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http://www.promedmail.org

Source: Potato News Today [abridged, edited]
https://www.potatonewstoday.com/2021/05/01/late-blight-studies-reveal-evolution-of-potato-disease-in-europe-and-asia/

The EuroBlight consortium has tracked the European spatial distribution of _Phytophthora infestans_ since 2013 and has added new data that visualises the distribution and diversity of dominant clones in the 2020 crop. The report [see link below] collates information from 1221 samples collected in 28 countries and genotyped in 2020.

'FTA cards' [chemically treated filter papers designed for the collection, preservation, and shipment of biological samples for subsequent DNA and RNA analysis] were distributed to disease 'scouts' who visited blight-infected crops. Disease lesions were pressed on the cards and the pathogen DNA was fingerprinted. The data were used to define the clonal lineages of the pathogen and combined with geolocation data to plot the diversity across Europe.

Dr David Cooke, James Hutton Institute, said: "The blight pressure in 2020 was lower than average with a prolonged spell of warm, dry weather early in the season which checked the development of the disease in many regions. The proportions of the main clones in the 2020 population were broadly similar to those reported in 2019. 3 clones that first appeared in 2013 (EU_41_A2), 2014 (EU_37_A2, EU_36_A2) and EU_43, named in 2020, made up 40% of the 2020 population."

The survival and spread of these newer clones, when others are decreasing or have failed to establish, suggests they are evolutionarily fit and supports anecdotal evidence that they are more challenging to manage in the field, Dr Cooke explained. "Data has been passed to partners across Europe to support integrated pest management approaches to blight control," he said.

The example of EuroBlight as an international scientific network is being followed with AsiaBlight. Dr Cooke is supporting the pathogen genotyping work. A review into the development of potato late blight in Asia from 1870 to 2020 [see link below] shows clear evidence of the spread to Asia of several clonal lineages of _P. infestans_ from Europe and, to a lesser extent, North America.

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[2] Asia
Date: February 2021
Source: Plant Pathology [summ., edited]
https://bsppjournals.onlinelibrary.wiley.com/doi/full/10.1111/ppa.13360


[ref: SG Roy, et al. The dynamics of _Phytophthora infestans_ populations in the major potato‐growing regions of Asia -- a review. Plant Pathol. 2021; Early View: doi: 10.1111/ppa.13360]
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Asia is now the largest potato‐producing region of the world and late blight, caused by _P. infestans_, is the most important pathogen limiting production.

Information regarding the stated or inferred clonal pathogen lineages present, population changes, and possible migration routes of the pathogen into the countries of this region have been reviewed to aid researchers and those involved in managing late blight. The single most important factor for population change and resultant epidemics in this region has been found to be the migration of pathogen genotypes from Europe and the Americas.

Reducing the impact of such migration in the future will necessitate putting in place improved phytosanitary measures. Asian populations of _P. infestans_ clearly illustrate the lack of effectiveness of political barriers in limiting the spread of aggressive, sometimes fungicide‐resistant pathogen genotypes, and exemplify the need for international cooperation.

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[Late blight of potato (PLB) and tomato is caused by the fungus-like organism (oomycete) _Phytophthora infestans_ and can cause 100 per cent crop loss. The pathogen can also affect some other solanaceous crops. In potato, it affects leaves as well as tubers; in tomato, it causes lesions and rotting of leaves, stems, and fruits. The disease is favoured by cool, moist conditions. It can spread rapidly within a crop and destroy it within a few days. Under favourable conditions, epidemics in tomatoes may be even more rapid than in potatoes.

The pathogen is spread by plant material (including potato seed tubers, tomato transplants, plant debris, volunteer crop plants), mechanical means (including human and insect activities), wind, and water. Disease management requires an integrated approach and may include removal of pathogen reservoirs, crop rotation, preventative fungicide treatments of planting material, as well as fungicide sprays of crops. Farm-saved or uncertified seed tubers have often been reported as sources of PLB outbreaks. Certified clean planting stock and management strategies for fungicide resistance of the pathogen are considered vital to control late blight outbreaks. Commercial crop cultivars vary in susceptibility to late blight. Development of resistant cultivars is being counteracted by the adaptability of the pathogen.

Late blight is considered an increasing problem worldwide. Considerable variation in aggressiveness between different pathogen strains has been observed, but more virulent strains are emerging frequently. The presence of both A1 and A2 mating types of the pathogen increases the chances of strains with additional fungicide resistances and increased yield losses developing. In Europe, regional differences in pathogen population diversity no longer exist and increasingly virulent strains have been reported to emerge mainly on potato (see previous ProMED posts in the archives), but recently also on tomato (ProMED post 20180611.5850443).

Maps
Europe, overview:
https://mapofeurope.com/wp-content/uploads/2018/03/europe-political-map.jpg and
http://healthmap.org/promed/p/6010
Asia, overview:
https://www.worldatlas.com/img/areamap/continent/asia_map.gif and
http://healthmap.org/promed/p/5626

Pictures
Late blight on potato:
http://farm1.static.flickr.com/81/281344513_74bbffe5fe.jpg,
https://onvegetables.com/wp-content/uploads/2018/08/Potato-late-blight-No-halo.jpg and
http://cdn.phys.org/newman/gfx/news/2013/keepingpacew.jpg (resistant vs. susceptible cultivars)
Late blight on tomato:
http://ipm.illinois.edu/ifvn/volume15/images/tomato_late_blight.jpg
Microscopy of PLB infected cells:
http://micro.magnet.fsu.edu/optics/olympusmicd/galleries/brightfield/images/potatoblight.jpg

Links
Additional news story:
https://www.hutton.ac.uk/news/blight-studies-reveal-evolution-potato-disease-europe-and-asia
Complete Euroblight report:
https://agro.au.dk/forskning/internationale-platforme/euroblight/currently/news/nyhed/artikel/results-of-the-euroblight-potato-late-blight-monitoring-in-2020/
Information on late blight:
https://gd.eppo.int/taxon/PHYTIN (with photo gallery),
https://www.cabi.org/isc/datasheet/40970,
http://vegetablemdonline.ppath.cornell.edu/factsheets/Potato_LateBlt.htm,
https://www.gov.mb.ca/agriculture/crops/plant-diseases/print,mgmt-late-blight-potatoes.html, and
https://www.hutton.ac.uk/research/departments/cell-and-molecular-sciences/epidemiology
PLB epidemiology and strains in Europe:
https://agro.au.dk/forskning/internationale-platforme/euroblight/pathogen-monitoring/genotype-frequency-chart/ (current populations),
https://agro.au.dk/forskning/internationale-platforme/euroblight/pathogen-monitoring/genotype-map/,
http://agro.au.dk/forskning/internationale-platforme/euroblight/currently/news/nyhed/artikel/new-emerging-clones-of-phytophthora-infestans-in-europe/, and
https://link.springer.com/article/10.1007/s11540-011-9187-0 (review & history)
PLB in Asia:
https://bsppjournals.onlinelibrary.wiley.com/doi/full/10.1111/ppa.13360 and
https://www.bspp.org.uk/potato-blight-in-asia-understanding-phytophthora-infestans-across-a-continent-a-plant-pathology-highlight/
_P. infestans_ taxonomy:
http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=232148
EuroBlight:
http://euroblight.net/
AsiaBlight:
https://www.asiablight.org/
Global Initiative on Late Blight:
https://research.cip.cgiar.org/confluence/display/GILBWEB/Home
James Hutton Institute:
https://www.hutton.ac.uk/
- Mod.DHA]