Increasing Outbreaks and Impact of Iris yellow spot virus in Bulb and Seed Onion Crops in the Imperial and Antelope Valleys of California

Outbreaks of IYSV were first observed in May 2003 in two Imperial County onion seed fields. In August, 2005, symptomatic onion plants were widespread in four fields in the Antelope Valley, Los Angeles County, CA. IYSV infection was confirmed by ELISA and RT-PCR. This was the first known recording of IYSV in Antelope Valley. Increasing incidence and impact of IYSV in a major onion-growing area highlights the need for research into developing managing options for this important disease of onion. Accepted for publication 22 January 2007. Published 8 May 2007.

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Outbreak of Iris yellow spot virus in Onion Seed Crops in Central Oregon

Plant Disease ◽

10.1094/pd-89-0105c ◽

2005 ◽

Vol 89 (1) ◽

pp. 105-105 ◽

Cited By ~ 14

Author(s):

F. J. Crowe ◽

H. R. Pappu

Keyword(s):

United States ◽

The United States ◽

Iris Yellow Spot Virus ◽

Yellow Spot ◽

N Gene ◽

Rt Pcr ◽

Spot Virus ◽

Seed Crop ◽

Onion Seed ◽

Seed Crops

Iris yellow spot virus (IYSV) of the genus Tospovirus, family Bunyaviridae is considered an emerging or reemerging pathogen affecting onions in the United States. The virus has been endemic to the Treasure Valley of southern Idaho for more than a decade (4). Reports of its further spread came from several states in the region, most recently from New Mexico and Washington (1,3). During the 2004 growing season, a few onion seed crops near Madras (Jefferson County) in central Oregon showed symptoms suggestive of IYSV infection, including characteristic diamond-shaped scape lesions (2). By July, scapes in one-half of a 4-ha field were 100% symptomatic and 95% lodged, leading to nearly total crop failure; in the other half, scapes were 30 to 40% symptomatic and 15% lodged, with symptoms and lodging increasing weekly at 8 weeks before harvest. The half of this crop with greater incidence was immediately adjacent to a field where very limited IYSV-like symptoms were noticed in a 2002–2003 onion seed crop that was harvested in mid-August 2003, after the highly symptomatic 2003–2004 onion seed crop was planted next to it in early July 2003. Both crops were planted from true seed. In another onion seed crop located 1,000 m away, IYSV-like symptoms were abundant around the field edges in July and through the field in August 2004, with approximately 5% lodging by mid-August. A small number of plants with IYSV-like symptoms were present in a few more distant fields, but not in most onion seed fields in central Oregon. Symptomatic plants were collected and tested in the laboratory for confirmation of IYSV infection. IYSV was confirmed using enzyme-linked immunosorbent assay (ELISA) with a commercially available antiserum (Agdia Inc., Elkhart, IN). Total nucleic acids were extracted, and using primers specific to the nucleocapsid (N) gene of IYSV (3), reverse transcription-polymerase chain reaction (RT-PCR) was done. RT-PCR gave DNA amplicons of the expected size. The DNA amplicons were cloned and sequenced. Nucleotide sequence comparisons with known IYSV N gene sequences confirmed virus identity. The rapid spread of IYSV in the Pacific Northwest and its severity of incidence often leading to 100% incidence is a cause for concern for onion growers and industry. Efforts to identify management practices to reduce its impact have to be undertaken on a regional basis because of its widespread occurrence across several states in the northwestern United States. References: (1) R. Creamer et al. Plant Dis. 88:1049, 2004 (2) L. J. du Toit et al. APSnet image of the week. On-line publication: http://apsnet.org/online/archive/ 2003/IW000030.asp , 2003. (3) L. J. du Toit et al. Plant Dis. 88:222, 2004. (4) J. M. Hall et al. Plant Dis. 77:952, 1993.

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Iris Yellow Spot Virus in Onion Bulb and Seed Crops in Washington

Plant Disease ◽

10.1094/pdis.2004.88.2.222a ◽

2004 ◽

Vol 88 (2) ◽

pp. 222-222 ◽

Cited By ~ 15

Author(s):

L. J. du Toit ◽

H. R. Pappu ◽

K. L. Druffel ◽

G. Q. Pelter

Keyword(s):

United States ◽

Iris Yellow Spot Virus ◽

Yellow Spot ◽

Onion Bulb ◽

Rt Pcr ◽

Spot Virus ◽

Seed Crop ◽

Onion Seed ◽

Seed Crops ◽

Np Gene

The geographic distribution of Iris yellow spot virus (IYSV, Genus Tospovirus, Family Bunyaviridae) in onion (Allium cepa L.) crops in the western United States has increased with the most recent report in Colorado (1,4). Furthermore, the incidence of IYSV has increased significantly in onion crops in the Treasure Valley of southern Idaho and eastern Oregon, where the disease was first detected in the United States (1,2). Surveys of onion seed crops in Washington during the past 2 years showed the presence of plants with symptoms characteristic of IYSV infection, including distinct diamond-shaped chlorotic or necrotic lesions, as well as indistinct circular to irregular, chlorotic or necrotic lesions of various sizes on the scapes of flowering plants. To date, symptomatic plants have been observed in five seed crops in Washington, at incidences ranging from <1% to approximately 20% in individual seed crops. Enzyme-linked immunosorbent assays carried out directly on symptomatic onion samples collected in July 2002, and on Nicotiana benthamiana plants mechanically inoculated with sap from these symptomatic plants, did not detect the presence of IYSV. In late July 2003, symptomatic plants were collected from an onion seed crop in Grant County and tested for IYSV infection by reverse transcription-polymerase chain reaction (RT-PCR). Total nucleic acid was extracted from symptomatic areas of the scapes with the procedure described by Presting et al. (3). Primers specific to the nucleocapsid (NP) gene of IYSV were designed based on sequences in GenBank: 5′-TCA GAA ATC GAG AAA CTT-3′ and 5′-TAA TTA TAT CTA TCT TTC TTG G-3′ (sense and antisense polarity, respectively). The RT-PCR assay produced an amplicon of the expected size (approximately 700 bp) that was cloned and sequenced. Comparison with the GenBank IYSV gene sequences showed 98% sequence identity of the NP gene. In August 2003, symptoms of IYSV infection were observed in two onion bulb crops, each located within 2 miles of the symptomatic onion seed crop in Grant County. The presence of IYSV in these crops was confirmed by RT-PCR with cloning and sequencing of the amplicon, as described for the seed crop samples. To our knowledge, this is the first confirmation of IYSV in onion bulb and seed crops in Washington, where 16,000 to 18,000 acres of onion bulb crops and 700 to 900 acres of onion seed crops are grown annually (USDA National Agricultural Statistics Service). The increase in prevalence of IYSV in the Pacific Northwest highlights the need for additional research to clarify the epidemiology of this potentially significant pathogen and to develop a regional management program for iris yellow spot. References: (1) J. M. Hall et al. Plant Dis. 77:952, 1993. (2) J. W. Moyer et al. (Abstr.) Phytopathology 93(suppl.):S115, 2003. (3) G. G. Presting et al. Phytopathology 85:436, 1995. (4) H. F. Schwartz et al. Plant Dis. 86:560, 2002.

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First Report of Iris yellow spot virus on Onion (Allium cepa) in Texas

Plant Disease ◽

10.1094/pd-90-1359b ◽

2006 ◽

Vol 90 (10) ◽

pp. 1359-1359 ◽

Cited By ~ 7

Author(s):

M. E. Miller ◽

R. R. Saldana ◽

M. C. Black ◽

H. R. Pappu

Keyword(s):

Disease Incidence ◽

Iris Yellow Spot Virus ◽

Yellow Spot ◽

N Gene ◽

Nucleotide Sequence Analysis ◽

Rt Pcr ◽

Onion Thrips ◽

Spot Virus ◽

Das Elisa ◽

Bulb Yield

Iris yellow spot virus (IYSV; family Bunyaviridae, genus Tospovirus) has emerged as a potentially devastating and widespread virus of onion. IYSV was first reported in the United States from Idaho in 1993 and has since spread to many of the onion-producing areas (1). In South America, the most recent reports of the virus on onion were from Peru and Chile (2,4). In 2005, onion plants in Uvalde County, Texas exhibited necrotic lesions on leaves typical of IYSV and disease incidence approached 100% in some fields with yield loss and quality problems. Five of six plants tested were positive for IYSV with double antibody sandwich-enzyme linked immunosorbent assay (DAS-ELISA; Agdia Inc., Elkhart, IN). In 2006, similar lesions were observed on onion plants in Uvalde County and approximately 400 km south in Hidalgo and Cameron counties. Infection points generally started as a single plant near the edge of fields and spread to plants in a 3- to 4-m area after 1 to 2 weeks. Early-season disease incidence was low in onions grown for bulbs and transplants, <10% in 2006. Disease incidence increased in some fields until the crop was harvested. Leaves of symptomatic plants were tested for IYSV and Tomato spotted wilt virus (TSWV) using DAS-ELISA, and 18 of 23 samples from the Hidalgo County area and 12 of 21 samples from the Uvalde County area were positive for IYSV. All samples tested for TSWV from these counties were negative. Virus infection in some ELISA-positive plants was verified by reverse transcription-polymerase chain reaction (RT-PCR) using primers derived from the small RNA of IYSV. The primers flanked the IYSV nucleocapsid (N) gene (5′-TAA AAC AAA CAT TCA AAC AA-3′ and 5′-CTC TTA AAC ACA TTT AAC AAG CAC-3′ (3). RT-PCR gave a PCR product of expected size (approximately 1.2 kb). The DNA amplicon was cloned and sequenced (GenBank Accession No. DQ658242). Nucleotide sequence analysis confirmed the identity of the amplicon as that of IYSV N gene and sequence comparisons with known IYSV N gene sequences showed 95 to 98% sequence identity. The primary vector of IYSV, onion thrips (Thrips tabaci), is a widespread and destructive pest of onion in south Texas. The year-to-year incidence of IYSV and the severity of the disease will probably depend on the onion thrips population levels. Bulb yield reduction could be severe during years with high thrips populations. More research is needed to determine the impact of IYSV on bulb yield in Texas, the relationship between IYSV incidence and T. tabaci population levels, and oversummering hosts. To our knowledge, this is the first known report of IYSV in Texas. References: (1) D. H. Gent et al. Plant Dis. 88:446, 2004, (2) S. W. Mullis et al. Plant Dis. 90:377, 2006, (3) H. Pappu et al. Arch. Virol. 151:1015, 2006. (4) M. Rosales et al. Plant Dis. 89:1245, 2005.

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Iris yellow spot virus in Onion Seed Crops in South Africa

Plant Disease ◽

10.1094/pdis-91-9-1203a ◽

2007 ◽

Vol 91 (9) ◽

pp. 1203-1203 ◽

Cited By ~ 6

Author(s):

L. J. du Toit ◽

J. T. Burger ◽

A. McLeod ◽

M. Engelbrecht ◽

A. Viljoen

Keyword(s):

South Africa ◽

Iris Yellow Spot Virus ◽

Yellow Spot ◽

Onion Bulb ◽

Western Cape ◽

Spot Virus ◽

Total Rna ◽

Onion Seed ◽

Seed Crops ◽

Np Gene

In December 2006, symptoms typical of iris yellow spot caused by Iris yellow spot virus (IYSV; genus Tospovirus, family Bunyaviridae) were observed on scapes (seed stalks) in an onion (Allium cepa L.) seed crop in the Klein Karoo of the Western Cape Province, South Africa. Symptoms included diamond-shaped chlorotic or necrotic lesions on the scapes, some of which had ‘green-islands’ with nested diamond-shaped lesions, as well as indistinct, circular to irregular, chlorotic or necrotic lesions of various sizes. At the time symptoms were observed, approximately 5% of the scapes had lodged as a result of extensive lesions resembling those caused by IYSV. The crop was 2 to 3 weeks from harvest. Symptomatic tissue from two plants (two samples from one plant and four samples from the other plant) was tested for IYSV by reverse-transcriptase (RT)-PCR. Total RNA was extracted from symptomatic scape tissue with the SV Total RNA Isolation System (Promega, Madison, WI) according to the manufacturer's instructions. First strand cDNA was synthesized with the RevertAid H Minus First Strand cDNA Synthesis kit (Fermentas Inc., Hanover, MD), followed by PCR amplification with primers IYSV-For (TGG YGG AGA TGY RGA TGT GGT) and IYSV-Rev (ATT YTT GGG TTT AGA AGA CTC ACC), which amplify the nucleocapsid (NP) gene of IYSV. An amplicon of expected size (approximately 750 bp) was observed for each of the symptomatic plants assayed and was sequenced. Comparison of the sequence (GenBank Accession No. EF579801) with GenBank sequences revealed 95% sequence identity with the NP gene of IYSV GenBank Accession No. EF419888, with eight amino acid differences. The known geographic distribution of IYSV in onion bulb or seed crops has increased rapidly in recent years in many areas of the world (1). To our knowledge, this is the first confirmation of IYSV in South Africa. Approximately 6,100 ha of onion bulb crops are grown annually in South Africa in the Western Cape, Kwazulu Natal, Limpopo, and Northern Cape provinces, and 600 ha of onion seed crops are grown primarily in the semi-arid regions of the Western Cape. Examination of an additional 10 onion seed crops in the Klein Karoo during January 2007 revealed the presence of iris yellow spot in three more crops at approximately 5% incidence in each crop. The four symptomatic crops had all been planted as bulb-to-seed crops, using vernalized bulbs produced on the same farm. This suggests that IYSV may have been disseminated into the seed crops on the vernalized bulbs, either as infected bulb tissue or in viruliferous thrips on the bulbs. Reference: (1) D. H. Gent et al. Plant Dis. 90:1468, 2006.

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First Report of Iris yellow spot virus in Onion in Hawaii

Plant Disease ◽

10.1094/pdis-07-10-0531 ◽

2010 ◽

Vol 94 (12) ◽

pp. 1508-1508 ◽

Cited By ~ 4

Author(s):

D. M. Sether ◽

W. B. Borth ◽

R. S. Shimabuku ◽

H. R. Pappu ◽

M. J. Melzer ◽

...

Keyword(s):

United States ◽

New Zealand ◽

Phylogenetic Analyses ◽

Leaf Tissue ◽

Iris Yellow Spot Virus ◽

Yellow Spot ◽

N Gene ◽

Sequence Variants ◽

Rt Pcr ◽

Spot Virus

Onion (Allium spp.) production in Hawaii is mostly comprised of green onion and the locally prized sweet bulb onions (Allium cepa L.) that include short- and medium-day cultivars. Iris yellow spot virus (IYSV; family Bunyaviridae, genus Tospovirus) is an important constraint to bulb and seed onion production in many onion-growing regions of the continental United States and the world (3). In June 2010, straw-colored, diamond-shaped lesions with occasional green islands were observed on leaves of sweet onion ‘Linda Vista’ in an insecticide trial on Maui for onion thrips (Thrips tabaci) control. Collapse and lodging occurred when lesions on leaves were severe. Seven bulbs with green leaves exhibiting lesions were collected from this onion field in the Pulehu Region of the lower Kula District on Maui. Leaf samples that included a lesion or were within 1 cm of a lesion were found to be positive in indirect ELISA with IYSV-specific polyclonal antisera (2). A405nm readings after 1 h ranged from 0.263 to 2.067 for positive samples and 0.055 to 0.073 for healthy onion controls. Four samples that were prepared from leaf tissue several centimeters away from a lesion tested negative in ELISA. Such uneven virus distribution in the plants has been previously reported (4). In July 2010, symptomatic sweet onion from a commercial farm in upper Kula, Maui at the 1,060 to 1,220 m (3,500 to 4,000 foot) elevation tested positive for IYSV by ELISA. Green onion samples collected from a commercial farm in Omaopio, Maui, located approximately 0.8 km (0.5 mile) north of Pulehu, have tested negative, suggesting distribution may be limited at this time. RNA was isolated from leaf tissue from the seven ‘Linda Vista’ sweet onions collected from the Maui insecticide trial. Reverse transcription (RT)-PCR with forward and complementary primers 5′-CTCTTAAACACATTTAACAAGCAC-3′ and 5′-TAAAACAAACATTCAAACAA-3′ flanking the nucleocapsid (N) gene encoded by the small RNA of IYSV was conducted as previously described (1). Amplicons approximately 1.1 kb long were obtained from all seven symptomatic onion samples but not from healthy samples or water controls. Sequencing of selected amplicons confirmed IYSV infection. Three sequence variants (GenBank Accession Nos. HM776014–HM776016) were identified from two RT-PCR reactions. Phylogenetic analyses of the three sequence variants with the neighbor-joining procedure available through NCBI-BLASTn Tree View showed that the highest nucleotide identities of 97 to 98% were shared with IYSV isolates from New Zealand (EU477515), Nevada (FJ713699), and northern California (FJ713700). Phylogenetic analyses with the N-gene showed the sequences from Hawaii are most closely related to isolates from the western United States, Texas, and New Zealand. To date, to our knowledge, IYSV has not been detected on the islands of Kauai, Oahu, Molokai, or Hawaii. The distribution and economic consequences of this disease to Hawaii's onion production are under investigation. References: (1) H. R. Pappu et al. Arch Virol. 151:1015, 2006. (2) H. R. Pappu et al. Plant Dis. 92:588, 2008. (3) H. R. Pappu et al. Virus Res. 141:219, 2009. (4) T. N. Smith et al. Plant Dis. 90:729, 2006.

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Susceptibility of Onion Relatives (Allium spp.) to Iris yellow spot virus

Plant Disease ◽

10.1094/pdis-11-10-0819 ◽

2011 ◽

Vol 95 (10) ◽

pp. 1319-1319 ◽

Cited By ~ 1

Author(s):

C. S. Cramer ◽

S. Bag ◽

H. F. Schwartz ◽

H. R. Pappu

Keyword(s):

Iris Yellow Spot Virus ◽

Yellow Spot ◽

N Gene ◽

Rt Pcr ◽

Sources Of Resistance ◽

Spot Virus ◽

Allium Species ◽

Elisa Kit ◽

Important Constraint ◽

Allium Cepa L

Iris yellow spot virus (IYSV; family Bunyaviridae, genus Tospovirus) is becoming an increasingly important constraint to the production of bulb and seed onions (Allium cepa L.) in many onion-growing regions of the continental United States and the world (4). During an evaluation of onion germplasm for susceptibility to IYSV, six other Allium species (A. altaicum, A. galanthum, A. roylei, A. schoenoprasum, A. tuberosum, and A. vavilovii) were also evaluated under natural field conditions. In July 2010, symptoms suggestive of IYSV infection (straw-colored necrotic lesions) were observed on leaves of these Allium spp. in experimental plots in Las Cruces, NM. IYSV was detected in symptomatic leaves of A. altaicum, A. vavilovii, A. tuberosum, A. schoenoprasum and A. roylei with a commercially available ELISA kit (Agdia Inc., Elkhart, IN). IYSV infection was confirmed by reverse transcription (RT)-PCR with forward and complementary primers 5′-CTCTTAAACACATTTAACAAGCAC-3′ and 5′-TAAAACAAACATTCAAACAA-3′ flanking the nucleocapsid (N) gene encoded by the small RNA of IYSV as previously described (1,3). Amplicons, approximately 1.1 kb long, were obtained from all symptomatic Allium spp. samples but not from healthy samples or water controls. Sequencing of selected amplicons confirmed IYSV infection. The highest nucleotide identity of 98% was shared with IYSV isolates from Japan (GenBank Accession No. AB180921). A. altaicum, A. vavilovii, and A. pskemense were previously reported from Washington to be susceptible to IYSV (2). Current findings expand the list of Allium spp. that are susceptible to IYSV and underscores the need for continued screening of other members of the genus to find sources of resistance to IYSV. References: (1) H. R. Pappu et al. Arch. Virol. 151:1015, 2006. (2) H. R. Pappu et al. Plant Dis. 90:378, 2006. (3) H. R. Pappu et al. Plant Dis. 92:588, 2008. (4) H. R. Pappu et al. Virus Res. 141:219, 2009.

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First Report of Iris yellow spot virus on Onion in New York

Plant Disease ◽

10.1094/pdis-91-3-0327a ◽

2007 ◽

Vol 91 (3) ◽

pp. 327-327 ◽

Cited By ~ 13

Author(s):

C. A. Hoepting ◽

H. F. Schwartz ◽

H. R. Pappu

Keyword(s):

United States ◽

New York ◽

Iris Yellow Spot Virus ◽

Yellow Spot ◽

N Gene ◽

Nucleotide Sequence Analysis ◽

Rt Pcr ◽

Onion Thrips ◽

Spot Virus ◽

First Report

Iris yellow spot virus (IYSV [family Bunyaviridae, genus Tospovirus]), a potentially devastating disease of onion vectored by onion thrips (Thrips tabaci Lindeman), has been reported from most states in the western United States where significant onion production occurs, with the most recent report from Texas (1). In June 2006, volunteer onion (Allium cepa) plants in Orleans County, New York (Elba muckland) were found to have symptoms indicative of IYSV infection. The scapes (seed stalks) of the volunteer onions found at the edge of a cull pile from a 2005 onion crop exhibited diamond-shaped lesions, each with a distinct green center and a double yellow border. Approximately 25 of 100 plants of red and yellow onion cultivars exhibited characteristic IYSV lesions. The cull pile was composed primarily of locally grown onions, although a few of the bulbs were grown from imported bare-root transplants imported from Arizona. Symptomatic plants tested positive for IYSV using IYSV-specific antiserum from Agdia Inc. (Elkhart, IN) in a double-antibody sandwich-ELISA. The presence of IYSV was verified by reverse transcription (RT)-PCR using primers derived from the small RNA of IYSV (S-RNA). The primers flanked the IYSV nucleocapsid (N) gene (5′-TAA AAC AAA CAT TCA AAC AA-3′ and 5′-CTC TTA AAC ACA TTT AAC AAG CAC-3′ (3). RT-PCR assays produced a PCR amplicon of expected size (approximately 1.2 kb) and the product was cloned and sequenced. Nucleotide sequence analysis confirmed the identity of the amplicon as that of the IYSV S-RNA. Sequence comparisons showed 95 to 98% identity with known IYSV N gene sequences available in GenBank. The virus is poorly transmitted to onion by mechanical inoculation and we did not have access to a noninfested colony of the onion thrips vector to transfer the virus from these samples to noninfected onions. No asymptomatic plants were tested. Among the onion-growing states in the eastern United States, IYSV has previously only been reported from Georgia (2). To our knowledge, this is the first report of IYSV in New York and the greater northeastern United States. The finding of this disease in New York 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 crops. References: (1) M. Miller et al. Plant Dis. 90:1359, 2006. (2) S. W. Mullis et al. Plant Dis. 90:377, 2006. (3) H. R. Pappu et al. Arch. Virol. 151:1015, 2006.

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Iris yellow spot virus: A New Onion Disease in Spain

Plant Disease ◽

10.1094/pd-89-1243a ◽

2005 ◽

Vol 89 (11) ◽

pp. 1243-1243 ◽

Cited By ~ 14

Author(s):

C. Córdoba-Sellés ◽

L. Martínez-Priego ◽

R. Muńoz-Gómez ◽

C. Jordá-Gutiérrez

Keyword(s):

Plant Protection ◽

Iris Yellow Spot Virus ◽

Yellow Spot ◽

Enzyme Linked Immunosorbent Assay ◽

Rt Pcr ◽

Pcr Assay ◽

Spot Virus ◽

Nucleocapsid Gene ◽

Pcr Product ◽

Mediterranean Plant

So far, only three viral diseases have been identified in onion crops grown in Spain. These are Tomato spotted wilt virus (TSWV), Onion yellow dwarf virus (OYDV), and Leek yellow stripe virus (LYSV). In September 2003, unusual virus-like symptoms including straw-colored, dry, tan, diamond-shaped lesions on the leaves and stalks, sometimes with necrotic lesions, curled leaves, and bulbs of reduced size, were observed on several onion plants (Allium cepa L.) in commercial fields in Albacete, Spain. Severely affected plants eventually died. To verify the identity of the disease found in the Spanish onions, double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) was performed on leaf extracts of symptomatic onions using specific polyclonal antibodies against OYDV, LYSV, Cucumber mosaic virus (CMV) (Biorad Phyto-Diagnostics, Marnes-La Coquette, France), Iris yellow spot virus (IYSV), and TSWV (Loewe Biochemica, Sauerlach, Germany). All samples of infected onion tissue were positive for IYSV and negative for the other viruses tested. To confirm the ELISA results, viral RNA was extracted from five of the ELISA-positive onion samples, a healthy onion plant, and a positive control for IYSV (DSMZ, Braunschweig. Germany). The extracted RNA was used in a One-Step reverse transcription-polymerase chain reaction (RT-PCR) assay using SuperScript Platinum Taq (Invitrogen Life Technologies, Barcelona, Spain) in the presence of the IYSV1S and IYSV1A primers for the nucleocapsid gene of IYSV (1). The RT-PCR assay produced an amplicon of the expected size of 790 bp. No amplification products were observed when healthy plants or a water control were used as templates in the RT-PCR reaction. To establish the authenticity of the virus from onion, the PCR products were purified (High Pure PCR Product Purification Kit, Roche Diagnostics, Mannheim, Germany), sequenced, and the nucleotide sequences obtained were analyzed and compared with the published sequences in GenBank. The PCR product was 97% identical to the sequence of the IYSV nucleocapsid gene (Genbank Accession No. AB121026). IYSV, an emerging tospovirus that is potentially a devastating pathogen of onion, has been reported in many locations in Brazil, Japan, the Netherlands, Israel, Australia, the western United States, Slovenia, and Iran (2). IYSV is included in the European and Mediterranean Plant Protection Organization alert list of viruses (2), and to our knowledge, this is the first report of IYSV in Spain. This tospovirus is transmitted in a propagative manner by Thrips tabaci. Although the vector is present in large populations in the onion-growing areas in Spain, the efficiency of the Mediterranean ecotype in transmitting IYSV is not known. References: (1) B. A. Coutts et al. Australas. Plant Pathol. 32:555, 2003. (2) European and Mediterranean Plant Protection Organization. EPPO on-line publication at www.eppo.org/QUARANTINE/Alert_List/Viruses/irysxx.html .

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Serological and Molecular Assays for Rapid and Sensitive Detection of Iris yellow spot virus Infection of Bulb and Seed Onion Crops

Plant Disease ◽

10.1094/pdis-92-4-0588 ◽

2008 ◽

Vol 92 (4) ◽

pp. 588-594 ◽

Cited By ~ 24

Author(s):

H. R. Pappu ◽

I. M. Rosales ◽

K. L. Druffel

Keyword(s):

Real Time ◽

Rapid Detection ◽

The United States ◽

Iris Yellow Spot Virus ◽

Yellow Spot ◽

Sensitive Detection ◽

Detection Methods ◽

Enzyme Linked Immunosorbent Assay ◽

Rt Pcr ◽

Spot Virus

Iris yellow spot virus (IYSV) has spread rapidly in the United States and has become an important economic constraint to the production of both bulb and seed onion crops. Symptoms caused by IYSV may be confused with those caused by other fungal and bacterial pathogens and virus-specific, reliable, sensitive, and rapid detection methods would improve the diagnosis. Antiserum was produced to Escherichia coli-expressed nucleocapsid protein of IYSV and an indirect format of the enzyme-linked immunosorbent assay (ELISA) was developed. IYSV could be detected in onion tissue at dilutions of up to 1:1,000. An IYSV-specific primer pair was designed and used in a real-time reverse-transcription polymerase chain reaction (RT-PCR) assay for the rapid detection of IYSV. Compared with standard RT-PCR, real-time RT-PCR was more rapid and sensitive. A commercially available RNA extraction kit and a total nucleic acid extraction method were compared for the quality of the templates obtained for use in real-time RT-PCR and there was no difference in limits of detection. Availability of ELISA- and PCR-based rapid and sensitive detection methods would facilitate accurate virus diagnosis and aid in better understanding of the epidemiology of the disease and in development of management strategies.

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First Report of Iris yellow spot virus in Commercial Leek (Allium porrum) in the United States

Plant Disease ◽

10.1094/pd-91-0113b ◽

2007 ◽

Vol 91 (1) ◽

pp. 113-113 ◽

Cited By ~ 5

Author(s):

H. F. Schwartz ◽

K. Otto ◽

H. R. Pappu

Keyword(s):

United States ◽

The United States ◽

Iris Yellow Spot Virus ◽

Yellow Spot ◽

N Gene ◽

Allium Porrum ◽

Rt Pcr ◽

Spot Virus ◽

Disease Symptoms ◽

First Report

Iris yellow spot virus (IYSV; family Bunyaviridae, genus Tospovirus) has a wide host range, with onion (Allium cepa L.) being one of the most economically important hosts. IYSV has been widely reported from this species throughout most onion-production regions of the United States and many areas of the world in recent years. A relative of onion, leek (Allium porrum L.), has been reported to be a host of IYSV in countries such as the Netherlands, Reunion Island, and Australia (1,4). A related tospovirus, Tomato spotted wilt virus (TSWV), was recently reported causing necrotic lesions and extended bleaching of leaf tips of leek in Georgia (2). In September of 2006, disease symptoms suspected to be caused by IYSV were observed on central and outer leaves of plants in a 2.6-ha section of commercial leeks being grown from seed (cvs. Tadorna and King Richard). The leek plants were adjacent to a 3.1-ha section of seeded onion (cv. Exacta) that had been harvested 2 weeks earlier. Twenty-five to thirty percent of unharvested onion plants next to the leek section also exhibited IYSV-type disease symptoms generally on the central leaves. Both Allium spp. were seeded 5 months earlier and grown under certified organic, pivot-irrigated conditions in Larimer County in northern Colorado. Disease symptoms on leek and onion leaves appeared as dry, white-to-straw-colored, spindle- or diamond-shaped lesions that ranged in size from 5 to 10 × 25 to 50 mm or larger depending on lesion age. Lesion centers, especially on leek, often had green centers with concentric rings of alternating green and straw-colored tissue. Green tissue near necrotic lesions of a single symptomatic leaf from 10 plants each of leek and onion was sampled and analyzed using a double-antibody sandwich (DAS)-ELISA (Agdia, Inc., Elkhart, IN). Five of ten leek and nine of ten onion samples were positive for IYSV. Using reverse transcription (RT)-PCR and primers specific to the small RNA of IYSV (5′-TAA AAC AAA CAT TCA AAC AA-3′ and 5′-CTC TTA AAC ACA TTT AAC AAG CAC-3′), the complete nucleocapsid (N) gene was amplified from symptomatic leek plants and then sequenced (3). Comparisons with IYSV N gene sequences available in the GenBank confirmed the identity of the virus as IYSV. Leek samples were negative for TSWV when tested by RT-PCR with TSWV-specific primers. In addition, three specimens of the presumed thrips vector recovered from five IYSV-infected leek plants were identified as Thrips tabaci (L. A. Mahaffey and W. S. Cranshaw, personal communication). Earlier in the season, T. tabaci was observed in the nearby planting of onion that also exhibited IYSV in September. To our knowledge, this is the first report of natural infection of commercial leek with IYSV in the United States. The incidence of plants (25 to 30%) with foliar lesions on multiple leaves and stunting of 5% of infected plants in both leek cultivars suggests that IYSV could seriously reduce leek stem development and marketability. References: (1) I. Cortes et al. Phytopathology 88:1276, 1998. (2) C. Nischwitz et al. Plant Dis. 90:525, 2006. (3) H. R. Pappu et al. Arch. Virol. 151:1015, 2006. (4) T. N. Smith et al. Plant Dis. 90:729, 2006.

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