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: February 2008
Source: European Plant Protection Organisation (EPPO) Reporting Service 2/2008/033 [edited] <http://archives.eppo.org/EPPOReporting/2008/Rse-0802.pdf>

Report of Iris yellow spot virus on onion in Germany

The NPPO [National Plant Protection Organisation] of Germany recently informed the EPPO secretariat of the 1st detection of _Iris yellow spot virus_ (_Tospovirus_, IYSV - EPPO Alert List) in Rheinland-Pfalz on onions (_Allium cepa_ and _Allium fistulosum_). In Rheinland-Pfalz, symptoms resembling those of IYSV had already been observed in 2003 on onion crops. In summer 2007, as typical symptoms of IYSV were observed again in the same onion-growing area, a survey was initiated and 25 sites were visually inspected. As a result, 9 symptomatic lots were tested in the laboratory and found to be infected by ISYV.

In the field, infected onion plants often showed white to straw-coloured oval, necrotic lesions on the leaves. At a later stage of the disease, the number of lesions increased and led to decay of the leaves. These symptoms could be confused with those caused by thrips infestations, hailstorms, herbicide phytotoxicity, or early infections by various fungal diseases. While at the beginning of the vegetation period, only isolated plants or small groups of plants appeared to be infected, onion plots were evenly infected at a later stage. So far, yield reduction could not be quantified but was considered moderate. Because _Thrips tabaci_ is thought to be the main vector of the disease, insecticide treatments were applied to control thrips populations.

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

[IYSV has only recently been confirmed as a member of the genus _Tospovirus_ by the International Committee on the Taxonomy of Viruses (ICTV). It has been included in the Alert List of the European Plant Pathology Organisation (EPPO). Known hosts include onion, leek, iris, amaryllis, lisianthus, and weeds including wild relatives of onion (_Allium_ species). IYSV has been reported from a number of locations in the Americas, Europe, Asia, South Africa, and Australia. The economic impact is low in some areas, but up to 100 percent loss has been observed in onion crops, for example, in Brazil.

The virus is transmitted by the onion thrips, _Thrips tabaci_. Thrips are the most common and serious insect pest of onions. High populations of thrips can reduce both yield and keeping quality of crops. Thrips are most damaging when they feed during the early bulbing stage of plant development. Both adults and nymphs cause damage. Severe scarring also creates an entry point for foliar leaf diseases.

Spread of IYSV occurs with infected plant material and viruliferous vector insects. Ornamentals and weeds may serve as pathogen reservoirs since thrips may also feed on them. The virus appears not to be seed transmitted. Tospovirus epidemiology is complex and natural resistance appears to be rare amongst their plant hosts.
Management of IYSV and its vector includes the use of clean propagative material, cultural practices, and pesticides.

It is reported above that symptoms were noticed for the 1st time in Rheinland-Pfalz in 2003, but no action seems to have been taken then.
While the current outbreak may be due to a new incursion, IYSV may well have persisted locally at low levels or in non-commercial hosts until finally being diagnosed in samples from the 2007 onion crop.

Maps
Germany:
<http://www.emansworld.com/JPEGS/map_germany-big.jpeg> and <http://healthmap.org/promed?v=51.1,10.4,5>
Europe:
<http://www.greece-map.net/europe/europe-map.gif>
IYSV worldwide distribution (December 2005):
<http://www.eppo.org/QUARANTINE/Alert_List/viruses/maps/IYSV00_map.htm>

Pictures
IYSV symptoms on onion plant:
<http://www.columbiapublications.com/onionworld/marchapril2006/irisyellowspot%20K8.jpg>
and
<http://www.apsnet.org/online/feature/tospovirus/images/figure4.JPG>
Lesions on onion leaf:
<http://www.bspp.org.uk/ndr/july2005/2005-33-2th.jpg>
Onion thrips vector:
<http://www.insectimages.org/images/768x512/1327078.jpg>

Links
Information on IYSV:
<http://www.eppo.org/QUARANTINE/Alert_List/viruses/IYSV00.htm>
Control of IYSV and the thrips vector:
<http://www.capitalpress.info/main.asp?SectionID=94&SubSectionID=801&ArticleID=39055&TM=77286.9>

_Tospovirus_ taxonomy and species list:
<http://phene.cpmc.columbia.edu/ICTVdB/11050000.htm>
Current list of recognised tospoviruses:
<http://www.oznet.ksu.edu/tospovirus/tospo_list.htm>
_Tospovirus_ resource centre:
<http://www.oznet.ksu.edu/tospovirus/welcome.htm>
General information and background on tospoviruses:
<http://www.apsnet.org/online/feature/tospovirus/Top.html>
ICTV:
<http://www.ictvonline.org/virusTaxonomy.asp?bhcp=1>
Description and management of onion thrips:
<http://www.nysaes.cornell.edu/ent/hortcrops/english/thrips.html>  and <http://www.ipm.ucdavis.edu/PMG/r584300111.html>
Thrips information:
<http://www.cals.ncsu.edu/course/ent425/text18/plantvectors.html>
EPPO quarantine and alert lists via:
<http://www.eppo.org/QUARANTINE/quarantine.htm>
- Mod.DHA]