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.     

Studies on two Serologically Distinct Raspberry Ringspot Virus Strains from Artichoke

Two raspberry ringspot virus variants, RRV-T and RRV-G, found in artichoke of Turkish and Greek origin, were compared biologically (indexing), biochemically and serologically to two strains of the same virus, RRV-S and RRV-E originating from Scotland and England, respectively. Molecular weight values of protein and nucleic acid of RRV-T and RRV-G were in good agreement with those already known for RRV. RRV-T and RRV-G appeared serologically very similar to each other (serological differentiation index = 1) and well distinguishable from RRV-S and RRV-E (serological differentiation indices varying between 3 and 6). Phaseolus vulgaris cv. La Victoire, Ocimum basilicum cv. Foglia di Lattuga, Cucumis sativus cv. Delicatezza, and Cucurbita pepo cv. Zucchetta striata d'ltalia seemed herbaceous hosts useful for differentiating each strain from the others on symptomatological basis.     

Ingestion,Retention, and Transmission of two Strains of Raspberry Ring-spot Virus by Longidorus macrosoma

The transmission of two strains of raspberry ringspot virus (RRV) by small numbers of nematodes was compared. A strain of RRV from Scotland (RRV-S), originally found in the field associated with Longidorus elongatus, was transmitted frequently by L. elongatus but only once by L. macrosoma. A strain from England (RRV-E) associated with L. macrosoma in the field was transmitted infrequently by each species of nematode. The reasons why L. macrosoma infected only a small proportion of bait plants with virus were investigated, and it was found that most of the nematodes tested had fed on the source plants and many had ingested virus. Most nematodes exposed to RRV-E or RRV-S had fed on the roots of the bait plants and, when thin sections were examined by electron microscope, had retained particles (thought to be those of the virus) in the region of the anterior odontostyle, Thus, most nematodes seem to have had ample opportunity to transmit virus, and the low frequency of transmission may have been due to a failure of the virus particles to be released from the site of retention or to a lack of infectivity of the virus when L. macrosoma was the vector and Petunia hybrida was the host.     

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.     

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.     

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

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

Effects of virus genotype and temperature on seed transmission of nepoviruses

Transmission of different nepoviruses through chickweed (Stellaria media) seed was differently affected by ambient temperature during seed production. Raspberry ringspot and tomato black ring (Scottish isolate) viruses were similarly and frequently transmitted at 14 , 18 and 22 ^oC, whereas arabis mosaic virus was transmitted most frequently at 14 ^oC, and strawberry latent ringspot and tomato black ring (German isolate) viruses at 22 ^oC. When infected by seed-borne nepoviruses, seedlings of S. media and other species were symptomless at 15–25 ^oC, and the viruses were therefore detected by inoculating sap to Chenopodium quinoa indicator plants. However, typical symptoms of arabis mosaic and tomato black ring viruses were induced by growing Nicotiana tabacum, N. clevelandii and C. quinoa seedlings infected with seed-borne virus at 33–37 ^oC during the third and fourth weeks after sowing, preceded and followed by periods at 15–25 ^oC. The proportion of N. tabacum seedlings developing symptoms was the same as that of untreated seedlings yielding sap-transmissible virus. Seed transmissibility of pseudo-recombinant isolates of raspberry ringspot and tomato black ring viruses, containing RNA-i from one virus strain and RNA-2 from another strain, depended greatly on the transmissibility of the strain contributing RNA-i. The source of RNA-2 had an additional but smaller influence. The satellite RNA (RNA-3) of tomato black ring virus was seed-transmitted in S. media and its occurrence in cultures did not affect the frequency of transmission of the virus. Results of testing the infectivity of extracts of seed from infected mother plants suggested that failure of seed transmission reflected failure to become established in the seed, not subsequent inactivation. Whereas seed transmissibility of raspberry ringspot virus is primarily dependent on information carried in RNA-i, transmissibility by nematode vectors, another property of major ecological importance, is determined by RNA-2. In the field, selection pressures presumably can act independently on the two parts of the genome but evidence was also obtained of selection for mutual compatibility of RNA-i and RNA-2.     

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.     

Thermal inactivation of cherry leaf roll virus in tissue cultures of Nicotiana rustica raised from seeds and meristem-tips

Nicotiana rustica tissue cultures derived from seeds or embryos infected with cherry leaf roll virus (CLRV), remained infected after culture at 22 ^oC. No infectivity was found in cultures held at 32 ^oC for 5 days but it was readily detected after such cultures were transferred to 25 ^oC for 8 days. Virus was permanently eradicated from most plants after 20 days incubation at 32 ^oC and from all plants after 7 days incubation at 40 ^oC. Partially purified preparations of CLRV lost infectivity after 9–12 days at 22^oC, 5 days at 32^oC and 3 days at 40^oC.     

Tests for transmission of cherry leaf roll virus using Longidorus, Paralongidorus and Xiphinema nematodes

The ability of 10 nematode species to transmit three strains of cherry leaf roll virus (CLRV) was tested by three methods: (1) virus-infected source plants and virus-free bait plants were grown concurrently in nematode-infested soil, (2) as for (1) but virus source plants were removed before bait plants were planted, and (3) nematodes were extracted from soil after access to virus source plants, and were added to pots containing bait plants. The occurrence of galls on roots showed that nematodes fed both on source and on bait plants in all experiments and, in some experiments, CLRV was detected by direct assays (slash tests) of Longidorus elongatus, L. leptocephalus and Paralongidorus maximus. Although the nematodes readily transmitted control viruses, for which they are known to be vectors, CLRV was detected by root assays in only a few bait plants exposed to L. elongatus, L. macrosoma, Xiphinema diversicaudatum or L. leptocephalus + X. vuittenezi in tests by method 1. The recovery of CLRV in these tests is interpreted as being due to contamination. These results add to the increasing circumstantial evidence against the involvement of nematodes in the transmission of CLRV. Other possible mechanisms of spread are discussed.     

Purification and properties of blackberry chlorotic ringspot, a new virus species in subgroup 1 of the genus Ilarvirus found naturally infecting blackberry in the UK

A mechanically transmissible virus was isolated from Bedford Giant blackberry plants showing chlorotic mottling and ringspot symptoms growing in Scotland. It infected several herbaceous test plants, many of them symptomlessly. This virus was also transmitted to several Rubus species and cultivars by graft inoculation with scions from the field‐infected Bedford Giant plant. Most grafted plants were infected symptomlessly, but Himalaya Giant blackberry and the hybrid berry Tayberry developed symptoms similar to those in the infected Bedford Giant plant. In the sap of infected Chenopodium quinoa, the virus lost infectivity when diluted 10^?4 but not 10^?3, after 6 h and 48 h when kept at 20°C and 4°C, respectively, but was infective for more than 8 days when kept at ?15°C. Preparations of purified virus from infected C. quinoa or spinach sedimented as three major nucleoprotein components and consisted of quasi‐isometric particles that varied in size from 24 to 32 nm in diameter and that were not penetrated by negative stain. Such virus particle preparations contained a major polypeptide of ca 28 kDa and three single‐stranded RNA species of estimated size 3.2, 2.8 and 2.1 kb. The complete sequence of the largest RNA (RNA 1, 3478 nt) and the partial sequence of the other RNAs (1863 and 2102 nt long, respectively) were determined and compared with sequences in databases. These findings, together with the biological and biochemical properties of this virus, indicate that it should be regarded as a distinct species in subgroup 1 of the genus Ilarvirus even though it was serologically unrelated to existing members of this subgroup. The virus showed a very distant serological relationship with prune dwarf virus (PDV) but differed significantly from it in the amino acid sequence of its coat protein, experimental host range and symptomatology and was unrelated to PDV at the molecular level. The virus, tentatively named blackberry chlorotic ringspot virus, is therefore a newly described virus and the first ilarvirus found naturally infecting Rubus in the UK.     

Seasonal Migration of Apolygus spinolae (Hemiptera: Miridae) between Grapevines and Herbaceous Plants

This study was conducted to verify the seasonal migration of Apolygus spinolae (Meyer-Dür) between grapevines and herbaceous plants. Overwintering eggs were hidden in the hair layer under grapevine bud scales. A. spinolae adults were captured on sticky traps in the grapevine yard from late spring to early summer, dwindled through the summer, and captured again in late fall. However, adults were observed from early summer in herbaceous plant fields. A. spinolae adults were abundant during the summer of July and August in the herbaceous field, and thereafter its density decreased through fall. A few or no A. spinolae was found on mesh-netted grapevines after the installation year of the mesh-net, which indicated that A. spinolae adults migrating to lay overwintering eggs during the autumn could not land at the grapevines because of the mesh-net. Damaged shoots by A. spinolae were concentrated near the edge of grapevine yards bordering the herbaceous plants. This distribution pattern of shoot damage was believed to be related to an oviposition behavior of A spinolae, reflecting that adults migrating from herbaceous plants lay eggs more frequently in grapevines adjacent to the summer host plants. Seasonal occurrence of A. spinolae in grapevine yards was suggested as follows: A. spinolae overwinter as eggs in dormant buds on grapevines and hatch in the spring. Nymphs feed on grapevines then develop to adults (spring population), and migrate to herbaceous plants. A. spimolae spends the summer on the herbaceous hosts (summer population). Then, adults migrate back to grapevines in late autumn and lay overwintering eggs.     

Some Properties of Cucumber Fruit Streak Virus

An isometric virus c. 30 nm in diameter with a single RNA species (mol.wt 1.45 × 10⁶) isolated from cucumber plants from the island of Crete (Greece) is described under the name of cucumber fruit streak virus (CFSV). The most evident symptom on naturally infected plants consisted of longitudinal chlorotic streak of the fruits. In glasshouse, the virus was soil-transmitted to C. sativus, and, mechanically, to a wide range of herbaceous hosts, most of which were infected only locally. Purified virus preparations sedimented as a single component with sedimentation coefficient of 132S. At equilibrium these preparations were homogeneous in CsCl gradients but formed two bands in Cs₂SO₄ gradients. Virus particles were stabilized by forces involving divalent cations, pH-dependent bonds and salt links between protein and RNA. Although some of the properties of CFSV are similar to those of other small spherical viruses with single RNA species there are differences which do not allow for the assignment of the virus to any of established taxonomic group of plant viruses.     

Some Properties of a Phloem-Limited Non Mechanically-Transmissible Grapevine Virus

Abstract Grapevine phloem-limited isometric virus (GPLIV) is the name proposed for a non mechanically-transmissible virus found in Italian and Tunisian grapevines. In density gradient centrifugation purified virus preparations sedimented as two components: T, made up of empty protein shells, and B, composed of intact nucleoprotein particles. B particles had a buoyant density of 1.45 g/cm³ at equilibrium in CsCl and contained 35% RNA consisting of a single molecule with an apparent size of 7.4 kb. The coat protein consisted of a single species with a mol.wt of 28,000 daltons. Purified virus preparations did not infect herbaceous hosts by manual inoculation. A specific antiserum with a titre of 1: 64 raised in rabbits, was used for identification of, GPLIV in field-grown Tunisian grapevines and in leafroll-affected Italian vines before and after heat treatment. Although heat treatment eliminated the virus from the majority of the plants, leafroll symptoms persisted in several GPLIV-free vines, indicating that there is no clear-cut relationship between GPLIV and this disease.     

Characterisation of a labile RNA virus-like agent from white clover

A labile virus has been identified in white clover in New Zealand. The virus was mechanically transmitted to nine species of herbaceous test plants. No virus-like particles were identified by electron microscopy in ultrathin sections or in negatively stained sap extracts, although in infected Chenopodium quinoa there were prominent membraneous inclusion bodies in the cell cytoplasm and membrane-bound structures c. 50 nm in diameter associated with the tonoplast in cell vacuoles. Double-stranded RNA species of approximately 6800, 3500 and 3300 bp were isolated from infected tissues. DsRNA denatured by boiling was infectious to C. quinoa, but undenatured dsRNA was not infectious. Total nucleic acid preparations from infected leaves were highly infective without boiling, indicating that most of the infectivity was single-stranded RNA. Infectivity was recovered in the poly (A)^- faction following oligo (dT)-cellulose chromatography, indicating that the RNA probably lacks a 3′ tract of poly (A). The labile white clover virus is tentatively named white clover virus L (WCIVL).     

The relationship between the Andean strain of potato virus S and pepino latent virus

The titres obtained in microprecipitin tests with purified preparations of pepino latent virus (PepLV) and the Andean strain of potato virus S (PVS^A) using PepLV antiserum and two antisera to the ordinary strain of PVS (PVS°) indicated a close serological relationship between PepLV and PVS^A. Using antiserum to PVS°, both viruses were detected by ELISA when infective Chenopodium quinoa sap was diluted to 10^-5but not to 10^-6. Particles of both viruses were decorated equally well by antibodies to PVS^o, PVS^Aand PepLV in all virus-antiserum combinations. When PepLV was inoculated to C. quinoa, C. amaranticolor and potato plants, the symptoms induced closely resembled those of PVS^Ain these hosts. It is concluded that PepLV is an isolate of PVS^Afrom pepino.     

植物罹病组织中南方、爪哇、花生根结线虫的LAMP快速检测

【目的】建立一种基于环介导等温扩增(loop-mediated isothermal amplification,LAMP)技术,从植物罹病组织中直接检测3种常见的根结线虫,为根结线虫的监测和防治提供技术支持。【方法】分别采用3种根结线虫的种类特异性引物对所选择的根结线虫的DNA片段进行PCR扩增,扩增产物纯化、回收并测序。根据3种根结线虫的测序结果,针对种类特异区段,采用PrimerExplorerV4软件,分别设计3种根结线虫的LAMP引物。设计的引物组人工合成后,以提取的纯化种群线虫DNA为模板,分别进行引物组的特异性测试,筛选出分别针对3种根结线虫的最佳引物组。【结果】研究设计的3种根结线虫的LAMP特异性引物能够直接从植物根结中检测出南方、花生、爪哇3种常见根结线虫,LAMP快速检测体系为:dNTPS浓度为1 mmol·L~(-1),Mg~(2+)的浓度为5 mmol·L~(-1),不添加甜菜碱,反应时间为45 min。【结论】本实验建立的南方、花生、爪哇根结线虫LAMP快速分子检测方法,具有特异性强、灵敏度高、简单、快速、经济等特征,能够从罹病植物组织中快速准确地检测出南方、花生和爪哇根结线虫,具有极高的实践应用价值。     

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.     

A yellow mosaic disease of horse chestnut (Aesculus spp.) caused by apple mosaic virus

A severe foliar yellow mosaic disease was observed in horse chestnut trees (Aesculus carnea and A. hippocastanum). Reactions in woody indicator plants grafted with diseased horse chestnut suggested the presence of an ilarvirus. Virus isolates obtained by mechanical inoculation of herbaceous test plants reacted with antisera to apple mosaic virus but not with antisera to its serotype prunus necrotic ringspot virus, or to prune dwarf virus. Yellow mosaic was induced in horse chestnut seedlings grafted with tissues from herbaceous hosts infected with horse chestnut isolates or with the European plum line pattern isolate of apple mosaic virus. Virus was detected by enzyme-linked immunosorbent assay (ELISA) in embryo and endosperm of immature seed from infected trees but not in mature seed, or progeny seedlings. Strawberry latent ringspot virus was detected in one of six A. hippocastanum trees with a leaf vein yellows disease.     

Investigations of carnation viruses

Carnation vein mottle virus (CarVMV) is rare in glasshouse carnations in Britain, although locally common in Dianthus barbatus in private gardens. In Sim carnations free from other viruses, CarVMV caused slight diffuse chlorotic mottling in the younger leaves, decreased flower yield by c. 22%, and caused flower breaking in cvs William Sim and Dusty. In non-Sim cultivars Pink Shibiuya, Orchid Beauty and Vesta, leaf symptoms and flower breaking were more pronounced. In mixed infections with carnation mottle virus, symptoms were much more severe. CarVMV was not eliminated from carnation or D. barbatus plants grown for 4 wk at 37^oC, and only rarely from cuttings then taken from them, but it was readily eliminated by meristem-tip culture. Myzus persicae adults or nymphs acquired and transmitted the virus within a total time of 4 min, and remained infective for 30–60 min if feeding, or for 75 min if starved. The carnation aphid, M. persicae f. dianthi, transmitted the virus much less efficiently. The virus was not transmitted by dodder (Cuscuta campestris), or through seed of D. barbatus or Chenopodium quinoa. The maximum infective dilution in sap of D. barbatus, carnation and C. quinoa ranged from 10^-2 to 10^-5. The virus withstood 10 min at 60 but not 65^oC, up to 9 days at c. 18^oC or 3–4 wk at c. 2^oC. CarVMV infected twenty-two of 107 plant species in six of thirty-seven families; suscepts were confined to the Chenopodiaceae, Caryophyllaceae and closely allied families. C. quinoa was the best local lesion assay host. Seedling clones of D. barbatus, selected as resistant to carnation mottle virus, proved the best indicator and propagation species. Up to 50 mg virus/kg tissue were obtained by butanol clarification followed by differential and density gradient centrifugation. The preparations contained a single sedimenting component, s_20w= 144S, and had flexuous filamentous particles, c. 790 times 12 run; the particles contained a single polypeptide, mol. wt 34800, and 5% of a single-stranded ribonucleic acid (RNA) with nucleotide base ratios of G21: A25: C25: U29. Serologically CarVMV was related distantly to turnip mosaic (cabbage black ring strain), pea mosaic, watermelon mosaic (Strain 2) and bean yellow mosaic viruses, more closely to pepper veinal mottle virus, but unrelated to twelve other potyviruses. CarVMV is not at present a danger to carnation crops in Britain, but the recent trend of sending carnation plants to overwinter outdoors in warmer countries involves potential risks of more rapid spread by effective vector races of M. persicae.