Bacterial ring rot in potato

Clavibacter sepedonicus (synonym: Clavibacter michiganensis ssp. sepedonicus)


Bacterial ring rot of potato is caused by the bacterium Clavibacter sepedonicus and poses a high potential threat to potato production worldwide. Clavibacter sepedonicus is listed as a Union quarate pest .

Damage symptoms

On infected potato plants under European climatic conditions, symptoms in field stands usually appear towards the end of the season. Infected plants show signs of wilting and the leaf margins curl upwards. Subsequently, chlorosis or necrosis often develop on the leaves. As the disease progresses, the leaves dry out from the edges and entire stems may die. Symptoms can easily be confused with symptoms of other wilt diseases or overlaid by other diseases and therefore overlooked.

On infected potato tubers, a slight glassiness or yellowing of the vascular ring is initially evident when the tubers are cut lengthwise, especially in the area of the umbilical end. As infection progresses, the vascular tissue is destroyed and the vascular ring turns brown. When light pressure is applied to infected tubers, a pale, pulpy substance oozes from the vessels. Later, browning appears on the tuber surfaces in the area of the eyes, as well as cracks in the skin. However, the tubers are often latently infested, i.e. they do not show any symptoms of damage.

Host plants

The potato is the most important host plant.


Clavibacter sepedonicus is found worldwide.

Propagation and transmission

One of the most important sources of infection is diseased or, above all, latently infected and thus apparently healthy planting material. The pathogen can also survive on plant residues in the soil. Infected potatoes that have grown through represent a further risk of infection. During planting, harvesting, grading, transport, and storage, infection of healthy tubers can occur through contact with infected tubers or contaminated equipment and storage facilities. When tubers are washed for consumption, bacteria from diseased tubers can enter the wash water.

Economic importance

Bacterial ring rot causes major damage, particularly in North America and Canada. In the EU, the disease occurs sporadically in individual member states. On the one hand, infestation causes yield losses due to reduced growth, reduced tuber set and the death of plants. On the other hand, the quality of the harvested crop is reduced due to the rotting of the tubers, in particular also due to secondary rotting pathogens. In addition, when bacterial ring rot occurs, the farms affected have to take extensive measures, some of which may be associated with high costs.

Prevention and control

  • Use of certified planting material
  • Infestation control towards the end of the growing season (best time: from mid-July until full maturity)
  • Destroy potato overgrowth on possibly infested areas
  • Establishment of closed cycles in the potato processing industry
  • Adherence to a crop rotation of at least three to four years

Phytosanitary status

Clavibacter sepedonicus is listed as a Union aquatic pest and is thus subject to legal regulations to prevent its introduction and spread into or within the member states of the EU.

Last updated: 25.05.2023

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