Elderberry latent virus: its relationship to Pelargonium ringspot virus and its identification as a distinct member of the genus Carmovirus, family Tombusviridae

The properties of Elderberry latent virus (ELV) and Pelargonium ringspot virus (PelRSV) were compared. The viruses were largely indistinguishable in herbaceous host range and symptomatology, particle morphology, sedimentation coefficient and RNA profiles and size. They were also very closely related serologically with SDI differences in agarose gel double‐diffusion tests of 1 to 3. Purified virus particle preparations of each virus contained isometric particles c. 30 nm in diameter that sedimented as a major component with an s^O_20W of 112–115S. Purified virus particle preparations contained a major and a minor ssRNA species that in polyacrylamide gel electrophoresis (PAGE) had estimated sizes of c. 3.8 kb and c. 1.6 kb respectively. Plants of Chenopodium quinoa infected with ELV or PelRSV each contained three dsRNA species of c. 3.8, 2.6 and 1.8 kbp, although the smallest of these species was not evident in all preparations. Protein from purified virus particle preparations contained a major polypeptide that, in SDS‐PAGE, had an estimated M^r of 40 000 (40K). However, after storage of purified virus particles for 7–10 days, protein preparations from PelRSV particles also contained an additional major polypeptide of estimated M^r of 37 000 that is probably derived by degradation of the 40K protein; this additional component was not observed in freshly prepared preparations of ELV. Neither virus was found to be related serologically to 16 other viruses with isometric particles and similar properties. These data, together with the recent finding by other researchers that the smallest RNA species is a sub‐genomic RNA, suggests that both viruses are members of the genus Carmovirus, and that PelRSV is a minor variant of ELV. However, the taxonomic status of these two viruses is discussed in relation to recent brief reports comparing the nucleotide and amino acid sequences of these two viruses.     

Particle properties of parsnip yellow fleck virus

Particle preparations of parsnip yellow fleck virus (PYFV) isolates A-421 and P-121, representing the two major serotypes, were made by clarifying leal extracts with ether or butan-1-ol and concentrating the virus particles by precipitation with polyethylene glycol and differential centrifugation. The preparations contained c. 31 nm-diameter particles comprising two sedimenting components. Top component (T) consisted of stain-penetrable protein shells with A₂₆₀/A₂₈₀= 0.8–0.9, sedimentation coefficient (S₂₀) = 56 S (A-421) or 60 S (P-121), and buoyant density = 1.297 g/cm³. Bottom component (B) consisted of nucleoprotein particles, not penetrable by negative stain, with A₂₆₀/A₂₈₀= 1.9, sedimentation coefficient (S⁰_20.w) = 148 S (A-421) or 153 S (P-121), and buoyant density = 1.520 g/cm³ (A-421) or 1.490 g/cm³ (P-121). Yields of B component particles were up to c. 1 mg/100 g leaf tissue (both isolates); yields of T component particles were up to c. 0.6 mg (A-421) or 5.5 mg (P-121) per 100 g leaf tissue. PYFV particles were found to contain a single RNA species (mol. wt c. 3.4 × 10⁶, c. 9800 nucleotides), constituting 40% of the particle weight, and three polypeptide species, of mol. wt (× 10 ³) 30 , 26 and 24 (A-421) or 31 , 26 and 23 (P-121).     

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.     

Properties of broad bean yellow band virus, a possible new tobravirus

A virus was transmitted from broad bean plants in Apulia (Southern Italy) with leaves showing yellow rings, line patterns or yellow vein banding and malformations and necrosis of pods. Symptoms in some, but not all, test plants were similar to those induced by tobraviruses. Purified virus preparations contained two classes of rod-shaped particles containing c. 5% nucleic acid with sedimentation coefficients of 186S and 276S. After centrifugation to equilibrium in CsCl gradients, two components were resolved, with buoyant densities of 1·298 and 1·316 g/cm³. Unfractionated virus preparations contained two species of single-stranded RNA with mol. wts of c. 1·06 × 10⁶ and 2·48 × 10⁶ and one species of coat protein with mol. wt of c. 21 300. The modal lengths of the two classes of particles, both in plant sap and in purified preparations, were 77 nm (S particles) and 202 nm (L particles). L particles accumulated in infected cells in paracrystalline aggregates, whereas S particles were randomly distributed in the cytoplasm of cells. The virus was serologically unrelated to two isolates of tobacco rattle virus and two isolates of pea early-browning virus. The virus, named broad bean yellow band, is considered a distinct tobravirus.     

Particle purification and properties of cassava Ivorian bacilliform virus

A virus found in cassava from the north-west of the Ivory Coast was transmitted by inoculation with sap extracts to herbaceous species in six plant families. Chenopodium quinoa was used as a propagation host and C. murale was used for local lesion assays. The virus particles are bacilliform, c. 18 nm in diameter, with predominant lengths of 42,49 and 76 nm and a structure apparently similar to that found in alfalfa mosaic virus. Purified preparations of virus particles had A₂₆₀/A₂₈₀ of 1.7 ±0.05, contained one protein of M_rc. 22 000, and yielded three species of RNA with M_r (× 10^-6) of c. 0.7, 0.8 and 1.2. Although the virus particles were poorly immunogenic, an antiserum was produced and the virus was detected by enzyme-linked immunosorbent assay (DAS-ELISA) in leaf extracts at concentrations down to c. 6 ng/ml. Four other field isolates were also detected, including a strain which caused only mild systemic symptoms in C. quinoa instead of necrosis. The naturally infected cassava source plants were also infected with African cassava mosaic virus (ACMV) but when the new virus was cultured in Nicotiana benthamiana, either separately or together with ACMV, its concentration was the same. The new virus did not react with antisera to several plant viruses with small bacilliform or quasi-bacilliform particles, and alfalfa mosaic virus reacted only weakly and inconsistently with antiserum to the cassava virus. The new virus, for which the name cassava Ivorian bacilliform virus is proposed, is tentatively classified as the second member of the alfalfa mosaic virus group.     

Further properties of wineberry latent virus and evidence for its possible involvement in calico disease

The flexuous filamentous particles of wineberry latent virus (WLV) were found to measure 620. 12 nm and not 510. 12 nm as previously reported. Analysis of dsRNA from infected plants detected a major species of c. 5.7. 10⁶ mol. wt and minor species of lower mol. wt. Purified virus particles formed a major and a minor buoyant density component in solutions of caesium salts with densities of 1.26 and 1.25 g cm^-3 in Cs₂SO₄ and 1.30 and 1.29 g cm^-3 in CsCl. The particles contained a single nucleic acid species, presumably single stranded RNA, and a single polypeptide of estimated mol. wt 2.78. 10⁶ and 31 000 respectively. In indirect ELISA, purified particles of WLV and particles in plant sap failed to react specifically with antiserum to nine carlaviruses, 12 potexviruses, three capilloviruses or apple chlorotic leafspot closterovirus, nor was WLV found to react with several of these antisera in immunosorbent electron microscopy or immunoblots. In Marion and Olallie blackberry, WLV in mixture with raspberry bushy dwarf virus (RBDV), but not RBDV alone, induced veinal line-pattern symptoms resembling those of calico disease reported from the USA.     

Host range and properties of potato black ringspot virus

Potato black ringspot virus (PBRV), obtained from cultivated potato in Peru, was found to have a very wide host range resembling that of tobacco ringspot virus (TRSV-B), to which PBRV is distantly related serologically. However, PBRV caused the more severe symptoms in many species and, unlike TRSV B, infected Lycopersicon esculentum and Cyamopsis tetragonoloba. In Solanum tuberosum, PBRV caused necrotic spots and ringspots in systemically infected leaves in the year of infection and was readily transmitted through tubers to progeny plants, most of which developed no obvious symptoms although systemically infected. TRSV-B infected non-inoculated S. tuberosum leaves only sporadically, did not induce symptoms in them and was not transmitted through tubers to progeny plants. PBRV was cultured in Nicotiana clevelandii and infectivity was assayed in Cheno-podium amaranticolor or C. quinoa. Virus particles were purified from leaf extracts, after clarification using chloroform, by precipitation with 6% polyethylene glycol and differential centrifugation. Purified preparations contained 25 nm diameter isometric particles with somewhat angular outlines, sedimenting as three components (T, M and B) at 49, 84 and 117 S, and containing a single protein species of mol. wt 59 000. Preparations of PBRV nucleic acid contained two species, estimated by polyacrylamide gel electrophoresis in non-denaturing conditions to have mol. wt of about 25 10⁶ (RNA-1) and 15 10⁶ (RNA-2). Infectivity was associated with B particles, preparations of which contained RNA-1 and RNA-2, presumably in different particles. M particles contained RNA-2, were not infective and enhanced infectivity only slightly when added to B particles. Similar relative amounts of RNA-1 and RNA-2 were extracted from unfractionated virus using phenol or Pronase, but preparations obtained using phenol were much the more infective. PBRV has properties typical of nepoviruses; its present cryptogram is (R/1):2–5/41 + 15/28 or 2 1 5/46:S/S:S/*, nepovirus group.     

Hydrangea mosaic virus, a new ilarvirus from Hydrangea macrophylla (Saxifragaceae)

A previously unrecognised virus isolated from Hydrangea macrophylla with chlorotic mosaic leaf symptoms in West Sussex was named hydrangea mosaic virus (HydMV). HydMV was mechanically transmitted without difficulty to four of 16 species from three of five families, and was seed transmitted in Chenopodium quinoa, but was not aphid transmitted. Although relatively unstable in vitro, HydMV was purified by clarifying leaf extracts by emulsification with chloroform and acidification with citric acid, followed by differential centrifugation and sucrose density gradient centrifugation. Purified virus incompletely separated on sucrose density gradients into three components (T. M and B) with sedimentation coefficients (s^o_20w) of 86, 97, and 105 S respectively, but all particles had buoyant densities in caesium chloride of 1.37 g/cm³. Virus contained a single polypeptide species (mol. wt 26.4 times 10³), appeared quasiisometric to ovoid or elliptical, and measured c. 28 times 30 (T), 30 times 30 (M) or 30 times 32–38 nm (B). Single-stranded RNA species or mol. wt 1–25, 1–08, 0–83, 0–36 and 0–27 (RNA-1 to 5 respectively) were obtained from virus preparations but mixtures containing RNA-1 to 3 plus either RNA-4 + 5 or the coat protein, were infective. These properties suggest that HydMV has affinities with ilarviruses, but it showed no serological relationship to any of six ilarviruses or 42 other viruses.     

Purification and some particle properties of anthriscus yellows virus, a phloem-limited semi-persistent aphid-borne virus

Anthriscus yellows virus (AYV), a phloem-limited virus transmitted in the semi-persistent manner by the aphid Cavariella aegopodii, was purified by treatment of leaf extracts with cellulasc, followed by differential and sucrose density gradient centrifugation. ‘The preparations contained isometric particles c. 29 nm in diameter which were unstable unless stored in buffer at pH 8.0 containing 1 mM CaCl₂,. The particles sedimented as two components, ’full‘ nucleoprotein particles with A₂₆₀/A₂₈₀= 1.83 containing about 42% nucleic acid, and ’empty‘ protein shells with A₂₆₀,/A₂₈₀= 0.73; their buoyant densities in CsCl solutions were 1.52 and 1.27 g/cm³. Respectively. Yields of ihe nircleoprotein particles were c. 1.75 mg/kg leaf tissue. The particles contained a single species of RNA, of mol. wt 3.6 × 10 “(10 000 nucleotides). Particle protein preparations contained four electrophoretic species, of mol. wt (× 10³) 35.0, 28.3, 23.3 and 22.3.C. aegopodii did not transmit AYV from purified preparations. A rabbit injected with AYV preparations produced antibodies that coated AYV particles in electron microscope tests, but gave variable reactions in immunosorbent electron microscopy (ISEM), depending on the composition of the medium. No reactions were obtained in enzyme-linked inimunosorbent asjay (ELISA). No serological relationship was detected in ISEM between AYV and any of 10 viruses that resembled it in one or more properties.     

Arracacha virus B, a second isometric virus infecting arracacha (Arracacia xanthorrhiza; Umbelliferae) in the Peruvian Andes

Arracacha virus B (AVB), a previously undescribed virus, was found together with arracacha virus A or with a 750 nm flexous filamentous virus in arracacha (Arracacia Xanthorrhiza; Umbelliferae) growing in the Huanuco region of the Peruvian Andes. AVB was transmitted by inoculation of sap to 30 species from eight families out of 45 species from 10 families tested. It was transmitted through seed of Chenopodium quinoa but not by Myzus persicae. AVB was best propagated in C. Quinoa or Tetragonia expansa and assayed in C. quinoa, C. murale or C. amaranticolor. Sap from infeted <C. Quinoa was occasionally infective after dilution to 10^-4 but not 10^-5, after 10 min at 65 d? C but not 70 d? C, and after 12 but not 14 days at 20 d? C. In neutral phosphotungstate, AVB has isometric partilces c. 26 nm in diameter with a hexagonal profile. About 50- 150 A1 cm₂₆₀ units of purified virus were obtained from 1 kg infected C. quinoa leaf by extraction in 0.5 M phosphate buffer at pH 7.5, containing 0.05 M ethylene-daiminetetra-acetate (EDTA) and 0.2% mercaptoethanol, and clarificatin with chloroform, followed by two precipitations with polyethylene glycol and three cylces of differential centrifugation. Purified virus coefficent (Sd?_{20 w},) of 126 S and A₂₆₀/A₂₈₀ ratio of 1.80, bnut formed two isopycnic bands in CsC1 of buoyant density 1.481 and 1.492 g/cm³ with estimated nucleic acid contents of 40 and 41% respectively. AVB particles contained two proteins of mol.wt 26 000 (major component) and 20 000. AVB was not serologically related to any of 20 other morphologically similar viruses. Its properties suggest that it does not fall into any recognised group of viruses. the cryptogram of AVB is */*:*/40–41:S/S:S/*     

Biological and biochemical properties of an isolate of cherry rasp leaf virus from red raspberry

A mechanically transmissible virus obtained from symptomless plants of a red raspberry selection imported into Scotland from Quebec, Canada was indistinguishable serologically from a cherry isolate of cherry rasp leaf virus (CRLV). The raspberry isolate, CRLV-R, was graft transmitted to several virus indicator species and cultivars of Rubus without inducing noticeable symptoms. In Chenopodium quinoa sap, CRLV-R lost infectivity after dilution to 10^-5 or heating for 10 min at 60°C but was infective after 16 days (the longest period tested) at 18°, 4° or - 15°C. The virus particles are isometric, c. 28 nm in diameter, and were purified with difficulty from infected C. murale and C. quinoa plants. The particles comprise two nucleoprotein components with sedimentation coefficients of 89 and 115 S and are prone to aggregate during purification. When centrifuged to equilibrium in CS₂SO₄ solution, purified virus preparations formed two major components with p= 1·28 and 1·36 g/cm³. Virus particles contained two RNA species which, when denatured in glyoxal and electrophoresed in agarose gels, had estimated mol. wt of 2·56 × 10⁶ (RNA-1) and 1·26 × 10⁶ (RNA–2). Infectivity of CRLV-R RNA was abolished by treatment with proteinase K, suggesting that the RNA is linked to protein necessary for infectivity; RNA molecules contained polyadenylate. In reticulocyte lysates, CRLV-R RNA stimulated the incorporation of ³H-leucine, mainly into two polypeptides of estimated mol. wt 200 000 and 102 000. When electrophoresed in polyacrylamide gels, protein obtained from CRLV-R particles purified by centrifugation to equilibrium in Cs₂SO₄ separated into three bands with estimated mol. wt 26 000 , 23 000 and 21 000.     

Purification and some properties of Tephrosia symptomless virus

Tephrosia symptomless virus (TSV), isolated from Tephrosia villosa, is widely distributed in coastal districts of Kenya. The virus was readily transmitted by inoculation of sap, but not by Aphis craccivora or Apion sp. (Curculionidae) or through soil. Host range was very restricted and it infected only 10 of 70 species tested in one of nine plant families; susceptible species were confined to five genera within the Papilionaceae. The virus was cultured, propagated and assayed in soybean. TSV remained infective after 10 min at 85°C, 3 wk at 20°C and 26 wk at -12°C; crude infective sap of Glycine max retained infectivity when diluted 10^-6 but not 10^-7. Virus was purified from systemically infected soybean by clarifying sap extracted in 0.06 m phosphate buffer containing 0.001 m EDTA and 0.1% thioglycollic acid (pH 7.5) with equal volumes of 1:1 n-butanol/chloroform followed by two cycles of differential and one of sucrose density gradient centrifugation. Purified preparations contained c. 33 nm isometric particles. TSV contained RNA and one protein of molecular weight 1.53. 10⁶ and c. 42 000, respectively. Analytical centrifugation indicated a single component with a sedimentation coefficient (s.20, w) of 127 S; in Cs₂SO₄ and CsCl isopycnic gradients a single virus band formed; buoyant density in CsCl was 1.361. TSV was not related serologically to any of 44 viruses in nine plant virus groups but it resembled the tombusviruses and other ungrouped viruses such as carnation mottle in some of its properties.     

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.     

Rottboellia yellow mottle virus,a new sobemovirus affecting Rottboellia cochinchinensis (Itch grass) in Nigeria1

A hitherto undescribed virus, termed rottboellia yellow mottle virus (RoYMV), affecting Rottboellia cochinchinensis (syn. R. exaltata, itch grass) at Ibadan, Nigeria, was investigated. RoYMV virions are isometric, c. 29 nm in diameter, and sediment homogeneously at 114s. In isopycnic CsCl gradients, RoYMV virions band sharply at a buoyant density of 1.379 g cm^-3, but in Cs₂SO₄ gradients, virions band at two zones, at the densities of 1.300 g cm^-3 and 1.325 g cm^-3. Treatment with EDTA at pH 8.0 reduced the sedimentation value of RoYMV to c. 87s and rendered it susceptible to proteinase-K, SDS and NaCl. The apparent molecular weight of RoYMV coat protein was c. 27 000. Virions encapsidate a single-stranded RNA of mol. wt 1.4 × 10⁶ Da. Besides R. cochinchinensis, RoYMV was mechanically transmissible only to maize (Zea mays). No reaction occurred when RoYMV was tested against antisera to 44 isometric plant viruses (belonging to 12 groups), including several that affect Gramineae. RoYMV exhibits striking similarities with other viruses belonging to the sobemovirus group, and it is tentatively designated as a new member of the sobemovirus group.     

Purification and some properties of oat golden stripe virus

Oat golden stripe virus (OGSV) was maintained in oats by mechanical inoculation and purified by extraction of leaves in borate buffer, two cycles of centrifugation through sucrose cushions and isopycnic centrifugation in CsCl. An antiserum with a titre of 1/1024 in precipitin tests was prepared. Particle length distribution was bimodal with median values, respectively, of 150 and 300 nm from dip preparations. Measurements from immunosorbent electron microscopy (ISEM) and purified preparations showed that the particles had partially degraded during these procedures. The virus sedimented as two components of 168 S and 218 S and had a buoyant density of 1321 g cm^-3. Four isolates of OGSV reacted with the antiserum. Antiserum to members and possible members of the furovirus group were tested in ISEM decoration tests and in ELISA. OGSV was related to soil-borne wheat mosaic virus but not to beet necrotic yellow vein virus, hypochoeris mosaic virus or potato mop-top virus.     

Melon rugose mosaic virus, the cause of a disease of watermelon and sweet melon

A mechanically transmissible virus with isometric particles c. 32 nm in diameter, was isolated from infected watermelons and sweet melons in the People's Democratic Republic of Yemen. Purified virus preparations contained two major sedimenting components with sedimentation coefficients of 61S and 117S. In isopycn ic centrifugation in CsCl the particles formed a single band of buoyant density 1.39 g cm^-3. Preparations of virus particles comprised of a single polypeptide of mol. wt c. 22 000 and ssRNA of mol. wt 2.1 × 10⁶. The virus was serologically related to three of six subgroups of tymoviruses tested. The name melon rugose mosaic virus is proposed for this newly described virus.     

Some properties of grapevine Bulgarian latent virus

Grapevine Bulgarian latent virus (GBLV), obtained from symptomless vines grown in Bulgaria, was readily transmitted by inoculation of sap to a restricted range of hosts. The virus was re-inoculated into virus-free rooted cuttings and seedlings of several grapevine cultivars without inducing symptoms. Purified preparations of GBLV contained isometric particles c. 30 nm in diameter which sedimented as three components at 52 , c. 120 and 1275, respectively. The slow-sedimenting component (T) contained non-infective protein shells, whereas the two heavier classes of particles (J5_X, B₂) each contained one molecule of single-stranded ribonucleic acid (RNA) with mol. wts of 2.1 and 2.2 times 10⁶ daltons. The RNA content of B₁ and B₂ components were 39 and 41 % by particle weight respectively. The capsid was composed of one type of protein with a mol. wt of 54000. GBLV did not react with antisera to any of twenty-eight viruses with isometric particles. Its present cryptogram is R/1: 2-2/41 +2-1/39:S/S:S/*.     

Purification and particle properties of groundnut rosette assistor virus and production of a specific antiserum*

Purified preparations of the luteovirus, groundnut rosette assistor virus (GRAV), were made by treatment of groundnut leaf extracts with cellulase, followed by sucrose density gradient centrifugation. Yields of virus particles were about 0·5-1·0 mg/kg leaf material. The preparations contained isometric particles c. 28 nm in diameter with a sedimentation coefficient (s_{20, w}) of 115 S, a buoyant density in Cs₂SO₄ of 1·34 g/cm³, and A₂₆₀/A₂₈₀ of 1·86. The particles contained a single species of nucleic acid (presumably RNA), of mol. wt 2·09 × 10⁶and with no detectable polyadenylate sequence, and a single protein species, of mol. wt 24 × 10³. An antiserum produced in a rabbit had a titre of 1/256 in gel diffusion tests and detected GRAV in leaf extracts by ELISA. GRAV particles reacted in F(ab')₂-ELISA and immunosorbent electron microscopy (ISEM) tests with antisera to bean leaf roll, potato leafroll and tobacco necrotic dwarf luteoviruses, but did not react with antisera to carrot red leaf luteovirus.     

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.     

Purification and properties of ginger chlorotic fleck virus

A previously undescribed isometric virus, named ginger chlorotic fleck virus (GCFV), was detected in ginger (Zingiber officinale) imported into Australia from a number of countries. The geographical distribution of the virus is uncertain, but is thought to include India, Malaysia and Mauritius. The virus apparently does not occur in Australian commercial ginger plantings. The virus has isometric particles c. 30 nm in diameter, with a sedimentation coefficient of 111 S, and was readily purified from infected ginger with yields of 50–90 mg/kg leaf tissue. Purified preparations contained a major species of single-stranded RNA of mol. wt 1.50 × 10⁶ and a major coat protein species of mol. wt 29.0 × 10³. At pH 7, the particles formed a single zone in both caesium chloride and caesium sulphate gradients, with buoyant densities of 1.355 g cm^-3 (fixed virus) and 1. 297 g cm^-3 (unfixed virus), respectively. The virus particles migrated as two electrophoretic components and were labile when treated with 10 mM EDTA, 1 M NaCI, 10 mM tris pH 8.25 or when negatively stained with potassium phosphotungstate. GCFV was mechanically transmitted only to ginger, and was not transmitted by the aphids Myzus persicae. Pentalonia nigronervosa, Rhopalosiphum maidis or R. padi. Possible affinities of GCFV with the sobemo-virus group are discussed. The present cryptogram of GCFV is ^R/_l: ^1.5/₂₀: ^S/_S: ^S/_*.