more pronounced, and chips processed from affected tubers show dark blotches, stripes or streaks. This colouring renders them commercially unacceptable and led to the disease being named zebra chip.

Infected tomatoes show stunting, leaf curling, leaf chlorosis or mottling, and have deformed fruit.

Infected capsicums display plant stunting, leaf curling, pale green or chlorotic leaves, sharply tapered leaves, shortened leaf internodes, and flower abortion.

Apiaceous crops

The bacterium can seriously damage carrot and fennel, showing as:

  • leaf curling
  • yellowish, bronze and purplish discoloration of leaves
  • stunting of the carrot shoots and roots
  • proliferation of secondary roots.

Diseased celery plants show an abnormal number of shoots, stem curling and yellowing.

Signs of infected parsley and parsnip plants include yellowing, proliferation and redness of leaves. Although parsley could be a major host for haplotypes D and E, it is not often reported as symptoms are less obvious in this plant.

Carrot plants infected by zebra chip – photo: J.E. Munyaneza, USDA-ARS, Konnowac Pass
Carrot plants infected by zebra chip – photo: J.E. Munyaneza, USDA-ARS, Konnowac Pass
Potato plants infected by zebra chip – photo: J.E. Munyaneza, USDA-ARS, Konnowac Pass (US)
Potato plants infected by zebra chip – photo: J.E. Munyaneza, USDA-ARS, Konnowac Pass (US)

Exotic Plant Pest Hotline

Suspected plant diseases, exotic pests, or noxious weeds must be reported immediately.

Call us if you find plant pests or diseases that could be a national threat, even if you are unsure. This can be done anonymously.

24 hours a day, 7 days a week

Freecall 1800 084 881
Page last reviewed: 17 Nov 2023

 


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