Results of the EuroBlight potato late blight monitoring in 2023

EuroBlight now reports on the 2023 results. Approximately 2800 samples from 28 countries genotyped.

Distribution of EU43

Results of the EuroBlight potato late blight monitoring in 2023

 

  • Late blight pressure in 2023 was higher than average across many parts of Europe and fungicide resistance issues increased sampling intensity to the highest ever recorded. Disease outbreaks from 28 countries were sampled by 30 teams in 2023 yielding 2830 genotyped samples.
  • The frequency of genotype EU_43_A1 (EU43) increased from 17 % in 2022 to 23 % of the population in 2023. It has extended its range to 10 European countries.
  • A new clone called EU46, related to EU43, emerged in the Netherlands and northern Germany in 2023 and comprised 3.5% of the population.
  • Reports of resistance to the CAA group of fungicides in the EU43 lineage across many regions made disease control challenging in affected areas in 2023. Resistance to the OSBPI group of fungicides was also reported, primarily in genotypes EU43 and EU46 which added to pressures on disease management.
  • EU37 was priviously found to be less sensitive to fluazinam. The reduced use of fluazinam continued to drive down the frequency of EU37 in Europe to 1.8% of the sampled population.
  • Comprising 37% of the 2023 samples, EU36 was the most frequently sampled genotype suggesting it remains fitter than other clones.
  • Primary inoculum is locally generated and spread. Better management of all inoculum sources is required.
  • The proportion of ‘other’ genotypes generated from sexual oospore inoculum was lower at 14.5% of the population but this was influenced by increased sampling in areas dominated by clones.

How did we do it?

Since its arrival in the nineteenth century, Phytophthora infestans, the cause of potato late blight, has remained an ongoing threat to European potato production. Although we are now better equipped to control the disease than in the past, evolving pathogen populations continue to challenge integrated management practices. Changes in P. infestans populations directly influence the deployment of resistant cultivars, the performance of disease warning systems and the efficacy of plant protection products.

Co-ordinated and continuous pathogen monitoring was thus proposed by the EuroBlight consortium in 2013 and has since been implemented as an EU-wide monitoring activity supported by many stakeholders. Such monitoring and characterisation of the population changes and invasive genotypes helps to optimise IPM strategies, as required by EU Directive 2009/128/EC on the sustainable use of plant protection products.

FTA sampling cards onto which lesions had been pressed were returned to laboratories in Scotland and France for pathogen DNA fingerprinting using simple sequence repeat (SSR) markers. Samples were assigned to existing clonal genotypes or defined as new genotypes and all results uploaded to the EuroBlight database. Support from international groups is generating similar data for parts of Asia, South America and Africa, allowing for a more global understanding of pathogen population changes.

After a relatively dry June in many parts, disease pressure was severe from July onwards which, in combination with concerns about fungicide resistance, resulted in the highest ever annual sample size since the EuroBlight monitoring started in 2013. Results for 2830 samples are mapped (Figure 1) and the genotype data from 2013-2023 now comprises over 19,000 samples from 37 European countries and is a valuable dataset.

The transition to relatively new genotypes such as EU36, EU37, EU41, EU43 and EU46 continued in 2023 with 68% of the samples being of genotypes that were unknown nine years ago. Conversely, the older genotypes such as EU_8_A1, EU_6_A1 and EU_13_A2 only represented 17% of the population compared to 68% in 2014.

A marked change in 2023 was the increase in samples of genotype EU43, from 2% of the sampled European population in 2021 to 23% in 2023. Unlike previous years where the increase centred on Denmark, the proportion of EU43 fell from 64 to 20% in this country. Conversely, marked increases in the frequency of EU43 were observed in The Netherlands from to 42 to 55 %, Germany from 7 to 50 % and in Belgium from 12 to 35% from the years 2022 to 2023, respectively. The sampled range of EU43 also widened to include France, Ireland (Kaur et al, 2024) and Spain in 2023 in addition to the seven other countries in which it was reported previously.

It is highly likely that the reported resistance to the CAA fungicides in EU43 (Abuley et al., 2023; FRAC CAA group, 2024) combined with reports of resistance to the OSBPI group in the same lineage in 2023 (FRAC OSBP group) accounts for the dominance of the EU43 lineage in the intensively sampled region of the Netherlands, Belgium and northern Germany in 2023. Industry reports show that there are resistant and sensitive isolates to both fungicide groups in SSR genotype EU43. A key paper on EU43 has been published and FRAC guidelines on the use of both actives have been updated for the 2024 season.

An additional clonal lineage, EU46, was defined in 2023. It was first sampled between the 10th and the 16th July in the Netherlands and northern Germany and increased to comprise 3.6% of the total population by the end of season; and 11 and 14 % of the population in the Netherlands and Germany.  On the basis of SSR marker data this clone appeared genetically similar to EU43 and has also been reported to be resistant to the OSBPI fungicides. Although mostly sensitive to the CAA fungicides there are also reports of resistance to this group in EU46.

As in previous seasons, the single most prevalent genotype sampled in 2022 was EU36 which comprised 37% of the genotyped samples with a dominance across sampled crops in the low countries, France and the United Kingdom. Since its appearance in 2015 it has spread across 21 countries and displaced other older genotypes. This spread, plus evidence from laboratory studies, and anecdotal evidence of it being challenging to manage, suggest it has an increased fitness over other genotypes. For example, in 2023 it comprised 46, 64 and 76% of the samples in Belgium, England and France, respectively. There is no evidence of any widespread shifts in its sensitivity to current fungicide active ingredients. Genotype EU37 continues to decline in prevalence. From an incidence of 14% of the sampled populations in 2017 and 2018 it has reduced to 7-8% over recent seasons and in 2022 and 2023 made up only 2.5 and 1.8% of samples respectively. Since 2018, fluazinam usage has declined which has reduced the positive selection pressure on EU37 isolates in the population. Initial reports suggested it was aggressive and competitive, even in the absence of fluazinam exposure, but the decline of EU37 in the population suggests otherwise. Its reduced incidence supports a continued role for fluazinam in late blight spray programmes when used in accordance with FRAC guidelines. Critically, this demonstrates the value of EuroBlight monitoring which has driven a change in best practice, prevented disease control failures and constrained increases in fluazinam resistance that may have driven the withdrawal of this fungicide from future use.

EU41 was a relatively recent genotype of concern that originated in Denmark in 2013 and then spread to 13 countries. In 2023 its frequency fell to 1% up slightly from 3.3% in 2021. In 2023 it was again sampled from blight outbreaks in Icelandic potato crops.

Older genotypes such as EU13 and EU6 have continued to decline and are confined to countries in the west of Europe. From around one quarter of the population in 2014, EU13 has now declined to only 5% of the 2023 sample.  Although EU6 remains at 11% of the sampled population in 2023, most of these samples were from UK crops.

Other recent genotypes such as EU44, EU39 and EU45 remained localised and rare at less than 1% of the population. Of these EU45 is the most prevalent at 1.4% with clusters in southern Germany, Belgium and France. Lastly, the genetically diverse ‘Other’ samples comprised 15 % of the sampled population in 2023 which was slightly lower than the 22% in 2022 and this reduction probably reflects the more intense sampling of the lowland and western potato growing parts of Europe that are dominated by clones than in recent years. These diverse range of genotypes are most prevalent in crops in the north and east of Europe (Figure 1) and are consistent with a soil-borne source of sexual oospores. There are ongoing epidemiological threats of earlier primary inoculum and evolutionary advantages to sexual recombination generating pathogen phenotypes within these oospore-borne populations.

The genetic diversity of the 2023 population has been visualised (Figure 2) using an analysis tool (poppr 2.0) linked to the EuroBlight pathogen database. The minimum spanning network shows sub-clonal diversity within each of the genotypes (also known as clonal lineages). The clonal and within-clone variation is being used to track the evolution and spread of these pathogen populations across Europe and beyond. ‘Other’ isolates (not shown) are genetically diverse and distributed across the whole network. With reports of variation in fungicide resistance to both CAA and OSBPI fungicides within clonal lineages, the interpretation and spread of the genomic mutations in sub-clonal populations is of increased relevance for effective disease management in the 2024 season.

The 2023 season emphasised the value of the EuroBlight model of pathogen tracking. It continues to provide a cost-effective and co-ordinated approach to understanding pathogen evolution on a European scale. Data on the dominant genotypes have been passed to growers, advisors, breeders and agrochemical companies to provide timely practical advice in support of potato blight control. Given the ongoing drive to more integrated pest management (IPM) approaches and the specific threats posed by CAA and OSBPI fungicide resistance, we propose to continue intense monitoring of the population of P. infestans in 2024. Working with our key sponsors, we will endeavour to provide timely feedback that includes within-season updates whenever possible.

The EuroBlight network continues to harmonise methods with other networks in the Americas, Asia and Africa and encourages continued co-operation between groups involved in managing late blight to exploit the database and tools for improved awareness and blight management on a global scale. Please contact the project team if you would like more information or if you would like to contribute in 2024. We thank all the partners who have contributed samples and thus sponsored this project.

The following participants/sponsors have contributed to the 2013-2023 monitoring.

Aarhus University, ACVNPT, ADAMA, AFBI, Agrifirm, Agricultural Institute of Slovenia, Agrico, Agriphar, Agroscope, AHDB Potatoes, ARVALIS-Institut du Végétal, BASF SE, Bayer AG CropScience Division, Bayerische Landesanstalt für Landwirtschaft, BSV Network (France), Bejo, Centre Wallon de Recherches Agronomiques, CertisBelchim, Cheminova, Corteva, CropSolutions, CUConsulting, CZAV, Delphi, Emsland Group, EMU, Estonian University of Life Sciences, Eurofins, FAB (UK sponsors), Germicopa/ Florimond Deprez, Hochschule Osnabrück, HZPC Holland B.V., INRAE, Institute of Plant Protection and Environment in Serbia, The James Hutton Institute, Julius Kuehn Institute, LfL Bayern, Meijer Potato, Neiker, Nordisk Alkali, NIBIO, PCA, The Plant Breeding and Acclimatization Institute (IHAR), Petla, Profytodsd, RML Iceland, Swedish University of Agricultural Sciences, Solynta, SRUC, SynTech Research, Staphyt, Syngenta,  TEAGASC, Technical University of Munich, UPL, Van Iperen, Vertify, University of Bologna, University of Freiburg, University of Vigo, and Wageningen Research.

Figure 1 Distribution of genotypes in 2023 season.

Figure 2. Minimum spanning network showing the genetic relatedness of genotypes sampled in 2023.

References

Abuley IK, Lynott JS, Hansen JG, Cooke DEL, Lees AK, 2023. The EU43 genotype of Phytophthora infestans displays resistance to mandipropamid. Plant Pathology 72, 1171-344.

Kaur A, Doyle D, Cooke DEL, Mullins E, Kildea S, 2024. First report of the Phytophthora infestans EU_43_A1 clonal lineage and associated PiCesA3 mutation G1105S in Ireland. New Disease Reports 49.

FRAC CAA working group, Annual Meeting Season 2023 on January 16th, 2024.

FRAC OSBPI Working Group, Annual Meeting 7 February 2024.

Contacts

Revideret 27.09.2022
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