Tobraviruses—plant pathogens and tools for biotechnology

The tobraviruses, Tobacco rattle virus (TRV), Pea early‐browning virus (PEBV) and Pepper ringspot virus (PepRSV), are positive‐strand RNA viruses with rod‐shaped virus particles that are transmitted between plants by trichodorid nematodes. As a group, these viruses infect many plant species, with TRV having the widest host range. Recent studies have begun to dissect the interaction of TRV with potato, currently the most commercially important crop disease caused by any of the tobraviruses. As well as being successful plant pathogens, these viruses have become widely used as vectors for expression in plants of nonviral proteins or, more frequently, as initiators of virus‐induced gene silencing (VIGS). Precisely why tobraviruses should be so effective as VIGS vectors is not known; however, molecular studies of the mode of action of the tobravirus silencing suppressor protein are shedding some light on this process.     

Analysis of the occurrence and distribution of tobacco rattle virus in field soil and disease in a subsequent tulip crop

The occurrence and distribution of tobacco rattle virus (TRV) in field plots was determined by soil bait-testing and disease incidence in tulips subsequently grown on these plots was studied. The virus occurred in patches, calculated as 1.5 m × 3.6 m. The presence of virus was not correlated with numbers of potential vector trichodorid nematodes. Of three trichodorid nematode species present, only Paratrichodorus teres transmitted TRV which, as with virus isolates obtained in bait-tests and from infected tulips, reacted in serological tests with an antiserum prepared against a Dutch isolate of pea-early browning virus (PEBV). Virus prevalence in a subsequent tulip crop was 0.8% and in a sample of tulip plants, virus was recovered only from plants showing virus symptoms. Plots from which TRV was recovered in bait-tests yielded significantly more virus diseased tulips than plots which tested negative for virus. Growing bait-plants in field-plots, as compared with greenhouse tests using soil collected as a series of sub-samples, resulted in an underestimate of the occurrence of TRV.     

Vector specificity of barley yellow dwarf virus serotypes and variants in southwestern Idaho

Plants with symptoms of barley yellow dwarf virus (BYDV) obtained in infection feeding assays of aphids collected in the field in Idaho between 1986 and 1988 were tested for virus transmissibility by possible aphid vectors. Isolates obtained during 1987–1988 were also tested with a range of polyclonal antisera which distinguished PAV, MAV, SGV, RPV and RMV serotypes. In 1989 some Idaho (ID) BYDV isolates, maintained as standards for comparison, were serotyped and tested for aphid transmissibility, using 11 species of aphids. There was not always the expected correspondence between serotype and vector specificity for ID isolates. For isolates obtained from field-collected Rhopalosiphum padi, vector transmissibility and serotype corresponded with previous reports; however, 44% of isolates which were serotyped as RMV were also transmissible by species other than Rhopalosiphum maidis. Similarly, the transmissibility of the ID laboratory standards did not always conform to the reported vector specificity of serotypes. The laboratory ID-MAV culture was transmitted by Metopolophium dirhodum and Myzus persicae as well as by Sitobion avenae. The laboratory ID-SGV culture was transmitted by R. padi and 5. avenae as well as by Schizaphis graminum. The ID-RPV culture was transmitted by S. graminum and Rhopalosiphum insertum as well as R. padi. Both of two laboratory ID-RMV cultures were transmissible by R. insertum and R. padi transmitted one of them. The results indicate that, for isolates collected in Idaho, vector specificity cannot be assumed from their serotypes.     

Rapid vascular movement of tobraviruses does not require coat protein: evidence from mutated and wild-type viruses

Early studies of the tobravirus Tobacco rattle virus (TRV) described two types of virus isolate with apparently different disease characteristics. M‐type isolates, which contain both viral genomic RNAs and form virus particles, could be passaged by mechanical inoculation and produced rapid but shortlived systemic symptoms. In contrast, NM‐type isolates, which contain only RNA1 and do not form virus particles, were difficult to passage by mechanical inoculation and were very slow to produce systemic symptoms. From the early observations on such isolates made in the 1960s, it has become accepted that M isolates with encapsidated TRV particles move rapidly through the vascular system whereas NM isolates containing only unencapsidated TRV RNA1 move only slowly via plasmodesmata from cell to cell and take many weeks to reach the upper parts of plants. However, we show that NM isolates of TRV and another tobravirus Pea early‐browning virus (PEBV) move into systemic tissue of TV. benthamiana and N. clevelandii by 6 days post inoculation, suggesting that this rapid movement occurs via the vasculature. The systemic movement of TRV and PEBV mutants lacking functional coat protein that have been modified to express the green fluorescent protein were examined by confocal microscopy. This confirmed that the tobraviruses do not require the CP for long distance movement via the phloem, a property that is shared with only a small group of plant viruses.     

Immunogold Localization of Tobacco Rattle Virus Particles within Paratrichodorus anemones

Unequivocal evidence of the viral nature of virus-like particles observed at the specific site of retention of tobacco rattle virus (TRV) in Paratrichodorus and Trichodorus nematodes has not previously been available. A new staining technique using safranin-O, which does not affect viral antigenicity, was used with an antiserum raised against the coat protein of TRV and prepared for use with immunogold labelling. Application of this method enabled the occurrence and localization of particles of TRV to be confirmed in the pharynx of the natural vector of the virus, Paratrichodorus anemones, and provided unequivocal evidence that the particles observed were TRV particles. The TRV particles were observed attached only to the cuticle lining the posterior tract of the pharyngeal lumen of the vector. Therefore, the specific site of retention of TRV particles in P. anemones is apparently more localized than reported to occur in other vector trichodorid species.     

Properties of spinach yellow mottle, a distinctive strain of tobacco rattle virus

A virus (isolate SYM) obtained from spinach plants in England with a severe yellow mottle disease induced symptoms resembling those of tobacco rattle virus (TRV) in several indicator species but caused systemic necrosis in Chenopodium amaranticolor and C. quinoa. It was transmitted to bait plants grown in soil containing the nematode Trichodorus primitivus. Purified virus preparations contained rod-shaped particles that were predominantly of four modal lengths: 188 nm (L particles), 101 nm (S particles), 57 nm and 48 nm (together called VS particles), containing RNA with mol. wts of 2.4, 1.5, 0.7 and 0.6 million, respectively. L particles (s°₂₀= 300 S) and S particles (230 S) greatly outnumbered VS particles (c. 150 S). All particles contained a single polypeptide species with estimated mol wt of 24 700, slightly larger than those previously reported for tobraviruses. Purified L particles were infective but both L and S particles were needed to induce the production of virus nucleoprotein particles. VS particles were not infective and apparently had no qualitative or quantitative effect on infection by L or by L plus S particles. S particles carried determinants for serological specificity and ability to invade C. amaranticolor systemically. Isolate SYM produced pseudo-recombinants with isolate PRN of TRV. Also, isolates CAM, OR and PRN of TRV, and isolate SYM, were found to be distantly related by three kinds of serological test. No relationship was detected between these isolates and pea early-browning virus in gel-diffusion precipitin tests or electron microscope serological tests, but a distant relationship between isolate SYM and pea early-browning virus was found by micro-precipitin tests. Isolate SYM therefore has closer affinities with TRV than with pea early-browning virus and is considered to be a distinctive strain of TRV.     

The role of weed hosts and the distribution and activity of vector nematodes in the ecology of tobacco rattle virus

At a site in eastern Scotland, nine common species of arable weeds were infected with tobacco rattle virus (TRV), and some of these, notably Viola arvensis and Stellaria media, comprised an overwintering reservoir of the virus. TRV was seed-borne both in naturally and in experimentally infected V. arvensis (2–10%), and occasionally in other weed species. In the glasshouse at 20 ^oC a naturally infective population of vector nematodes (Tricho-dorus spp.) kept in soil free of plants retained its infectivity for 20 wk, although few Trichodorus survived for this period. In the field, the incidence of TRV infection in potato (spraing disease) in plots kept free of weeds for 1–5 years was 3–4 times that in weed-infested plots but Trichodorus numbers did not differ appreciably between the two treatments. Presumably the virus is retained for long periods in its vectors and these feed on potato more frequently when other hosts are not available. Weeds are probably important in the long term as hosts of both TRV and its vectors, but in the short term weed control seems unlikely to prevent potato spraing because of the long persistence of TRV in vector populations. In the field, Trichodorus accumulated near the interface between topsoil and subsoil, and the incidence of spraing was greatest where the topsoil was shallowest. When cucumber seedlings were exposed to virus-carrying Trichodorus, TRV reached a greater concentration in roots at 20 ^oC than at 24 ^oC, and the virus was not detected in roots at 29 ^oC. In a sandy soil, TRV was transmitted only when the water content exceeded 15%, and at least 30 % water was needed for maximum transmission. Annual records of rainfall and spraing disease suggest that spraing is most prevalent when the summer is wettest. TRV is not confined to cultivated land. Stabilized sand dunes supporting a pure stand of Ammophila armaria were colonized by Trichodorus pachyder-mus, but TRV was detected only where the plant community had enlarged to include V. arvensis and other dicotyledons. In such situations, TRV may be introduced in the seed of V. arvensis, and the movement of soil by wind probably contributes to the dispersal of Trichodorus.     

Lipopolysaccharides as Determinants of Serological Variability in Pseudomonas corrugata

The variation in biochemical and serological features of 128 isolates of Pseudomonas corrugata has been studied with 56 isolates from Spain and 72 isolates from other countries. Isolates were analyzed with common diagnostic tests and with the AP150CHE system. Variability among isolates for some standard tests usually listed as positive or negative for this species, such as arginine dihydrolase and gelatin hydrolysis, lipase and lecithinase activities, pigment production, and wrinkled colony morphology, was observed. Three antisera were raised against the type strain and two Spanish isolates from tomato and pepper plants. Serological reactions were studied by indirect immunofluorescence and indirect enzyme-linked immunosorbent assay. Eighty-three isolates reacted with a single antiserum, 6 reacted with two antisera, and none reacted with three antisera. Thirty-nine isolates did not react with any of the three antisera. These results suggest that serology will not be a useful method for routine diagnosis of P. corrugata unless common antigens can be identified. Electrophoresis and immunoelectrotransfer were used to study the antigens involved. Each antiserum reacted with whole-cell lysates, giving two common bands for P. corrugata isolates and other Pseudomonas species and a ladder-like pattern characteristic of lipopolysaccharides (LPS). Common bands were not observed after proteinase K treatment. More than 10 LPS patterns were distinguished in 98 isolates after silver staining of polyacrylamide gels. There was no correlation between the geographical origin or host of the isolates and the LPS patterns. A correlation between LPS groups and serological reaction was observed.     

Identification of enteropathogenic and enterohaemorrhagic Escherichia coli strains by immunoserological detection of intimin

Aims: To evaluate the sensitivity and specificity of polyclonal and monoclonal antibodies (Mabs) against intimin in the detection of enteropathogenic and enterohaemorrhagic Escherichia coli isolates using immunoblotting. Methods and Results: Polyclonal and Mabs against the intimin‐conserved region were raised, and their reactivities were compared in enteropathogenic E. coli (EPEC) and enterohaemorrhagic E. coli (EHEC) isolates using immunoblotting analysis. In comparison with rat antiserum, rabbit anti‐intimin IgG‐enriched fraction had a stronger recognition pattern to a wide spectrum of intimin types in different EPEC and EHEC serotypes. On the other hand, murine monoclonal IgG2b specific to intimin, with dissociation constant of 1·3 × 10^?8 mol l^?1, failed in the detection of some of these isolates. Conclusion: All employed antibodies showed 100% specificity, not reacting with any of the eae‐negative isolates. The sensitivity range was according to the employed antisera, and 97% for rabbit anti‐intimin IgG‐enriched fraction, followed by 92% and 78% sensitivity with rat antisera and Mab. Significance and Impact of the Study: The rabbit anti‐intimin IgG‐enriched fraction in immunoblotting analysis is a useful tool for EPEC and EHEC diagnoses.     

Distribution of trichodorid nematodes in Great Britain

This survey describes the distribution of trichodorid nematodes in Great Britain. Twelve species were recorded, including the newly described species Trichodorus hooperi Loof, 1973 and the first British record of T. sparsus Szczygiel, 1968. In the survey 3614 samples and records were analysed using the Statistical Package for Social Sciences computer programme. Seven hundred and ninety-two positive sites, containing 971 trichodorid populations, were located. Outline maps show the geographical distribution of each species. T. primitivus de Man, 1880 was the most commonly found species and had a cosmopolitan distribution. Paratrichodorus pachy-dermus Seinhorst, 1954 was the next most prevalent and occurred mostly in eastern England and Scotland. Populations of the other ten species were more restricted in both number and distribution. The distribution of trichodorid spp. with respect to altitude, soil type, pH and primary vegetation was tested using chi-squared contingency tests. A significant relationship between nematodes and environmental factors was found in all cases examined. However, interactions were found between several environmental factors and further tests were applied to study the independence of the species distributions with respect to these interactions.     

Detection of <Emphasis Type="Italic">Actinobacillus pleuropneumoniae</Emphasis> by PCR on Field Strains from Healthy and Diseased Pigs

We investigated whether primers able to specifically amplify a 0.7-kb DNA fragment from the conserved cpx genes could be applied to analyze A. pleuropneumoniae field isolates. The specific cpx primers were tested on 120 strains of A. pleuropneumoniae and other NAD-dependent field isolates from healthy and diseased animals to analyze A. pleuropneumoniae isolates from pigs in Brazil. We found that PCR and hybridization were able to discriminate between isolates of A. pleuropneumoniae and other bacteria. The 0.7-kb cpx DNA fragments were amplified from all 63 A. pleuropneumoniae isolates from herds with clinical symptoms and were isolated from lesions of acute cases of swine pleuropneumonia, both serotypable and nonserotypable. The PCR was also applied to 57 field isolates obtained from animals of apparently healthy herds, and the amplified cpx product was present in four serotypable and only two out of eleven A. pleuropneumoniae nonserotypable isolates. All nonserotypable A. pleuropneumoniae isolates revealed the apxA amplification pattern compatible with previously known serotypes. Some nonserotypable isolates might represent a population of isolates that originally were serotypable but lost the ability to react with serotype-specific antisera or might belong to novel serotypes. The PCR method applied is highly sensitive for serotypable A. pleuropneumoniae strains and for nonserotypable strains isolated from acute cases of swine pleuropneumoniae in Brazil. Received: 13 June 2002 / Accepted: 5 August 2002     

Transmission of strains of raspberry ringspot and tomato black ring viruses by Longidorus elongatus (de Man)

Scottish isolates of raspberry ringspot (RRV) and tomato black ring viruses (TBRV) showing slight serological differences were associated in the field with the nematode Longidorus elongatus and were all transmitted equally efficiently by this species in laboratory experiments. Forms of both viruses from southern England and Germany that are distantly serologically related to the Scottish isolates were also transmitted experimentally by L. elongatus, although in the field they are associated with other Longidorus species. L. elongatus transmitted English isolates of RRV almost as efficiently as the Scottish isolates but it transmitted English and German isolates of TBRV only occasionally. Four isolates each of TBRV and RRV were detected by inoculating plants with extracts of nematodes; the results paralleled those of the vector studies.     

Serological and biological characterisation of isolates of barley yellow dwarf virus in Sweden in 1983

In 1983, cereal plants showing symptoms of barley yellow dwarf virus (BYDV), collected from 15 localities in Sweden, were tested for BYDV using enzyme-linked immunosorbent assay (ELISA). Antisera against two Swedish isolates of BYDV were used, a mild isolate (27/77) transmitted specifically by Sitobion avenae and a severe one (39/78) transmitted mainly by Rhopalosiphum padi. No virus was detected in 57 of 607 plants of oats and barley tested. Of the 550 plants in which virus was detected, 366 were infected with viruses similar to isolate 27/77, 116 with viruses similar to 39/78 and the remaining 68 reacted strongly with both antisera. When tested, the latter isolates were shown to be mixtures. Thirty-nine selected samples were also tested with antisera against the USA isolates RPV, RMV, MAV and PAV, and for transmission by S. avenae and R. padi. Twenty-six of these samples were transmitted specifically by S. avenae, one was transmitted only by R. padi and the remaining 12 samples were shown to be infected with a mixture of an S. avenae-specific isolate and one transmitted mainly by R. padi. Antisera against PAV and MAV each detected all isolates tested and the results were very similar to those with the antisera to the 39/78 and 27/77 isolates, respectively. None of the field isolates reacted with antisera against RMV or RPV. It was concluded that 1983 was an epidemic year for BYDV in Sweden and that isolates specifically transmitted by S. avenae predominated. Symptoms of infection by these isolates on oat plants ranged from mild to severe.     

中国新记录——毛齿藓短蒴变种(新拟)

该研究首次报道了毛齿藓短蒴变种(新拟)在中国的分布和毛齿藓属在新疆的分布。研究表明：(1)毛齿藓短蒴变种的主要识别特征为：叶基部鞘状,突然狭窄成线状披针形,背仰,叶缘平展,中肋充满叶上部,背面粗糙,远轴面有厚壁细胞束分化,叶细胞长方形至短长方形;有假根生芽胞;孢蒴椭球形,稍弓形弯曲,蒴齿线状披针形,二裂至近基部。(2)毛齿藓属的3个分类单位在中国均有分布,毛齿藓短蒴变种以较短的孢蒴和蒴柄区别于原变种,以有根生芽胞、叶基部呈明显鞘状、叶缘平展区别于云南毛齿藓的无假根生芽胞、叶基部略呈鞘状、叶缘背卷。(3)在牛毛藓科中有许多类群与毛齿藓短蒴变种形态相似,但仅有毛齿藓属的叶在横切面上主细胞的远轴面有厚壁细胞束,而其他类群的叶在横切上主细胞的近轴面和远轴面均有厚壁细胞束。该变种的叶背仰不同于牛毛藓科其他属的叶直立;以具鞘部的叶、表面光滑的孢蒴、内弯的蒴齿区别于无鞘部的叶、表面有纵沟槽的孢蒴、直立的蒴齿的牛毛藓属。(4)该变种属北极 高山分布类型,表现出了明显的欧洲 亚洲 北美洲间断分布模式,可作为研究气候变化、海陆变迁的重要材料。     

Biological characteristics of grass geminiviruses from eastern Australia

Two serotypes of chloris striate mosaic virus (CSMV), paspalum striate mosaic virus (PSMV) and geminiviruses infecting Bromus catharticus and Digitaria didactyla were investigated. Their field occurrence and experimental hosts are listed. Serial transmission data for CSMV by single Nesoclutha pallida show a minimum latent period of 12–14 h, and regular transmission with occasional breaks for up to 50 days. Cicadulina bimaculata did not transmit any isolates after plant feeding acquisition, but transmitted CSMV inefficiently after insect injection. The vector of PSMV was found to be a specific biotype of N. pallida which bred only on Paspalum spp. The rate of transmission of CSMV with the Chloris biotype of N. pallida and of PSMV with the Paspalum biotype reached c. 50% with single insects, but only when freshly-infected source plants were used. Geminate particles were found in thin sections of leaf tissue infected with all four viruses, and partially purified preparations were made of three of these. In gel diffusion tests, the virus from Microlaena stipoides produced a spur reaction with CSMV, when reacted with CSMV antiserum. The B. catharticus and D. didactyla isolates failed to react serologically with CSMV, maize streak or Vanuatu digitaria streak viruses.     

Observations on the population dynamics and vertical distribution of trichodorid nematodes in a Scottish forest nursery

The population dynamics of Trichodorus primitivus, T. velatus and Paratrichodorus pachydermus was followed between April 1974 and March 1977 in a forest nursery growing young Sitka spruce (Picea sitchensis) trees. Soil samples taken at 10 cm intervals between 0–50 cm indicated that nematode and root distribution were not correlated and numbers of T. velatus were greatest between 0–29 cm and T. primitivus between 30–49 cm. After 3 yr trichodorid numbers between 0–19 cm had increased and those between 40–49 cm had decreased. The sex ratio of T. primitivus and T. velatus males to females was 1:1.6 and 1:1.5 respectively while for P. pachydermus it was 1:1.0. The ratios of adults to larvae varied with depth, the proportion of T. primitivus and T. velatus larvae increasing with depth but for P. pachydermus the greatest larval to adult ratio was in the top 10 cm. No consistent seasonal fluctuations were observed in the populations of all three species although larval numbers were proportionally greater than adult numbers in the summer and autumn of 1975 and 1976.     

Sequences of Tobacco Rattle Viruses from Potato

The RNA2 of the tobacco rattle virus (TRV) isolate 'Rostock' (TRV-R), and the coat protein gene (CP) of TRV isolate 'Mirow' (TRV-M) were sequenced. Both were isolated from potato. Sequence analysis revealed a 5' noncoding-region (NCR) and a CP gene, which are among the shortest of any tobravirus RNA2 sequenced so far. Downstream of the CP open reading frame (ORF) there was an ORF for a 8 k protein, that is probably a truncated 9 k protein, followed by an ORF for a 16 k protein and the 3' NCR. The 16 k protein and the 3' NCR showed a considerable sequence identity with the 3' end of TRV RNA1 and RNA2 from other TRV isolates. The high identity in the amino acid sequences of the CPs from TRV-R and TRV-M as well as other TRV isolates suggested that they are related to the TCM group of the genus Tobravirus and belong serologically to the RQ-serotype. This could be confirmed using a rabbit antiserum that was prepared against recombinant TRV-R CP expressed in bacteria. This serum was found to be suitable for differentiation of TRV-isolates.     

Root bacteria from nematicidal plants and their biocontrol potential against trichodorid nematodes in potato

Trichodorid nematodes (Nematoda: Trichodoridae) are vectors of tobacco rattle virus (TRV), one of the causal agents of spraing disease in potato. Root bacteria from nematicidal plants and their control potential against Trichodoridae were the focus of this study. Bacteria isolated from the roots of 12 nematicidal plants and potato were characterized for their production of hydrolytic enzymes, hydrogen cyanide, phenol oxidation ability and antifungal activity towards the potato pathogen Rhizoctonia solani. Based on these functional traits, bacteria isolates were selected and tested in greenhouse conditions on potato (cv. Saturna) for their effect on plant growth, and screened for nematicidal activity against Paratrichodorus pachydermus and Trichodorus primitivus in naturally infested soil. Sixteen bacteria isolates out of 44 reduced nematode densities by 50–100%. Nine selected isolated were further tested by bacterizing potato tubers (cv. King Edward) which were planted in a trichodorid and TRV-infested soil. Four bacterial isolates consistently reduced nematode densities (by 56.7–74.4%) with no visual negative effect on plant growth. These isolates were tentatively identified, partly by fatty acid methyl ester (FAME) analysis as: Stenotrophomonas maltophilia, Bacillus mycoides, Pseudomonas sp., and one unidentified bacterium. The isolates originated from potato, Plantago major, Thymus vulgaris and Asparagus officinalis, respectively. Two Pseudomonas isolates obtained from Zinnia elegans and selected for their strong nematicidal activity in soil screening tests, did not reduce the nematode population when tested on potato. It is concluded that plants releasing nematicidal compounds may harbour nematode-antagonistic bacteria as well.     

The oral susceptibility of South African field populations of Culicoides to African horse sickness virus

Twenty‐two isolates of African horse sickness virus (AHSV), representing its distinct serotypes, geographical and historical origins, were fed to three populations of South African livestock‐associated Culicoides spp. (Diptera, Ceratopogonidae). Infective blood meals included 12 recent isolates, nine historical reference strains and one live attenuated vaccine strain serotype 7 (AHSV‐7) of the virus. Field‐collected midges were fed through a chicken‐skin membrane on sheep blood spiked with one of the viruses, which concentrations ranged from 5.4 to 8.8 log₁₀TCID₅₀/mL of blood. After 10 days incubation at 23.5°C, AHSV was isolated from 11 Culicoides species. Standard in vitro passaging of AHSV‐7, used for the preparation of live attenuated vaccine, did not reduce its ability to infect Culicoides species. Virus recovery rates in orally infected Culicoides midges differed significantly between species and populations, serotypes, isolates and seasons. Significant variations in oral susceptibility recorded in this study emphasize a complex inter‐relationship between virus and vector, which is further influenced by multiple intrinsic and extrinsic factors. As it is not possible to standardize all these factors under laboratory conditions, conclusive assessment of the role of field‐collected Culicoides midges in the transmission of orbiviruses remains problematic. Nevertheless, results of this study suggest the potential for multi‐vector transmission of AHSV virus in South Africa.     

A comparison of the effectiveness of the four British virus vector species of Longidorus and Xiphinema

The frequency with which the four virus-vector species of longidoroid nematodes occurring in Britain transmitted their associated plant viruses were compared in a series of experiments using a standard procedure. In these tests Xiphinema diversicaudatum proved an effective vector of British isolates of arabis mosaic virus and strawberry latent ringspot virus and Longidorus attenuatus of an isolate of tomato black ring virus from England. In comparison, isolates of raspberry ringspot virus and tomato blackring virus from Scotland and of raspberry ringspot virus from England were transmitted much less readily by their respective vectors, L. elongatus and L. macrosoma. These differences in ability to transmit virus were not related to differences in feeding access on the virus source- or bait-plants, in the extent to which virus was retained within the nematode feeding apparatus or in the frequency with which virus was recovered from Longidorus in concurrent slash tests. Three Scottish isolates of raspberry ringspot and tomato black ring viruses were transmitted equally infrequently by two populations of L. elongatus and the frequency with which virus was transmitted was not greatly increased when the species of source or bait plants was changed.