Tomato Spotted Wilt Tospovirus Research Articles

Impact of Thrips (Thysanoptera: Thripidae) Management Practices on Suppression of Tomato Spotted Wilt Virus and Aphid (Homoptera: Aphididae) Control in Flue-Cured Tobacco

Tomato spotted wilt tospovirus (TSWV) has become a major economic problem for tobacco growers in Georgia. Several species of thrips have been reported as vectors of TSWV. Three of these species, commonly observed on tobacco in Georgia, include Frankliniella fusca (Hinds), F. occidentalis (Pergande), and F. bispinosa (Morgan). This study examined the effectiveness of several thrips management practices on controlling thrips populations and suppressing the incidence of TSWV. Replicated field plots were used to evaluate aldicarb, acephate, imidacloprid, acibenzolar-S-methyl, spinosad, thiamethoxan alone and in combination, applied as pre-plant incorporated, tray drench, transplant water or foliar treatments. The insecticides imidacloprid (Admire® 2F or Provado® 1.6F) and thiamethoxan (Platinum 2® SC), applied in the transplant water or as a tray drench, were effective in reducing the early-season thrips populations and reducing the seasonal cumulative incidence of TSWV. These two products also were effective in reducing the seasonal mean population of tobacco aphids, Myzus nicotianae. The plant activator, acibenzolar-S-methyl (Actigard®), was effective in suppressing TSWV symptoms, but had no effect on thrips and minor impact on aphid population densities. The combination of acibenzolar-S-methyl with either imidacloprid or thiamethoxan provided better suppression of TSWV than any of the products alone. Acephate in the transplant water plus four early-season foliar sprays also was effective in reducing thrips numbers and TSWV incidence. Aldicarb and spinosad were not effective for thrips control or TSWV suppression. Acephate and aldicarb were effective in reducing aphid populations, but spinosad was not. Frankliniella fusca was the predominate thrips species at all test sites, ranging from 90 to 98% of the thrips complex. From 1.9 to 4.6% of the thrips collected were confirmed vectors of TSWV, based on ELISA test results. Imidacloprid, thiamethoxan, acibenzolar-S-methyl, and acephate provide thrips management options that can reduce the tobacco production losses associated with TSWV.

Effects of imidacloprid on transmission of tomato spotted wilt tospovirus to pepper, tomato and tobacco by Frankliniella fusca Hinds (Thysanoptera: Thripidae)

Rates of transmission of tomato spotted wilt tospovirus (TSWV) by tobacco thrips, Frankliniella fusca Hinds, to imidacloprid-treated and untreated tomato, pepper and tobacco were measured in greenhouse and small-plot field trials. The incidence of TSWV was reduced in greenhouse assays with all 3 crops receiving a soil application of imidacloprid at a rate of 9.9 g [AI]/1000 plants. Levels of TSWV were also reduced in small-plot field trials of tomato and pepper plants receiving transplant applications of imidacloprid at the same rate. No F. fusca were recovered from imidacloprid-treated tobacco (9.9 g [AI]/1000 plants) 24 days following an initial infestation. In the greenhouse, F. fusca populations reached higher levels on healthy than TSWV-infected tobacco. Applications of soil-applied imidacloprid reduced the number and duration of probing/feeding bouts by F. fusca on pepper and mustard ( Brassica rapa L.). Reduced probing and feeding by viruliferous thrips on imidacloprid-treated plants may contribute to less TSWV incidence as observed in the field and greenhouse experiments.

Tillage and Pest Management Considerations in a Peanut–Cotton Rotation in the Southeastern Coastal Plain

Radical changes in crop production have occurred in the southeastern USA in recent years. Peanut (Arachis hypogaea L.) and cotton (Gossypium hirsutum L.) are now planted in direct rotation, and conservation tillage is commonly used for both crops. Comprehensive data is lacking on crop and pest management recommendations in those systems, so a long‐term study was conducted in Tifton, GA on the effects of tillage systems on crop and pest management in a peanut–cotton rotation. Systems evaluated were conventional, reduced, and minimum tillage. Plots in conventional tillage systems were harrowed, deep‐turned, and planted each year. In reduced tillage systems, plots were harrowed in the fall and planted to rye (Secale cereale L.), and crops were planted into killed rye. In minimum tillage systems, plots were neither tilled nor planted to rye and remained nontilled during the winter, and crops were planted directly into the previous crop stubble. Weed control was based on species present and tillage system. Peanut was either treated with flutolanil [3′‐isopropoxy‐2‐(trifluoromethyl) benzanilide] for soil‐borne disease control or not treated (control). Yields were sustained for 5 yr with no difference in peanut or cotton yields among tillage systems. Flutolanil controlled soil‐borne diseases and increased peanut yields, working equally well in all three tillage systems. Weed densities and species composition changed, causing more intensive and costly weed control in reduced and minimum tillage systems than in conventional tillage systems. Spotted wilt (tomato spotted wilt tospovirus) incidence was 42% lower in reduced and minimum tillage systems than in conventional tillage systems and is now part of the recommended strategy to manage the disease.

Geographical Distribution of Genetic Diversity in Arachis hypogaea

Abstract The U.S. maintains a large (> 8000 accessions) and genetically diverse collection of peanut (Arachis hypogaea L.) germplasm. It is costly to screen all accessions within this collection for traits that could be useful in cultivar development. The objective of this research was to identify countries of origin that are rich sources of resistance to important peanut diseases. This would allow peanut breeders to focus their efforts on smaller subsets of the germplasm collection. Accessions in the peanut core collection were evaluated for resistance to late (Cercosporidium personatum Berk. & M. A. Curtis) and early (Cercospora arachidicola Hori) leaf spot, tomato spotted wilt Tospovirus (TSWV), the peanut root-knot nematode [Meloidogyne arenaria (Neal) Chitwood race 1], and Cylindrocladium black rot (CBR)[Cylindrocladium crotalarie (Loos) Bell & Sobers]. These data then were examined to determine if genes for resistance clustered geographically. Several geographical areas that appear to be rich sources for disease-resistant genes were identified. China had a relatively large number of accessions with resistance to the peanut root-knot nematode. Peru appeared to be a rich source of material with resistance to CBR. Resistance to late leaf spot was more frequent than expected in accessions from Bolivia and Ecuador. Bolivia was also a valuable source of resistance to early leaf spot. Early leaf spot resistance also was more prevalent than expected in accessions from India, Nigeria, and Sudan. India, Israel, and Sudan were valuable origins for material with resistance to TSWV. Accessions with multiple disease resistance were most common in India, Mozambique, and Senegal. This information should enable plant breeders to utilize more efficiently the genes for disease resistance that are available in the U.S. germplasm collection.

Status of the Arachis Germplasm Collection in the United States

Abstract An extensive working collection of Arachis germplasm is maintained by the USDA at the Southern Regional Plant Introduction Sta. in Griffin, GA. Much of this collection is maintained also under long-term seed storage at the Nat. Seed Storage Lab. in Ft. Collins, CO. The working collection consists of 9027 accessions of A. hypogaea and 684 accessions of Arachis species. About half of the A. hypogaea accessions are unimproved landraces collected in the crop's centers of diversity in South America. The other half is comprised of germplasm obtained from countries outside of South America. The U.S. germplasm collection of peanut was the first major germplasm collection to have a working core collection. Research has verified that this core collection can be used to improve the efficiency of germplasm utilization. This has stimulated a great amount of germplasm evaluation work and has resulted in the identification of numerous sources of resistance to several economically significant pathogens. Considerable efforts in the U.S. also have been devoted to the use of wild species of Arachis for sources of resistance to pathogens. Programs are ongoing to introgress high levels of resistance or immunity to early (Cercospora arachidicola Hori) and late (Cercosporidium personatum Berk. & M.A. Curtis) leaf spots, nematodes, and viruses. Genetic resources have been particularly useful in adding disease resistance to peanut cultivars. This has had a significant economic impact on U.S. peanut farmers. The largest impacts have been from the development of cultivars with resistance to Sclerotinia blight (Sclerotinia minor Jagger), the peanut root-knot nematode [Meloidogyne arenaria (Neal) Chitwood race 1], and tomato spotted wilt Tospovirus. Use of these resistant cultivars has an estimated economic impact of more that $200 million annually for U.S. peanut producers.

Use of fluorogenic Scorpions for fast and sensitive detection of plant viruses*

Very recently, a novel nucleic acid detection technology based on a primer with a quenched fluorophore and a probe complementary to an internal portion of the amplicon has been developed. The primer probe, named ‘Scorpion’, fluoresces only upon hybridization with its target, i.e. if the specific extension product of the primer is synthesized during the reaction. We have used Scorpion primers in RT‐PCR assays to detect Tomato spotted wilt tospovirus and Plum pox potyvirus in naturally infected plants. Amplified products of the expected size were detected either by real‐time measurements or by visual estimation of fluorescence emission from tubes placed over an ultraviolet light source at the end of the Scorpion‐RT‐PCR. In serially diluted plant sap, the visual method allowed detection of 7.5 pg of infected plant tissue and proved at least as sensitive as visual estimation of ethidium bromide‐stained amplicons separated by gel electrophoresis.

003 Viruses Associated to Alstroemeria Varieties and Epidemiology of Tomato Spotted Wilt in the Cultivar Rosario

Viruses associated to eight Alstroemeria varieties and the relationship of thrips density and environmental factors with Tomato Spotted Wilt (TSW) intensity as well as the TSW effect on yield were studied in `Rosario' in Central Mexico. Using hosts range the viruses detected were Tomato Spotted Wilt Tospovirus (TSWV), Impatiens Necrotic Spot Tospovirus (INSV), Alstroemeria Mosaic Potyvirus (AlMV), Alstroemeria Streak Potyvirus (ASV), Arabis Mosaic Nepovirus (ArMV) and Cucumber Mosaic Cucumovirus (CMV). With serology, the presence of TSWV was confirmed in `Jubilee', `Rosario', and `Regina'; INSV in `Anabel', `Jubilee', and `Red Sunset'; and AlMV in `Rosario', `Red Sunset', `Rosita', `Yellow King', `Jubilee', and `Rojo Sangria'. TSWV and AlMV were found coinfecting `Rosario' plants. Five percent of plants were serologically positive to TSWV in the first flower harvest (25 Jan.-5 Apr.), 10% in the second (12 Apr.-21 June), and third (5 July-13 Sept.) and 18% in the last harvest (24 Sept.-6 Dec.). The highest peak density of thrips (520 to 630 individuals per sticky trap) were registered when the maximum temperature was higher than 35 °C and the relative humidity was between 40% to 60%. However, such peak density was not correlated with a significant increase of TSW incidence. Number and quality of inflorescences and the stem growth rate were significantly higher (P = 0.05) in plots with asymptomatic plants than that with plants showing putative symptoms of TSW.

001 Viruses Associated to Alstroemeria Varieties and Epidemiology of Tomato Spotted Wilt in cv. `Rosario'

Viruses associated to eight Alstroemeria varieties and the relationship of thrips density and environmental factors with Tomato Spotted Wilt (TSW) intensity as well as the TSW effect on yield were studied in `Rosario' in Central Mèxico. Using hosts range the viruses detected were Tomato Spotted Wilt Tospovirus (TSWV), Impatiens Necrotic Spot Tospovirus (INSV), Alstroemeria Mosaic Potyvirus (AlMV), Alstroemeria Streak Potyvirus (ASV), Arabis Mosaic Nepovirus (ArMV), and Cucumber Mosaic Cucumovirus (CMV). With serology it was confirmed the presence of TSWV in `Jubilee', `Rosario', and `Regina' varieties; INSV in `Anabel', `Jubilee', and `Red Sunset'; and AlMV in `Rosario', `Red Sunset', `Rosita', `Yellow King', `Jubilee'. and `Rojo Sangria'. TSWV and AlMV were found coinfecting `Rosario' plants. Five percent of plants were serologically positive to TSWV in the first flower harvest (25 Jan.-5 Apr.), 10% in the second (12 Ap.-21 June), and third (5 July-13 Sept.), and 18% in the last harvest (23 Sept.-6 Dec.). The highest peak density of thrips (520 to 630 individuals per sticky trap) were registered when the maximum temperature was higher than 35 °C and the relative humidity was between 40% to 60%. However, such peak density was not correlated with a significant increase of TSW incidence. Number and quality of inflorescences and the stem growth rate were significantly higher (P = 0.05) in plots with asymptomatic plants than that with plants showing putative symptoms of TSW.

Tospoviruses infecting vegetable crops in Israel

Symptoms of vein clearing, stem necrosis, curling, necrotic spots and rings on the leaves associated with infection by tomato spotted wilt tospovirus (TSWV) were documented among vegetable crops growing in commercial glasshouses and open fields in Israel. Plants exhibiting symptoms were collected, from 1994‐01 to 1998‐12. Among cultivated vegetable crops analysed for TSWV by ELISA, the following plants were found to be infected: tomato, capsicum, aubergine, lettuce, cabbage and cucumber. These incidences of the virus were all correlated with the occurrence in high population of Frankliniella occidentalis. Transmission of the virus from infected Datura stramonium to Petunia leaf discs, by F. occidentalis, was up to 26%. TSWV antigens were readily detected by ELISA in seeds harvested from naturally infected vegetable crops. However, we failed to show virus transmission to the progeny plants. Iris yellow spot tospovirus (IYSV) was detected in onion. High incidence of the disease was associated with large populations of Thrips tabaci.

Identification of the principal viruses infecting tomato crops in Tunisia

Serological tests have been used to detect viruses associated with tomato in 257 samples collected in different regions in Tunisia, Cap‐Bon, Sahel and South during successive seasons. The viruses detected were cucumber mosaic cucumovirus (CMV) and tomato aspermy cucumovirus (TAV), potato Y potyvirus (PVY), tobacco etch potyvirus (TEV) and pepper veinal mottle potyvirus (PVMV), tomato mosaic tobamovirus (ToMV) and tobacco mosaic tobamovirus (TMV), tobacco rattle tobravirus (TRV), alfalfa mosaic alfamovirus (AMV), tomato spotted wilt tospovirus (TSWV), tomato ringspot nepovirus (TomRSV) and potato X potexvirus (PVX). Some were detected in all three regions surveyed, at variable frequencies: TMV, CMV, TEV, PVY, ToMV, AMV, TAV, TSWV and TRV. Others were only detected in two regions (PVMV in Cap‐Bon and Sahel and PVX in Sahel and in the south) or one region (TomRSV in Cap‐Bon). Movement of individual viruses from one region to another may be due to movement of specific vectors, as in the case of the thrips‐transmitted TSWV moving from the south to the north. Some of these viruses were found for the first time in Tunisia.

Biodiversity of viruses infecting tomato in Italy: methods for diagnosis and diversification*

An account is given of strain‐specific diagnostic methods currently adopted in Italy to detect alfalfa mosaic alfamovirus (AMV), cucumber mosaic cucumovirus (CMV) and tomato spotted wilt tospovirus (TSWV). These viruses are highly detrimental to tomato crops as the introduction of new virus strains has deeply changed the population structure of resident viruses. RT‐PCR coupled with restriction analysis of amplicons proved suitable for differentiating CMV and AMV strains whereas single‐stranded conformational polymorphism (SSCP) was used for the identification of TSWV isolates. Application of strain‐specific diagnostic methods to phytosanitary inspection of plant propagules is suggested as a powerful tool for timely identification of new virus strains

Effect of acibenzolar-S-methyl and imidacloprid on suppression of tomato spotted wilt Tospovirus in flue-cured tobacco

Tomato spotted wilt virus (TSWV) has become a major constraint to tobacco production in Georgia. No single control measure has been found effective for minimizing the impact of the disease. Foliar applications of acibenzolar-S-methyl (Actigard ®) were tested in replicated field trials singly and in combination with imidacloprid (Admire ® and Provado ®) for their effect on reducing the impact of TSWV in tobacco. Results showed that Actigard significantly reduced final disease incidence in one trial in 1997 and another trial in 1998 in Georgia. Imidacloprid, when applied alone, suppressed disease incidence in one of four trials. Significant reduction in incidence occurred at three of the four locations when both were applied together. The fourth location had very low levels of incidence and no differences were detected among treatments. The percent ELISA positive plants was higher than the percent of symptomatic plants for three of the four locations. Actigard reduced percent ELISA positive plants for two of the four locations and imidacloprid alone and with Actigard reduced percent ELISA positive plants at all four locations. Use of plant defense activators such as Actigard alone or in combination with imidacloprid potentially offers an alternative and effective management tool for spotted wilt suppression on tobacco. This is the first report of effective suppression of an economically important plant viral disease using Actigard.

Simplified, rapid method for cloning of virus-binding polypeptides (putative receptors) via the far-Western screening of a cDNA expression library using purified virus particles

A simplified, alternative method for cloning virus-binding polypeptides (receptor candidates) is described. The method is based on a far-Western assay using purified tomato spotted wilt tospovirus (TSWV, Bunyaviridae) for screening a lambda-phage cDNA expression library. The western flower thrips, Frankliniella occidentalis Pergande, the principal vector of TSWV, in which the virus replicates, was used for library construction. Using this method several virus-binding polypeptides were identified, it eliminated the need for (a) a cellular infection or binding system, (b) the identification, cloning and expression of a functional viral attachment protein, or (c) the purification of the virus receptor. Using this method, virus-binding polypeptides can be selected and cloned in a very short period of time and used in subsequent experiments for determination of their biological relevance as virus receptors and/or tested for potential usefulness as inhibitors of virus transmission and/or infection.

Virus Assessment of Ajuga reptans Cultivars Reveals Alfalfa Mosaic, Tobacco Streak, and Cucumber Mosaic (CMV) Viruses, and a CMV Satellite RNA

Ajuga reptans L. is an herbaceous ornamental mint grown in borders or as a groundcover, and is commonly propagated vegetatively and by seed. Three hundred and fifty-six A. reptans samples were obtained from growers in Washington, Michigan, Iowa, and Ohio, and screened for alfalfa mosaic virus (AMV), tobacco streak ilarvirus (TSV), cucumber mosaic cucumovirus (CMV), tomato aspermy cucumovirus (TAV), tomato spotted wilt tospovirus (TSWV), impatiens necrotic spot tospovirus (INSV), tobacco mosaic tobamovirus (TMV), potato virus × potexvirus (PVX), and 80 potyviruses, using direct antibody sandwich (DAS) and indirect enzyme-linked immunosorbent assay (ELISA). Viral-associated double-stranded ribonucleic acid (dsRNA) analysis was used to detect an apparent satellite (sat) RNA, and northern hybridization using a digoxigenin (DIG) labeled (S) CARNA-5 cDNA probe was used to confirm the identity of the apparent satRNA. No incidences of TAV, TMV, TSWV, INSV, PVX, or potyviruses were detected. CMV was detected in 11%, AMV in 22.2%, TSV in 3.7%, and mixed infections of CMV and AMV in 1.1% of the samples. SatRNA was detected in 36 A. reptans `Royalty', two `Rainbow', and two `Burgundy Glow' samples by dsRNA analysis, and confirmed by hybridization in 29 `Royalty' and one `Burgundy Glow' samples. Sixteen A. reptans `Royalty' seedlings grown from seed harvested from CMV-infected plants were tested by ELISA for CMV, AMV, and TSV. All were positive for CMV, and two were positive for a mixed infection of CMV and AMV. SatRNA was detected in all 16 seedlings by RT-PCR.

Immunoprecipitation of a 50-kDa protein: a candidate receptor component for tomato spotted wilt tospovirus ( Bunyaviridae) in its main vector, Frankliniella occidentalis

A 50-kDa protein that binds to viral particles in solid-phase assays and that is recognized by anti-idiotypic antibodies made against anti-viral glycoproteins G1/G2 (anti-Ids) has been proposed as a receptor candidate for tomato spotted wilt tospovirus (TSWV) in its main thrips vector, Frankliniella occidentalis Pergande (Bandla et al., 1998. Phytopathology 88, 98–104). Here we show the immunoprecipitation of the 50-kDa protein by anti-Ids and by an anti-G1/G2-TSWV conjugate — a new immunoprecipitation method. In addition, we show that anti-Ids made against anti-G1 (anti-IdG1) block virus replication in an insect tissue replication assay. The results indicate that (a) the TSWV–50-kDa protein interaction occurs in solution, as it must do in vivo; (b) G1 is a viral attachment protein; and (c) the 50-kDa protein is a candidate host factor essential for TSWV entry. These results provide additional support for the role of the 50-kDa thrips protein as a viral receptor. Additionally these experiments provide the basis for testing saturable binding and represent an important step toward the first cloning and identification of a cellular receptor for a plant virus.

The movement protein NSm of tomato spotted wilt tospovirus (TSWV): RNA binding, interaction with the TSWV N protein, and identification of interacting plant proteins.

The nonstructural NSm protein of tomato spotted wilt tospovirus (TSWV) represents a putative viral movement protein involved in cell-to-cell movement of nonenveloped ribonucleocapsid structures. To study the molecular basis of NSm function, we expressed the protein in Escherichia coli and investigated protein-protein and protein-RNA interactions of NSm protein in vitro. NSm specifically interacts with TSWV N protein and binds single-stranded RNA in a sequence-nonspecific manner. Using NSm as a bait in a yeast two-hybrid screen, we identified two homologous NSm-binding proteins of the DnaJ family from Nicotiana tabacum and Arabidopsis thaliana.

Nucleocapsid Gene-Mediated Transgenic Resistance Provides Protection Against Tomato spotted wilt virus Epidemics in the Field

ABSTRACT Transformation of plants with the nucleocapsid (N) gene of Tomato spotted wilt tospovirus (TSWV) provides resistance to disease development; however, information is lacking on the response of plants to natural inoculum in the field. Three tobacco cultivars were transformed with the N gene of a dahlia isolate of TSWV (TSWV-D), and plants were evaluated over several generations in the greenhouse. The resistant phenotype was more frequently observed in 'Burley 21' than in 'KY-14' or 'K-326', but highly resistant 'Burley 21' transgenic lines were resistant to only 44% of the heterologous TSWV isolates tested. Advanced generation (R(3) and R(4)) transgenic resistant lines of 'Burley 21' and a 'K-326' F(1) hybrid containing the N genes of two TSWV isolates were evaluated in the field near Tifton, GA, where TSWV is endemic. Disease development was monitored by symptom expression and enzyme-linked immunosorbent assay (ELISA) analysis. Whereas incidence of TSWV infection in 'Burley 21' susceptible controls was 20% in 1996 and 62% in 1997, the mean incidence in transgenic lines was reduced to 4 and 31%, respectively. Three transgenic 'Burley 21' lines were identified that had significantly lower incidence of disease than susceptible controls over the two years of the study. In addition, the rate of disease increase at the onset of the 1997 epidemic was reduced for all the 'Burley 21' transgenic lines compared with the susceptible controls. The 'K-326' F(1) hybrid was as susceptible as the 'K-326' nontransformed control. ELISA analysis demonstrated that symptomless plants from the most resistant 'Burley 21' transgenic lines accumulated detectable nucleocapsid protein, whereas symptomless plants from more susceptible lines did not. We conclude that transgenic resistance to TSWV is effective in reducing incidence of the disease in the field, and that accumulation of transgene protein may be important in broad-spectrum resistance.

Reaction of Peanut Cultivars to Spotted Wilt

Abstract Field tests were conducted in 1997 and 1998 in Georgia and Florida to compare the effects of 10 and 12 peanut (Arachis hypogaea L.) cultivars, respectively, on epidemics of spotted wilt caused by tomato spotted wilt Tospovirus. Epidemics of spotted wilt were suppressed for the moderately resistant standard Georgia Green, and in Southern Runner, Florida MDR 98, ViruGard, and NC-V11. The reponse of these five cultivars to spotted wilt were similar and resulted in lower final disease intensity and areas under the disease progress curves than in the susceptible standard Georgia Runner, and in SunOleic 97R and Tamrun 96. Southern Runner and Florida MDR-98 consistently had higher yields than the TSWV-susceptible Georgia Runner. Georgia Green and NC-V11 had higher yields than Georgia Runner in three of the four tests. No consistent differences were found among the cultivars for numbers of adult tobacco thrips (Frankliniella fusca) or western flower thrips (F. occidentalis). Differences among cultivars for numbers of larvae of Frankliniella spp. also were few and inconsistent. There was no indication that differences in thrips populations were responsible for differences in severity of spotted wilt in the field.

Transmission of tomato spotted wilt tospovirus by Thripstabaci populations originating from leek

The transmission of tomato spotted wilt tospovirus (TSWV) by Thrips tabaci collected from leek was studied using the petunia local‐lesion leaf‐disc assay. After an acquisition‐access period of 72 h given to newborn larvae up to 8 h old, the efficiency of transmission by adults was determined in three inoculation‐access periods of 48 h. This efficiency varied for six T. tabaci populations from 0.7 to 11.6% in experiments using the Greek TSWV isolate GR‐04. Males were more efficient transmitters than females (19 out of 176 versus five out of 494). Frankliniella occidentalis transmitted the same virus with a higher efficiency (34.8%). The transmission rate differed also among TSWV isolates, as shown in tests with four T. tabaci using two isolates. The virus was more efficiently acquired from infected leaf material of Datura stramonium than from that of Emilia sonchifolia. Plants of the latter species were more susceptible than Nicotiana tabacum in thrips transmission tests.

First Report of Natural Infection of Peanut (Groundnut) by Impatiens Necrotic Spot Tospovirus (Family Bunyaviridae).

Impatiens necrotic spot tospovirus (INSV) of the family Bunyaviridae is an important viral pathogen of ornamentals and a major constraint in the greenhouse industry (2). Evidence of natural infection of peanut (groundnut, Arachis hypogaea L.) by INSV was found in samples collected from three sites in Frio County, TX, and one site each in Mitchell and Tift counties, GA, during October 1998. Roots from several plants were tested by enzyme-linked immunosorbent assay for tomato spotted wilt tospovirus (TSWV) and INSV. Symptoms on individual mature plants positive for INSV were the same as those associated with late-season TSWV infections: plants appeared yellow and wilted, internal taproot and crown were necrotic, and plant death resulted (1). At one Texas site, three of five composite samples were positive only for INSV. One composite sample at a second Texas site was positive for both TSWV and INSV. Double infections were found in three of four TSWV-positive samples at a third Texas site. In Mitchell County, GA, three of four samples tested were positive only for TSWV, and one was positive for both TSWV and INSV. In Tift County, GA, 11 of 23 samples tested were positive only for INSV, whereas 4 were positive only for TSWV. Double infections were found in 5 of 23 samples. The presence of INSV in the sample from Mitchell County was verified by immunocapture-polymerase chain reaction (PCR) (4). The apparently low titer of INSV in the doubly infected plant necessitated two cycles of PCR for detection of INSV sequences. A primer pair that can amplify most tospoviruses was used for the first PCR cycle (3). Using the PCR product obtained, a second PCR cycle was performed with one tospovirus-specific and one INSV-specific primer. This approach resulted in a product of the expected size (≈298 bp). The PCR product was cloned in a pGEM-T vector and sequenced. Comparisons indicated the sequence obtained from the infected peanut sample from Georgia was 99% identical to the respective S RNA region from known INSV isolates. Serological and molecular sequence data suggest the peanut samples were infected by INSV. Future surveys and screenings of peanut plants for spotted wilt disease should include a test for INSV.