Iris Yellow Spot Virus Research Articles

Trap Crops in Onion to Reduce Onion Thrips andIris Yellow Spot Virus

Onion thrips, Thrips tabaci Lindeman, a primary insect pest of onions, Allium cepa L., worldwide, reduces yield and transmits a devastating Tospovirus, Iris yellow spot virus. Costly and frequent insecticide application and increased resistance of onion thrips to insecticide prompted interest in alternative pest management options. Three trap crops, lacy phacelia (Phacelia tanacetifolia Benth.), buckwheat (Fagopyrum esculentum Moench.), and carrot (Daucus carota L.) planted in commercial onion fields during two growing seasons were evaluated for attractiveness to onion thrips. Abundance of thrips adults, larvae, and eggs were monitored on trap crops and onion plants, and dispersing adults were counted on aerial traps 0, 0.8, 6.4, and 12.8 m from trap crop rows. All trap crops when flowering or with lush vegetation supported all life stages of onion thrips during at least 1 of 2 years; trends in preference by onion thrips varied. Incidence of Iris yellow spot virus was low ranging from 6.6 to 8.2% in year 2; however, in late September of the second year, incidence was greater near trap crops than at farther distances, as measured by enzyme-linked immunosorbent assay (ELISA). Trap crops were attractive to onion thrips adults in June and July which suggests promise for decreasing numbers of thrips on onion during critical periods of bulb sizing and spread of Iris yellow spot virus; however, the short distance of influence suggested need for larger plot sizes or better sampling methods. Potential for planting trap crops along field edges to attract migrating adult thrips early in the season is discussed.

AN AFRICAN PERSPECTIVE ON TOSPOVIRUSES

Tospoviruses, an emerging group of plant viruses, infect food crops and ornamental plants causing billions of dollars in losses worldwide. There are at least 28 Tospovirus species worldwide, most of which are found in tropical and subtropical environments. Despite having a largely tropical climate, Africa has only five reported species namely: Tomato spotted wilt virus (TSWV), Groundnut ringspot virus (GRSV), Impatiens necrotic spot virus (INSV), Tomato yellow ring virus (TYRV) and Iris yellow spot virus (IYSV). The low tospovirus diversity on the continent is mainly due to lack of surveys. Most Tospovirus species have only been reported in the last twenty-five years, yet no surveys have been done in most African countries. Most African countries lack institutional and infrastructural capacities to carry out virology research. This article reviews the characteristics and control of tospoviruses, with a bias towards those found in Africa.

Amaranthus sp. and Eleusine indica are natural hosts of Iris yellow spot virus in Zimbabwe

<i>Amaranthus</i> sp. and <i>Eleusine indica</i> are natural hosts of <i>Iris yellow spot virus</i> in Zimbabwe

Iris yellow spot virus in Zimbabwe: Incidence, severity and characterization of Allium-infecting isolates

Iris yellow spot virus (IYSV), an emerging pathogen of alliaceous crops, has been reported in many countries worldwide. The pathogen has recently been reported infecting garlic (Allium sativum), leek (A. ampeloprasum) and onion (A. cepa) in Zimbabwe. A study was carried to determine its incidence, severity and distribution in Zimbabwe. IYSV disease surveys were conducted in 18 districts across six provinces. Symptomatic alliaceous leaf samples were tested for IYSV by double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA). Furthermore, the pathogen was characterized by transmission studies, transmission electron microscopy and molecular assays. The pathogen was detected in garlic, leek, shallot (A. aggregatum) and onion crops in all districts, with disease incidences ranging from 26.7 to 78.8% and disease severities of up to 3.7 in some districts. Up to 70% of onion seedlings that were mechanically inoculated with sap from diseased onion plants produced typical IYSV symptoms characterized by green chlorotic tissues surrounded by tan-colored necrotic tissues. Electron microscopy studies revealed spherical enveloped particles that were 80–120 nm in diameter. Analysis of the partial nucleocapsid protein (N) gene of the Zimbabwean IYSV isolates revealed that they were at least 94.89% identical and similar to each other at nucleotide and amino acid levels. These isolates were closely related to isolates from Asia, Australia, Europe, South Africa and the USA, but were distinct from isolates from Brazil, The Netherlands and The UK. Further work to ascertain the pathogen's economic impact needs to be carried out. In addition, farmers need to be educated about the disease so that they can control it by growing resistant varieties and/or controlling the vector.

Effect of Jojoba Seed Extract and Riboflavin in Preventing the Transmission of Iris Yellow Spot Virus (IYSV): Tospovirus by Thrips tabaci L. to Onion Plants in Egypt

Effect of Jojoba Seed Extract and Riboflavin in Preventing the Transmission of Iris Yellow Spot Virus (IYSV): Tospovirus by Thrips tabaci L. to Onion Plants in Egypt

First Report of Iris yellow spot virus Infecting Green Onion (Allium fistulosum) in the United States

First Report of <i>Iris yellow spot virus</i> Infecting Green Onion (<i>Allium fistulosum</i>) in the United States

First Confirmed Report of Iris yellow spot virus in Onion Nurseries in Zacatecas, Mexico

First Confirmed Report of <i>Iris yellow spot virus</i> in Onion Nurseries in Zacatecas, Mexico

First Report of Iris yellow spot virus Infecting Garlic and Leek in Zimbabwe

First Report of <i>Iris yellow spot virus</i> Infecting Garlic and Leek in Zimbabwe

First report of Iris yellow spot virus infecting onion in the Pichincha and Tungurahua provinces of Ecuador

Onion ( Allium cepa ) is one of the most important vegetable crops and is widely cultivated throughout the world. In Ecuador onion is grown on an area of 16,000 ha with a production of 103,316 tonnes (Ministerio de Agricultura, Ganaderia,…

First Report of Iris yellow spot virus Infecting Onion in Zimbabwe

First Report of <i>Iris yellow spot virus</i> Infecting Onion in Zimbabwe

Pathogenesis-related genes as tools for discovering the response of onion defence system against Iris yellow spot virus infection

The Iris yellow spot virus (IYSV) is a viral pathogen of onions and causes severe damage and economic loss in affected onion crops. Pathogenesis-related (PR) genes are part of the innate immune response that onions harbour against viral diseases, which to date remains unclear. Using a sensitive and reliable real-time quantitative PCR method, the dynamic expression of five different genes in infected onions were investigated after biological inoculation with virulent isolate of Thrips tabaci (Lindeman). The transcription levels of PR1, PR2, PR3, PR4, and PR5 genes were highly expressed 1 day post inoculation (dpi). Furthermore, statistical analysis revealed a significant change in peak expression levels of PR1 after 8 dpi and PR3 after 9 dpi. In contrast, the expression level change for the other genes was only moderate. Further, we determined and ranked the expression stability of three reference genes (EF1-α, 18S rRNA, and β-actin) using geNorm and NormFinder. The overall analysis demonstrated that β-actin is the most informative gene, which can be utilised as an internal control for quantitative gene expression. Our study findings not only provide guidelines for selection of appropriate reference genes in virally infected onions, but also valuable information concerning immune response related genes associated with the initial plant defences against viral infection. Moreover, the PR1 gene appears to be a disease-specific gene related to the IYSV infection in onion tissues.

Using monoclonal antibodies against the common epitopes of NSs proteins for the prompt detection and differentiation of tospoviruses prevalent in Euro-America and Asia Regions

Virus species in the genus Tospovirus can be classified into serogroups based on the serology of nucleocapsid protein, one of the key criteria for the identification of a tospovirus. Most globally important tospoviruses belong to the serogroups containing Tomato spotted wilt virus (TSWV), Watermelon silver mottle virus (WSMoV) and Iris yellow spot virus (IYSV) as type species. In this investigation, we attempted to develop a generic monoclonal antibody (MAb) against the common epitopes of the NSs proteins of TSWV and Impatiens necrotic spot virus (INSV), two representative tospoviruses prevalent in Europe and America. The NSs proteins of TSWV and INSV were individually expressed in the bacterial pET system, and the purified recombinant proteins, denoted TNSs and INSs, respectively, were used to produce MAbs. Results from indirect enzyme-linked immunosorbent assays (ELISAs) and western blotting indicated that the selected MAb-INSs-55G4E7 against INSs broadly reacts with the NSs proteins of INSV, Groundnut ringspot virus (GRSV) and Tomato chlorotic spot virus (TCSV), two members of the TSWV serogroup. All obtained MAbs against TNSs are TSWV specific. Our results indicate that the combination of MAb-INSs-55G4E7 and TSWV-specific MAb-TNSs-81D9E2 reacted with four tested Euro-America-type tospoviruses. Remarkably, the three-in-one combination of MAb-INSs-55G4E7, MAb-TNSs-81D9E2 and the previously prepared MAb-WNSs, which reacts with the common epitope of the NSs proteins of Asia type tospoviruses, reacts with all 12 tested tospoviruses from different geographic regions. Here, we report an efficient serological tool for the prompt detection and differentiation of the most economically important tospoviruses prevalent in Europe, America and Asia.

Overwintering Sites ofIris yellow spot virusandThrips tabaci(Thysanoptera: Thripidae) in Colorado

Iris yellow spot virus (family Bunyaviridae, genus Tospovirus) and its insect vector, onion thrips, Thrips tabaci Lindeman, are of economic concern worldwide in regions where onions (Allium cepa L.) are grown. Several weed species have been described as additional hosts and likely green bridges for survival of Iris yellow spot virus, however, there is little work regarding the overwintering habits and potential of onion thrips as a source of inoculum during the following season. The results of this work confirm onion thrips and Iris yellow spot virus presence near three Colorado onion fields throughout the winter, onion thrips reproduction on six non-allium plant species, and larval acquisition of Iris yellow spot virus from two non-allium plant species. Thrips were monitored by sticky traps during the winter months from 2011 to 2013. Thrips activity seemed to cease when the average temperature was cooler than 0°C and resumed once the average temperature warmed above 0°C. Onion cull piles were constructed and were apparently conducive to survival of thrips, but no live thrips were collected from the piles after onion bulbs began to decay. Iris yellow spot virus was detected by RTPCR in live adult and larval thrips from onion; common mallow, Malva neglecta Wallr.; dandelion, Taraxacum officinale Weber in Wiggers; flixweed, Descurainia sophia (L.) Webb. Ex Prantl; prickly lettuce, Lactuca serriola L.; and salsify, Tragopogon dubius Scop. during the winters from 2010 to 2013. Iris yellow spot virus was detected in prickly lettuce and flixweed. The five weed species were grown from seed in a greenhouse and exposed to viruliferous thrips to elucidate their potential as green bridges. Of the five weeds, Iris yellow spot virus was detected in eight of 15 salsify leaf samples and in three of six thrips larval samples reared on the plant. Winter annuals play a role in overwintering survival of onion thrips and Iris yellow spot virus, providing inoculum the next growing season, and weed management during the winter might be warranted.

Long-Distance Dispersal Potential for Onion Thrips (Thysanoptera: Thripidae) and Iris yellow spot virus (Bunyaviridae: Tospovirus) in an Onion Ecosystem.

Onion thrips, Thrips tabaci Lindeman, is a worldwide pest of onion whose feeding damage and transmission of Iris yellow spot virus (IYSV) may reduce onion yields. Little is known about the seasonal dynamics of T. tabaci dispersal, the distance of dispersal, or the movement of thrips infected with IYSV during the onion-growing season. To address these questions, T. tabaci adults were collected using transparent sticky card traps in commercial onion fields three times during the onion-growing season (June, July, and late August) at varying heights above the canopy (0.5-6 m above soil surface) and with trap-equipped unmanned aircraft (UAVs) flying 50-60 m above onion fields during August sampling periods in 2012 and 2013. Randomly selected subsamples of captured T. tabaci were tested for IYSV using RT-PCR. Most T. tabaci adults were captured in late August and near the onion canopy (<2 m) throughout the season. However, 4% of T. tabaci adults captured on sticky cards were at altitudes ≥2 m, and T. tabaci were also captured on UAV-mounted traps. These data strongly suggest that long-distance dispersal occurs. More T. tabaci captured on sticky cards tested positive for IYSV in August (53.6%) than earlier in the season (2.3 to 21.5% in June and July, respectively), and 20 and 15% of T. tabaci captured on UAV-mounted traps tested positive for IYSV in 2012 and 2013, respectively. Our results indicate that T. tabaci adults, including viruliferous individuals, engage in long-distance dispersal late in the season and likely contribute to the spread of IYSV.

Onion Thrips (Thysanoptera: Thripidae) Biology, Ecology, and Management in Onion Production Systems

Onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), is a well-known onion pest worldwide. Onion thrips cause both direct and indirect damage to onion by feeding and ovipositing on leaves that may cause green onions (scallions) to be unmarketable and dry bulb onion size to be reduced. Onion thrips can also transmit several plant pathogens that reduce onion bulb size and quality. One of the most economically damaging onion pathogens transmitted by onion thrips is Iris yellow spot virus (Bunyaviridae: Tospovirus). In this article, we discuss onion thrips geographical distribution, host range, biology, damage, monitoring, economic thresholds, and management in onion production.

Evaluation of acibenzolar-S-methyl-induced resistance against iris yellow spot tospovirus

Acibenzolar-S-Methyl (ASM) is a functional analog of salicylic acid (SA) that activates local and systemic acquired resistance (SAR) responses in plants against a wide variety of pathogens. Iris yellow spot virus (IYSV) is an economically important tospovirus of onion that causes severe economic losses to both bulb and seed crops. IYSV resistant onion cultivars are not available to date and there are limited control options. To explore the possibility of utilizing SAR as a control option, we first used two different hosts of IYSV, Datura stramonium and Nicotiana benthamiana, to study the ability of ASM in triggering SAR against IYSV infection. Quantitative descriptors based on both symptom expression and relative levels of IYSV nucleoprotein and viral small RNA were developed and used to determine the SAR in ASM- and buffer-treated plants. A significant reduction in virus levels in ASM-treated plants was noticed by ELISA and PCR. The level of SAR response was also assessed by measuring the IYSV lesion size and number on the inoculated leaves of ASM-treated plants. ASM-treated plants showed reduced symptoms compared to buffer-treated plants. This study could be useful in potentially developing novel SAR-based options for virus management.

Thrips Settling, Oviposition and IYSV Distribution on Onion Foliage.

Thrips tabaci Lindeman (Thysanoptera: Thripidae) adult and larval settling and oviposition on onion (Allium cepa L.) foliage were investigated in relation to leaf position and leaf length at prebulb plant growth stages under controlled conditions. In the laboratory, four and six adult females of T. tabaci were released on onion plants at three-leaf stage and six- to eight-leaf stage, respectively, and thrips egg, nymph, and adult count data were collected on each of the three inner most leaves at every 2-cm leaf segment. Thrips settling and oviposition parameters were quantified during the light period on the above ground portion of onion plants from the distal end of the bulb or leaf sheath "neck" through the tips of the foliage. Results from studies confirmed that distribution of thrips adults, nymphs, and eggs were skewed toward the base of the plant. The settling distributions of thrips adults and nymphs differed slightly from the egg distribution in that oviposition occurred all the way to the tip of the leaf while adults and nymphs were typically not observed near the tip. In a field study, the foliage was divided into three equal partitions, i.e., top, middle, basal thirds, and thrips adults by species, primarily Frankliniella fusca (Hinds) and T. tabaci, were collected from each partition to determine if there was a similar bias of all adult thrips toward the base of the plant. The results suggested that adults of different species appear to segregate along leaf length. Finally, thrips oviposition on 2-cm segments and Iris yellow spot virus positive leaf segments were quantified in the field, irrespective of thrips species. Both variables demonstrated a very similar pattern of bias toward the base of the plant and were significantly correlated.

In vivo localization of iris yellow spot tospovirus (Bunyaviridae)-encoded proteins and identification of interacting regions of nucleocapsid and movement proteins.

BackgroundLocalization and interaction studies of viral proteins provide important information about their replication in their host plants. Tospoviruses (Family Bunyaviridae) are economically important viruses affecting numerous field and horticultural crops. Iris yellow spot virus (IYSV), one of the tospoviruses, has recently emerged as an important viral pathogen of Allium spp. in many parts of the world. We studied the in vivo localization and interaction patterns of the IYSV proteins in uninfected and infected Nicotiana benthamiana and identified the interacting partners.Principal FindingsBimolecular fluorescence complementation (BiFC) analysis demonstrated homotypic and heterotypic interactions between IYSV nucleocapsid (N) and movement (NSm) proteins. These interactions were further confirmed by pull-down assays. Additionally, interacting regions of IYSV N and NSm were identified by the yeast-2-hybrid system and β-galactosidase assay. The N protein self-association was found to be mediated through the N- and C-terminal regions making head to tail interaction. Self-interaction of IYSV NSm was shown to occur through multiple interacting regions. In yeast-2-hybrid assay, the N- and C-terminal regions of IYSV N protein interacted with an N-terminal region of IYSV NSm protein.Conclusion/SignificanceOur studies provide new insights into localization and interactions of IYSV N and NSm proteins. Molecular basis of these interactions was studied and is discussed in the context of tospovirus assembly, replication, and infection processes.

Movement and nucleocapsid proteins coded by two tospovirus species interact through multiple binding regions in mixed infections

Negative-stranded tospoviruses (family: Bunyaviridae) are among the most agronomically important viruses. Some of the tospoviruses are known to exist as mixed infections in the same host plant. Iris yellow spot virus (IYSV) and Tomato spotted wilt virus (TSWV) were used to study virus–virus interaction in dually infected host plants. Viral genes of both viruses were separately cloned into binary pSITE-BiFC vectors. BiFC results showed that the N and NSm proteins of IYSV interact with their counterparts coded by TSWV in dually infected Nicotiana benthamiana plants. BiFC results were further confirmed by pull down and yeast-2-hybrid (Y2H) assays. Interacting regions of the N and NSm proteins were also identified by Y2H system and β-galactosidase activity. Several regions of the N and NSm were found interacting with each other. The regions involved in these interactions are presumed to be critical for the functioning of the tospovirus N and NSm proteins. This is the first report of in vivo protein interactions of distinct tospoviruses in mixed infection.

Sequence analysis of Indian iris yellow spot virus ambisense genome segments: evidence of interspecies RNA recombination.

The nucleotide sequence of M- and S-RNA segments of an Indian iris yellow spot virus (IYSV) were determined. Sequence comparisons showed that both of these sequences shared less than 95% identity with those other known IYSV isolates. Phylogenetic analysis revealed that the S- and M-RNA sequences of known IYSV isolates clustered with those of the tospoviruses, tomato yellow ring virus, polygonum ringspot virus and hippeastrum chlorotic ringspot virus. Further, multiple recombination detection methods detected inter- and intra-species recombination events that clustered primarily within the intergenic regions of S- and M-RNA, suggesting that these are possibly recombination hotspots in IYSV and closely related tospoviruses.