A ProMED-mail post <http://www.promedmail.org>
ProMED-mail is a program of the International Society for Infectious Diseases <http://www.isid.org>
Date: December 2019
Source: New Disease Reports [abridged, edited] <https://www.ndrs.org.uk/article.php?id=040020>
[Ref: N Nnadi et al. (2019): First report of the EU_33_A2 clonal lineage of _Phytophthora infestans_ causing late blight disease of potato in Nigeria. New Disease Reports 40, 20; DOI:
10.5197/j.2044-0588.2019.040.020]
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Potato (_Solanum tuberosum_) cultivation was introduced into Nigeria in the Jos Plateau [Plateau state] in the early 20th century. Nigeria is the 4th biggest producer of potato in sub-Saharan Africa.
The late blight pathogen, _Phytophthora infestans_, has been present in Nigeria since at least 1978, but its severity in the Jos Plateau was reported to have increased dramatically in the 2012, 2013, and
2014 seasons. Favourable conditions for late blight and the importation of seed were hypothesised to be drivers. The epidemics were again very severe in 2018 [ProMED-mail post http://promedmail.org/post/20190130.6286551] despite application of fungicides, so a survey of the pathogen population was conducted.
Samples from 7 diseased crops were collected at random in May and July 2018. Data on the origin of 42 samples (location, host, and cultivar) were also recorded. The fields were located on different farms in 3 districts. The sampled areas [were either] affected with about 10% of plants diseased [or] severely affected with almost all plants diseased. Pathogen genotyping was conducted using multiplex PCR.
A comparison with a database of national and international late blight genotypes confirmed the identity of the pathogen as _P. infestans_ and identified a single genotype, EU_33_A2, from all the sampled diseased leaves. Genotype EU_33_A2 was 1st found in the Netherlands in 2010 but has not been reported previously in Africa.
This result indicates a wider distribution of the 33_A2 genotype than previously thought and a possible migration from Europe to Nigeria on seed potatoes. All the potatoes cultivars obtained in this study (Nicola Green, Roselyn Ruka, Christian Lady, Nicola Yellow, Yona, and
Marabel) showed susceptibility to _P.infestans_ 33_A2.
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Communicated by: ProMED-mail <promed@promedmail.org>
[Late blight of potato (PLB) and tomato is caused by the fungus-like organism (oomycete) _Phytophthora infestans_ and can cause 100% 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. Presence of both A1 and A2 mating types of the pathogen increases the chances of strains with additional fungicide resistances and increased yield losses to develop. 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-mail posts in the archives), but recently also on tomato (ProMED-mail post http://promedmail.org/post/20180611.5850443).
Amongst the emerging strains, 33_A2 (also called Green 33, EU-33; see ProMED-mail post http://promedmail.org/post/20120202.1031230) has shown increased aggressiveness and reduced sensitivity to fluazinam, a pyridinamine fungicide introduced in the 1990s that established itself for PLB control. It has a multi-site mode of action and has strong persistence of effect against the pathogen. It can suppress secondary infection in the field through inhibition of sporulation. Until the emergence of Green 33_A2, no fluazinam resistance was known in blight populations.
Previously, strain 13_A2 (Blue 13) was found to be imported with seed potatoes from Europe to India (ProMED-mail post http://promedmail.org/post/20180418.5755980). With the report above suggesting the introduction of 33_A2 to Africa in the same way, this is yet another example of the importance of reliable national biosecurity diagnostic and certification systems.
Maps
Nigeria:
<https://i.infopls.com/images/mnigeria.gif>
Nigerian states:
<https://maps-nigeria.com/img/1200/map-of-nigeria-showing-the-geopolitical-zones.jpg>
Africa, overview:
<http://www.worldatlas.com/webimage/countrys/africa/maps/africa.jpg>
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>
PLB photo gallery:
<https://gd.eppo.int/taxon/PHYTIN/photos>
Links
Information on late blight:
<http://vegetablemdonline.ppath.cornell.edu/factsheets/Potato_LateBlt.htm>,
<https://www.gov.mb.ca/agriculture/crops/plant-diseases/print,mgmt-late-blight-potatoes.html>,
<https://www.cabi.org/isc/datasheet/40970>,
<https://gd.eppo.int/taxon/PHYTIN> and
<http://www.scri.ac.uk/research/pp/pestanddisease/blightepidemiologyandpopulationbiology>
PLB disease cycle:
<http://bit.ly/2lnDBQg>
_P. infestans_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=232148>
Global Initiative on Late Blight:
<https://research.cip.cgiar.org/confluence/display/GILBWEB/Home>
Information on fluazinam fungicides:
<http://www.iskweb.co.jp/products/pdf/fluazinam.pdf> and <http://www.alanwood.net/pesticides/fluazinam.html>
- Mod.DHA]
[See Also:
2019
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Late blight, potato - Europe (02): UK, strain 36_A2
http://promedmail.org/post/20190712.6562717
Undiagnosed disease, tomato - Nigeria: (JI)
http://promedmail.org/post/20190429.6446450
Late blight, potato - Europe: emerging strains
http://promedmail.org/post/20190416.6424462
Crop diseases - Rwanda, Burundi: impact
http://promedmail.org/post/20190325.6385018
Late blight, potato - Europe: emerging strains
http://promedmail.org/post/20190416.6424462
Late blight, potato - Nigeria: (PL)
http://promedmail.org/post/20190130.6286551
2018
----
Late blight, tomato - USA: new A2 strain
http://promedmail.org/post/20181025.6110781
Late blight, potato - Malawi: (DE)
http://promedmail.org/post/20180817.5971029
Late blight, tomato - UK: new strain susp
http://promedmail.org/post/20180611.5850443
Blight diseases, coffee & vegetable crops - Kenya
http://promedmail.org/post/20180604.5837538
Late blight, potato - India: strain Blue 13
http://promedmail.org/post/20180418.5755980
2017
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Late blight & post harvest rot, potato - Ireland & UK (NI)
http://promedmail.org/post/20171124.5462543
Late blight, potato - UK: strain Dark Green 37
http://promedmail.org/post/20171029.5412307
Undiagnosed disease, potato - Nigeria (02): late blight
http://promedmail.org/post/20170910.5307592
Undiagnosed disease, potato - Nigeria: (PL)
http://promedmail.org/post/20170828.5278346
2016
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Late blight, potato - Uganda: (South West)
http://promedmail.org/post/20160602.4260691
2014
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Late blight, potato - Nigeria, UK
http://promedmail.org/post/20140611.2533396
2013
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Late blight, potato: new strains threat
http://promedmail.org/post/20130111.1492024
2012
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Late blight, potato - UK: strain Green 33
http://promedmail.org/post/20120202.1031230
and additional items on late blight in the archives]
Topics
Species
