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: Fri 24 Apr 2009
Source: FarmingUK [edited]
<http://www.farminguk.com/?show=newsArticle&id=15471>

Blight outbreaks from dumps are on the rise

More blight may be originating from outgrade piles as a result of growers losing focus on control, according to Potato Council. "During the 2003 season, blight scouts reported that over 18 percent of outbreaks originated from outgrade piles. This led to a campaign to target this major source of infection," notes Potato Council blight specialist Gary Collins.

"The result was to reduce the level dramatically, with only 1.6 percent of outbreaks in 2007 attributed to outgrade piles. During
2008 the level rose to 5.8 percent, showing that everyone needs to be vigilant when it comes to controlling any growth from this potential blight source."

The rise in potatoes grown in allotments poses another risk for growers. Mr Collins comments: "The credit crunch has increased the trend in producing home-grown potatoes, grown in gardens and allotments. This may result in increased levels of blight from areas that are seldom treated."

There is still little evidence to suggest that recombination is taking place in British crops, which would result in the formation of oospores, but it is important to look out for the common signs, which will indicate that blight possibly originated from this soil-borne source.

"An early indication of infection from oospores will be many small lesions affecting lower leaves that are touching, or close to, the soil surface. Airborne blight typically affects the upper leaves first. Infection will look particularly aggressive and needs urgent treatment," warns Mr Collins. "Although the viability of oospores over time in different British soils is not known, growers should remain alert."

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[Potato late blight (PLB) is caused by the fungus-like organism _Phytophthora infestans_ and can cause 100 percent crop losses in potato and tomato. The pathogen is spread by plant material (including seed tubers), wind, and water. Volunteer potato plants, which are often found on sites were crop residue is being dumped, may serve as pathogen reservoirs and source of crop infection. PLB disease management generally relies on fungicide treatments of seed tubers and crops. These treatments may be insufficient in home grown potato crops.

Where both A1 and A2 mating types of the pathogen are present, reproduction occurs sexually via oospores as well as asexually. A1 is present worldwide, and a dramatic increase in the frequency of A2 in western Europe is causing changes in the UK population of fungal strains. Recombinants of A1 and A2 strains would emerge from the soil affecting lower leaves first, in contrast to windborne spores, which land on upper plant parts.

The item above describes several important sources of PLB inoculum, which need to be addressed in disease management programmes. For more information on PLB see links and previous ProMED-mail posts below.

Maps of UK:
<http://www.lib.utexas.edu/maps/europe/united_kingdom.gif> and <http://healthmap.org/r/008E>

Pictures
PLB symptoms:
<http://www.potatomuseum.com/images/exblightfieldwithinsert.jpg>,
<http://farm1.static.flickr.com/81/281344513_74bbffe5fe.jpg> (tuber), and
<http://www-biol.paisley.ac.uk/bioref/Chromista/potato_blight.jpg> (leaves)
Potato field destroyed by late blight:
<http://www.apsnet.org/education/LessonsPlantPath/LateBlight/images/fig29.jpg>

Links
Late blight fact sheets:
<http://ohioline.osu.edu/hyg-fact/3000/3102.html>  and <http://vegetablemdonline.ppath.cornell.edu/factsheets/Potato_LateBlt.htm>
Disease history and background:
<http://www.apsnet.org/online/feature/lateblit/>,
<http://www.olympusmicro.com/micd/galleries/brightfield/potatoblight.html>,
and
<http://www.agric.wa.gov.au/pls/portal30/docs/FOLDER/IKMP/PW/PH/DIS/VEG/FS0401_REVIEW.PDF>
Late blight information and resources:
<http://www.potato.org.uk/department/knowledge_transfer/fight_against_blight/advice_blight.html>
_P. infestans_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=232148>
UK 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 - Algeria: update 20090420.1490 Late blight, potato - UK, Bangladesh 20090406.1332 Late blight, potato - India, Bangladesh: update 20090310.0989 Blight & undiagnosed disease, potato, chilli - Bhutan 20090211.0612 Late blight, potato - India (02): (WB) 20090131.0435 Leaf blight, potato - Bangladesh: (KH) 20090121.0255 Late blight, potato - Nepal (BR) 20090114.0162 Late blight, potato & tomato: USA (FL), Ireland 20090109.0083 Late blight, potato - India: (PB) 20090103.0018
2008
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Late blight, potato - Papua New Guinea (02): recovery 20081103.3454 Late blight, potato - India, Canada alert 20080815.2534 Late blight, potato - Bhutan: (TM) 20080811.2473 Late blight type A2, tomato - Taiwan: 1st report 20080615.1891 Late blight, potato - UK: (Scotland), alert 20080430.1482 Late blight, tomato, potato - USA: (FL) 20080219.0664 Potato diseases - India: (West Bengal) 20080206.0477 Late blight, potato - Papua New Guinea: recovery 20080121.0256 Fungal diseases, potato - Bangladesh 20080107.0091
2007
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Late blight, potato - India (02): (Punjab, W Bengal) 20071221.4099 Late blight, potato - UK: new strains 20071207.3939 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
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Late blight, potato - India (Kashmir) 20060424.1200 Late blight, potato - USA (AK), Bangladesh 20060324.0911 and older items in the archives]