November 27, 2005
From: American Phytopathological Society, Plant Disease Notes, November 2005 [edited] <http://www.apsnet.org/pd/searchnotes/2005/PD-89-1245C.asp>

Iris yellow spot virus in onion in Chile
M. Rosales, Instituto de Investigaciones Agropecuarias, Centro Regional de Investigacion La Platina, Santiago, Chile; H. R. Pappu, Department of Plant Pathology, Washington State University, Pullman 99164-6430; L. Lopez, Laboratorio de Virologia, Servicio Agricola y Ganadero, Santiago, Chile; and R. Mora and A. Aljaro, Instituto de Investigaciones Agropecuarias, Centro Regional de Investigacion La Platina, Santiago, Chile. Plant Dis. 89:1245, 2005; published on-line as DOI: 10.1094/PD-89-1245C. Accepted for publication 24 Aug 2005.

Iris yellow spot virus (IYSV) (genus _Tospovirus_, family _Bunyaviridae_) has become endemic in several parts of the world. Between 2000 and 2004, the virus was reported from several states in the United States, and the most recent report was from Georgia (2). In South America, IYSV was 1st reported from Brazil (3).

Symptoms indicative of IYSV infection (1), such as diamond-shaped and irregular chlorotic and necrotic lesions, were observed during 2004 and 2005 in onion fields in Colina and Tiltil (Chacabuco Province) and Rengo (Cachapoal Province) located in central Chile. In the sampled fields, as much as 50 percent of the crop showed symptoms. In all 3 locations, the crop was destined for bulb production, and the cultivar was a long-day Valenciana-type.

Approximately 50 and 5 ha in Chacabuco and Cachapoal provinces, respectively, were surveyed. Symptomatic plants were collected and tested in the laboratory for confirmation of IYSV infection. A commercially available IYSV-specific enzyme-linked immunosorbent assay kit was used (Adgen Limited, Ayr, Scotland, UK) that confirmed the samples were infected with IYSV.

Total nucleic acids were extracted, and, using primers flanking the nucleoprotein (NP) gene of IYSV, reverse transcription-polymerase chain reaction was used to verify virus identity. Primer sequences were 5'-TAA AAC AAA CAT TCA AAC AA-3' and 5'-CTC TTA AAC ACA TTT AAC AAG CAC-3'.

The resulting 1.2-kb DNA amplicons from 5 samples were cloned and sequenced (GenBank Accession No. DQ150107). Nucleotide sequence comparisons with known IYSV NP gene sequences showed 95 to 98 percent
identity, confirming the virus as IYSV.

The presence of IYSV in Brazil, and now in Chile, indicates its potential to become established in onion crops in the region.

References:
(1) L. J. du Toit et al. APSnet Image of the Week.
<http://apsnet.org/online/archive/2003/IW000030.asp, 2003>.
(2) S. W. Mullis et al. Plant Dis. 88:1285, 2004.
(3) L. Pozzer et al. Plant Dis. 83:345,1999.

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[IYSV is transmitted by the Onion thrips (_Thrips tabaci_), but does not appear to be transmitted by the Western flower thrips (_Frankliniella occidentalis_). It mainly infects onion, garlic, leek, lisianthus and iris (it was 1st isolated from iris, hence the name Iris yellow spot virus). There is no evidence of it being seedborne. The industry is concerned about the potential impact of IYSV in Washington state, particularly because it has been recorded as present in Colorado, Arizona, Utah and California.

IYSV-infected onions cannot be cured. Infected plants should be removed and destroyed, along with cull piles and volunteers. Maintaining good cultural management practices will help to reduce stress on the plants, thus lessening the disease's effect. 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 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.

Links:
<http://www.cahe.nmsu.edu/pubs/_h/H-255.pdf>
<http://edis.ifas.ufl.edu/PP134>
<http://www.cce.cornell.edu/~Ontario/agriculture/commercial_vegetables/vegetable_newsletter/000232.php>
<http://www.nysaes.cornell.edu/ent/hortcrops/english/thrips.html>
<http://www.biocontrol.ucr.edu/WFT.html>
- Mod.DH]

[see also in the archive:
Iris yellow spot, onion - USA (OR) 20050112.0110
Iris yellow spot, onion - France (Reunion Island): 1st report 20050502.1219
Iris yellow spot, onion - India (Maharashtra): 1st rep. 20050507.1266
Iris yellow spot virus, onion - Spain: 1st report 20051121.3384
2004
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Iris yellow spot virus, onion - USA (WA) 20040215.0492
Iris yellow spot virus, onion - USA (NM) 20040911.2529
2002
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Iris yellow spot virus, onion - USA (Colorado) 20020613.4489
Iris yellow spot virus, onion - USA (Colorado) 20020614.4495]