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 20 May 2015
Source: HortiDaily [edited]
<http://www.hortidaily.com/article/17749/New-race-of-downy-mildew-in-lettuce-receives-official-designation>
The International _Bremia_ Evaluation Board (IBEB) has officially designated a new race of downy mildew in lettuce: Bl:32. This isolate was already known, but has now become much more widespread in Europe, according to research by the IBEB into the _Bremia_ isolates identified in 2014 and earlier.
Most outbreaks of _Bremia_ caused by these new isolates have only local consequences. In recent years, however, Bl:32 has been identified in France, Germany, The Netherlands, the United Kingdom, Austria, Switzerland and Belgium, and it has recently also spread to Portugal and northern Spain.
The large majority of Bl:16-31-resistant varieties are also resistant to this new race.
--
Communicated by: ProMED-mail <promed@promedmail.org>
[Downy mildew of lettuce caused by the fungus-like organism _Bremia lactucae_ and is a common disease of both glasshouse and field-grown crops. It affects all types of lettuce and can result in severe losses by reducing both yield and quality of crops. Multiple pathotypes of the pathogen exist affecting different hosts, but lettuce strains are specific to lettuce and close relatives. Symptoms on lettuce may include yellow patches on upper leaf surfaces and white growth on the corresponding underside, followed by browning and death of infected tissue. Systemic infections may also occur leading to internal rotting of stem and leaf veins. The disease is favoured by humid conditions.
Spores are spread within a crop mainly by splashing rain, wind or mechanical means. The pathogen survives between crops on infected plant material or as oospores in the soil which may infect the roots of the next crop. Disease management may include cultural measures to reduce humidity within a crop, crop rotation, phytosanitation and preventative fungicide applications. The most effective means of control is planting resistant varieties.
Downy mildews include many species in several genera which cause similar symptoms on a range of hosts, including many crops. Individual species usually have a narrow host range affecting only 1 or a few different hosts.
Maps
Europe, overview:
<http://www.edinphoto.org.uk/0_MAPS/0_map_europe_political_2001_enlarged.jpg>
Pictures
Downy mildew on lettuce:
<http://wrir4.ucdavis.edu/PHOTOS/pest/images/Lettuce%20Downy%20Mildew%20Salinas,%20CA.jpg>,
<http://qbelab.plantpathology.ucdavis.edu/wp-content/uploads/2014/04/D-CC-BLAC-FO.001.jpg>,
<https://apps.rhs.org.uk/Advice/ACEImages//SCN0002223_337834.jpg> and <http://ucanr.org/blogs/SalinasValleyAgriculture/blogfiles/3823.jpg>
(systemic infection)
Links
Additional news stories:
<http://www.nunhems.com/www/NunhemsInternet.nsf/id/CW_EN_New-race-of-Bremia-in-lettuce>
and
<http://www.enzazaden.co.uk/AboutUs/news/company/2015/new_bremia_race_bl32.aspx>
Information on lettuce downy mildew:
<https://www.rhs.org.uk/advice/profile?pid=216>,
<http://www.ipm.ucdavis.edu/PMG/r441100411.html>,
<http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=2735> and via <http://qbelab.plantpathology.ucdavis.edu/DownyMildewLeafyGreens>
_B. lactucae_ taxonomy and synonyms:
<http://www.indexfungorum.org/names/NamesRecord.asp?RecordID=220062>
and
<http://www.speciesfungorum.org/GSD/GSDspecies.asp?RecordID=220062>
Information on IBEB and _Bremia_ races via:
<http://www.worldseed.org/isf/ibeb.html>
- Mod.DHA]
Topics
Species
