The NVWA detected brown rot infections in September and October at two different companies in Friesland. In total, three seed potato batches were affected. Measures have been taken to destroy infected batches and prevent the spread of the brown rot bacterium.
During the comprehensive testing of seed potatoes in the Netherlands, seed potatoes are tested for two bacterial diseases that have quarantine status in the EU: Ralstonia solanacearum, the cause of brown rot, and Clavibacter michiganensis, the bacterium that causes ring rot.
First detection
At the beginning of September, the first detection of brown rot was made in a seed potato batch at a company in the north of the Netherlands (Friesland). At the beginning of October, a second batch of seed potatoes was found to be infected at the same company. The batches have been multiplied on the company’s own premises in recent years. Nothing from the infected batches has been delivered to other companies. Further investigation at the company did not reveal new infections in seed potatoes. Measures are being taken to destroy infected batches and prevent the spread of the brown rot bacterium. The introduction of the infection most likely took place in 2024 through contact with contaminated surface water. The infected seed potato batches were located close to each other along the same watercourse in 2024. This watercourse tested positive for the presence of the brown rot bacterium during the tracing investigation this autumn.
Tracing investigation at second company
At the beginning of October, a third detection of brown rot was made in a seed potato batch at a second company in the north of the Netherlands (Friesland). This concerns a combined batch of 2 clonal lines originating from two different seed potato suppliers in 2023. The tracing investigation is still ongoing. Clonally related batches delivered to two other companies in 2023 are currently still under investigation. A sister batch of the infected batch delivered in 2024 tested positive for brown rot in Germany. The investigation into the possible source of infection is still ongoing.
Measures
When a seed potato batch is suspected, the company concerned is recorded. The entire potato cultivation on the company and the clonal line of the suspected batch are mapped. Risk factors such as water use and machine contacts are also examined. Subsequently, all seed potato batches on the company are sampled. If an infection is suspected from the clonal line, all delivered sister batches are also included and recorded in the investigation. Ultimately, infected batches must be destroyed. If a batch is not found to be infected but there are reasons to believe that the batch has been in contact with an infection, the batch is declared probably infected. The batch then loses its seed potato status. The tracing investigation will further determine whether it is possible and responsible to allow seed potato cultivation on agricultural land belonging to the company in the first year after the infection.
For more information, visit Brown rot (Ralstonia solanacearum and Ralstonia pseudosolanacearum).
