EuroBlight, the European network of scientists devoted to examining the ongoing evolution of the potato late blight pathogen, has recently published a report on its 2019 results, where it draws conclusions after examining approximately 1800 samples from 27 countries.

The report points out that three emerging clones of P. infestans (37_A2, 36_A2 and 41_A2) increased their combined frequency from 10% in 2016 to 40% of the population in 2019.

Regional differences exist in the frequency of the emerging clones e.g. the frequency of clone 37_A2 has declined to 10% or less between 2018 and 2019 in the Netherlands and Britain, but remains 25% in Belgium and France. These recent clones are displacing the established 13_A2, 6_A1 and 1_A1 clones which decreased in frequency from 60 to 30% of the samples collected between 2016 and 2019.

A quarter of the population comprised ephemeral, genetically diverse isolates consistent with oospore-borne inoculum. A regional pattern in the dominance of clones versus sexual recombinants was observed across Europe. The weather in 2019 was dry and unfavorable for late blight development in some regions, but very convenient for blight in others like Denmark and Northern Britain.

EuroBlight ran a coordinated sampling campaign involving the industry and many research institute partners, and analyzed the sampled isolates using SSR genotyping at the James Hutton Institute and INRAE (French public research institute) as in previous years.

Despite the overall low disease pressure in 2019, 17 partner organizations collected over 1900 FTA card samples from 27 European countries, from which 1816 generated genotype data. The genotype data from 2013-2019 now comprises over 10000 samples from 35 European countries.

Over the last seven years, 60-79% of the sampled population comprised known clonal lineages that recur over multiple seasons. The remaining samples were novel, genetically diverse genotypes, found at a single location in one season and grouped in a category termed ‘Other’.

For the first time since 2013, the clonal lineage EU_13_A2 (blue-13) was not the most frequently sampled and dropped to 9.3% of the samples collected. Although in decline, this metalaxyl-resistant clone is widespread and continues to affect disease management efficacy in Europe, parts of Asia and North Africa. The frequency of EU_6_A1 rose to 20.4% due to severe outbreaks in parts of Britain where it remains dominant. The frequency of EU_1_A1 further decreased from 1.6 to 0.4% of the population.