News report | 06-01-2026 | 08:00

The NVWA has discovered a new variant of the fungus that causes wart disease. This is already the third new pathotype (physio) detected in the Netherlands since 2020. This new finding shows that wart disease is no longer stable, making it more difficult to combat and control this potato disease. The NVWA is researching a new approach to the disease. In the current situation, it is especially important that potato growers work hygienically to prevent the spread of wart disease.

Warts on highly resistant variety

The NVWA examined material from wart disease findings from 2022-2024 in the laboratory. During the examination of material from 2023, an unexpected reaction occurred. The wart material from 2 findings was able to form warts on Belita, a potato variety previously considered highly resistant. Wart formation on this variety had not been observed before.

The outcome of the research was so unexpected that the NVWA conducted additional tests. It appeared that the wart material contained a new pathotype. This has no official name yet but is provisionally called SenBelita breaker.

Third new pathotype within 5 years

This new pathotype is not alone:

  • At the beginning of 2025, after laboratory research on wart material from 2023, a new pathotype was identified: pathotype 42 (Erica). This breaks the resistance in the Seresta variety. The NVWA has informed sector organizations about this.
  • In 2020, pathotype 38 (Nevşehir) was first detected in the Netherlands. This pathotype was found at 6 locations in 2020, 2021, and 2022.

Within 5 years, 3 new pathotypes have been found in the Netherlands. They mainly occur in areas in the northeast where potatoes are grown more intensively.

In 2025, there was one finding of wart disease in the municipality of Midden-Groningen. An NVWA inspector found symptoms of wart disease on the Festien and BMC varieties. It is not yet known which pathotype it was. This will be investigated in the coming months.

Fungus changes

Molecular research confirms the suspicion that the fungus causing wart disease changes faster. This is probably because the fungal populations exchange genetic material during multiplication. New variants can then arise, increasing the risk of resistance breakdown.

It is expected that there are more new variants of wart disease and that more will appear. This makes laboratory research less reliable when wart disease is found. For example, it is possible that wart material used in research does not contain all the diversity of the local fungal population. This also makes it harder to determine if a potato variety is resistant to the fungal populations in that area.

Uncertainty for potato growers

The main tool to combat and control wart disease is the use of resistant varieties on the buffer zone (the part of the plot next to an infection). But in the new situation, it cannot be said with certainty whether a variety is resistant.

As a grower, you therefore do not know for sure which variety you can safely grow on the buffer. It is especially unfortunate that using a susceptible variety carries the risk of developing new pathotypes. If you see symptoms of wart disease in your crop, you should report this to the NVWA via info@nvwa.nl.

The NVWA is working with sector organizations, researchers, and breeders to find a solution for this uncertain situation. As soon as there is more clarity, we will report it on nvwa.nl. In the meantime, it is especially important that you take measures to prevent the spread of wart disease, for example through good farm hygiene.

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