Evidence that maize wallaby ear disease is caused by an insect toxin

Colonies of the leafhopper Cicadulina bimaculata were established from single male and female insects raised from surface sterilised eggs and shown to be free of leafhopper A virus (LAV). Insects from these colonies were as capable of inducing maize wallaby ear disease (MWED) in maize seedlings as those with LAV indicating that the virus is not involved in the etiology of MWED. Maize seedlings colonised by C. bimaculata in glasshouse trials developed initial MWED symptoms within 6–8 days of infestation. The symptoms intensified thereafter and many plants died after more than 16 days' exposure, even after the insects were killed with insecticide. However, when freed from the insects before symptoms became very severe, plants recovered and assumed normal growth. These observations support the view that MWED is caused by an insect toxin.     

Transmission of rayado fino virus of maize (Zea mays) by Dalbulus tnaidis

Rayado fino virus (RFV) of maize (Zea mays) was transmitted by the leaf-hopper Dalbulus maidis in a manner characteristic of viruses that multiply in their insect vectors. Individual insects fed on infected plants transmitted the virus after incubation periods of 8–22 days; males had shorter incubation periods than females but died sooner. Insects retained infectivity for 1–20 days. Transmission by most insects was intermittent. Inoculativity by D. maidis decreased with time, but the virus was recovered from insects that had lost their ability to transmit. Extracts of plants infected with RFV and viruliferous insects were injected into healthy insects, which became viruli-ferous. Infectivity of the extracts was not affected by tetracycline hydrochloride (Achromycin). D. maidis was able to transmit simultaneously RFV and the corn stunt agent. Other than maize, Teosinte (Euchlaena mexicana) was the only plant susceptible to the virus, among a number of species of Gramineae tested.     

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.     

Confirmation of the transmission of barley yellow mosaic virus (BaYMV) by the fungus Polymyxa graminis

Resting spores (cystosori) of Polymyxa graminis, selected from roots of barley plants infected with barley yellow mosaic virus (BaYMV), were used to start mono-fungal sand cultures. Out of 20 attempts using over 800 cystosori, P. graminis became established in 12, and in two of these BaYMV symptoms also occurred. BaYMV was detected by ELISA in extracts of dried roots heavily infected with cystosori and in zoospores of P. graminis. Calculations suggested that, on average, each zoospore carried less than 100 virus particles. In two virus acquisition experiments, non-viruliferous isolates of P. graminis failed to acquire BaYMV from roots of mechanically-inoculated plants. In two further experiments, non-viruliferous isolates were grown on rooted tillers produced from healthy plants and those infected with BaYMV by either vector or mechanical inoculation. Zoospores and cystosori of P. graminis subsequently transmitted the virus, but only from plants where it had been introduced by the vector. Repeated mechanical transmission appeared to have selected a strain of virus that could not be acquired and/or transmitted by the vector. The results provide convincing evidence that P. graminis is a vector of BaYMV but suggest that, in natural populations, only a small proportion of spores may be viruliferous.     

The particle morphology and some other properties of chloris striate mosaic virus

The causal agent of Chloris striate mosaic disease appears to be a virus with polyhedral particles 18 nm in diameter usually occurring as paired structures about 18 times 30 nm in negatively stained preparations. These particles were detected in the nuclei of infected plants forming characteristic inclusions in all cells except those of the epidermis. Such particles were not detected in thin sections of viruliferous leaf hopper vectors (Nesoclutha pallida). Purified virus preparations were shown to be highly infective when assayed by feeding vector leaf hoppers through membranes and confining them on indicator plants. In particle morphology, chloris striate mosaic virus (CSMV) differs from other viruses of Gramineae in Australia but resembles maize streak virus isolated in Africa, which however is serologically unrelated.     

Transmission characteristics and some other properties of bean yellow vein-banding virus, and its association with pea enation

Bean yellow vein-banding virus (BYVBV) has been found occasionally in mixed infection with pea enation mosaic virus (PEMV) in spring-sown field beans (Vicia faba minor) in southern England. Glasshouse tests confirmed that, like PEMV, BYVBV is transmissible by manual inoculation and by aphids in the persistent manner. However, BYVBV can be transmitted by aphids only from plants that are also infected with a helper virus, usually PEMV. Thus after separation from PEMV by passage through Phaseolus vulgaris it was no longer aphid-transmissible. It became aphid-transmissible again only after re-mixing in plants with PEMV or with a substitute helper, bean leaf roll virus (BLRV). It was not transmitted by aphids that fed sequentially on plants singly infected with PEMV and BYVBV. Thus the interaction between BYVBV and PEMV (or BLRV) that enables BYVBV to be transmitted by aphids seems to occur only in doubly infected plants. However, it was not transmitted by aphids from plants doubly infected with BYVBV and broad bean wilt virus (BBWV). BYVBV and PEMV were transmitted more readily by Acyrthosiphon pisum than by Myzus persicae; neither virus was transmitted by Aphis fabae. Phenol extracts of BYVBV-infected leaves were more infective than phosphate buffer or bentonite-clarified extracts and were sometimes infective when diluted to 1/1000. The infectivity of BYVBV in phosphate buffer extracts of leaves singly infected with BYVBV, unlike that in extracts of leaves doubly infected with BYVBV and PEMV (or BLRV), was destroyed by treatment with organic solvents. BYVBV infected 11 of 28 plant species that were inoculated with phenol extracts; seven of the infected species were legumes. No transmission of BYVBV was detected through seed harvested from infected field bean plants. Isometric particles c. 30 nm in diameter were seen in extracts of plants doubly infected with BYVBV and PEMV but not in extracts of plants infected with BYVBV alone. Leaves of plants infected with BYVBV, alone or with PEMV, contained membrane-bound structures c. 50–90 nm in diameter associated with the tonoplast in cell vacuoles. These structures were not found in healthy leaves. BYVBV has several properties in common with other known aphid-borne viruses that are helper-dependent and transmitted in a persistent manner. Possibly, as suggested for some of them, aphid transmission of BYVBV depends on the coating of its nucleic acid with helper virus coat protein.     

Detection of strains of African cassava mosaic virus by nucleic acid hybridisation and some effects of temperature on their multiplication

DNA probes, made by cloning double-stranded forms of each of the genome parts (DNA-1 and DNA-2) of the Kenyan type isolate of African cassava mosaic virus (ACMV-T), reacted strongly with extracts from Nicotiana benthamiana plants infected with ACMV-T, or with Angolan or Nigerian isolates that are closely serologically related to the type isolate. However, only the DNA-1 probes reacted with extracts of TV. benthamiana infected with a Kenyan coast isolate (ACMV-C), which is serologically less closely related to ACMV-T. DNA-1 and DNA-2 probes also reacted with extracts of mosaic-affected Angolan cassava plants, including some which have not yielded ACMV particles detectable by immunosorbent electron microscopy and from which virus isolates have not been transmitted to TV. benthamiana. These anomalous plants, unlike other naturally infected cassava plants, showed mosaic symptoms on all their leaves which, however, contained only traces of virus particle antigen detectable by enzyme-linked immunosorbent assay. They contain isolates of ACMV that are probably defective for particle production. ACMV-T particles accumulated optimally in N. benthamiana at 20–25°C. At 30°C fewer particles, which apparently had a slightly greater specific infectivity, were produced. At 15°C, considerable quantities of virus particle antigen, virus DNA and virus particles were produced but the particles were poorly infective, and the few that could be purified contained an abnormally large proportion of polydisperse linear DNA molecules, and fewer circular molecules than usual. Angolan isolates, whether particle-producing or not, likewise replicated better in cassava plants at 23 °C than at 30 °C. In contrast, ACMV-C attained only very low concentrations in N. benthamiana, but these were greater at 30 °C than at 23°C.     

Cucurbit aphid‐borne yellows virus (CABYV) modifies the alighting,settling and probing behaviour of its vector Aphis gossypii favouring its own spread

Plant pathogens are able to influence the behaviour and fitness of their vectors in such a way that changes in plant–pathogen–vector interactions can affect their transmission. Such influence can be direct or indirect, depending on whether it is mediated by the presence of the pathogen in the vector's body or by host changes as a consequence of pathogen infection. We report the effect that the persistently aphid‐transmitted Cucurbit aphid‐borne yellows virus (CABYV, Polerovirus) can induce on the alighting, settling and probing behaviour activities of its vector, the cotton aphid Aphis gossypii. Only minor direct changes on aphid feeding behaviour were observed when viruliferous aphids fed on non‐infected plants. However, the feeding behaviour of non‐viruliferous aphids was very different on CABYV‐infected than on non‐infected plants. Non‐viruliferous aphids spent longer time feeding from the phloem in CABYV‐infected plants compared to non‐infected plants, suggesting that CABYV indirectly manipulates aphid feeding behaviour through its shared host plant in order to favour viral acquisition. Viruliferous aphids showed a clear preference for non‐infected over CABYV‐infected plants at short and long time, while such behaviour was not observed for non‐viruliferous aphids. Overall, our results indicate that CABYV induces changes in its host plant that modifies aphid feeding behaviour in a way that virus acquisition from infected plants is enhanced. Once the aphids become viruliferous they prefer to settle on healthy plants, leading to optimise the transmission and spread of this phloem‐limited virus.     

Transmission,Particle Size and Additional Hosts of the Rhabdovirus Causing Maize Mosaic in Shiraz,Iran1

The rhabdovirus causing maize mosaic in Shiraz, Iran, is transmitted by Ribautodelphax notabilis Logvinenko (Homoptera, Delphacidae). Average size of bullet-shaped virus particles in negatively stained leaf-dip preparations of naturally or experimentally infected plants was 81 × 179 nm. The virus is transmitted to wheat and barley causing mosaic and severe stunting. Similar virus particles have been observed in leaf-dip preparations of naturally infected wheat, barley and Sudangrass. This is believed to be the first record of the involvement of R. notabilis in virus transmission. The relationship of the described isolate with similar viruses infecting gramineous plants is discussed.     

Viruses associated with chlorotic rosette and green rosette diseases of groundnut in Nigeria*

Groundnut (Arachis hypogaea) plants from Nigeria with chlorotic rosette disease contained a manually transmissible virus, considered to be a strain of groundnut rosette virus (GRV(C)). GRV(C) infected nine out of 32 species in three out of nine families. It caused local lesions without systemic infection in Chenopodium amaranticolor, C. murale and C. quinoa, and systemic symptoms in Glycine max, Nicotiana benthamiana, N. clevelandii and Phaseolus vulgaris as well as in groundnut. Some ‘rosette-resistant’ groundnut lines were also infected. GRV(C) was transmitted by Aphis craccivora, but only from groundnut plants that were also infected with an aphid-transmissible second virus, which was not manually transmissible and was considered to be groundnut rosette assistor virus (GRAV). Plants infected with GRAV contained isometric particles c. 25 nm in diameter which were detectable by immunosorbent electron microscopy on grids coated with antisera to several luteoviruses, especially with antisera to bean leaf roll, potato leafroll and beet western yellows viruses. No virus-like particles were observed in extracts from plants infected with GRV(C) alone. A single groundnut plant obtained from Nigeria with symptoms of green rosette contained luteovirus particles, presumed to be of GRAV, and yielded a manually transmissible virus that induced symptoms similar to those of GRV(C) in C. amaranticolor but gave only mild or symptomless infection of N. benthamiana and N. clevelandii. It was considered to be a strain of GRV and designated GRV(G).     

Detection of maize rough dwarf virus by enzyme-linked immunosorbent assay in plant hosts and in the planthopper vector

SVPs were efficiently detected by ELISA in individual male and female insects. Females carried more virus per insect and per unit fresh weight, but no significant difference was detected between males and females in vector efficiency. Of insects positive in ELISA, 15–20% were unable to transmit the virus to host plants. Storage of viruliferous hoppers at-20°C decreased the level of viral antigen detected by half in about 240 days. Subviral particles (SVPs) of maize rough dwarf virus were detected in the planthopper vector Laodelphax striatellus and in maize and barley plants using double antibody sandwich ELISA. In purified preparations diluted in buffer, as little as 36 ng/ml of SVPs was detectable whereas after dilution in extracts of healthy frozen planthoppers the sensitivity was reduced to 50 ng/ml. Freezing the hoppers prior to extraction lowered to one third the background reading due to normal components. Neither the dissociated proteins of the SVP nor the viral double-stranded RNA contributed to the ELISA readings.     

Relations of the semi-persistent viruses, parsnip yellow fleck and anthriscus yellows, with their vector, Cav arietta aegopodii

Studies were made of the relations of parsnip yellow fleck virus (PYFV) and its helper virus, anthriscus yellows (AYV), with their aphid vector, Cavariella aegopodii. Apterous insects were more efficient vectors than alates; apterous nymphs were as efficient as apterous adults. C. aegopodii never transmitted PYFV in the absence of AYV, but aphids carrying both viruses infected some test plants with one or other virus alone. C. aegopodii that fed first on a source of AYV and then on a source of PYFV transmitted both viruses to test plants, but aphids that fed on the sources in the reverse order transmitted only AYV. Test plants receiving some aphids from a source of AYV, and others from a source of PYFV, became infected only with AYV. C. aegopodii acquired AYV or the AYV/PYFV complex from plants in a minimum acquisition access time (AAT) of 10–15 mm and inoculated the viruses to test plants in a minimum inoculation access time (IAT) of 2 min. Increasing either AAT or IAT, or both, to 1 h or longer increased the frequency of transmission of each virus. Starving the insects before the acquisition feed on AYV or AYV/PFYV sources did not affect transmission. Aphids already carrying AYV acquired PYFV from plants in a minimum AAT of only 2 min; they acquired and inoculated PYFV in a minimum total time of 12 min. The data suggest that AYV is confined to deeply lying tissues whereas PYFV is distributed throughout the leaf. C. aegopodii transmitted both PYFV and AYV in a semi-persistent manner: the aphids retained both viruses for up to 4 days but lost them on moulting. Neither virus was passed to progeny of viruliferous adults. Earlier results suggesting that AYV is a persistent virus may have been caused by contamination of the AYV culture with carrot red leaf virus.     

Horizontal transmission of begomoviruses between Bemisia tabaci biotypes

We have previously shown that the monopartite Tomato yellow leaf curl virus (TYLCV), a begomovirus (family Geminiviridae, genus Begomovirus) infecting tomato plants can be transmitted in a gender-dependent manner among its insect vector the whitefly Bemisia tabaci type B (Gennaduis) (Aleyrodidae: Hemiptera) during mating. Viruliferous females were able to transmit the virus to non-viruliferous males and vice versa, in the absence of any other virus source. The recipient insects were able to infect tomato plants. In this communication, we present evidence that two bipartite begomoviruses infecting cucurbits, Squash leaf curl virus (SLCV) and Watermelon chlorotic stunt virus (WmCSV) can be transmitted in a gender-dependent manner among whiteflies. In addition we show that TYLCV can be transmitted during mating among individuals from the same biotype (from B-males to B-females and vice versa; and from Q-males to Q-females and vice versa). However, viruliferous males of the B biotype are unable to transmit the virus to females of the Q biotype (and vice versa); similarly, viruliferous males of the Q biotype are unable to transmit the virus to females of the B biotype (and vice versa). These findings support the hypothesis that a pre-zygotic mating barrier between the Q and B biotypes is the cause for the absence of gene flow between the two biotypes, and that virus transmission can be used as a marker for inter-biotype mating. To be transmitted during mating, the virus needs to be present in the haemolymph of the donor insect. Abutilon mosaic virus (AbMV), a bipartite begomovirus that can be ingested but not transmitted by B. tabaci, is absent in the whitefly haemolymph, and cannot be transmitted during mating. Mating was a precondition for horizontal virus transfer from male to female, or female to male. Virus was not transmitted when viruliferous B. tabaci were caged with the non-vector non-viruliferous whitefly Trialeurodes vaporariorum (Westwood) (Aleyrodidae: Hemiptera) and vice versa.     

Properties of cherry ring mottle, a distinctive strain of prune dwarf virus

A virus was transmitted from sweet cherry trees with cherry ring mottle disease to cucurbitaceous plants with the aid of liquid nitrogen, caffeine or polyethylene glycol, which were more effective than sodium diethyldithiocarbamate, polyvinylpyrrolidone and other materials used in sap-transmission studies. The virus was transmitted from dormant buds, petals, young leaves, anthers and pollen. Of 172 herbaceous species and varieties tested, twenty-five (thirteen spp.) became infected with virus. Ribes nigrum and peach seedlings were also infected. Of the systems produced in woody plants, those in Italian Prune resembled the symptoms caused by prune dwarf virus, but those in other Prunus spp. did not. In cucumber extracts the thermal inactivation point was between 40 and 44 d?C; dilution end-point was 1/16 to 1/32 and longevity in vitro 8–16 h. Formaldehyde (4%) fixed the particles and preserved their shape for electron microscopy; they were spherical, with a mean diameter of 24 nm. The virus reacted with prune dwarf virus antiserum but differed in several ways from other isolates     

Aphid-injection experiments with carrot mottle virus and its helper virus, carrot red leaf

Carrot mottle virus (CMotV) and its helper virus, carrot red leaf (CRLV), were not transmitted by aphids (Cavariella aegopodii) that had fed through membranes on, or had been injected with, sap from mixedly infected chervil plants or partially purified preparations of CMotV. However, the viruses were transmitted by recipient aphids injected with haemolymph from donor aphids that had fed on mixedly infected plants but not by a second series of recipients injected with haemolymph from the first series. Some of the first series of recipients transmitted both viruses for up to 11 days but others transmitted erratically and many lost ability to transmit after a few days. The results confirm that both viruses are circulative but provide no evidence for multiplication in the vector. Non-viruliferous aphids, or aphids that had acquired CRLV by feeding, did not transmit CMotV when they were injected with haemolymph from aphids that had fed on a source of CMotV alone, confirming that they can only transmit CMotV when they acquire it from a mixedly infected plant. When extracts from donor aphids were treated with ether before injection, recipient aphids transmitted both CRLV and CMotV, although the infectivity of CMotV grown in Nicotiana clevelandii in the absence of CRLV is destroyed by ether treatment. CMotV particles acquired by aphids from mixedly infected plants therefore differed in some way from those in singly infected plants. A plausible explanation of these results, and of the dependence of CMotV on CRLV for aphid transmission, is that doubly infected plants contain some particles that consist of CMotV nucleic acid coated with CRLV protein.     

Purification and Characterization of Indian Cassava Mosaic Virus

The Indian cassava mosaic virus (ICMV) was transmitted by the whitefly Bemisia tabaci and sap inoculation. ICMV was purified from cassava and from systemically infected Nicotiana benthamiana leaves. Geminate particles of 16–18 × 30 nm in size were observed by electron microscopy. The particles contained a single major protein of an estimated molecular weight of 34,000. Specific antiserum trapped geminate particles from the extracts of infected cassava and N. benthamiana plants in ISEM test. The virus was detected in crude extracts of infected cassava, ceara rubber, TV. benthamiana and N. tabacum cv. Jayasri plants by ELISA. ICMV appeared serologically related to the gemini viruses of Acalypha yellow mosaic, bhendi yellow vein mosaic, Croton yellow vein mosaic, Dolichos yellow mosaic, horsegram yellow mosaic, Malvastrum yellow vein mosaic and tobacco leaf curl.     

Vector and Host-Plant Relationships of the Leafhopper-Borne Maize Yellow Stripe Virus

Maize yellow stripe virus (MYSV), associated with tenuivirus-like filaments, is transmitted in a persistent manner by the leafhopper Cicadulina chinai. In this vector, MYSV acquisition and inoculation threshold times were 30 min each, latent period ranged from 4.5 to 8 days depending on temperature (14-25 °C), and retention periods were as long as 27 days. Up to 26 % of C, chinai collected from maize fields in Giza, Egypt, during September and October 1985 were naturally infective with MYSV. Two symptom-types (fine and coarse stripe) appeared on experimentally infected plants, usually on separate leaves of the same plant. However, these two symptom-types could not be isolated on separate plants through transmission by single C. chinai leafhoppers. MYSV was transmitted by nymphs and adults of C. chinai from maize to maize, wheat and barley, and from wheat to maize plants. Up to 6 % of the wheat plants examined in Naga Hamadi (Southern Egypt) in February 1986, were naturally infected. It is suggested that wheat, barley and possibly graminaceous weeds may serve as winter hosts or reservoirs for MYSV and its leafhopper vector in Egypt.     

Settling preferences of the whitefly vector Bemisia tabaci on infected plants varies with virus family and transmission mode

Virus infection may change not only the host‐plant phenotypic (morphological and physiological) characteristics, but can also modify the behavior of their insect vector in a mutualistic or rather antagonistic manner, to promote their spread to new hosts. Viruses differ in their modes of transmission and depend on vector behavior for successful spread. Here, we investigated the effects of the semi‐persistently transmitted Tomato chlorosis virus (ToCV, Crinivirus) and the persistent circulative Tomato severe rugose virus (ToSRV, Begomovirus) on alighting preferences and arrestment behavior of their whitefly vector Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) Middle East Asia Minor 1 (MEAM1) on tomato plants (Solanum lycopersicum L. cv. Santa Clara, Solanaceae). The vector alighting preferences between infected and uninfected plants in choice assays were apparently influenced by the presence of ToCV and ToSRV in the whiteflies or by their previous exposure to infected plants. The observed changes in vector behavior do not seem to benefit the spread of ToCV: non‐viruliferous insects clearly preferred mock‐inoculated plants, whereas ToCV‐viruliferous insects landed on mock‐inoculated and ToCV‐infected plants, indicating a partial change in insect behavior – ToCV was able to directly affect the preference of its vector B. tabaci, but this change in insect behavior did not affect the virus spread because viruliferous insects landed on mock‐inoculated and infected plants indistinctly. In contrast, ToSRV‐viruliferous insects preferred to land on mock‐inoculated plants, a behavior that increases the probability of spread to new host plants. In the arresting behavior assay, the majority of the insects remained on mock‐inoculated plants when released on them. A greater number of insects moved toward mock‐inoculated plants when initially released on ToCV‐ or ToSRV‐infected plants, suggesting that these viruses may repel or reduce the nutritional quality of the host plants for B. tabaci MEAM1.     

Increased sensitivity of detection of plant viruses obtained by using a fluorogenic substrate in enzyme-linked immunosorbent assay

The fluorogenic substrate 4-methylumbelliferyl phosphate (MUP) of alkaline phosphatase was compared with the chromogenic substrate p-nitrophenyl phosphate (NPP) in tests for plant viruses by enzyme-linked immunosorbent assay (ELISA). In tests on leaf extracts of squash infected with prune dwarf virus, Chenopodium quinoa and apple infected with apple mosaic virus (ApMV), and potato infected with potato leafroll virus (PLRV), MUP increased sensitivity 2–16 times, the smallest and greatest increases being obtained with ApMV (in apple) and PLRV respectively. In similar tests on 21 dormant PLRV-infected potato tubers, sensitivity was increased 2–4 times with 13 tubers, but the two substrates gave the same detection end-points with eight tubers. When individual seeds of potato plants infected with the Andean potato calico strain of tobacco ringspot virus were tested, the virus was detected in virtually all seeds by MUP-ELISA, but detection by NPP-ELISA was inefficient unless absorbance values were measured after overnight incubation at 4 °C, instead of after 2 h at room temperature. In tests on Myzus persicae carrying PLRV and Sitobion avenae carrying barley yellow dwarf virus (BYDV), both viruses were consistently detected in a greater proportion of individual aphids by MUP-ELISA than NPP-ELISA irrespective of whether incubation was for 2 h at room temperature or overnight at 4 °C. The effeciency of detection of virus in single viruliferous aphids by MUP-ELISA was not decreased by grouping with one or four non-viruliferous aphids but was decreased (PLRV) or greatly decreased (BYDV) by grouping with nine. MUP-ELISA and transmission tests to Physalis floridana seedlings (2–3 day inoculation access periods) both detected PLRV in most individual M. persicae, but the results obtained with the two methods did not correlate completely. In similar tests for BYDV in individual S. avenae, virtually all aphids transmitted BYDV to oat seedlings during a 3-day inoculation access period but it was subsequently detected by MUP-ELISA in less than half of them. By contrast, MUP-ELISA detected PLRV in most viruliferous M. persicae even after they had fed for 3 days on Chinese cabbage, a non-host for this virus.     

Identification of Rubus yellow net virus as a distinct badnavirus and its detection by PCR in Rubus species and in aphids

Rubus yellow net virus (RYNV) infects Rubus species and cultivars worldwide and is an essential component of raspberry veinbanding mosaic (RVBMD), a virus disease complex that causes serious decline in plant vigour and productivity. The virus is transmitted, probably in a semi‐persistent manner, by the large raspberry aphid, Amphorophora idaei in Europe, and A. agathonica in North America. The particles of RYNV are bacilliform in shape and measure 80–150 × 25–30 nm, similar to those of badnaviruses. A1.7 kb fragment of the viral DNA was amplified by PCR and then directly sequenced. Analysis of this sequence suggests that RYNV is possibly a distinct species in the genus Badnavirus and is most closely related to Gooseberry vein banding associated virus (GVBAV) and Spiraea yellow leaf spot virus, two other badnaviruses described recently. Using the sequence derived from the PCR‐amplified viral DNA fragment, RYNV‐specific primers were designed and used in PCR to assay for RYNV in a range of Rubus germplasm infected with RYNV, with other unrelated viruses and virus‐like diseases found in Rubus, and in healthy plants. RYNV was detected in all glasshouse cultures of RYNV‐infected plants, whether alone or in complex infections with other viruses, but not from healthy Rubus plants, nor from plants infected with other viruses. It was also detected in field‐grown raspberry plants with and without symptoms of RVBMD and in raspberry plants infected with RYNV by viruliferous A. idaei. RYNV was also detected by PCR in A. idaei following access feeds on RYNV‐infected plants of 1 h or more. PCR failed to amplify DNA from gooseberry infected with GVBAV confirming the specificity of the RYNV analysis. PCR detection of RYNV in dormant raspberry buds allows assays to be made outside the natural growing season, providing a useful application for plant introduction and quarantine programmes.