Non-propagative translocation of velvet tobacco mottle virus in the mirid, Cyrtopeltis nicotianae

Nymphs of the mirid, Cyrtopeltis nicotianae became infective when injected with velvet tobacco mottle virus (VTMoV). Injections of amounts between 1 and 154 ng into the haemocoele induced 2/60 to infect test plants and these two nymphs contained 50 and 63 ng of virus respectively. Injection of amounts between 15 and 2400 ng rendered 11/47 nymphs infective. This observation is characteristic of a circulative association. However, there is no evidence that the salivary glands are involved in transmission and the virus is therefore defined as translocating, rather than circulating, in the mirid vector. Mirids which acquired infectivity by feeding lost it between 5 and 9 days after completion of acquisition, and the most rapid loss of infectivity occurred within 2 days. Nine days after acquisition none contained antigen detectable by ELISA, but detectable antigen decreased less rapidly than infectivity, and at all times more mirids contained antigen than were able to transmit. Mirids containing antigen carried between 150 and 3340 ng each. Thus, although VTMoV can be transmitted by its mirid vector following introduction of virus into the body cavity by injection, VTMoV is not propagative. Nor does the presence of virus within the mirid guarantee an ability to transmit.     

Relations of carrot red leaf and carrot mottle viruses with their aphid vector, Cavariella aegopodii

Studies with Scottish isolates of carrot red leaf (CRLV) and carrot mottle (CMotV) viruses confirmed the dependency of CMotV on CRLV for transmission by the aphid Cavariella aegopodii. CMotV was transmitted by aphids only when the two viruses were present in the same source plant, and its transmission was not assisted by anthriscus yellows virus, which acts as a helper for parsnip yellow fleck virus. Some test plants became infected with CRLV alone, and a few with CMotV alone. In winter, aphid transmission of CRLV and CMotV was greatly increased when the source plants received supplementary lighting whereas the CMotV infectivity of sap was not increased. C. aegopodii acquired CRLV and CMotV after minimum acquisition access times of 30 min and inoculated them after minimum inoculation access times of 2 min. There was a minimum latent period of 7–18 h. The viruses were retained by the aphid after moulting and are therefore circulative in the vector, but were not transmitted to progeny insects. Aphids allowed 24 h to acquire the viruses continued to transmit them for at least 12 days, but some aphids allowed 6 h or less for virus acquisition ceased to transmit after 3 or 4 days. CRLV is considered a tentative member of the luteovirus group.     

Distribution of velvet tobacco mottle virus in its mirid vector and its relationship to transmissibility

Following acquisition by feeding, velvet tobacco mottle virus (VTMoV) was detected in the gut, haemolymph and faeces of the mirid vector, Cyrtopeltis nicotianae, but not in the salivary glands. Virus antigen was detected in the gut and haemolymph for up to nine days following acquisition. Infective virus was detected in the secretions and excretions of the mirids immediately after acquisition and was also detected in the faeces of nymphs after six days. Insoluble nigrosin dye was eliminated intermittently from the gut up to six days after ingestion, in a manner similar to the loss of virus infectivity. Non-infective mirids were able to inoculate plants from infectious sap deposits on the upper epidermis. An ingestion-defecation model of insect transmission in which the salivary glands are not implicated is proposed as one explanation for the persistence of transmission in this mirid-virus association.     

Peanut stripe virus - a new seed-borne potyvirus from China infecting groundnut (Arachis hypogaea)1

A new virus, peanut stripe (PStV), isolated from groundnut (Arachis hypogaea) in the USA, induced characteristic striping, discontinuous vein banding along the lateral veins, and oakleaf mosaic in groundnut. The virus was also isolated from germplasm lines introduced from the People's Republic of China. PStV was transmitted by inoculation of sap to nine species of the Chenopodiaceae, Leguminosae, and Solanaceae; Chenopodium amaranticolor was a good local lesion host. PStV was also transmitted by Aphis craccivora in a non-persistent manner and through seed of groundnut up to 37%. The virus remained infective in buffered plant extracts after diluting to 10^-3, storage for 3 days at 20°C, and heating for 10 min at 60°C but not 65°C. Purified virus preparations contained flexuous filamentous particles c. 752 nm long, which contained a major polypeptide of 33 500 daltons and one nucleic acid species of 3·1 × 10⁶ daltons. In ELISA, PStV was serologically related to blackeye cowpea mosaic, soybean mosaic, clover yellow vein, and pepper veinal mottle viruses but not to peanut mottle, potato Y, tobacco etch, and peanut green mosaic viruses. On the basis of these properties PStV is identified as a new potyvirus in groundnut.     

Comparative transmission of bean leaf roll and pea enation mosaic viruses by aphids

Acyrthosiphon pisum was a more efficient vector than Myzus persicae of bean leaf roll virus (BLRV), but the two species transmitted pea enation mosaic virus (PEMV) equally well and much more often than Megoura viciae. M. viciae did not transmit BLRV, and Aphis fabae did not transmit BLRV or PEMV. BLRV and PEMV were transmitted more often by nymphs of A. pisum than by adult apterae or alatae that fed on infected plants only as adults, but both viruses were readily transmitted by adults that had developed on infected plants. The shortest time in which nymphs acquired BLRV was 2 h, and 50 % transmitted after an acquisition period of 4 days. Some nymphs acquired PEMV in 30 min and 50% in 8 h. The shortest time for inoculation of BLRV by adults was 15 min, but some transmitted PEMV in probes lasting less than 1 min. The median latent periods of BLRV and PEMV in aphids fed for 12 h on infected plants were, respectively, 105 and 44 h. Clones of A. pisum differed in their ability to transmit BLRV and PEMV, and efficiency in transmitting the two viruses seemed to be unrelated. Some aphids that fed successively on plants infected with each virus transmitted both viruses, and infectivity with one virus did not seem to affect transmission of the other.     

Nicotiana velutina mosaic virus: purification, properties and affinities with other rod-shaped viruses

Nicotiana velutina mosaic virus (NVMV), found in Australia, was transmitted by inoculation of sap to twenty species in the Solanaceae and Chenopodiaceae, and to Gomphrena globosa; its host range closely resembles that of potato mop-top virus (PMTV). Infectivity was abolished when sap was kept at room temperature between 1 and 4 days, or when heated for 10 min between 60 and 70 °C. NVMV was frequently transmitted through the seed of four Nicotiana spp. NVMV and PMTV were purified by a method that involved redissolving virus particles sedimented by low speed centrifugation of leaf extracts, followed by sedimentation through sucrose cushions. NVMV preparations contain rod-shaped particles about 18 nm wide and with a large range of lengths, the commonest being 125–150 nm. The particles have a helical structure with a pitch of 2–9 nm, break easily, and contain a single protein of apparent mol. wt. 21|400, slightly larger than that of PMTV (19 800). In serological tests assessed by electron microscopy, no relationship was detected between NVMV and PMTV, or barley stripe mosaic, beet necrotic yellow vein, soil-borne wheat mosaic, tobacco mosaic or tobacco rattle viruses. However, antiserum to soil-borne wheat mosaic virus reacted quite strongly with PMTV and weakly with tobacco mosaic virus. NVMV is considered to be a distinct member of the tobamovirus group; its frequent transmission through seed may be an adaptation to the arid environment where it was found. Its cryptogram is */*:*/*:E/E:S/*.     

Transmission of tomato spotted wilt virus by Frankliniella occidentalism median acquisition and inoculation access period

To quantify the transmission of tomato spotted wilt virus (TSWV) by Frankliniella occidentalis, the median acquisition access period (AAP₅₀) and median inoculation access period (IAP₅₀) were determined. These parameters were established using transmission rates obtained after AAPs and in IAPs which both ranged from 5 to 2560 min. An AAP₅₀ of 106 min was found when larvae acquired virus from TSWV-infected Impatiens plants. IAP₅₀s of 58 or 137 min, respectively, were calculated when petunia or Datura stramonium leaf disks were used to test the inoculation efficiency of viruliferous thrips. The virus could successfully be acquired or inoculated in periods of 5 min. Transmission reached an optimum after an AAP of 21.3 h (AAP_opt) and in an IAP of 42.7 h (IAP_opt). These results show that TSWV can be acquired and transmitted efficiently by F. occidentalis in short feeding periods.     

Response of Membrane-bound Mg-activated ATPase of Tobacco Leaves to Tobacco Mosaic Virus

Infectious material was formed at an early stage, and migrated into the mesophyll from the epidermis of tobacco leaves (Nicotiana tabacum cv. Samsun NN) during the period of 1 to 3 hours after inoculation with tobacco mosaic virus (TMV). The activity of membrane-bound Mg²⁺-activated ATPase from the mesophyll was stimulated two to four times within 30 minutes after inoculation with 1.0 microgram per milliliter of TMV. Maximum TMV stimulation of membrane-bound Mg²⁺-activated ATPase activity in epidermis and mesophyll was observed at 0.5 and 3.0 hours after inoculation, respectively. This stimulation was also observed with ultraviolet irradiated TMV (only RNA was destroyed), whereas, the stimulation was not observed with heat-irradiated TMV (both coat and RNA were destroyed). Stimulation equal to that of TMV was observed by inoculation with cucumber green mottle mosaic virus and to a lesser extent with cucumber mosaic virus.

These results illustrate that the stimulus resulting from inoculation with TMV transfers to underlying cells faster than the migration of TMV particles. This stimulus might be closely correlated to the structure of virus, but not to the infectivity of virus.

     

The relation between cowpea golden mosaic and its vector, Bemisia tabaci

Adult whiteflies (Bemisia tabaci) acquired the agent of cowpea golden mosaic (CGM-A) within 7 min and transmitted during 2 min inoculation access. Nymphs also acquired CGM-A and retained it through the pupal stage. Efficiency of transmission reached 90% when the acquisition period was increased to 36 h. The minimum latent period of CGM-A in B. tabaci was 8 h, and the median latent period (LP50) about 12 h. Transmission was generally intermittent and declined throughout the period of 21 days which was the maximum time insects remained infective. Female whiteflies were more efficient vectors than males. B. tabaci acquired CGM-A from plants inoculated only 60 h previously. The epidemiological implications of these findings are discussed.     

Characterisation of pumpkin yellow vein mosaic virus from India

Yellow vein mosaic disease symptoms occur frequently in pumpkin in India. Diseased plants show vein yellowing, which sometimes coalesces to form chlorotic patches. Infected plants are stunted and flowers drop prematurely, greatly reducing yields. Diseased plants are infected by a begomovirus, designated pumpkin yellow vein mosaic virus (PYVMV), which is transmitted readily and in a persistent manner by the whitefly, Bemisia tabaci. Transmission of PYVMV requires minimum acquisition and inoculation access periods of 30 min and 10 min, respectively. The minimum latent period in the insect is 6 h and the virus persists in the vector for at least 8 days. PYVMV has a narrow host range consisting of a small number of cucurbit species and some tobacco cultivars. It was detected serologically in diseased plants and in viruliferous B. tabaci using polyclonal antibodies in a double‐antibody sandwich enzyme‐linked immunosorbent assay. Reactions with monoclonal antibodies in a triple‐antibody sandwich ELISA showed that PYVMV has an epitope profile distinct from those of other begomoviruses from the Indian sub‐continent. Polymerase chain reaction amplified fragments from the putative viral coat and movement protein genes. Based on comparative phylogeny of complete coat protein gene sequences, PYVMV was most similar to the bipartite Tomato leaf curl New Delhi virus from India and appears to be a new strain of this virus.     

Transgenic tobacco plants expressing a coat protein gene of tobacco mosaic virus are resistant to some other tobamoviruses

Transgenic tobacco plants expressing the coat protein (CP) gene of tobacco mosaic virus were tested for resistance against infection by five other tobamoviruses sharing 45-82% homology in CP amino acid sequence with the CP of tobacco mosaic virus. The transgenic plants (CP+) showed significant delays in systemic disease development after inoculation with tomato mosaic virus or tobacco mild green mosaic virus compared to the control (CP-) plants, but showed no resistance against infection by ribgrass mosaic virus. On a transgenic local lesion host, the CP+ plants showed greatly reduced numbers of necrotic lesions compared to the CP- plants after inoculation with tomato mosaic virus, pepper mild mottle virus, tobacco mild green mosaic virus, and Odontoglossum ringspot virus but not ribgrass mosaic virus. The implications of these results are discussed in relation to the possible mechanism(s) of CP-mediated protection.     

Vector relationships and other characteristics of barley yellow striate mosaic virus (BYSMV)

Barley yellow striate mosaic virus (BYSMV) was inoculated by its planthopper vector Laodelphax striatellus (Homoptera, Delphacidae) to 44 species of Gramineae, 26 of which in eight tribes were infected. The virus was not transmitted through wheat seed nor did it infect five dicotyledonous hosts of other rhabdoviruses. The most susceptible species were in the tribes Festuceae and Hordeae. Barley, Bromus spp., oats, Phalaris canariensis, Setaria italica, Sorghum spp., and sweet corn cv. Golden were diagnostic hosts. Electron microscopy of crude sap was also a sensitive diagnostic method. Properties of BYSMV were determined by injecting L. striatellus with crude sap from infected barley. Sap was infectious after 10 min at 50–55 °C but not after 10 min at 60 °C, when diluted with buffer to 10^--² but not to 10^--³, when stored for 2 but not 4 days at 5 °C or when kept for 1 but not 2 days at 22 °C. The planthopper Javesella pellucida was an experimental vector of BYSMV but the virus was not transmitted by the leafhoppers Macrosteles sexnotatus or Psammotettix striatus (Homoptera, Cicadellidae). The latent period of BYSMV in L. striatellus was most commonly 15 or 16 days (minimum, 9 days; maximum, 29 days). The minimum acquisition access period for transmission was between 1 h and 5 h, and the minimum inoculation feeding time was 15 min. After 24 h and 8 day acquisition feeds, 30.4% and 42.8% respectively of L. striatellus transmitted BYSMV. When transferred daily, infective hoppers transmitted virus intermittently. The maximum retention of infectivity by L. striatellus was 36 days. Two of five infective females transmitted BYSMV transovarially. Larvae became infective in the second wk after hatching and transmitted for up to 3 wk.     

Virus-vector relationships of chickpea chlorotic dwarf geminivirus and the leafhopper Orosius orientalis (Hemiptera: Cicadellidae)

Chickpea chlorotic dwarf geminivirus (CCDV) is one of the viruses associated with chickpea stunt disease. It is transmitted by the leafhopper Orosius orientalis. The minimum acquisition access period (AAPmin) and inoculation access period (IAPmin) were found to be less than 2 min, while the minimum latency period (LPmin) was less than 2 h. The median AAP, IAP and LP were 8.0 h, 2.3 h and 27.7 h, respectively. No difference in transmission rates (proportion of leafhoppers able to transmit) was observed between male and female leafhop-pers. In serial transmission experiments, transmission was shown to be persistent, and after a 2-day AAP about 80% of the leafhoppers transmitted the virus for most of their life. The virus could be detected in individual leafhoppers by DAS-ELISA. It did not multiply in the leafhopper, but, instead, decreased in concentration during leafhopper feeding on a non-host of the virus.     

RED CLOVER MOTTLE VIRUS

A virus, provisionally named red clover mottle virus (RCMV), isolated from red clover plants in England, seems distinct from any previously described. It was transmitted by mechanical inoculation of sap to many legumes and to Gomphrena globosa L., but it was not transmitted by six aphid species, or through soil or through seeds.
RCMV is inactivated in 10 min. between 60 and 63°C., and in 8 days at 18°C., but survives for long periods at -20; sap was not infective when diluted more than 1/1000. The virus is soluble in the pH range (4–7) in which it is stable. It was precipitated without inactivation by 50% saturated ammonium sulphate solution, but it was inactivated by ethanol or acetone. Partially purified preparations contained polygonal particles about 28 mμ in diameter. Serological tests showed no antigens in common with broad bean mottle, true broad bean mosaic or lucerne mosaic viruses.     

Aphid-transmitted viruses from lilies in Britain

Three aphid-transmitted viruses, tulip breaking, lily symptomless and cucumber mosaic, were obtained from lilies in Britain. Tulip breaking virus was detected by the leaf mottle produced in Lilium formosanum, cucumber mosaic virus by inoculation of sap to Nicotiana clevelandii and Chenopodium quinoa, and lily symptomless virus by electron microscopy of crude leaf extracts from symptomless L. formosanum. Liiy symptomless virus was transmitted by Myzus persicae, Macrosiphum euphorbiae, Aulacorthum solani and Aphis fabae. M. persicae, which in a small experiment appeared a more efficient vector than A. fabae, transmitted the virus in a non-persistent manner. This conflicts with the original report of transmission in a persistent manner by A. gossypii but no transmission by M. persicae. The possibility that there are two distinct viruses with similar pathological effects is discussed. Tulip breaking and lily symptomless viruses spread to bait plants of L. formosanum within a field planting of lilies in Scotland especially during July to September; lily symptomless virus was the more prevalent. No spread of cucumber mosaic virus was detected.     

Rate of Loss of Infectivity of Maize Dwarf Mosaic Virus by Schizaphis graminum Rondani After Different Acquisition Access Periods

The rate of loss of infectivity for greenbugs, Schizaphis graminum Rondani, carrying maize dwarf mosaic virus (MDMV) was similar for adult apterae and alates regardless of the acquisition access period (AAP) given. The rate was rapid during the first 2 h post-acquisition and then decreased. Weighted least squares linear regression of log % transmission were plotted against retention-time intervals to obtain regression slopes for each of the AAP groups tested (1, 3, 17, and 30 min). There were no significant differences among the regression slopes using F-test comparisons. In serial transmission trials, transmission frequencies among aphids allowed 1-min or 30-min timed acquisition probes followed by 30-see or 1-min timed inoculation probes were not significantly different when statistical tests that quantify categorical data were applied. This suggests little difference in the amount of virus obtained by these groups of aphids. Transmission and retention data are discussed in relation to the two principal theories of the mechanism of non-persistent virus transmission by aphids. Transmission of MDMV by the greenbug by a two mechanism process (stylet-borne and ingestion-egestion) is not confirmed.     

Vector and graft inoculations of Potato yellow mosaic virus reveal recessive resistance in Solanum pimpinellifolium

Transmission of Potato yellow mosaic virus (PYMV) (bipartite begomovirus) to tomato by 50 Bemisia tabaci biotype B individuals was observed when the acquisition access period (AAP) was at least 3 h and the inoculation access period (IAP) at least 30 min. The transmission efficiency increased with the access period to reach 92% transmission after a 48‐h IAP and 48‐h AAP. The transmission efficiency decreased when whiteflies were fed on PYMV non‐host plant between AAP and IAP. According to these results, we inoculated nine Solanum accessions with 50 whiteflies (48‐h APP and 48‐h IAP) to assess their resistance level. Four of these accessions with various levels of resistance were graft inoculated with PYMV. Although none of the accessions were immune, we observed a high level of resistance to PYMV in Solanumpimpinellifolium LA2187‐5 (no symptoms after vector or graft inoculation) and in Solanum chilense LA1969 (no symptoms after vector inoculation and one plant with symptoms after graft inoculation). Inheritance of LA2187‐5 resistance, investigated in F1 and F2 populations, appeared to be recessive. Fewer plants were infected by PYMV in S. pimpinellifolium LA1478 after vector inoculation than after graft inoculation. We hypothesised that this was because of vector resistance, which could also be effective against other begomoviruses.     

Host range, vector relations and serological relationships of cotton leaf curl virus from southern India

In 1989 to 1991, leaf curl disease was observed in cotton (Gossypium bar-badense cv. Local) grown in kitchen gardens in five districts in Karnataka State, India, and in 1994 it was recorded in G. hirsutum cv. Sharada in two districts. Symptoms consist of leaf curling, vein thickening, leaf enations, and stunting and distortion of plants. The disease is caused by cotton leaf curl virus (CLCuV-K), which was transmitted by the whitefly Bemisia tabaci to 24 plant species in six families. Hosts include bean (Phaseolus vulgaris), pepper, tobacco, tomato and several weeds, almost all of which developed leaf curl, with or without vein thickening. CLCuV-K was transmitted from cotton to cotton by adult B. tabaci after an acquisition access period of 1 h, could be inoculated in 5 min, had a minimum latent period of 8 h and was retained by viruliferous insects for up to 9 days. Female B. tabaci transmitted more frequently than males. CLCuV-K is a whitefly-transmitted geminivirus. It reacted with two out of 17 monoclonal antibodies (MAbs) raised to African cassava mosaic virus and five out of 10 MAbs raised to Indian cassava mosaic virus. CLCuV-K isolates from different locations in Karnataka had similar epitope profiles. As judged by these profiles, CLCuV-K is closely related to Indian tomato leaf curl virus from Karnataka, is distinguishable from several other whitefly-transmitted geminiviruses found in India and is still more distantly related to those, including cotton leaf crumple virus from the USA, found in other continents. CLCuV-K infected all cultivars tested of G. barbadense and one of six cultivars of G. hirsutum but none of G. arboreum or G. herbaceum.     

The effect of the transmission of the beet mosaic virus on the variability of its incubation period

The variability of the incubation period of the beet mosaic virus [Beta virus 2(Lind) Smith] was investigated in a three year experiment. The virus was transmitted by the black bean aphid (Aphis fabae Scop.) or by a mechanical inoculation onAmaranthus caudatus L. Variability characterized by the standard deviation indicates a closer distribution of measurements when the virus was transmitted by mechanical inoculation. The differences in variability of the incubation period between the two methods of virus tramission are statistically significant; dispersion and standard deviation are lower after mechanical inoculation. The average length of the incubation period after virus transmission by aphids and by mechanical inoculation was 10.8 and 7.7 days, respectively. The difference was found statistically significant and may be explained by the higher number of viral particles transmitted by mechanical inoculation which may accelerate the process of infection. A significant correlation between the temperature of the environment and the length of the incubation period was also found in some experiments.     

Glycine mosaic virus: a comovirus from Australian native Glycine species

Two strains of a virus designated Glycine mosaic virus (GMV) were found in Glycine clandestina and G. tabacina, legumes indigenous to Australia and the western Pacific region. When transmitted by sap inoculation, GMV infected mostly leguminous species, and caused mosaic and mottling symptoms. The virus was not found naturally in soybean G. max, but it infected all of the 21 cultivars tested. GMV has isometric particles of c. 28 nm diameter, and produces three components with sedimentation coefficients of 60 S (top), 103 S (middle), and 130 S (bottom). Both middle and bottom components are required for infectivity. The virions contain two major proteins with molecular weights of c. 21 500 and 42 000. GMV produces large aggregates of particles in the cytoplasm of the mesophyll cells of pea Pisum sativum, and also induces amorphous membrane-bound bodies and cytoplasmic vesicles. The type strain (from New South Wales) reacts with antisera to Echtes Ackerbohnenmosaik, broad bean stain, and a Californian isolate of squash mosaic virus. The GW strain (from Queensland) reacts with all of the latter antisera, as well as with antisera to cowpea mosaic virus (Sb and Ark strains), bean pod mottle, and red clover mottle viruses, and is serologically related to, but not identical with, the type strain. These properties clearly establish GMV as a new member of the comovirus group.