.

Date: November 30, 2007
Source: Farmers Guardian [edited]
<http://www.farmersguardian.com/story.asp?sectioncode=19&storycode=14809>

New potentially more aggressive blight strains increased their dominance of the potato blight pathogen population during 2007, BPC [British Potato Council] -funded monitoring has revealed. But with scientists unsure as to why the incidence of the so-called genotype
13 A2 blight strain has increased so dramatically, growers are being advised to stick with current best practice approaches to blight control for the time being.

Speaking at a BPC blight survey seminar, Dr David Cooke of the Scottish Crop Research Institute [SCRI] said that of 300 total blight outbreaks sampled by SCRI and the Central Science Laboratory during 2007, 82 percent of the samples were A2 strain only. Two-thirds of
2006 samples were A2. "We've done tests and can confirm that it (A2) is a slightly more aggressive, fitter genotype under test conditions," said Dr Cooke.

While the incidence of A2 strains has increased, the incidence of mixed A1 and A2 outbreaks -- which gives an indicator of the risk of the 2 types combining to produce oospores -- appears to have remained constant. This season's sampling revealed no evidence of blight infections caused by oospores.

Vigilance will be the best way to keep blight in check. Growers should expect to see high disease pressure early in the season in 2008, he said.

[Byline: Teresa Rush]

--
Communicated by:
ProMED-mail
<promed@promedmail.org>

[Potato late blight (PLB) is caused by the fungus _Phytophthora infestans_, which can also infect other solanaceous crops such as tomato or eggplant. It is the most devastating disease threatening potato crops worldwide and can cause 100 percent crop loss. The fungus affects leaves as well as tubers. It is spread by plant material (including seed tubers), wind and water, and solanaceous weeds can serve as pathogen reservoirs. Other fungi and bacteria often invade blight-infected tubers resulting in total tuber breakdown. Disease management includes preventative fungicide treatment of seed tubers and additional fungicide applications to the crop. Some PLB resistant potato varieties are available.

Worldwide, considerable variation in aggressiveness between different isolates of _P. infestans_ has been observed. A severe form of PLB was responsible for the Irish potato famine in the late 1840s. PLB is considered an increasing problem in many areas because new and even more virulent strains continue to emerge. Some of these can destroy a potato plant in a matter of hours and a complete crop within days.

Where both A1 and A2 mating types are present, reproduction occurs sexually as well as asexually, leading to strains with higher fungicide resistance and increased yield losses. A1 was the 1st mating type to spread worldwide; A2 began to spread later and is now present in northern Europe, northern and Central America, and parts of Asia. Within each mating type there are a number of genotypes (strains). In Western Europe, a dramatic increase in the frequency of the A2 mating type is being recorded recently, with a single lineage apparently accounting for much of the change in the UK population of fungal strains.

Maps of the UK:
<http://www.lib.utexas.edu/maps/europe/united_kingdom.gif> and <http://healthmap.org/promed?v=54.5,-2,5>

Pictures
Diseased potato tubers:
<http://www.sciencedaily.com/images/2007/01/070102132649.jpg>
Leaf symptoms:
<http://www-biol.paisley.ac.uk/bioref/Chromista/potato_blight.jpg>
Microscopy of infected cells:
<http://micro.magnet.fsu.edu/optics/olympusmicd/galleries/brightfield/images/potatoblight.jpg>
Microscopy of sporangiophores:
<http://www-biol.paisley.ac.uk/bioref/Chromista/Phytoph_infestans.jpg>

Links
Disease information, history and background:
<http://www.apsnet.org/online/feature/lateblit/>,
<http://www.agric.wa.gov.au/pls/portal30/docs/FOLDER/IKMP/PW/PH/DIS/VEG/FS0401_REVIEW.PDF>
and
<http://www.olympusmicro.com/micd/galleries/brightfield/potatoblight.html>
Management of potato diseases including PLB:
<http://archives.eppo.org/EPPOStandards/PP2_GPP/pp2-02-e.doc>
PLB information and resources via:
<http://www.potato.org.uk/department/knowledge_transfer/fight_against_blight/advice_blight.html>
_P. infestans_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=232148>
SCRI, UK populations of late blight and map of A2 distribution:
<http://www.scri.ac.uk/research/pp/pestanddisease/blightepidemiologyandpopulationbiology>
British Potato Council:
<http://www.potato.org.uk>
Global Initiative on Late Blight:
<http://gilb.cip.cgiar.org/>. - Mod.DHA]

[see also in the archive:
Late blight, potato - India: (Punjab), alert 20071116.3715 Fungal diseases, vegetable crops - Canada: cucumber, potato 20070730.2442 Late blight, potato & vegetable fungal diseases - Europe 20070708.2174 Late blight, potato - India, UK 20070509.1491
2006
----
Late blight, potato - India (Kashmir) 20060424.1200 Late blight, potato - USA (AK), Bangladesh 20060324.0911
2003
----
Late blight, potato - Papua New Guinea 20030306.0554
2002
----
Potato late blight, potato - Canada (Newfoundland) 20020818.5091
2001
----
Phytophthora infestans, potato late blight - Russia 20010620.1177 2000
----
Potato late blight, global research efforts 20001031.1903 Potato late blight: global initiative 20000516.0765
1996
----
Potato late blight: global threat 19960617.1123]

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