Marked variation in countries’ potato blight samples

While overall frequency of newer blight strains increased in 2025, EuroBlight results reveal clear differences in sponsors’ samples, with some seeing decreases and Denmark having no detection of EU46 whatsoever.  

MORE than 1,200 samples from sponsors across Europe were genotyped but sample numbers were much lower in some key countries, according to Dr David Cooke.

“For example, the Netherlands, Germany and Belgium collected over 1,000 samples in 2024 but only 166 in 2025. This smaller sample means results may be influenced more by trial sites or specific local outbreaks.”

The overall frequency of EU43 had decreased from 23% in 2023 to 9% in 2024 with a slight increase to 12% of all early samples in 2025, and a marked variation between countries

The Netherlands reported 20%, from a sample of 69. Germany reported 12% from a sample of 58; Belgium 13% from a sample of 30 and Denmark 4% from a sample of 103. France had a notable increase from 10% to 25%, from a sample of 345.

Although the frequency of EU46 sampled across European crops increased from 4% in 2024 to 7% in 2025, again there was considerable regional variation. The strain decreased in the Netherland to 1%, from a sample of 69, while it increased in Belgium and Great Britain, to 5% from a sample 39 and 20% from a sample of 278 respectively.

It was not detected in Denmark, from a sample of 103.

Key findings so far are:

• The P. infestans population in Europe remained dominated by the EU36 genotype, which made up around one third of samples.
• The decline in EU43 has stabilised. Its overall frequency rose slightly but increased strongly in France. EU43 was also found in Switzerland and Latvia for the first time.
• EU46 increased from 4% to 7% of samples and spread to more countries, including England, Norway, Sweden, Latvia and France.
• EU36 dominated in western and central Europe, while more genetically diverse “other” types were more common in north-eastern Europe. 
• The relatively new clones, EU43 and EU46, with reported resistance to some active fungicide ingredients, have been broadly suppressed through modified approaches to fungicide use, with more mixing and alternation of the Fungicide Resistance Action Group (FRAC) active ingredient groups.  More information on EU43 and EU46 and fungicide resistance can be found in this recent paper, New Mechanisms of Resistance to CAA and OSBPI Fungicides in Phytophthora infestans.

With EU36, there was a fall in overall frequency from 52% in 2024 to 34% in 2025. Once more, there was considerable regional variation, with it making up 43% of samples in the Netherlands, 64% in France and 74% in Belgium. Bar a single sample in Denmark, it was not found in the Nordic countries.

Other blight clones of note included:

• EU41 increased slightly from 2% in 2024 to almost 5% in 2025 and remains localised, mainly in Norway and Denmark, where it comprised 2-5% of the population and in Scotland, where it comprised 25% of the 113 samples.  In Denmark, all 10 isolates of EU41 were found at the same trial location.
• EU45 which had been steadily expanding after its initial sampling in 2019, to comprise 4% of the samples in 2024, fell to 1% with its range expanded to eight countries, including Poland
• EU37, which is resistant to fluazinam, stayed at a very low level, around 1%, compared to its high of 14% in 2017 and 2018.
• EU47, which has novel virulence against R8 and R9 resistance genes, was first reported in 2024 but was not detected in 2025. This may be linked to the reduced blight pressure and smaller population size.

Around one third of samples fell into the highly diverse “Other” category, double the proportion seen in 2024. This is owing to a higher proportion of 2025 samples from northern and eastern regions that are not dominated by clonal populations of P. infestans. In Denmark and Norway, for example, 85% of samples were classed as “Other”. Data from many years shows a consistent incidence of highly-localised and ephemeral multi-locus genotypes that do not reach the threshold for being named as clones. This is consistent with oospore inoculum in the soil that germinates and causes.

2025 potato blight campaign kicks off

FIVE-YEAR STUDY BEGINS THAT WILL DETERMINE POTATO BLIGHT CAUSES

SILICON PRODUCTS SHOW POSITIVE POTATO BLIGHT DEFENCE