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: Wed 19 Oct 2016
Source: Swedish University of Agricultural Sciences (SLU) [edited] <http://www.slu.se/en/ew-news/2016/10/early-blight-disease-on-potato-is-becoming-immune-to-fungicides/>
Early blight on potato becoming resistant to fungicides
A new study from SLU shows how a resistant mutant of _Alternaria solani_, the fungus causing early blight on potato, has arrived in southern Sweden, and how it has grown more resistant ever since. Early blight is common in Swedish potato farming.
Strobilurins are commonly used against the disease, but reports of a drop in efficacy have emerged from several countries. An acquired resistance against the fungicide is linked to mutation F129L in the gene for cytochrome b. It was 1st described in the US and has since arrived in Europe through Germany.
In Sweden, several unofficial observations tell of a drop in effect of strobilurin against early blight, but it has so far not been clarified whether this is due to F129L. The resistance is spreading [and] Eva Edin, SLU, is one of the authors of a study. In 2011, the mutant was present in one field outside of Kristianstad [Skane county], in every sample taken. In 2014, it had dispersed and was also present in another field [in the area].
"[In 2011], the fungicide was only one tenth as efficient against fungi carrying the substitution", says Eva Edin. "In 2014, the mutant strains had become even more resistant and the fungicide was at 1/13th of its original power. It is necessary to start using other methods, such as biological control agents or fungicides of different mode of action."
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Communicated by: ProMED-mail <promed@promedmail.org>
[Early blight of potato and tomato is caused by the fungus _Alternaria solani_. It causes leaf spots and tuber blight on potato; leaf spots, fruit rot and stem lesions on tomato; and it can also affect other solanaceous crops like capsicum. The disease can occur over a wide range of climatic conditions and can result in complete defoliation and severe yield losses. The pathogen often causes no visible symptoms until plants approach maturity.
The fungus is spread with infected plant material (including potato tubers, tomato transplants and seed), by mechanical means, wind and rain. Solanaceous weeds and volunteer crop plants may serve as pathogen reservoirs. Disease management includes use of certified clean propagation material, fungicides, crop rotation and use of cultivars with reduced susceptibility.
Strobilurins are strongly antifungal agents produced by fungi. Being derived from natural products, they are considered environmentally safe. Like several other fungicide classes, they have single-site activity and therefore pathogens must be expected to develop resistance or tolerance over time. Since they are used against most major fungal crop diseases, pathogen resistance is of major concern to many primary industries worldwide. Rotating or mixing chemical classes of fungicides is used to extend the useful life of the compounds.
Strobilurin resistant strains of _A. solani_ have also been reported, for example, from Canada where in a sampling of over 100 field isolates more than 80 per cent were found to carry the F129L mutation (ProMED-mail post http://promedmail.org/post/20090325.1163).
Maps
Sweden (and neighbours):
<http://geology.com/world/norway-map.gif>
Swedish counties:
<http://www.worldatlas.com/webimage/countrys/europe/lgcolor/secounties.htm>
Location of Kristianstad:
<http://www.worldclimateguide.co.uk/images_regions/SW.gif>
Europe, overview:
<http://www.edinphoto.org.uk/0_MAPS/0_map_europe_political_2001_enlarged.jpg>
Pictures
Early blight on potato:
<http://www.potatogrower.com/Images/0513/EB%20lesions1_opt.jpeg>,
<http://www.suttonelms.org.uk/early-blight-1.jpg>,
<http://www.suttonelms.org.uk/early-blight-2.jpg> and <http://www.extension.umn.edu/garden/yard-garden/vegetables/early-blight-of-tomatoes-and-potatoes/img/fig2.jpg>
(tubers)
EB on tomato:
<http://www.omafra.gov.on.ca/IPM/images/tomatoes/diseases/tomato_D2b-Early-blight---RPitblado_zoom.jpg>,
<http://erec.ifas.ufl.edu/tomato-scouting-guide/images/diseases/early-blight131.JPG>,
<http://www.hort.cornell.edu/livegpath/images/early_blight_plantsx1200.jpg>,
<https://extension.umd.edu/sites/default/files/_images/programs/grow_it_eat_it/diseases/EarlyBlight/early_blight_with_fruit_l.jpg>
and
<http://f.tqn.com/y/gardening/1/S/Y/7/1/Early-Blight-Tomato.jpg>
(fruit)
Links
Information on early blight of potato and tomato:
<http://www.extension.umn.edu/garden/yard-garden/vegetables/early-blight-of-tomatoes-and-potatoes/>,
<http://www.potatodiseases.org/earlyblight.html>,
<http://erec.ifas.ufl.edu/tomato-scouting-guide/diseases/early-blight.shtml>
and
<https://extension.umd.edu/growit/early-blight-vegetables>
Early blight fact sheets (with pictures):
<http://vegetablemdonline.ppath.cornell.edu/factsheets/Potato_EarlyBlt.htm>,
<http://www.aces.edu/pubs/docs/A/ANR-1052/ANR-1052.pdf> and <http://utahpests.usu.edu/IPM/htm/vegetables/vegetable-insect-disease/early-blight/>
Early blight disease cycle:
<http://www.potatodiseases.org/images/earlyblight/earlyblight-fig-8.jpg>
Research on early blight fungicide resistances:
<http://www.potatogrower.com/2013/05/early-blight-tranquility>
_A. solani_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=444460>
Information on strobilurins:
<http://grounds-mag.com/mag/grounds_maintenance_strobilurin_fungicides_natures/index.html>
- Mod.DHA
A HealthMap/ProMED-mail map can be accessed at:
<http://healthmap.org/promed/p/9462>.]
[See Also:
2011
----
Alternaria blight, capsicum - India: (HP)
http://promedmail.org/post/20110708.2064
2010
----
Early blight & Dickeya, potato - UK (02)
http://promedmail.org/post/20100705.2229
Dickeya, leaf blights, potato - UK, Ireland
http://promedmail.org/post/20100528.1775
Early blight & Dickeya, potato - UK: update
http://promedmail.org/post/20100208.0421
2009
----
Potato diseases - UK, USA http://promedmail.org/post/20090821.2960
Early blight, potato - Canada: new strains
http://promedmail.org/post/20090325.1163
Blight & undiagnosed disease, potato, chilli - Bhutan
http://promedmail.org/post/20090211.0612
Leaf blight, potato - Bangladesh: (KH)
http://promedmail.org/post/20090121.0255
2008
----
Fungal diseases, potato - Bangladesh
http://promedmail.org/post/20080107.0091]
Topics
Species
