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.     

Occurrence of tomato spotted wilt and cucumber mosaic viruses in field-grown tomato crops and associated weeds in northeastern Spain

The occurrence of cucumber mosaic (CMV) and tomato spotted wilt (TSWV) viruses in the main vegetable producing regions of northeastern Spain was studied during the growing seasons of 1992 and 1993. by sampling in July and September. Both viruses were found widely distributed in field tomato crops and surrounding weeds. Coastal areas were the most affected by both CMV and TSWV, whereas inland TSWV was nearly absent. Higher levels of infection were found in autumn for TSWV in tomato crops and weeds, and for CMV in tomatoes. From the 51 weed species of 19 families collected. 25 species were found infected with CMV and 15 with TSWV. Among them, Convolvulus arvensis. Malva sylvestris , and Sonchus tenerrimus could be of special importance as local reservoirs; commonly associated with tomato crops. they were infected quite frequently with CMV and/or TSWV and being perennial, could maintain the viruses between cropping seasons.     

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.     

Seasonal abundance of the western flower thripsFrankliniella occidentalis in the arava valley of Israel

Flowers of 22 plant species grown in the Arava region of Israel were sampled at periodic intervals to study the seasonal abundance ofFrankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). Samples were collected from the most common cut-flower and vegetable plant species in this area during 1997 and from pepper in 1996–1998. Western flower thrips (WFT) was detected on 19 of the plant species surveyed, and it reproduced on numerous plant species. WFT counts peaked in late February–April and in October–December. The peak density of WFT during March in our survey corresponded to the peak flowering of cut-flower plants (during spring) and sweet pepper (during autumn). Thrips population was less abundant during autumn than in spring and was very low during summer. The possible reasons for fluctuations in thrips densities are abiotic factors (temperature and relative humidity), and availability of flowering plants. The high temperature (>40°C) and low humidity (∼20%) in summer caused a drastic reduction in WFT populations, although some flowering plant species were available in this season. WFT population remained low until October, when adults appeared in large numbers on flowering pepper. We assume that the thrips had survived the hottest months by aestivation and migrated to the plants when air temperature decreased. In most samples from the cut-flower fields, 84.8% were adult WFT; only during the period from the end of January to March, did the proportion of immature stages in the thrips population increase to 31.6%. Females always outnumbered males (71% females). In pepper fields during the first cropping month the thrips population included 96% adults; from November onwards, the proportions of adults and immatures were almost equal; and females outnumbered males. Organic pepper fields were not infested with thrips because of the presence of the predatory bugOrius albidipennis (Fieber). Contribution from the Agricultural Research Organization. No. 534/00, 2000 series. http://www.phytoparasitica.org posting July 16, 2002.     

RAPID SEROLOGICAL DETECTION OF TOMATO SPOTTED WILT VIRUS IN INDIVIDUAL THRIPS BY SQUASH-BLOT ASSAY FOR USE IN EPIDEMIOLOGICAL STUDIES

Squash blotting on nitrocellulose membranes was used to detect tomato spotted wilt virus (TSWV) in individual Frankliniella occidentalis adult thrips using a specific polyclonal antiserum. This method offers a simple and reliable procedure to test a large number of thrips and was less time-consuming than alternative techniques available. A 95% agreement was found between the results of squash-blot and plant transmission assay. Based on this agreement, this technique was used to study the relative number of viruliferous thrips in F. occidentalis field populations collected from a farm in Catalonia where TSWV causes important economic losses. The percentages of viruliferous individuals detected from a total of 1509 collected thrips increased from 0% to 2% in the different surveys conducted in the 1993 growing season. Squash-blot proved to be a rapid and inexpensive technique to screen TSWV viruliferous thrips from field populations. The results obtained by this method could be used together with other epidemiological data to forecast TSWV-induced diseases.     

露地栽培番茄斑萎病毒病发生流行规律调查及TSWV重要寄主植物监测

为明确云南省昆明市露地栽培条件下番茄斑萎病毒病的发生流行特征,于2014—2015年采用病害系统调查法结合病毒ELISA及RT-PCR检测方法研究露地栽培条件下由番茄斑萎病毒(tomato spotted wilt virus,TSWV)引起的病毒病发生规律及其重要寄主种类,并研究利用防虫网隔离蓟马对番茄斑萎病毒病的防控效果。结果表明:番茄斑萎病毒病在露地番茄主要种植期3—10月普遍发生,番茄苗期和移栽初期是该病毒病防控的关键期,带毒种苗调运是该病毒病的主要传播途径;田间多种茄科和菊科植物是TSWV的重要中间寄主。在田间,菊科寄主植物油麦菜、莴苣、鬼针草、牛膝菊上TSWV的检出率均较高,在42.53%～81.63%之间;茄科寄主植物中辣椒上TSWV的检出率最高,为41.99%,其次为马铃薯,TSWV检出率为27.78%,在番茄上TSWV的检出率为19.02%,因此生产中应对这些TSWV重要中间寄主给予更多关注和防控。应用防虫网能有效隔离蓟马,使番茄斑萎病毒病发病率和病情指数较对照分别降低了6.44个百分点和5.31,可有效降低番茄苗期及定植期斑萎病毒病的发生。     

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.     

Assessing the susceptibility of chrysanthemum cultivars to tomato spotted wilt virus

Three methods were compared to assess the susceptibility of vegetatively propagated chrysanthemum to tomato spotted wilt tospovirus (TSWV): mechanical and thrips-mediated inoculation of whole plants, and a leaf-disc assay. As symptom expression was often poor or even absent, TSWV infections and subsequent susceptibility to TSWV were determined by ELISA. All 15 chrysanthemum cultivars tested were susceptible to TSWV, irrespective of their degree of vector resistance (based on feeding-scar damage rates). Thrips-mediated inoculation using different numbers of thrips revealed that 100% infection was obtained when plants were challenged by six thrips per plant, whereas 80 and over 50%, respectively, of the plants became infected when inoculated by a single male or female thrips. However, false negatives were scored even after intensive sampling because of erratic, cultivar-specific and time-dependent virus distribution after inoculation in the plants. Labour-intensive samplings and long incubation periods could be overcome by a readily applicable leaf-disc assay. This assay was as reliable as thrips-mediated inoculation of whole plants, and its use is therefore favoured to assess chrysanthemum cultivars for TSWV susceptibility.     

Cultural management of tomato yellow leaf curl disease in Cyprus

Cultural management of tomato yellow leaf curl virus (TYLCV) by roguing old, overwintered tomato crops was investigated in a small, isolated production centre in the southern coastal zone of Cyprus. Control measures were applied on an area-wide basis during March-April, before emergence of adult whitefly ( Bemisia tabaci Genn.) vectors, for three consecutive years (1980-82). In all three years, primary virus spread to spring plantings was almost completely prevented, while further secondary spread to summer plantings was kept below 5%, compared with 40-50% in 1978 and 1979. When control measures were discontinued disease incidence increased to 15% in 1983 and 40% in 1984. The disease could also be controlled by early transplanting in the spring or by late transplanting in the autumn. Several cultural practices were evaluated to prevent or reduce infection of seedlings before transplanting. Seedlings produced in the summer in a coastal region were infected by TYLCV (virus incidence 7-42%), with a higher incidence in seedbeds situated near infected tomato crops. Infection was significantly reduced by covering seedbeds with an insect-proof tunnel, and was completely prevented by producing seedlings in inland areas, where no commercial tomato crops were grown. The use of healthy transplants delayed subsequent disease development in the field but had little effect on final disease incidence.     

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.     

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.     

Incidence of weed reservoirs and vectors of tomato spotted wilt tospovirus on southern Tasmanian lettuce farms

Thrips species and tomato spotted wilt virus (TSWV) alternate weed hosts were surveyed on two lettuce farms in southern Tasmania during 1994 and 1995. Only one known vector species, Thrips tabaci, was found at either site, comprising on average 36.8% of the total monthly catch. A major peak of thrips activity in the summer corresponded with an increase of disease in autumn harvested lettuce. Two thrips species new for Tasmania were recorded, Pseudanaphothrips achaetus and Tenothrips frici . Infection patterns within the crop indicated that localized weed infestations were the most likely reservoir of virus. ELISA testing showed that TSWV was present in a range of dicotyledonous weed species, although usually infecting only a low percentage of the plants. Arctotheca calendula appeared to be the single most important reservoir host species at one property, whilst this species and Sonchus oleraceus, Malva sylvestris, Brassica rapa ssp. silvestris, Erodium moschatum and Trifolium sp. were probably the most important reservoirs at the other property. Two new natural TSWV host species were recorded, Erodium moschatum and Brassica rapa ssp. silvestris . The property with the highest incidence of TSWV-infected lettuce had a relatively higher proportion of virus-infected weeds but less thrips activity during the infection period.     

浙南菜区番茄曲叶病毒病发生规律

通过两年调查,明确了浙南菜区越冬番茄曲叶病毒病的主要侵染期在9月下旬至10月上旬,即番茄苗龄20~30 d。温州近郊常年蔬菜生产基地,番茄曲叶病毒病的侵染循环主要通过携毒烟粉虱在越冬番茄和早春番茄间传播完成。苍南、瑞安等季节性番茄生产基地,该病的侵染循环主要通过携毒烟粉虱在越冬番茄、大田番茄苗和夏季南瓜等中间寄主传播完成。随着播种期推迟,番茄曲叶病毒病发生轻,目前浙南菜区生产上‘托马雷斯’、‘好韦斯特’、‘合作903’等主栽番茄品种均表现感病。田间调查还表明,通过50目防虫网覆盖育苗栽培可以有效控制番茄曲叶病毒病发生,防控效果达到90%以上。     

SSR assessment of Phytophthora infestans populations on tomato and potato in British gardens demonstrates high diversity but no evidence for host specialization

Phytophthora infestans populations can differ in composition as a result of host specialization on tomato and potato hosts. In Great Britain many amateur gardeners grow outdoor tomatoes but there is little or no commercial tomato production outdoors. This study analysed isolates of P. infestans from British gardens with 12 multiplexed simple sequence repeat markers that are used to monitor the disease on commercial potato crops. Samples of P. infestans from tomato hosts were collected in 3 years and from potato in 1 year from across Great Britain. Seven previously unreported clonal lineages were detected in garden populations and higher frequencies of unique clonal lineages (28–40%) were present compared with populations from British commercial potato crops reported elsewhere. Garden populations had a lower proportion (11–48% less) of the most common lineages (13_A2 and 6_A1) that together made up at least 86% of the commercial potato populations during the sampling period. Host species accounted for only 2·0% of molecular variance detected between garden potato‐ and tomato‐hosted samples. No significant difference in clonal lineage composition was found between host species in Great Britain and this could be due to the whole P. infestans population overwintering on potato. British garden populations on both hosts were much more diverse than those on commercial potato crops; this finding may be influenced by less frequent fungicide use by gardeners and a higher diversity of unsprayed susceptible potato cultivars, enabling metalaxyl‐sensitive and less aggressive genotypes to survive in gardens.     

Evaluation of metabolic detoxifying enzyme activities and insecticide resistance in Frankliniella occidentalis

The western flower thrips Frankliniella occidentalis (Pergande) is a very significant pest of a number of different agricultural crops in the south-east of Spain. The importance of thrips as a pest is not due mainly to the direct damage inflicted on the plant, but to the loss in commercial value which occurs as a consequence of the development of dark spots caused by the tomato spotted wilt virus (TSWV) which they transmit. The economic threshold is therefore almost zero, which enhances the problems of resistance management. The present work is part of a global project that attempts to evaluate the status of insecticide resistance in field populations of thrips obtained from several agricultural crops. We have studied, in either individual or pooled insects, some enzyme systems classically related to detoxification of insecticides: esterase and glutathione-S-transferase (GST). The activity of these enzymes from laboratory populations selected with various classes of insecticides has also been measured using several appropriate substrates. An increase in GST mean activity was found in two field-collected strains. Differences in frequency distributions of esterase and GST activities were found for both field-collected strains and for a laboratory strain selected with acrinathrin. These activities were compared with those of a wild-type reference strain.     

Use of azadirachtin as a larvicide or feeding deterrent for control of western flower thrips in orchard systems

Field trials were carried out to assess the efficacy of a 4% azadirachtin (aza)-containing neem seed extract EC, against damage by western flower thrips [Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae)] on nectarine crops in the Similkameen Valley, British Columbia, Canada. Several trials were conducted during the years 1993 to 1995 to assess the repellent and larvicidal properties of aza, specifically: whether it was effective against adult or larval thrips; how the effects differed with concentration of aza; and whether female WFT avoided aza-treated flowers. Our results showed that aza has only limited effectiveness as a control agent against WFT on nectarines and the current formulation does not appear to limit larval development sufficiently to be deemed a possible control agent in this field situation.     

Dynamics of Tomato spotted wilt virus Replication in the Alimentary Canal of Two Thrips Species

ABSTRACT Transmission of Tomato spotted wilt virus (TSWV) is dependent on virus uptake in the midgut prior to virus movement to the salivary glands. Replication of TSWV in the alimentary canal of tobacco thrips (TT, Frankliniella fusca) and western flower thrips (WFT, F. occidentalis) was investigated by immunolocalization of the nonstructural protein (NSs) encoded by the small RNA of TSWV and fluorescence microscopy. Analysis of cohorts during development from larva to adults following virus acquisition by first instar larva indicated that virus replication followed a specific time-course pattern in the foregut, regions of the midgut, salivary glands, and ligaments between the midgut and salivary glands. Initial virus replication occurred only in epithelial cells of midgut-1 but, upon infection of muscle cells, the virus moved to the midgut-2, foregut, midgut-3, and salivary glands. The ligaments between the midgut and salivary glands appeared to be a route for virus to invade the salivary glands. No virus replication was observed in the hindgut, Malpighian tubules, or tubular salivary glands. The dynamics of TSWV replication, as measured by NSs accumulation, were similar in both TT and WFT.     

Eradication of Frankliniella occidentalis and tomato spotted wilt virus in Finland: a case study on costs and benefits

Western flower thrips ( Frankliniella occidentalis ) invaded Finland in 1987/1988. In the following year, tomato spotted wilt virus (TSWV) was identified in vegetable and ornamental crops. An eradication campaign was initiated in autumn 1987. Growers were ordered to take measures against F. occidentalis and TSWV and were advised how to avoid these new pests; the import regulations were amended to intensify pre-export and pre-entry control; a research programme was started to develop biological control of F. occidentalis. At present, F. occidentalis occurs only sporadically in a few places and is not a problem for the growers. TSWV has not been identified since 1989. Eradication measures cost the government FIM 1.6 million in 1987/1990. The financial cost of eradication to the industry has been impossible to assess. It has been calculated that 'living with' F. occidentalis and TSWV cost at least FIM 35 million over a period of 4 years. The cost/benefit ratio is thus about 1:20. The eradication campaign has therefore been highly profitable.     

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.     

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.