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First report of Iris yellow spot virus on onions in New Zealand and Serbia

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A ProMED-mail post
ProMED-mail is a program of the International Society for Infectious Diseases

A ProMED-mail post
<http://www.promedmail.org>
ProMED-mail is a program of the
International Society for Infectious Diseases <http://www.isid.org>

[1] New Zealand
[2] Serbia

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[1] New Zealand
Date: July 2008
Source: British Society for Plant Pathology, New Disease Reports
(NDR) vol. 17 (February-July 2008) [edited] <http://www.bspp.org.uk/ndr/july2008/2008-43.asp>

[Ref: LI Ward et al: First report of _Iris yellow spot virus_ on _Allium cepa_ in New Zealand. BSPP New Disease Reports, vol. 17]
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During a disease survey of _Allium_ crops in New Zealand in 2007, characteristic diamond-shaped lesions, suggestive of _Iris yellow spot virus_ (IYSV; genus _Tospovirus_, family _Bunyaviridae_) infection, were observed on a few brown onion seed plants in the Blenheim area of the South Island (Fig. 1).

The plants with symptoms tested positive for IYSV using a DAS-ELISA [double antibody sandwich-enzyme-linked immunosorbent assay]. Total RNA was extracted from the scape lesions and tested by RT-PCR [reverse transcriptase polymerase chain reaction]. Amplicons of the expected size were cloned and sequenced. Sequence comparisons showed 98-100 percent nucleotide identity with other IYSV N [nucleocapsid] gene sequences in GenBank [database]. A phylogenetic analysis of the deduced amino acid sequences of the N gene showed that the New Zealand isolate of IYSV grouped most closely with isolates from California and Texas, USA (Fig. 2).

Samples from a further 28 _Allium_ crops (100 plants per crop) and 4 ornamental _Allium_ species (one plant of each: _A. senescens_, _A.
murryanum_, _A. caesium_ and _A. moly_), collected around New Zealand, were tested for IYSV by ELISA. The results showed that IYSV was widespread in onion (10 of 12 crops) and shallot (3 out of 3 crops), in both the North and South Islands. However, all 13 garlic crops tested negative. The infected crops showed a significant amount of thrips damage, but most plants had no IYSV symptoms. Two of the ornamental _Allium_ species (_A. senescens_ and _A. murryanum_), which were also without symptoms, tested positive for IYSV by ELISA.
Unfortunately attempts to amplify the viral genome by RT-PCR for sequencing were unsuccessful.

Reports of new IYSV outbreaks continue to be made from different parts of the world and the virus is a major production constraint to onion bulb and seed production in some countries. This is the 1st report of IYSV in onion and shallot in New Zealand and its economic impact on these crops in New Zealand is still to be determined.

Figure 1: Diamond-shaped lesions characteristic of _Iris yellow spot virus_ on the scape of an _Allium cepa_ plant.
<http://www.bspp.org.uk/ndr/july2008/2008-43-1.jpg>

Figure 2: _Iris yellow spot virus_ phylogeny (Neighbor Joining
Method) based on deduced amino acid sequences of the complete nucleocapsid gene. The New Zealand isolate of IYSV is indicated as NZ.
<http://www.bspp.org.uk/ndr/july2008/2008-43-2.jpg>

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

******
[2] Serbia
Date: August 2008
Source: The American Phytopathological Society, Plant Disease 2008;
92(8): 1247 [edited]
<http://apsjournals.apsnet.org/doi/abs/10.1094/pdis-92-8-1247a>

[Ref: A Bulajic et al: First report of _Iris yellow spot virus_ on onion (_Allium cepa_) in Serbia. Plant Dis 2008; 92(8): 1247; DOI:
10.1094/PDIS-92-8-1247A]
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_Iris yellow spot virus_ (IYSV; genus _Tospovirus_, family
_Bunyaviridae_) is established in several European countries (France, Italy, The Netherlands, Poland, Slovenia, Spain, and the UK) and its distribution in the EU region has increased since 2002. In July 2007, symptoms resembling those of IYSV were observed in an onion (_Allium
cepa_) seed crop in the Sirig locality in Serbia. Onion plants exhibited characteristic symptoms of chlorotic or necrotic spindle and diamond-shaped lesions on the leaves and scapes. Symptomatic plants were found throughout the field and disease incidence was estimated at 80 percent.

Leaf and scape samples were tested for the presence of IYSV and 2 other tospoviruses, _Tomato spotted wilt virus_ (TSWV) and _Impatiens necrotic spot virus_ (INSV), using commercial double-antibody sandwich (DAS)-ELISA diagnostic kits. All samples tested negative for TSWV and INSV. IYSV was detected serologically in 26 of 34 onion samples. To determine an experimental host range, samples of IYSV-infected onion plants were homogenized and host plants were inoculated with the sap. Mechanical transmission of the virus occurred rarely. All inoculated test plants were assayed by DAS-ELISA and only 4 species tested positive for IYSV, but not in all replications. Inoculated _Chenopodium quinoa_ developed local chlorotic lesions, _Nicotiana tabacum_ cvs. Samsun and Prilep showed mild mosaic, while infected _N. benthamiana_ were symptomless [symptom development on these species is used as a biological assay for virus identification - Mod.DHA]

For further confirmation of IYSV, conventional reverse transcription (RT)-PCR was performed on extracts made from symptomatic onion leaf material and from the ELISA-positive symptomless leaves of _N.
benthamiana_. A product of the correct predicted size (896 basepairs) was obtained from each of the plants assayed, and one isolate was sequenced. Analyses revealed 86 to 97 percent sequence identity with the corresponding gene from all other IYSV [isolates]. The highest identity (97 percent) was with leek and onion isolates from Spain.

To our knowledge, this is the 1st report of IYSV infection of onion seed crop in Serbia. Thorough inspections and subsequent testing would be needed to establish the distribution and incidence of IYSV in Serbia.

--
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_. Spread of IYSV occurs with infected plant material and viruliferous [virus-carrying] vectors.

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.

_Tomato spotted wilt virus_ (TSWV) and _Impatiens necrotic spot virus_ (INSV) also belong to the genus _Tospovirus_. This is an extremely important group of plant viruses affecting a large range of crops, and new members are being discovered frequently.

Maps
New Zealand
<http://www.backpack-newzealand.com/images/new-zealand-map.gif>  and
<http://healthmap.org/promed?v=-42.4,172.7,5>
Serbia and neighbouring countries:
<http://www.commondreams.org/kosovo/kosovoimages/bceurope1.jpg>
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>
IYSV lesions on onion leaf:
<http://www.bspp.org.uk/ndr/july2005/2005-33-2th.jpg>
Electron micrograph of _Tospovirus_ particles (TSWV):
<http://www.rothamsted.bbsrc.ac.uk/ppi/links/pplinks/virusems/b6.jpeg>
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/00.011.0.05.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>
EPPO quarantine Alert List:
<http://www.eppo.org/QUARANTINE/Alert_List/alert_list.htm>.  - Mod.DHA]

[see also in the archive:
Iris yellow spot virus, onion - Germany: 1st rep.(RP) 20080320.1072 Iris yellow spot virus, multicrop - UK, Canada: 1st reps 20080221.0698
2007
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Iris yellow spot virus, onion - South Africa: 1st rep 20070920.3129
2006
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Iris yellow spot virus, onion - Peru: 1st report 20060225.0612
2005
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Iris yellow spot virus, onion - Chile 20051128.3444 Iris yellow spot virus, onion - Spain: 1st report 20051121.3384 Iris yellow spot, onion - India (Maharashtra): 1st rep. 20050507.1266 Iris yellow spot, onion - France (Reunion Island): 1st report 20050502.1219 Iris yellow spot, onion - USA (OR) 20050112.0110
2004
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Tomato spotted wilt, Iris yellow spot, onion - USA (GA) 20041031.2938 Iris yellow spot virus, onion - USA (NM) 20040911.2529 Iris yellow spot virus, onion - USA (WA) 20040215.0492
2002
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Iris yellow spot virus, onion - USA (Colorado) 20020614.4495]

 

 

 

 

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