February 26, 2006
From: ProMED-mail<promed@promedmail.org>
Source: American Phytopathological Society, Plant Disease Notes, March 2006 [edited] <http://www.apsnet.org/pd/searchnotes/2006/PD-90-0377A.asp>

First report of onion naturally infected with iris yellow spot virus in Peru
SW Mullis, RD Gitaitis, C Nischwitz, AS Csinos, Department of Plant Pathology, Coastal Plain Experiment Station, University of Georgia, PO Box 748, Tifton 31794; ZC Rafael Mallaupoma, EH Inguil Rojas, National Onion
Labs, Lima, Peru. Plant Dis 2006; 90: 377, published online as DOI: 10.1094/PD-90-0377A. Accepted for publication 26 Dec 2005.

Onions have become an important export crop for Peru in the past few years. The onions produced for export are primarily short-day onions and include Grano- or Granex-type sweet onions. The 1st of 2 growing seasons for onion in Peru occurs from February/March until September/October and the 2nd occurs from September/October to December/January.

Iris yellow spot virus (IYSV [family Bunyaviridae, genus Tospovirus]), primarily transmitted by onion thrips (_Thrips tabaci_), has been reported in many countries in recent years, including the United States (1,2). In
South America, the virus was reported in Brazil in 1999 (3) and most recently in Chile in 2005 (4). In 2003 an investigation of necrotic lesions and dieback in onions grown near the towns of Supe and Ica, Peru led to the
discovery of IYSV in this region.

Of 25 samples of symptomatic plants collected from 5 different fields near Supe, 19 tested strongly positive and an additional 3 tested weakly positive for IYSV using double antibody sandwich-enzyme linked immunosorbent assay (DAS-ELISA) (Agdia Inc, Elkhart, IN). None of the samples tested positive for Tomato spotted wilt virus (TSWV). A number of onions with necrosis and dieback symptoms were also observed in 2004 and 2005. In September 2005, 25 plants with symptoms suspected to be caused by IYSV or TSWV in the Supe and Casma valleys were collected and screened for both viruses using DAS-ELISA. All plants screened were positive for IYSV.
There was no serological indication of TSWV infection in these samples. The positive samples were blotted onto FTA cards (Whatman Inc, UK) to bind the viral RNA for preservation and processed according to the manufacturer's protocols.

The presence of IYSV was verified by reverse transcription-polymerase chain reaction (RT-PCR) using (5(prime)-TCAGAAATCGAGAAACTT-3(prime)) and (5(prime)-TAATTATATCTATCTTTCTTGG-3(prime)) as forward and reverse primers (1), respectively. The primers amplify the nucleocapsid (N) gene of IYSV, and the RT-PCR products from this reaction were analyzed with gel electrophoresis with an ethidium bromide stain in 0.8 per cent agarose to verify the presence of this amplicon in the samples. After the September 2005 sampling, 72 additional samples from regions in northern and southern Peru were analyzed in the same manner. The amplicons obtained were cloned, sequenced, and compared with known IYSV isolates for further verification. Onions have become a significant export crop for Peru, and more research is needed to determine the impact of IYSV on the Peruvian onion export crop. To our knowledge, this is the first report of IYSV in onion in Peru.

References:
1. L du Toit, et al. Plant Dis 2004; 88: 222.
2. SW Mullis, et al. Plant Dis 2004; 88: 1285.
3. L Pozzer, et al. Plant Dis 1999; 83: 345.
4. M Rosales, et al. Plant Dis 2005; 89: 1245.

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ProMED-mail
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[This is the 1st report of the tospovirus iris yellow spot virus (IYSV) in onions (_Allium cepa_) in Peru. The samples tested were collected in 2003 and 2005 near the towns of Supe and Ica (see maps) in Peru, extending the range of the virus in South America from previous reports in Brazil (1999) and Chile (2005). See link to the disease distribution map for other countries, including USA, Spain, and Australia. It causes disease in the
crop plants onion and leek and in the ornamental plant iris (where it was first detected). Affected onion plants show numerous eyelike spots on the leaves and flower stalks resulting in flower abortion. The economic impact
of iris yellow spot virus can be severe in Brazil, where up to 100 per cent loss has been observed in onion fields.

_Thrips tabaci_ can transmit the virus, but _Frankliniella schultzei_ and _F. occidentalis_ are not thrip vectors. Recent studies showed that onion bulbs and seeds did not transmit the virus to progeny. Further studies are
needed to better understand the epidemiology of the disease in the field. In order to manage the disease, infected plants should be removed and destroyed, along with cull piles and volunteers. Other management practices include maintaining good soil fertility and adequate irrigation supplemented with good management of thrips and weeds. Onion thrips are best managed with chemical insecticides. Although no onion cultivars are
known to be resistant to IYSV, research has shown that cultivars vary in their susceptibility to both the virus and the thrips vector.

Maps:
Supe, Peru
Ica, Peru

Map of worldwide distribution of IYSV
<http://www.eppo.org/QUARANTINE/Alert_List/viruses/maps/IYSV00_map.pdf>
Pictures:
Symptoms of IYSV on an individual onion plant.
<http://www.apsnet.org/online/Archive/2003/IW000030.jpg >
Collection of images of IYSV infected onions in an infected field with thrips damage and virus symptoms.
<http://66.54.153.89/CSUag.ASP?WCI=Select_view1&WCE=CD;60;2403;1;1;2;;2403;;;;;&WCU=6/19/20047:08:24%20PM;TT;5;4;1>
Links:
<http://extension.usu.edu/plantpath/exoticpests/iris_yellow_spot_virus.pdf>
<http://www.eppo.org/QUARANTINE/Alert_List/viruses/irysxx.htm> - Mod.JAD]

[see also in the archive:
ProMED-Plant Disease Report: July - December 2005 20060201.0331
2005
---
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
Allium viruses - USA (WA): 1st reports 20050218.0535
Iris yellow spot, onion - USA (OR) 20050112.0110
2004
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Quarantine pests, new data - EPPO (05) 20041106.3007
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
Iris yellow spot virus, onion - USA (Colorado) 20020613.4489]