Properties of cocksfoot streak and cocksfoot cryptic, two viruses infecting cocksfoot (Dactylis glomerata) in Scotland

A Scottish isolate of cocksfoot streak virus (CSV-S) was found to have flexuous filamentous particles which, in sap of infected cocksfoot plants, had a modal length of 712 nm. It was transmitted from infected to healthy cocksfoot plants in a non-persistent manner by Myzus persicae and by mechanical inoculation of infective sap extracts containing an anti-oxidant. Apart from cocksfoot, mechanical inoculation of infective sap succeeded in infecting only four of 22 plant species tested. The infectivity of sap extracts containing 0.2% thioglycerol was lost after heating for 10 min at 55^oC but not 50^oC, storage at room temperature for 48 but not 24 hours, and after diluting 10^-2to 10^-3. Highly purified preparations of CSV-S particles sedimented as a single component with a sedimentation coefficient of 139S and had a buoyant density in rubidium bromide of 1.31 g/cm³. Virus particles were composed of one protein and one ssRNA species with estimated M_r of 31 000 and 3.2 times 10⁶respectively. In ELISA, an antiserum prepared to CSV-S detected the virus in all aerial parts of infected cocksfoot plants and, when present in the ratio of 1 infected leaf: 1000 healthy leaves. Both CSV-S-infected and -uninfected cocksfoot also contained a previously undescribed virus with isometric particles c. 30 nm in diameter. This virus, named cocksfoot cryptic virus (CCV), was seed-borne in two cvs of cocksfoot tested and its particles contained two dsRNA species of estimated M_r of 1.14 times 10⁶and 1.27 times 10⁶. Despite the fact that particles of CSV-S were largely free from CCV particles following exclusion chromatography on agarose beads prior to immunisation, immunoelectron microscopy (IEM) showed that the antiserum prepared to CSV-S also contained some antibodies to CCV. Evidence from IEM suggested a possible distant serological relationship of CCV to ryegrass and beet (BCV 1 or BCV 2, or both) cryptoviruses, all members of sub-group A of crypto viruses.     

Some properties of cocksfoot mottle virus

Cocksfoot mottle virus (CFMV) was transmitted by manual inoculation of sap to cocksfoot (Dactylis glomerata L.), wheat, oats and barley, but not to nineteen other monocotyledonous and thirteen dicotyledonous plant species. The virus was also transmitted by cereal leaf beetles (Lema melanopa L.). Adult beetles infected plants more frequently than larvae, and remained infective for up to 2 weeks after they had fed on infected plants. Seed from infected cocksfoot and oat plants produced virus-free seedlings. The infectivity of sap was lost during 10 min. at 65° C., and 2 weeks at 20° C., but survived many months at — 15° C. Purified virus preparations, made by various methods, contained numerous nearly spherical particles, about 30 mμ in diameter. In electron micrographs some of the particles were penetrated by negative stain though most appeared intact. However, all the particles migrated together in a centrifugal (sedimentation coefficient = 118 S) or electrophoretic field. The ultraviolet absorption spectrum, and the phosphorus and nitrogen contents of the virus preparations, were typical of a nucleoprotein containing about 25 % nucleic acid. Serological tests failed to show any relationship between CFMV and eleven other viruses with particles of similar shape and size.     

THE TRANSMISSION BY MITES, HOST-RANGE AND PROPERTIES OF RYEGRASS MOSAIC VIRUS

A virus that causes chlorotic streaks on ryegrass leaves was transmitted by the eriophyid mite Abacarus hystrix (Nalepa). Virus-free mites acquired the virus in 2 hr. feeding on infected ryegrass and the proportion that became infective increased with increased feeding time up to 12 hr.; vectors lost infectivity within 24 hr. of leaving the infected leaves. All instars of A. hystrix transmitted the virus.
The virus was transmitted by manual inoculation of sap to other species of Gramineae, including oats, rice, cocksfoot and meadow fescue, but none of these hosts seemed to contain as much virus as ryegrass; their saps did not precipitate specifically with antiserum prepared against the virus in ryegrass, whereas sap from infected ryegrass precipitated up to a dilution of 1/32. Infective sap of S22 Italian ryegrass contained flexuous rod-shaped particles; the dilution end-point of the virus was about 1 in 1000; the virus was inactivated when held for 10 min. at 60°C. and most of its infectivity was lost after 24 hr. at room temperature.     

Purification and properties of lucerne Australian symptomless virus, a new virus infecting lucerne in Australia

A virus with isometric particles c. 26–28 nm in diameter isolated from naturally infected lucerne (Medicago sativa) in Australia and reported there to be a strain of lucerne Australian latent virus (LALV), is shown to be a distinct virus. The virus, called lucerne Australian symptomless (LASV), was mechanically transmitted to 10 of 22 plant species inoculated, but only induced symptoms in three Chenopodium species and Gomphrena globosa. Virus particles occurred in relatively low concentrations in plant sap, and the virus could not be reliably maintained in culture by serial transmission to plants during winter (October-April). During the summer, sap of infected C. quinoa remained infective after diluting 10^-2 but not 10^-3, after heating for 10 min at 50 but not 55 ^oC and after storage for 24 days (the longest period tested) at 20, 4 and -15 ^oC. LASV was seed-borne to 6% of C. quinoa seedlings. Partially purified preparations of virus particles contained one nucleoprotein component with a sedimentation coefficient of c. BOS. Particles contained two polypeptide species of estimated mol. wts 26 000 and 40 000, and two ssRNA species which, when denatured in glyoxal, had apparent mol. wts of 2–5 times 10⁶ and 1–4 times 10⁶. The infectivity of virus RNA was abolished by incubation with proteinase K. Purified particles of LASV reacted with homologous antiserum (gel diffusion titre 1:256) but not with antiserum to LALV or to 13 other plant viruses with isometric particles including arracacha B (AVB), broad bean wilt, rubus Chinese seed-borne (RCSV) and strawberry latent ringspot (SLRV) viruses, and five comoviruses. These properties distinguish LASV from LALV and from all recognised nepoviruses and comoviruses. Its closest affinities are with SLRV, RCSV and possibly AVB; these viruses may comprise a distinct virus group or nepovirus subgroup.     

Association of cocksfoot mild mosaic and cocksfoot streak viruses in Dactylis glomerata and their simultaneous transmission by aphids

Macrosiphum (Sitobion) fragariae transmitted cocksfoot mild mosaic and cocksfoot streak viruses two to three times more frequently from plants in which they occurred together than from plants in which they occurred alone. In cells of doubly infected plants, particles of the two viruses commonly occurred in close association.     

Electron microscopy of cocksfoot streak virus and its differentiation from ryegrass mosaic virus in naturally infected Dactylis glomerata plants

The length and rigidity of some cocksfoot streak virus (CSV) particles were greater (1) in ammonium molybdate negative stain at pH 5 than at pH 8 and (2) when magnesium was added either directly to extracted plant sap or indirectly via increased plant uptake. Most CSV particles were flexuous and 750–760 run long in low concentrations of magnesium but many were rigid and 800–810 nm long in higher concentrations. In sodium phosphotungstate and ammonium molybdate at pH 5, frequency distributions of particle lengths from cocksfoot plants infected with both CSV and ryegrass mosaic virus (RMV) produced two modal peaks, one at less than 700 nm (RMV) and the other at more than 750 nm (CSV); in ammonium molybdate at pH 8, however, only one peak (at 725 nm) was resolved. In ultrathin sections of CSV-infected cocksfoot leaves, virus-like particles were scattered or in bundles within the cytoplasm, or aligned in aggregates near the tonoplast. Some cells contained pinwheel inclusions, often with attached or associated laminar plates and occasionally with scroll-like or circular tubes. These CSV-induced inclusions were easily distinguished from those induced by RMV, even when both types occurred in the same cell.     

Some properties of pelargonium flower-break virus

A virus obtained from pelargonium cvs Irene and Paul Crampel appears to differ from any previously reported; although symptomless in most pelargonium cvs tested, it caused colour break in the flowers of two seedling clones. It seems uncommon in pelargoniums. The virus was readily transmitted by inoculation of sap, but not by Myzus persicae with short feeds, by dodder or through seed. It infected only fifteen of 100 species tested in six of thirty-five plant families. Pelargoniums were freed from the virus by heat-treatment. The virus remained infective after 10 min at 85 ^oC, 3 wk at 20 ^oC or 27 wk at 2 ^oC; it was infective at 1/500000 dilution of Nicotiana clevelandii or Chenopodium quinoa sap. Purified preparations were readily made by several methods, and contained isometric particles c. 30 nm diameter. Although a good antigen, the virus was serologically unrelated to any of forty-two isometric viruses. In immunoelectrophoresis, the virus moved as a single antigenic component towards the cathode. It gave a single, specific zone in density-gradient centrifugation, and one moving component (s⁰_{20 w}= 125 S) in analytical centrifugation. The virus contained one protein of mol. wt. c. 41000. The present cryptogram of the virus is (R)/*: */*:S/S:S/*, and the name pelargonium flower-break virus is proposed.     

Host range, purification and properties of potato virus T

Potato virus T (PVT) infected nine species of tuber-bearing Solanum, most of them symptomlessly, and as a rule was transmitted through the tubers to progeny plants: two genotypes of S. tuberosum ssp. andigena were not infected. The virus was also transmitted by inoculation with sap to 37 other species in eight plant families. Chenopodium amaranticolor is useful as an indicator host, C quinoa as a source of virus for purification, and Phaseolus vulgaris as a local-lesion assay host; the systemic symptoms in Datura stramonium, Nicotiana debneyi and in these three species are useful for diagnosis. Attempts to transmit PVT by aphids failed, but the virus was transmitted through seed to progeny seedlings of four solanaceous species, and from pollen to seed of S. demissum. PVT was purified by clarifying sap with n-butanol or bentonite, followed by precipitation with polyethylene glycol, differential centrifugation and sedimentation in a sucrose density gradient. Purified preparations had an E260/E280 ratio of 1.18 and contained a single infective component with a sedimentation coefficient of 99 S. This component consisted of flexuous filamentous particles of about 640 times 12 nm that showed a characteristic substructure when stained with uranyl acetate. The virus particles contained a single species of infective single-stranded RNA, of molecular weight 2–2 times 106 daltons, and a single species of polypeptide of molecular weight about 27 000 daltons. PVT is serologically related to apple stem grooving virus but not to four other common potato viruses with flexuous filamentous particles. Apple stem grooving virus and PVT cause similar symptoms in several hosts, but also differ somewhat in host range and symptomatology. Apple stem grooving virus did not infect potato, caused additional symptoms in C. quinoa also infected with PVT, and its particles did not show the structural features specific to PVT. The two viruses are considered to be distinct. The cryptogram of PVT is R/1:2–2/(5): E/E: S/C.     

Narcissus mosaic virus

Narcissus mosaic virus (NMV) is widespread in British crops of trumpet, large-cupped and double daffodils, but was not found in Narcissus jonquilla or N. tazzeta. Many commercial daffodil cultivars seem totally infected, and roguing or selection is therefore impracticable. Strict precautions by breeders and raisers to prevent infection of new cultivars is recommended. Healthy daffodil seedlings were readily infected with NMV by mechanical inoculation, but the virus was not detected in them until 17 months after inoculation, when a mild mosaic appeared. NMV infected twenty-eight of fifty-three inoculated plant species; only five (Nicotiana clevelandii, Gomphrena globosa, Medicago sativa, Trifolium campestre and T. incarnatum) were infected systemically, and NMV was cultured in these and assayed in Chenopodium amaranticolor and Tetragonia expansa. The virus was not transmitted to and from G. globosa or N. clevelandii by three aphid species, or through the seeds of Narcissus, G. globosa and N. clevelandii but was transmitted by handling. G. globosa sap was infective at a dilution of 10 ^-5 but not at 10^-6, when heated for 10 min. at 70° C. but not at 75° C, and after 12 weeks at 18° C, or 36 weeks at 0–4° C. NMV withstood freezing in infected leaves and sap, and purified preparations and freeze-dried sap remained infective for over 2 years. NMV was precipitated without inactivation by ammonium sulphate (313 g./l.) but was better purified by differential centrifugation of phosphate-buffer extracts treated with n-butanol. Such virus preparations from G. globosa, N. clevelandii, C. amaranticolor and T. expansa were highly infective, serologically active, produced a specific light-scattering zone when centrifuged in density-gradients and contained numerous unaggregated particles with a commonest length of 548–568 mμ. Antisera prepared in rabbits had precipitin tube titres of 1/4096. NMV was detected in three experimental hosts but not in narcissus sap. Unlike some viruses with elongated particles, NMV precipitates with antiserum in agar-gel. Purified preparations reacted with antiserum to a Dutch isolate of NMV but not with antisera to seven other viruses having similar particles and in vitro properties, or to narcissus yellow stripe virus.     

Properties of an unusual isolate of raspberry ringspot virus from grapevine in Germany and evidence for its possible transmission by Paralongidorus maximus

An isolate of raspberry ringspot nepovirus (RRV-P) commonly found infecting grapevine in localised areas of the German Palatinate, was serologically closely related to, but distinguishable from, the English type strain of this virus (RRV-E) which is transmitted by Longidorus macrosoma. However, unlike RRV-E, RRV-P had a restricted herbaceous host range and produced symptoms reliably in only two hosts, Chenopodium quinoa and Nicotiana occidentalis-accession 37B: these symptoms were a faint systemic vein clearing which, on most occasions in C. quinoa, was transient. In in vitro studies with herbaceous plant sap, RRV-P infectivity was lost after diluting 1/100-1/500, after storage at 20^oC for 1–3 days and at 4^oC for 45 days: for similar studies with RRV-E, the values were 1/125 000, and more than 15 days at 20^oC and 4^oC, respectively. RRV-P was difficult to purify in quantity and in most preparations seemed to sediment as a single component corresponding to ‘bottom’ component of RRV-E. Purified particles of RRV-P, like those of RRV-E, contained a major polypeptide and two RNA species of Mx 54 000, 2.6 × 106 and 1.6 × 106 respectively. There was no evidence from RNA preparations from purified virus particles or, from analysis of dsRNA from infected plants, that RRV-P contained a satellite RNA. The incidence of RRV-P in vineyards was not associated with the presence in soils of Longidorus nematodes, but was associated with the distribution in the Palatinate of Paralongidorus maximus. Furthermore, results from an experiment in Germany in a vineyard planted with healthy grapevines in soil fumigated to destroy nematodes, showed spread of RRV-P into these plants from an adjoining source of infected grapevines and soil infested with P. maximus. In laboratory studies, RRV-P was transmitted by P. maximus at a very low level between grapevines (used as the virus source and test plants) but not to, or between, herbaceous hosts.     

The adaptation of tomato mosaic virus to resistant tomato plants

Tomato mosaic virus derived from susceptible tomato plants (the standard virus) was cultured in resistant plants. Sap from non-inoculated leaves of resistant tomato plants infected with virus from the resistant host was more infective and contained more virus particles than leaf sap of resistant plants infected with the standard virus. Leaves of resistant tomatoes infected with virus from the resistant host also showed more obvious symptoms. Susceptible plants infected with virus from resistant plants not only showed fewer symptoms than when infected with standard virus, but samples were less infective and contained less virus up to 26 weeks, when values for infectivity were similar. This modification in activity was not reversible and was obtained with two lines of tomato having different types of resistance. Passage of virus from resistant plants through susceptible plants did not impair its ability to infect resistant plants.     

Propagation of black raspberry necrosis virus (BRNV) in mixed culture with solanum nodiflorum mottle virus, and the production and use of BRNV antiserum

The concentration of particles of black raspberry necrosis virus (BRNV), which is normally extremely low in herbaceous plants, increased about 1000-fold when Nicotiana clevelandii plants were inoculated with a mixture of BRNV and an unrelated virus, solanum nodiflorum mottle (SNMV). In sap from N. clevelandii infected with the mixed culture, BRNV infectivity survived dilution to 10?⁴ but not 10?⁵, and storage for 6 but not 8 days at 20 ^oC, for 6 but usually not 10 days at 4 ^oC and for more than 13 days at – 15 ^oC. When plants were inoculated with the mixed culture, BRNV induced typical symptoms in several Chenopodium species and infected several previously unreported hosts. Purified preparations of particles of the mixed culture contained only a small proportion of BRNV particles, which sedimented in sucrose density gradients as two components, one, probably non-infective, of c. 505, and the other, infective, of 120-130S. An antiserum prepared to purified particles of the mixed culture was cross-absorbed with SNMV particles and used in indirect ELISA to detect BRNV in herbaceous plants infected with the mixed culture, and also in a wide range of Rubus species, cultivars and hybrids infected naturally, by grafting or by inoculation with the aphid Amphorophora idaei. The reliability of ELISA for detecting BRNV in raspberry leaves depended on the cultivar and time of year. Some cultivars, such as Glen Clova, had low concentrations of BRNV, which was detected reliably only in late spring/early summer, whereas other cultivars, such as Lloyd George and Mailing Enterprise, had greater BRNV concentrations. In small-scale surveys in eastern Scotland, BRNV was detected by ELISA in many raspberry cvs, including some that contain major gene resistance to the vector, A. idaei; in five of nine raspberry stocks entered for the Standard grade certificate but in none of five stocks entered for the Stock Cane certificate; and in 40% of wild raspberry and 14% of wild bramble plants growing near commercial raspberry crops. The significance of these findings for the control of BRNV is discussed.     

Properties of some defective strains of tobacco mosaic virus and their behaviour as affected by inhibitors during storage in sap

From the type strain of tobacco mosaic virus, defective strains were isolated that produced chlorotic or ringspot type symptoms in tobacco and were difficult to transmit without carborundum in the inoculum. Their concentration was less than 0–1 μg/ml of sap instead of the usual 2 mg/ml with the type strain. Phenol extracts of infected leaves were a little more infective than extracts in buffer, whereas phenol extracts of leaves infected with type strain were very much less infective than extracts in buffer. Electron microscopy of infective sap rarely showed any virus particles, but preparations concentrated by ultracentrifugation contained virus particles, many of which were broken or seemed inadequately assembled. Changing the ambient temperature at which infected plants were kept from 20 to 35°C did not increase the amount or improve the appearance of the virus. Some of the strains were inactivated during heating for 10 min between 70 and 80 °C. Undiluted sap lost its infectivity in 3 days at 20 °C, as did the type strain when diluted to 0–1 μg/ml in sap from healthy leaves. This is because substances that inhibit infection were produced by microbes in the sap. The ability of sap from healthy leaves to inhibit infection increased by more than twenty-five times when left 3 days at 20 °C. Infectivity of appropriate mixtures of type strain and aged sap was restored by diluting them in buffer. Sodium azide at 0·02% in sap prevented formation of the inhibitor. The infectivity of the defective strains increased when inoculated together with the type strain.     

Properties of Scottish isolates of cocksfoot mild mosaic virus and their comparison with others

Two isolates of cocksfoot mild mosaic virus obtained from cocksfoot (Dactylis glomerata) in Scotland differed in symptomatology, and apparently in host range, from isolates obtained in Germany and Wales. They were serologically more closely related to a Dutch isolate from cocksfoot, and to a Scottish isolate from timothy (Phleum pratense), than was the German isolate from cocksfoot. The Scottish isolate from timothy was somewhat more virulent than, but serologically closely related to a Welsh isolate from timothy. Particles of Scottish isolates from cocksfoot and timothy were best preserved for electron microscopy by fixation with osmium tetroxide. In 1.0 m KCl or 0.01 m ethylene diamine tetraacetate they were stable at pH 5.2–5.3 but unstable above pH 7; they were disrupted by 0.5% sodium dodecyl sulphate. The particles contained major and minor RNA components of mol. wt c. 1.5. 10⁶(RNA-1) and 0.5. 10⁶(RNA-2) respectively, together with polydisperse RNA of intermediate mol. wt and protein of mol. wt c. 27 000. In CsCl gradients, major and minor nucleoprotein components of density 1.39 and 1.38 g/ml respectively were distinguished. The less dense particles contained a larger proportion of intermediate-sized RNA molecules and of RNA- 2 , and a smaller proportion of RNA- 1 , than did the denser particles. Particles seem to contain either RNA-1 or various combinations of smaller RNA molecules. Despite the differences in antigenic constitution, symptomatology and particle stability between virus isolates obtained from cocksfoot and timothy in different countries, these isolates seem sufficiently similar to be considered one virus.     

Purification and properties of elm mottle virus

A virus obtained commonly from Wych elm (Ulmus glabra) in Scotland showing ringspot and line-pattern leaf symptoms was serologically related to elm mottle virus (EMotV) from East Germany. The virus was seed-borne in elm and was transmitted by inoculation of sap to elm and twenty-one herbaceous species. No symptoms developed in infected elm seedlings kept in the glasshouse. In Chenopodium quinoa sap, EMotV lost infectivity after diluting to 10^-4, after 10 min at 60 ^oC, or 9 days at 18 ^oC. When purified from C. quinoa sap by clarification with n-butanol (8-5 %, v/v) and differential centrifugation, preparations contained quasi-spherical particles mostly 26–29 nm m diameter (mean = 28 nm) which sedimented as three nucleo-protein components with sedimentation coefficients (s^o₂o, w) of 83, 88 and 1 or S; most infectivity was associated with the 101 S component but infectivity was enhanced by adding the slower sedimenting components. When centrifuged to equilibrium in caesium chloride solution at 4 ^oC, purified virus preparations were largely degraded and contained many non-infective particles c. 15–22 nm in diameter, and intact infective particles which formed a band of density c. 1–34 g/cm³. Polyacrylamide gel electrophoresis indicated that EMotV contained a single major protein species of estimated mol. wt. 25000 and five RNA species of estimated mol. wt. 1–30, 1.15, 0–82, 0 39 and 0–30 times10⁶. Gel electrophoresis of RNA extracted from the separated components indicated that the 101 S component contained 1–30 x io⁶ mol. wt. RNA and the 83 S component 0–82 times 10⁶ mol. wt. RNA. In these and other properties, EMotV resembles the serologically unrelated tobacco streak virus.     

Properties of lucerne transient streak virus, and evidence of its affinity to southern bean mosaic virus

A virus obtained from naturally infected lucerne ( Medicago sativa ) in New Zealand reacted with antiserum to an Australian isolate of lucerne transient streak virus (LTSV). Some plants infected with New Zealand isolates showed yellow flecks along lateral veins of leaves; symptoms were transient in some lucerne plants but persistent in others. A New Zealand isolate (LTSV-NZ) infected 14 of 39 plant species tested by mechanical inoculation, but was not transmitted by five aphid species. In sap of Nicotiana clevelandii , LTSV-NZ was infective after storage for 4 wk at 20 ^oC, diluting to 10^-5, or heating for 10 min at 70 ^oC. Purified virus preparations contained a single electrophoretic component and a single sedimenting component (s_20w= 112 S ) which formed a single buoyant density component in CsCl (1.37 g cm^-3) but two density components in Cs₂SO₄ (1.26 and 1.32 g cm^-3). LTSV-NZ particles were stable in 10 ITIM EDTA at pH 5, but not at pH 8, being degraded into two sedimenting components of 105 S and 92 S. Particles contained c. 18% RNA in the form of one single-stranded RNA molecule of mol. wt 1–4 times 10⁶, and a polypeptide of mol. wt c. 32 400. LTSV-NZ was serologically unrelated to 24 other isometric plant viruses. However, its properties are similar to those of southern bean mosaic virus and allied viruses. The present cryptogram of LTSV is R/l: 1–4/(18):S/S:S/*.     

Some properties of a previously undescribed virus from cassava: Cassava American Latent Virus

A virus with spherical particles c. 28 nm in diameter was sap-transmitted from different cassava (Manihot esculenta) cultivars to a limited range of species in the families Chenopodiaceae and Solanaceae. Cassava seedlings infected by inoculation with sap or with purified virus preparations did not show any symptom, although the virus was readily detected by ELISA or by further inoculations. Leaf extracts from infected Nicotiana benthamiana were infective after dilution of 10^--³but not 10^--⁴, and after heating for 10 min at 70°C, but not at 72°C. The virus was purified from N. benthamiana, N. clevelandii or from cassava. On sucrose gradients, the virus particles sediment as three components all containing a protein of mol. wt c. 57000. The genome of the virus is composed of two RNAs of mol. wt c. 2.54 times 10⁶(RNA-1) and 1.44 times 10⁶(RNA-2). RNA-2 was detected in the middle and the bottom nucleoprotein components, and RNA-1 only in the bottom component. An antiserum prepared to purified virus particles was used to readily detect the virus in cassava and other host plants by ELISA and by ISEM. No serological relationship was shown between this virus and eight nepoviruses, including the recently described cassava green mottle nepovirus infecting cassava in the Solomon Islands (Lennon, Aiton & Harrison, 1987). The virus described here is the first nepovirus isolated from cassava in South America, and is named cassava American latent virus.     

The elimination of cocksfoot streak virus, cocksfoot mild mosaic virus and cocksfoot mottle virus from Dactylis glomerata by shoot tip and tiller bud culture

Shoot tips from 0.2 to 4.8 mm long and tiller buds 0.2 to 5.1 mm long were cultured from cocksfoot ( Dactylis glomerata ) plants known to be infected with combinations of cocksfoot streak, cocksfoot mild mosaic and cocksfoot mottle viruses. Regenerated plants were tested for the presence of viruses by electron microscopy, serology and the expression of symptoms. All viruses were eliminated by culturing shoot tips and tiller buds less than 1.2 mm long but the maximum explant size capable of regenerating healthy plants depended upon the infecting virus. Viruses were not detected in shoot tip and tiller bud samples of similar size to the explants that gave healthy plants. The method is of value in eliminating viruses from desirable stocks of D. glomerata that must be vegetatively propagated.     

Pepper veinal mottle virus associated with a streak diseaseof tomato in Nigeria

A destructive streak disease of tomato (Lycopersicon esculentum) was observed on the University of Ife farm. The disease killed many plants and greatly diminished the quantity and quality of fruit produced by the other plants. A virus that is readily transmitted by mechanical inoculation, by the green peach aphid (Myzus persicae) and by grafting was isolated consistently from diseased plants. The virus was propagated in Nicotiana occidentalis and assayed in Physalis angulata. It was infective after dilution to io^-3 but not io^-4; after iomin at 55 but not 60^oC; or after 5 days but not 7 days at 20–26^oC. Electron microscope examination of sap from infected N. occidentalis leaves revealed flexuous rods with a modal length of about 780 nm. Based on the host range and symptomatology, particle morphology and size, properties in vitro and serology, the virus is shown to be related to, and possibly indistinguishable from, pepper veinal mottle virus.     

Purification and properties of Australian lucerne latent virus, a seed-borne virus having affinities with nepoviruses

An isolate of Australian lucerne latent virus (ALLV) from lucerne in New Zealand was mechanically transmitted to a few herbaceous hosts. It induced diagnostic symptoms in several species of the Chenopodiaceae, but was symptomless in most other hosts including lucerne and Trifolium subterraneum. It was seed transmitted in lucerne. When assayed to Chenopodium quinoa, infective C. quinoa sap lost infectivity after diluting to 10^-4, heating for 10 min at 55°C and storage for 4 days at 4°C. ALLV was purified from infected C. quinoa or pea plants by extracting sap in 0.1 m borate buffer (pH 7) containing 0.2% 2-mercaptoethanol and clarifying with 15% bentonite suspension, high and low speed centrifugation and sucrose density gradient centrifugation. Purified virus preparations contained isometric particles about 25 nm in diameter and sedimented as three virus components with sedimentation coefficients (s_20-w⁰) of 56 S, 128 S and 133 S. The 56 S component appeared to consist of nucleic acid-free protein shells. Polyacrylamide gel electrophoresis of virus preparations showed that ALLV contained a single protein species of mol. wt 55 000 and two RNA species of mol. wt 2.1 × 10⁶ and 2.4 × 10⁶. An antiserum to ALLV had an homologous titre of 1/256 to purified virus but failed to detect ALLV in infective sap of C. quinoa, pea or lucerne. Purified ALLV failed to react to antisera to 28 distinct isometric plant viruses including those to 10 nepoviruses.