Management Of Tomato Spotted Wilt Virus Research Articles

First Report on Anti-TSWV Activities of Quinazolinone Derivatives Containing a Dithioacetal Moiety.

Tomato spotted wilt virus (TSWV) is a plant virus with strong infectivity and destructive power. Given the lack of effective control agents, TSWV causes significant economic damage to several vegetables and ornamental plants worldwide. In this study, we designed and synthesized a series of novel quinazolinone derivatives containing a dithioacetal moiety and evaluated their antiviral activity in vitro and in vivo against TSWV. Some candidate compounds showed good anti-TSWV activity. Compound 6n shows excellent anti-TSWV activity in vivo, and the EC50 value is 188 mg/L, which is notably better than that observed for ribavirin (642 mg/L), xiangcaoliusuobingmi (420 mg/L), and ningnanmycin (257 mg/L). In addition, compound 6n interacts with TSWV coat protein at sites ARG94 and ARG95 forming four π-alkyl interactions. Compound 6n (9.4 μM) shows a better binding affinity with TSWV coat protein than ribavirin (67.8 μM), xiangcaoliusuobingmi (33.8 μM), and ningnanmycin (24.3 μM). Therefore, compound 6n can serve as a lead compound for the discovery of new antiviral agents for the management of TSWV.

Receiver Operating Characteristic curve analysis determines association of individual potato foliage volatiles with onion thrips preference, cultivar and plant age.

Tomato spotted wilt virus (TSWV) causes sporadic but serious disease in Australian potato crops. TSWV is naturally spread to potato by thrips of which Thrips tabaci is the most important. Prior studies indicated possible non-preference of potato cultivars to T. tabaci. Select potato cultivars were assessed for non-preference to T. tabaci in paired and group choice trials. Cultivars ‘Bismark’, ‘Tasman’ and ‘King Edward’ were less preferred than ‘Atlantic’, ‘Russet Burbank’ and ‘Shepody’. Green leaf volatiles were sampled using solid-phase microextraction from the headspace of potato cultivars of two ages that differed in T. tabaci preference. Analysis of headspace volatile data using Receiver Operating Characteristic curves identified individual volatiles associated with T. tabaci preference and non-preference, young and old plants and individual cultivars. These data could be used to inform breeding programs for selection of T. tabaci resistance to assist with TSWV management, and biological testing of novel thrips management compounds.

Tomato spotted wilt virus Can Infect Resistant Tomato when Western Flower Thrips Inoculate Blossoms.

Tomato spotted wilt is a major disease of crops worldwide. Resistant cultivars carrying the Sw-5 allele for resistance to tomato spotted wilt disease (TSW) provide the most effective control method in tomato (Solanum lycopersicum). However, infections of fruit on Sw-5+ tomato plants suggest the virus resistance may not be fully expressed in blossoms or developing fruit. The objective of this study was to determine if the thrips vector, the western flower thrips (Frankliniella occidentalis), can transmit non-resistance breaking Tomato spotted wilt virus (TSWV) isolates when confined to blossoms on plants with and without the Sw-5 resistance allele. Twenty-one percent of 33 Sw-5+ plants inoculated by adult thrips feeding on blossom clusters or small fruit developed infections in the reproductive tissue, whereas 68% of 25 Sw-5- plants developed infections. Systemic infections also occurred following inoculation of blossoms in host genotypes with and without Sw-5. These results were further supported by field experiments that showed high proportions of infected fruit as well as a limited infection of foliage on the same stem as the infected fruit in Sw-5+ plants when F. occidentalis were abundant in blossoms. These findings help to explain observations of abundant late season infections of Sw-5 cultivars in commercial plantings and suggest that management of F. occidentalis infestations during the bloom period may be important for effective management of TSWV in susceptible tomato cultivars as well as cultivars expressing the Sw-5 allele for TSW resistance.

A severe symptom phenotype in pepper cultivars carrying the Tsw resistance gene is caused by a mixed infection between resistance-breaking and non-resistance-breaking isolates of Tomato spotted wilt virus

Pepper (Capsicum annuum) plants with the Tsw resistance gene showing unusually severe symptoms consisting of local lesions, chlorosis, stunting and systemic necrosis on the apical leaves were found in a commercial field in north eastern Spain in 2009. The presence of Tomato spotted wilt virus (TSWV) was confirmed in all diseased plants. After mechanical inoculation of Nicotiana glutinosa with infected field samples, biological clones of the virus were isolated from individual local lesions. These biological clones produced two different types of symptoms after inoculation on Tsw resistant pepper plants: (i) typical symptoms caused by resistance-breaking (RB) isolates characterized by chlorosis and stunting, and (ii) severe symptoms as observed in the field plants. Similar symptoms in pepper plants carrying the Tsw resistance gene were reproduced under controlled conditions, after simultaneous inoculation of RB and non-resistance-breaking (NRB) isolates. The NRB isolate was detected in a low proportion in the apical uninoculated leaves, whereas NRB isolates could not infect resistant pepper when inoculated alone. Co-infection by NRB and RB isolates induced disease synergism with systemic necrosis on the apical leaves. To our knowledge, this is the first case in which a synergic interaction between isolates of the same virus has been described, which has the ability to overcome a natural genetic resistance. This finding could have epidemiological implications for the management of TSWV.

Host Plant Resistance Against Tomato spotted wilt virus in Peanut (Arachis hypogaea) and Its Impact on Susceptibility to the Virus, Virus Population Genetics, and Vector Feeding Behavior and Survival

Tomato spotted wilt virus (TSWV) severely affects peanut production in the southeastern United States. Breeding efforts over the last three decades resulted in the release of numerous peanut genotypes with field resistance to TSWV. The degree of field resistance in these genotypes has steadily increased over time, with recently released genotypes exhibiting a higher degree of field resistance than older genotypes. However, most new genotypes have never been evaluated in the greenhouse or laboratory against TSWV or thrips, and the mechanism of resistance is unknown. In this study, TSWV-resistant and -susceptible genotypes were subjected to TSWV mechanical inoculation. The incidence of TSWV infection was 71.7 to 87.2%. Estimation of TSWV nucleocapsid (N) gene copies did not reveal significant differences between resistant and susceptible genotypes. Parsimony and principal component analyses of N gene nucleotide sequences revealed inconsistent differences between virus isolates collected from resistant and susceptible genotypes and between old (collected in 1998) and new (2010) isolates. Amino acid sequence analyses indicated consistent differences between old and new isolates. In addition, we found evidence for overabundance of nonsynonymous substitutions. However, there was no evidence for positive selection. Purifying selection, population expansion, and differentiation seem to have influenced the TSWV populations temporally rather than positive selection induced by host resistance. Choice and no-choice tests indicated that resistant and susceptible genotypes differentially affected thrips feeding and survival. Thrips feeding and survival were suppressed on some resistant genotypes compared with susceptible genotypes. These findings reveal how TSWV resistance in peanut could influence evolution, epidemiology, and management of TSWV.

Effectiveness of Tomato-Spotted Wilt Virus Management Tactics

Tomato-spotted wilt (TSW) is caused by the tomato-spotted wilt virus (TSWV) and is a major disease affecting the production of tomato and pepper in the Southeastern United States. Before initiating a multistate, regional project addressing this issue, a survey was conducted in North Carolina, South Carolina, Georgia, and Florida to assess the need for improved management of TSWV in these crops. We investigated farmer's stated effectiveness of four common TSWV management tactics (reflective mulch, resistant cultivar, imidacloprid, and Actiguard) in pepper and tomato production using logistic regression. We found that the odds that farmers were satisfied with the use of reflective mulch alone in controlling TSWV is 9-1, about one and a half times the amount obtained from using Actiguard alone. Moreover, the odds that farmers were satisfied with a practice that combines reflective mulch and Actiguard was far greater than that obtained from using each of the technique separately. We found some similarities between farmer's stated effectiveness and revealed effectiveness from experiments.

Supplementary data for: Effectiveness of Tomato-Spotted Wilt Virus Management Tactics

Supplementary data for: Effectiveness of Tomato-Spotted Wilt Virus Management Tactics

The effect of three rates of cyantraniliprole on the transmission of tomato spotted wilt virus by Frankliniella occidentalis and Frankliniella fusca (Thysanoptera: Thripidae) to Capsicum annuum

Tomato spotted wilt virus (TSWV) is a thrips-transmitted virus that causes major losses in many crops worldwide. Management of TSWV is complex, requiring multiple preventive measures. Currently, there are few chemical options that control thrips populations before they feed upon and transmit TSWV to crop plants. Cyantraniliprole (Cyazypyr™) is an anthranilic diamide insecticide currently under development that exhibits anti-feedant properties. Transmission of TSWV by Frankliniella fusca (Hinds) to Capsicum annuum L. seedlings was reduced in plants treated with Cyazypyr™ applied to the soil at the rates of 1.45, 2.90 and 4.41 mg ai/plant. Mortality of F. fusca at 3 days post treatment did not differ significantly on excised foliage of Cyazypyr™ treated and control plants, but feeding injury was significantly less on treated foliage. Transmission of TSWV by Frankliniella occidentalis (Pergande) was not reduced in plants treated with 4.41 mg ai/plant.

Biological and Molecular Analyses of the Acibenzolar-S-Methyl-Induced Systemic Acquired Resistance in Flue-Cured Tobacco Against Tomato spotted wilt virus

Tomato spotted wilt virus (TSWV) is an economically important virus of flue-cured tobacco. Activation of systemic acquired resistance (SAR) by acibenzolar-S-methyl (ASM) in flue-cured tobacco was studied under greenhouse conditions by challenge inoculation with a severe isolate of TSWV. ASM restricted virus replication and movement, and as a result reduced systemic infection. Activation of resistance was observed within 2 days after treatment with ASM and a high level of resistance was observed at 5 days onward. Expression of the pathogenesis-related (PR) protein gene, PR-3, and different classes of PR proteins such as PR-1, PR-3, and PR-5 were detected at 2 days post-ASM treatment which inversely correlated with the reduction in the number of local lesions caused by TSWV. Tobacco plants treated with increased quantities of ASM (0.25, 0.5, 1.0, 2.0, and 4.0 g a.i./7,000 plants) showed increased levels of SAR as indicated by the reduction of both local and systemic infections by TSWV. The highest level of resistance was at 4 g a.i., but this rate of ASM also caused phytotoxicity resulting in temporary foliar spotting and stunting of plants. An inverse correlation between the TSWV reduction and phytotoxicity was observed with the increase of ASM concentration. ASM at the rate of 1 to 2 g a.i./7,000 plants activated a high level of resistance and minimized the phytotoxicity. Use of gibberellic acid in combination with ASM reduced the stunting caused by ASM. Present findings together with previous field experiments demonstrate that ASM is a potential option for management of TSWV in flue-cured tobacco.

BIOLOGY AND ECOLOGY OF FLOWER THRIPS IN RELATION TO TOMATO SPOTTED WILT VIRUS*

Tomato Spotted Wilt Virus (TSWV) is transmitted exclusively by certain species of thrips. Because TSWV can only be acquired by larvae and transmitted by adults, it is essential to determine the ecology of these different life stages to improve management of thrips and TSWV. Furthermore, interspecific differences among vector species complicate management issues. Herein, aspects of the biology and ecology of thrips vectors of tomato spotted wilt virus are discussed and an overview of vector-pathogens interaction is given. The complex of native and adventive Frankliniella species that occur in the southeastern USA is used as a model system for comparing and contrasting species-specific behavioral attributes that affect large-scale spatial and temporal population dynamics. The common Frankliniella species in the southeastern USA include Frankliniella occidentalis, F. fusca, F. bispinosa, and F. tritici. The western flower thrips, F. occidentalis, is considered the predominant vector of TSWV, but F. bispinosa and F. fusca are also vectors. These Frankliniella species have rapid generation times, and adults are highly polyphagous. Numerous hosts may serve as sources for thrips entering tomato fields, yet tomato is a poor reproductive host. Therefore, most of the thrips infesting fields are immigrants. Consequently, thrips dispersal behavior is a key component of TSWV epidemiology. F. occidentalis is a less mobile species than either F. bispinosa or F. tritici. These interspecific differences in the activity levels of adults affect how the species colonize plants and the field efficacy of insecticides against each species. These results show the importance of understanding interspecific variation among vectors for management of TSWV.

Tissue Blot Immunoassay for Detection of Tomato spotted wilt virus in Ranunculus asiaticus and Other Ornamentals.

A tissue blot immunoassay (TBIA) was developed to detect Tomato spotted wilt virus (TSWV) in Ranunculus asiaticus tubers and other ornamentals. TBIA was comparable to double-antibody sandwich enzyme-linked immunosorbent assay for accuracy and reliability. A nondestructive sampling method was used with R. asiaticus tubers to determine: (i) the relationship between tuber infection and size; (ii) the distribution of TSWV in tubers; and (iii) the relationship between tuber infection and tuber germination. Small tubers had a higher percentage (44%) of infection than large tubers (19%). When destructive sampling was acceptable, the central stem tissue was the most reliable to test. TSWV infection was associated with a significant reduction of tuber germination. Among the tubers that tested positive for TSWV infection, 48% of those that germinated produced foliage in which TSWV was detected. The remaining 52% of the infected tubers planted that germinated developed into plants that were asymptomatic and in which TSWV was not detectable after germination. Only 4% of tubers that tested negative produced infected plants after germination. Our results indicate that TBIA can be used in TSWV management programs to identify infected plants and to index tuber crops.

Selection, biological properties and fitness of resistance‐breaking strains of Tomato spotted wilt virus in pepper

SummaryIn glasshouse tests, infective sap from plants infected with 17 different isolates of Tomato spotted wilt virus (TSWV) from four Australian states was inoculated to three Capsicum chinense accessions (PI 152225, PI 159236 and C00943) carrying single genes that confer hypersensitive resistance to TSWV. The normal response to inoculation was development of necrotic (hypersensitive) local lesions in inoculated leaves without systemic invasion, but 3/1386 infected plants also developed systemic susceptible reactions in addition to hypersensitive ones. Similarly when two isolates were inoculated to C. chinense backcross progeny plants, 1/72 developed systemic susceptible reactions in addition to localised hypersensitive ones. Using cultures from the four plants with susceptible reactions and following three to five further cycles of serial subculture in TSWV‐resistant C. chinense plants, four isolates were obtained that gave systemic susceptible type reactions in the three TSWV‐resistant accessions, and in TSWV‐resistant cultivated pepper (C. annuum). When three of these isolates were inoculated to tomato (Lycopersicon esculentum) breeding lines with single gene resistance to TSWV, resistance was not overcome. Similarly, none of the four isolates overcame partial resistance to TSWV in Lactuca virosa. When TSWV isolates were inoculated to tomato breeding lines carrying partial resistance from L. chilense, systemic infection developed which was sometimes followed by ‘recovery’. After four successive cycles of serial passage in susceptible cultivated pepper of a mixed culture of a resistance‐breaking isolate with the non resistance‐breaking isolate from which it came, the resistance‐breaking isolate remained competitive as both were still found. However, when the same resistance‐ breaking isolate was cultured alone, evidence of partial reversion to wild‐type behaviour was eventually obtained after five but not four cycles of long term serial subculture in susceptible pepper, as by then the culture had become a mixture of both types of strain. This work suggests that resistance‐breaking strains of TSWV that overcome single gene hypersensitive resistance in pepper are relatively stable. The findings have important implications for situations where resistant pepper cultivars are deployed widely in the field without taking other control measures as part of an integrated TSWV management strategy.

Field Isolates of Tomato spotted wilt virus Overcoming Resistance in Pepper and Their Spread to Other Hosts in Italy.

Isolates of Tomato spotted wilt virus (TSWV) severely and systemically infecting commercial pepper cultivars with resistance introgressed from Capsicum chinense PI152225 were found in Albenga (northwestern Italy) in July 2000. Experimentally, these resistance-breaking (RB) isolates overcame the resistance in C. chinense PI152225, but they produced infection in other hosts similarly to non-RB isolates from the same area. The RB isolates were indistinguishable from TSWV by serology and electron microscopy, and they were efficiently transmitted by Frankliniella occidentalis. Such isolates were recovered on the same farm in tomato, pepper, and artichoke 2 and 12 months later, suggesting natural spread from the resistant plants and survival. The RB isolates survived in experimental mixed infections with a non-RB isolate in susceptible pepper and C. chinense, but cross-protection in pepper acted against them. Commercial TSWV-resistant pepper but not resistant tomato cultivars from different companies were susceptible to these RB isolates after mechanical inoculation. Similar isolates were not detected among TSWV samples collected from 1993 to 2000 in the area. The management of TSWV and thrips using resistant pepper cultivars is discussed.

Overwintering Hosts and Wingform of Thrips, Frankliniella spp., in Georgia (Thysanoptera: Thripidae): Implications for Management of Spotted Wilt Disease

Forty-five plant species were surveyed for thrips during the winter and spring in Georgia. The western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), was collected from 44 plant species, and the tobacco thrips, Frankliniella fusca (Hinds), was collected from 25 plant species. Adults of both species were 60–100% female in most samples. Thrips larvae were collected from 37 plant species, but were relatively uncommon until mid-March. Western flower thrips and tobacco thrips were most abundant during the spring on Trifolium spp. and volunteer peanut, Arachis hypogaea L., respectively. Volunteer peanut was intensively sampled for thrips during the fall and spring. Adults were 60–95% tobacco thrips in most samples, with western flower thrips comprising the remainder. Thrips larvae were collected in all samples, but were more numerous during the spring. Adult tobacco thrips were predominantly brachypterous during the late fall and early spring, suggesting that some populations of tobacco thrips overwinter in old peanut fields. Brachypterous adults were rarely observed on peanut transplanted during late March into an old pearl millet, Pennisetum americanum (L.), field, but were common on peanut transplanted into an adjacent old peanut field. The potential of tobacco thrips, western flower thrips, and their plant hosts as winter reservoirs for tomato spotted wilt virus (TSWV) is discussed. Destruction of overwintering thrips, volunteer crops, and winter annual weeds in cultivated fields is suggested as a potential strategy for TSWV management.