Role of weed hosts and the western flower thrips, Frankliniella occidentalis, in epidemiology of Tomato spotted wilt virus in the Çukurova region of Turkey

Surveys of thrips and Tomato spotted wilt virus (TSWV) on weeds were conducted in the eastern Mediterranean region of Turkey during the years 2004–2006. Thrips species were collected by vigorously shaking weedy plants into a white container for 15 sec. Plant material collected during field surveys and plants which were used for mechanical inoculation of TSWV, were tested by DAS–ELISA. The weed species Ranunculus muricatus, Melilotus officinalis, Sinapis arvensis and Portulaca oleracea were used for the virus transmission experiments in an enclosed high plastic tunnel and in cage experiments. Western flower thrips, Frankliniella occidentlis (Pergande) (Thysanoptera: Thripidae), was the most common thrips, inhabiting 80 of the 82 weed species sampled. Adults of F. occidentalis and thrips larvae were significantly more abundant on S. arvensis than on the other weed species sampled (P<0.05). Adult and larval thrips showed peak densities on most weeds in April or May. Summer annual weeds were not good hosts for reproduction of the thrips. A total of 90 samples from 17 plant species belonging to 11 plant families were ELISA positive for TSWV. No TSWV was detected on 65 weed species belonging to 26 plant families. High numbers of plant samples infected by TSWV were obtained in P. oleracea (21 samples) and in R. muricatus (15 samples). In field surveys symptoms of TSWV were detected on only R. muricatus. Incidence of the TSWV on weeds ranged between 5% and 25%. Transmission rates of TSWV by F. occidentalis to the weeds ranged from 33% to 83% in the pepper plastic tunnel and cage experiments.     

深度测序技术分析番茄斑萎病毒病害寄主及介体中病毒种类

 正番茄斑萎病毒属病毒(orthotospoviruses)是严重危害云南蔬菜等重要农业经济作物的病毒病原之一。采用血清学检测、小RNA深度测序以及RT-PCR验证相结合的方法,从云南省昆明市晋宁区的主要作物寄主(番茄、辣椒、油麦菜)、重要中间寄主(鬼针草)和传毒介体(蓟马)中鉴定到TSWV、TZSV、PCSV和INSV 4种病毒,其中TSWV为该地区的主要优势病毒,而PCSV则是首次报道侵染鬼针草。通过对云南番茄斑萎病毒病害重病区作物寄主、中间寄主及蓟马三者进行病毒种类分析研究,明确TSWV为引起云南省昆明市晋宁区作物的主要病毒,TZSV、PCSV和INSV零星发生于不同寄主中。     

Detection of tomato spotted wilt virus and transmission by Frankliniella occidentalis in France

Tomato spotted wilt virus (TSWV) was isolated from pepper, tomato, eggplant, broad bean, lettuce, basil, chrysanthemum, aster, New Guinea impatiens, anemone and gloxinia plants. Virus identification was based on host range, vector transmission, serology and electron microscopy. TSWV was readily detected by ELISA in naturally or artificially infected cultivated or weed plants. The virus was also detected in individual F. occidentalis thrips. The spread of TSWV in vegetable and ornamental plants in greenhouses and/or in the open is related to the close relationship of the virus with the vector.     

Binding of Tomato Spotted Wilt Virus to a 94-kDa Thrips Protein

ABSTRACT Using protein blot assays, a 94-kDa thrips protein was identified that exhibited specific binding to tomato spotted wilt virus (TSWV) particles. Renaturation of the 94-kDa protein, which is conserved among the two major vector species of TSWV, Frankliniella occidentalis and Thrips tabaci, was crucial for its virus-binding properties, whereas under the same conditions no specific binding was observed with aphid (Myzus persicae) proteins. The 94-kDa protein species was present in all developmental stages of both vectoring thrips, whereas it was present mainly in the adult stage of a nonvectoring thrips species, Parthenothrips dracenae. Using antibodies against the different TSWV structural proteins, the G2 envelope glycoprotein was identified as the viral determinant involved. Because the virus-binding protein is present throughout the thrips body, but not in the gut, it may represent a receptor protein involved during circulation of the virus through its vector but probably not during viral uptake in the midgut.     

Tomato spotted wilt virus Infection Improves Host Suitability for Its Vector Frankliniella occidentalis

ABSTRACT The effect of Tomato spotted wilt virus (TSWV) infection on plant attractiveness for the western flower thrips (Frankliniella occidentalis) was studied. Significantly more thrips were recovered on infected than were recovered on noninfected pepper (Capsicum annuum) plants in different preference tests. In addition, more offspring were produced on the virus-infected pepper plants, and this effect also was found for TSWV-infected Datura stramonium. Thrips behavior was minimally influenced by TSWV-infection of host plants with only a slight preference for feeding on infected plants. Offspring development was positively affected since larvae hatched earlier from eggs and subsequently pupated faster on TSWV-infected plants. These results show a mutualistic relationship between F. occidentalis and TSWV.     

The competence of four thrips species to transmit and replicate four tospoviruses

The tospoviruses Tomato spotted wilt virus (TSWV), Tomato chlorotic spot virus (TCSV), Groundnut ringspot virus (GRSV) and Chrysanthemum stem necrosis virus (CSNV) are well-known pathogens on tomato in Brazil. The thrips species Frankliniella occidentalis , F. schultzei , Thrips tabaci and T. palmi were studied for their competence to transmit these tospoviruses. Frankliniella occidentalis transmitted all four tospoviruses with different efficiencies. Frankliniella schultzei transmitted TCSV, GRSV and CSNV. Although F. schultzei has been reported as a vector of TSWV, the F. schultzei population in the present study did not transmit the TSWV isolate used. A population of T. tabaci known to transmit Iris yellow spot virus (onion isolate) did not transmit any of the studied tospoviruses, and nor did T. palmi . Replication of these tospoviruses could be demonstrated by ELISA, not only in the thrips species that could transmit them, but also in those that could not. The results strongly suggest that competence to transmit is regulated not only by the initial amount of virus acquired and replication, but also by possible barriers to virus circulation inside the thrip's body.     

Occurrence of viruses in field-grown pepper crops and some of their reservoir weed hosts in Samsun, Turkey

Pepper production is affected by several viral diseases in Samsun, Turkey. To determine the identity of these viruses, a total of 313 samples from field-grown peppers were collected during surveys in 1998 and 1999, and tested by enzyme linked immunosorbent assay (ELISA). Six viruses,Alfalfa mosaic virus (AMV),Cucumber mosaic virus (CMV),Potato virus Y (PVY),Tomato mosaic virus (ToMV),Tobacco mosaic virus (TMV) andTomato spotted wilt virus (TSWV) were detected in the samples. Of 313 plants tested, 42 were doubly infected, and TMV+PVY (15.4%) was the most common double infection. This is also the first report of AMV in pepper fields in Turkey. The effect of some weed species that may act as reservoir of these viruses was also investigated in the region and of 24 weed species belonging to 15 families tested, 16 were found to be infected with at least one virus.Amaranthus retroflexus (Redroot pigweed) appeared to be a common host of CMV, PVY, ToMV, TMV and TSWV, whereasHibiscus trionum (Venice mallow) was recorded as a new weed host of PVY and TSWV. The majority of weed species found to be virus infected were very common in the pepper growing areas of the region. This indicates that pepper fields contaminated with these weeds are under risk of viral infections. http://www.phytoparasitica.org posting July 21, 2005.     

Ornamental plants and thrips populations associated with tomato spotted wilt virus in Greece

A survey was conducted in order to record the ornamental plants that are hosts of tomato spotted wilt virus (TSWV) and impatiens necrotic spot virus (INSV) in Greece. Polyclonal antibodies prepared against the N protein of a Greek isolate of TSWV fromGerbera jamesonii (GR-34) were used. Leaf samples were taken from plants showing typical symptoms of tospovirus infection such as chlorotic and necrotic rings on the leaves and malformation and necrosis of the flowers. The samples were tested by double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) using polyclonal antibodies to the N proteins of TSWV and INSV (NL-07). ELIS A-positive samples were mechanically transmitted to plants ofPetunia hybrida, Nicotiana rustica andN. benthamiana to confirm infection. Although none of the samples was found infected with INSV, TSWV presence was recorded in 42 botanical species that belong to 40 genera in 27 families. Among them the speciesBeloperone guttata, Coleus barbatus, Impatiens petersiana andLilium auratum are reported for the first time as hosts of TSWV, whereasBegonia sp.,Catharanthus roseus Celosia cristata, Dianthus chinensis, Fuchsia hybrida andStephanotis floribunda are found as new hosts of the virus in Greece. Thrips collected from TSWV-infected plants were in most cases identified asFrankliniella occidentalis, except from plants ofDendranthema sp. andDianthus caryophyllus whereThrips tabaci individuals were also identified. Different percentages of transmitters were noticed when the thrips populations collected from TSWV-infected ornamental hosts were tested for transmission of TSWV.     

Replication of Tomato spotted wilt virus After Ingestion by Adult Thrips setosus is Restricted to Midgut Epithelial Cells

ABSTRACT If acquisition access feeding (AAF) is first given after adult eclosion, none of the nine thrips species able to serve as tospovirus vectors can become infective. The previous cellular investigations of this phenomenon, carried out only in Frankliniella occidentalis, suggested that infectivity was prevented because the type member of the tospoviruses, Tomato spotted wilt virus (TSWV), was unable to enter the midgut of adult thrips. The present study extends a cellular view of tospovirus-thrips interactions to a species other than the western flower thrips, F. occidentalis. Our findings show that TSWV enters and replicates within the midgut of adult Thrips setosus, but does not infect cells beyond the midgut epithelia. After AAF as adult, TSWV replicated in T. setosus midgut cells as indicated by significant increases in nucleocapsid (N) protein detected by double-antibody sandwich enzyme-linked immunosorbent assay, and the presence of inclusions containing the S RNA-encoded nonstructural and N proteins revealed by microscopic observations. Electron microscopic observations of adult insects showed that no infection occurred in cells beyond the midgut epithelia, and insects subsampled from the same cohorts could not transmit TSWV. In contrast, electron microscopy observations of larval T. setosus revealed that TSWV infected the midgut and muscle cells, and adult insects developing from these cohorts had infected salivary glands and were able to transmit TSWV. Mature virions were observed only in the salivary glands of adults developing from infected larvae. Our findings suggest that the barrier to infectivity in T. setosus adults differs from that shown for F. occidentalis adults.     

Comparative host reactions and Frankliniella occidentalis transmission of different isolates of tomato spotted wilt tospovirus from Spain

The abilities of different isolates of tomato spotted wilt tospovirus (TSWV) collected from northeastern and eastern Spain to infect 10 host species, and to be acquired and transmitted by the western flower thrips (WFT), Frankliniella occidentalis were compared. Two isolates of TSWV from a single source plant could be separated according to the different type of local lesions they induced in Nicotiana glutinosa. Host ranges of the studied TSWV isolates were very similar, but differences were found in the symptoms induced and in their capacity to infect specific hosts systemically. Lycopersicon esculentumDatura stramonium were evaluated for their potential as virus acquisition host species. The proportion of transmitter adult thrips obtained from WFT larvae fed on L. esculentum was greater than from D. stramonium. No differences were detected between TSWV isolates in their ability to be acquired and transmitted by WFT. No evidence was obtained of alterations in TSWV particles which could affect WFT transmissibility due to the repeated mechanical transfers used to clone the isolates. Our findings do not support the existence of pathological effects of TSWV on WFT.     

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.     

Studies on the mechanism of transmission of pollen-associated tobacco streak ilarvirus virus by Thrips tabaci

Mixed instars of Thrips tabaci were allowed to feed on test seedlings of cucumber, the thrips were removed and wounds caused by thrips feeding dusted with tobacco streak virus (TSV) carried in tomato pollen. Transmission of TSV occurred in three out of the four experiments conducted. When Chenopodium amaranticolor test seedlings were dusted with infective tomato pollen, and thrips introduced for varying periods before being killed with insecticide, TSV transmission occurred after exposure to thrips for 1 h, 5 h, 1 day or 2 days, but not 5 min. Pollen-washing experiments indicated that TSV was carried both internally and externally in pollen of tomato and several weed hosts. T. tabaci was able to transmit TSV from pollen of Nicotiana clevelandii and Nicandra physalodes , and TSV from tomato pollen was transmitted to several weed species. It is concluded that T. tabaci transmits TSV associated with tomato pollen by a mechanical mechanism whereby virus carried externally, or released from inside the pollen, infects feeding wounds.     

Overwintering of Frankliniella fusca (Thysanoptera: Thripidae) on Winter Annual Weeds Infected with Tomato spotted wilt virus and Patterns of Virus Movement Between Susceptible Weed Hosts

ABSTRACT Overwintering of tobacco thrips, Frankliniella fusca, was investigated on common winter annual host plants infected with Tomato spotted wilt virus (TSWV). Populations of tobacco thrips produced on TSWV-infected plants did not differ from those produced on healthy plants, whereas populations varied greatly among host plant species. The mean per plant populations of F. fusca averaged 401, 162, and 10 thrips per plant on Stellaria media, Scleranthus annuus, and Sonchus asper, respectively, during peak abundance in May. Adult F. fusca collected from plant hosts were predominately brachypterous throughout the winter and early spring, but macropterous forms predominated in late spring. Weed hosts varied in their ability to serve as overwintering sources of TSWV inoculum. Following the initial infection by TSWV in October 1997, 75% of Scleranthus annuus and Stellaria media retained infection over the winter and spring season, whereas only 17% of Sonchus asper plants remained infected throughout the same interval. Mortality of TSWV-infected Sonchus asper plants exceeded 25%, but mortality of infected Stellaria media and Scleranthus annuus did not exceed 8%. TSWV transmission by thrips produced on infected plants was greatest on Stellaria media (18%), intermediate on Scleranthus annuus (6%), and lowest on Sonchus asper (2%). Very few viruliferous F. fusca were recovered from soil samples collected below infected wild host plants. Vegetative growth stages of Stellaria media, Sonchus asper, and Ranunculus sardous were more susceptible to F. fusca transmission of TSWV than flowering growth stages, whereas both growth stages of Scleranthus annuus were equally susceptible. In a field study to monitor the spatial and temporal patterns of virus movement from a central source of TSWV-infected Stellaria media to adjacent plots of R. sardous, the incidence of infection in R. sardous plots increased from <1% in March to >42% in June 1999. Infection levels in the Stellaria media inoculum source remained high throughout the experiment, averaging nearly 80% until June 1999 when all Stellaria media plants had senesced. Dispersal of TSWV from the inoculum source extended to the limits of the experimental plot (>37 m). Significant directional patterns of TSWV spread to the R. sardous plots were detected in April and May but not in June. R. sardous infections were detected as early as March and April, suggesting that overwintering inoculum levels in an area can increase rapidly during the spring in susceptible weed hosts prior to planting of susceptible crops. This increase in the abundance of TSWV inoculum sources occurs at a time when vector populations are increasing rapidly. The spread of TSWV among weeds in the spring serves to bridge the period when overwintered inoculum sources decline and susceptible crops are planted.     

The Efficiency by Which Thrips tabaci Populations Transmit Tomato spotted wilt virus Depends on Their Host Preference and Reproductive Strategy

ABSTRACT Arrhenotokous and thelytokous populations of Thrips tabaci from tobacco or leek plants were evaluated for their ability to transmit Tomato spotted wilt virus (TSWV) and for their host preference. Transmission efficiencies were comparatively studied using leaf disks of Petunia hybrida, Datura stramonium, and Nicotiana tabacum cv. Basmas. Adults of arrhenotokous populations collected on infected tobacco plants in the field were efficient transmitters (up to 48.5% transmission) and remained so when maintained on tobacco for several generations. Arrhenotokous T. tabacipopulations from leek plants were poor transmitters (up to 3.1% transmission), whereas no transmission was obtained with thelytokous populations from leek. All populations could infest leek, however none of the arrhenotokous and thelytokous populations from leek plants was able to infest tobacco. TSWV could be acquired by both first and second larval instars of a T. tabacipopulation from tobacco. However, the transmission by adults decreased with the age at which the virus was acquired by larvae. The highest efficiencies (61% of males and 51% of females transmitted) were obtained when newborn (0- to 24-h old) larvae acquired the virus. The majority of thrips started to transmit after becoming adult and rates were positively correlated with the temperature at which the thrips were kept. The median latent period values found for adults decreased with increasing temperature. The median acquisition access period (AAP50) of the population was 41 min, whereas the AAP(50) was 65 min for males and 35 min for females. The median inoculation access period of males was 246 and 365 min on tobacco and petunia, respectively, and 96 and 345 min for females. The results show that T. tabaci forms a complex in terms of host preference, reproductive strategy, and ability to transmit TSWV. The transmission parameters show that the thrips of arrhenotokous populations infesting tobacco are highly efficient vectors.     

Thrips Resistance in Pepper and Its Consequences for the Acquisition and Inoculation of Tomato spotted wilt virus by the Western Flower Thrips

ABSTRACT Different levels of thrips resistance were found in seven Capsicum accessions. Based on the level of feeding damage, host preference, and host suitability for reproduction, a thrips susceptible and a resistant accession were selected to study their performance as Tomato spotted wilt virus (TSWV) sources and targets during thrips-mediated virus transmission. Vector resistance did not affect the virus acquisition efficiency in a broad range of acquisition access periods. Inoculation efficiency was also not affected in short inoculation periods, but was significantly lower on plants of the thrips resistant accession during longer inoculation access periods. Under the experimental conditions used, the results obtained show that transmission of TSWV is little affected by vector resistance. However, due to a lower reproduction rate on resistant plants and a lower preference of thrips for these plants, beneficial effects of vector resistance might be expected under field conditions.     

Transmissibility of four tospoviruses by a thelytokous population ofThrips tabaci from Liguria, Northwestern Italy

Studies were carried out on a population ofThrips tabaci Lindeman (Thysanoptera: Thripi-dae) from Liguria to assess its sex-ratio and its ability to transmit four tospoviruses: tomato spotted wilt (TSWV), impatiens necrotic spot, tomato chlorotic spot and groundnut ringspot. The population was composed of females only (therefore thelytokous). The first instar larvae were allowed to acquire the virus for 48 h on infected leaves of datura, basil or pepper, and then reared on cucumber until emergence, which medially occurred 9.5 days after hatching. Transmission capacity was checked using two inoculation access periods (lAPs) of 48 h each on pepper leaf disks.T. tabaci was able to transmit TSWV isolate P105 with an efficiency of 16.7% and 4.4% in the first and second IAP, respectively, and TSWV isolate BR-01 with an efficiency of 2.0%. The onion thrips did not transmit the three other tospoviruses. During the IAPs, almost all adults fed on the leaf disks, producing evident silvery scars. The presence of tospovirus nucleocapsids in thrips was assayed by Triple Antibody Sandwich (TAS) and cocktail ELISA. Not all adults that had transmitted TSWV were positive in the tests, whereas some non-transmitter individuals proved positive. For each of the other tospoviruses, some thrips were positive in at least one test, although none was able to transmit the virus.     

Interaction of Tomato Spotted Wilt Tospovirus (TSWV) Glycoproteins with a Thrips Midgut Protein, a Potential Cellular Receptor for TSWV

ABSTRACT Interactions between viral and cellular membrane fusion proteins mediate virus penetration of cells for many arthropod-borne viruses. Electron microscope observations and circumstantial evidence indicate insect acquisition of tomato spotted wilt virus (TSWV) (genus Tospovirus, family Bunyaviridae) is receptor mediated, and TSWV membrane glycoproteins (GP1 and GP2) serve as virus attachment proteins. The tospoviruses are plant-infecting members of the family Bunyaviridae and are transmitted by several thrips species, including Frankliniella occidentalis. Gel overlay assays and immunolabeling were used to investigate the putative role of TSWV GPs as viral attachment proteins and deter mine whether a corresponding cellular receptor may be present in F. occidentalis. A single band in the 50-kDa region was detected with murine monoclonal antibodies (MAbs) to the TSWV-GPs when isolated TSWV or TSWV-GPs were used to overlay separated thrips proteins. This band was not detected when blots were probed with antibody to the non-structural protein encoded by the small RNA of TSWV or the TSWV nucleocapsid protein, nor were proteins from nonvector insects labeled. Anti-idiotype antibodies prepared to murine MAbs against GP1 or GP2 specifically labeled a single band at 50 kDa in Western blots and the plasmalemma of larval thrips midguts. These results support the putative role of the TSWV GPs as viral attachment proteins and identified potential cellular receptor(s) in thrips.     

Acquisition of Tomato spotted wilt virus by Adults of Two Thrips Species

ABSTRACT Only larval thrips that acquire Tomato spotted wilt virus (TSWV), or adults derived from such larvae, transmit the virus. Nonviruliferous adults can ingest virus particles while feeding on TSWV-infected plants, but such adult thrips have not been shown to transmit TSWV. Immunofluorescence microscopy was used to show that thrips 1, 5, 10, and 20 days after adult emergence (DAE) fed on TSWV-infected plants acquired TSWV with virus replication and accumulation occurring in both epithelial and muscle cells of Frankliniella fusca (tobacco thrips [TT]) and F. occidentalis (western flower thrips [WFT]), as indicated by immunodetection of the nonstructural (NSs) protein encoded by the small RNA and the nucleocapsid (N) protein, respectively. Adult WFT acquired TSWV more efficiently than TT. There was no significant effect of insect age on TSWV acquisition by TT. In contrast, acquisition by adult WFT at 1 and 5 DAE was higher than acquisition at 10 and 20 DAE. Subsequent transmission competence of adult cohorts was studied by vector transmission assays. All adult thrips tested that had an acquisition access period as an adult were unable to transmit the virus. These results indicate the susceptibility of adult TT and WFT to infection of midgut cells by TSWV and subsequent virus replication and confirm earlier studies that adult thrips that feed on virus-infected plants do not transmit the virus. The role of a tissue barrier in TSWV movement and infection from midgut muscle cells to the salivary glands is discussed.     

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.     

Spread of Tomato spotted wilt virus from an internal virus source by thrips species in Samsun, Turkey

The temporal and spatial distribution of Tomato spotted wilt virus (TSWV) was studied in a 2,085 m² tomato field with a total of 4,080 plants during 10 weeks from 5 July to 6 September in 2004. First infected plants were detected 4 weeks after the source plants were placed in the field and their number continued to increase by week 7. A total of 147 plants (3.6%) were recorded to be infected according to symptom occurrence and serological test by the end of the experiment. Thrips monitoring was carried out from May 25 to October 25 in the same year. Two thrips species, Frankliniella intonsa (Tryborn) and Thrips tabaci (Lindemann), were determined in the experimental area, with the latter one being the more prevalent (84.9%) species. There was a significant correlation (r?=?0.988, P?<?0.01) between the number of thrips species and the number of infected plants in the field. Majority of infected plants were not located near (0–10 m) an internal virus source within the experimental area, whereas 45.6% of the infected plants were located at a distance of 21–30 m. The number of infected plants at a distance of 21–25 m was significantly higher than at all other distances (P?<?0.05). There was no gradual increase in the distances of TSWV-infected plants within 0–30 m as time progressed. The virus seems to be transmitted by vectors through primary infections and scattered within 30-m distance, but limited secondary infections seem likely to occur after this distance in the case of a small internal virus source.