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Source: European Plant Protection Organisation (EPPO) Reporting Service 09/2021/200 [summ. Mod.DHA, edited]

The National Plant Protection Organisation (NPPO) of the Netherlands has reported the 1st detection of the pathotype 38 (Nevsehir) of _Synchytrium endobioticum_ (EPPO A2 List, agent of potato wart disease). The pathogen was detected in October 2020 in 3 fields (total of 14.43 ha) in the province of Groningen [ProMED post 20201214.8018156). Potatoes presented typical warts.

A pathotype was determined by bioassay in combination with sequencing of the mitochondrial DNA of the isolates. It is the 1st time that this pathotype is found in the Netherlands. The NPPO considers that the source of the outbreak is outside the country. Pathotype 38 is only known to occur in Turkey (where it was initially reported), Bulgaria, and Georgia.

Phytosanitary measures are being taken. All the fields have been demarcated as infested for at least 20 years. The production of potatoes is prohibited in the infested area, and only resistant potato varieties may be grown in added buffer and safety zones. The production of plants for propagation (e.g., seed potatoes) is prohibited in all these areas.
Communicated by:

[Potato wart disease (PW) is caused by the fungus _Synchytrium endobioticum_, which is considered one of the most important pathogens of the crop. It is endemic in Europe and has also been reported from a number of locations in the Americas, Australasia, and Africa. The pathogen can also affect tomato and some solanaceous weeds. On infected tubers, "eyes" develop into characteristic warty, cauliflower-like swellings. If infected early, the whole tuber can be replaced by a warty proliferation. Warts darken with age, eventually rot, and disintegrate. Plant vigour is reduced, and both quantity and quality of harvested tubers are severely affected. Diagnosis requires laboratory confirmation, as similar symptoms can be caused by other pathogens. The fungus goes through cycles of proliferation and re-infection as long as cool, wet conditions prevail and is, therefore, less damaging in warm, light, well-drained soils.

The disease is spread with soil (for example on farm tools), by infected seed tubers, and also in manure from animals fed on infected potatoes. The fungus can survive in soil for up to 40 years in the absence of a host. Disease management is based on pathogen exclusion by quarantine regulations and the control of local pathogen spread. Use of certified clean seed tubers is crucial; contaminated seed lines pose major risks of losses both in yield and international trade. Fungicides are ineffective, but some experimental fumigation treatments have been shown to kill resting sporangia (see link below).

There are several pathotypes defined by their virulence on different host cultivars. Potato varieties resistant to a number of them have been developed, but new pathogen strains are emerging, compromising the efficacy of host plant resistance.

A wart outbreak of unknown origin was also reported from Germany (ProMED post 20200223.7017959) from Lower Saxony, which borders the Dutch Groningen province. It still seems unclear whether the 2 outbreaks may be due to a joint incursion of the same pathotype or are in any other way related.

Netherlands: (with provinces)
Europe, overview:

Potato wart symptoms:, and
_S. endobioticum_, microscopy:

Information on potato wart disease: (with country information),,,, and
Potato wart life cycle:
_S. endobioticum_ taxonomy:
EPPO A2 quarantine list:
- Mod.DHA


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