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[1] _Iris yellow spot virus_, lisianthus - United Kingdom: 1st report, (Suffolk)
[2] _Iris yellow spot virus_, onion - Canada: 1st report, (Ontario)


[1] _Iris yellow spot virus_, lisianthus - United Kingdom: 1st report, (Suffolk)
Date: January 2008
Source: British Society for Plant Pathology, New Disease Reports (NDR) vol. 16 [edited]
<http://www.bspp.org.uk/ndr/jan2008/2007-105.asp>

[Reference: RA Mumford et al: _Iris yellow spot virus_ (IYSV) infecting lisianthus (_Eustoma grandiflorum_) in the UK: 1st finding and detection by real-time PCR. BSPP New Disease Reports, vol. 16]

In June 2007, a sample of leaves was received from a year-round crop of lisianthus (_Eustoma grandiflorum_) growing under glass in Suffolk, England. The sample exhibited necrosis, mainly observed as pale, necrotic lesions (Fig. 1). In the worst affected block up to 20 percent of plants were reported as showing similar symptoms.

A test performed by another laboratory had previously detected _Iris yellow spot virus_ (IYSV) in the symptomatic plants. To confirm this diagnosis officially, an ELISA [enzyme linked immunosorbent assay] test was performed. This test was positive. The result was confirmed using a new real-time PCR [polymerase chain reaction] assay. This new assay was designed using an available IYSV nucleocapsid (NC) protein gene sequence and further alignments against 45 other IYSV sequences available on public databases. It was validated with 4 known IYSV isolates.

For further confirmation, conventional RT [reverse transcription]-PCR was performed on extracts made from leaf material with symptoms. A product of the correct predicted size (822 basepairs) was obtained and sequenced. The deduced NC gene sequence obtained was analysed and shown to share at least 84 percent nucleotide identity with all other IYSV NC sequences; the highest homology (98 percent) being with a Dutch isolate from _Iris hollandica_.

Widely distributed around the world in onion and leek crops, IYSV has been identified in various ornamental crops, including lisianthus.
However, this is the 1st finding of IYSV in the UK. The infected crop has now been removed and measures taken to eradicate the infection.

Figure 1: Pale-coloured necrotic lesions on lisianthus from the UK outbreak. <http://www.bspp.org.uk/ndr/jan2008/2007-105-1.jpg>

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[2] _Iris yellow spot virus_, onion - Canada: 1st report, (Ontario)
Date: February 2008
Source: The American Phytopathological Society, Plant Disease 2008;
92(2): 318 [edited]
<http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-92-2-0318A>

[Reference: CA Hoepting et al: 1st report of _Iris yellow spot virus_ on onion in Canada. Plant Dis 2008; 92(2): 318; DOI: 10.1094/PDIS-92-2-0318A]

_Iris yellow spot virus_ (IYSV; family _Bunyaviridae_, genus _Tospovirus_) is an economically important viral pathogen of onion vectored by onion thrips (_Thrips tabaci_ Lindeman). Rapid spread of IYSV has occurred in the western United States and Georgia, with recent reports of IYSV from New York in the northeastern United States.

In June and mid-July of 2007, symptomatic plants were found in Ontario, Canada in onions grown from sets in a home garden in Grey County (44 deg 27 min N, 80 deg 53 min W) and on a small commercial farm in Ottawa-Carleton County (45 deg 14 min N, 75 deg 28 min W), respectively. In the home garden, bleached, elongated lesions with tapered ends occurred on middle-aged leaves of 30 percent of 100 plants. By August 2007, 91 percent of these plants were symptomatic. In Ottawa-Carleton, 2 lesions with green centers and yellow borders occurred on a single leaf of a single plant in a field of 1120 plants.

Symptomatic leaf tissue tested positive for IYSV in a double-antibody sandwich (DAS)-ELISA. These 2 isolated and remote finds of IYSV in Ontario prompted a survey in early August of 2007 of the Holland Marsh (44 deg 5 min N, 79 deg 35 min W), the largest onion-producing region in Ontario. A total of 9 onion fields separated geographically
across the Holland Marsh Region were scouted and one to 3 samples of symptomatic tissue per field were analyzed by DAS-ELISA. IYSV was confirmed in 7 of 9 (78 percent) fields surveyed and in 13 of 16 (81 percent) of the individual samples.

A reverse transcription (RT)-PCR assay was used to verify the presence of IYSV in one new symptomatic tissue sample per field collected from three of the fields where IYSV was confirmed by ELISA. RT-PCR specific to the small (S) RNA of IYSV was used. The resulting product, which included the 772 basepair nucleocapsid (N) gene was cloned and sequenced. Sequence analysis showed that the N gene of the Ontario isolate shared 92 to 98 percent nucleotide sequence identity with known IYSV N gene sequences.

To our knowledge, this is the 1st report of IYSV infection of onion in Ontario and Canada. This finding confirms further spread of the virus within North America and the need for research to develop more effective management options to reduce the impact of IYSV on onion production. The finding of IYSV in remote and isolated locations
where onions were grown from sets implies that the spread of IYSV via infected bulbs warrants further investigation as a potentially important route of distribution of the virus.

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[IYSV has only recently been confirmed as a member of the genus _Tospovirus_ by the International Committee on the Taxonomy of Viruses (ICTV). New tospoviruses are being found frequently, and the type member of the genus _Tomato spotted wilt virus_ (TSWV), has had a serious impact on many crop species worldwide.

IYSV (as well as TSWV) 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 North and southern America, 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. Ornamental hosts, such as lisianthus, 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.

Maps
UK:
<http://www.lib.utexas.edu/maps/europe/united_kingdom.gif>  and
<http://healthmap.org/promed?v=54.5,-2,5>
Suffolk:
<http://www.eastanglia24.co.uk/suffolk/suffolk_map.jpg>
Canada:
<http://www.lib.utexas.edu/maps/americas/canada_pol_1986.gif>  and
<http://healthmap.org/promed?v=55.4,-101.9,4>
Ontario:
<http://atlas.nrcan.gc.ca/site/english/maps/reference/provincesterritories/ontario/referencemap_image_view> 

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 alert list:
<http://www.eppo.org/QUARANTINE/listA2.htm>.  - Mod.DHA]