Arabis Mosaic Nepovirus Research Articles

Development of parasite complexes in the ecosystem of the rose garden of the main Botanical Garden of the Russian Academy of Sciences

The article reports on studies (2011-2022) monitoring harmful organisms in the ecosystem of the rose garden of the Main Botanical Garden of the Russian Academy of Sciences. The studies yielded data on the detection of pathogens and pests, as well as the phenotypic manifestation of pathologies and lesions. A total of 21 species of pathogens and 16 species of phytophages were identified. The species composition of harmful organisms in the ecosystem of the rose garden was defined. It is shown that at the initial stage (2011- 2013) of ecosystem establishment, no external signs of viral diseases were observed, and a low level of fungal infections was noted. The development of such harmful pathogens as Peronospora sparsa Jacz., Sphaerotheca pannosa Lev., Phragmidium disciflorum James, and Ph. tuberculatum Mull. was controlled by culling plants of susceptible varieties. The predominant pathogens included Marssonina rosae (Lib.) Died., Phyllosticta rosae Desm., and Septoria rosae Desm., and the susceptibility of specific varieties to these pathogens was established. The populations of pathogens causing spot anthracnose (Sphaceloma rosarum Pass.), ascochyta leaf spot (Ascochyta rosicola Sacc.), and cercospora leaf spot (Cercospora rosicola Pass.) were slightly less common. A wide range of signs of viral infections was identified. Nine viruses belonging to five genera were detected. The frequency of their occurrence was analyzed, and the most common viruses were identified: Prunus necrotic ring spot ilarvirus, Apple mosaic ilarvirus, Tobacco ring spot nepovirus, and Arabis mosaic nepovirus. The species diversity of phytophages was noted: leaf beetles, snout beetles, leafroller moths, sawflies, blossom weevils, earwigs, moths, leafhoppers, aphids, and true bugs. It was found that damage to plants by a range of pests reached only an average level, except for individual varieties (Red Blanket and Prosperity). In general, the phytosanitary assessment of the rose gene pool of the garden according to the phytosanitary monitoring and integrated detection revealed a wide range of parasite complexes: fourteen types of pathogenic complexes, four types of entomological complexes, and five types of entomopathogenic complexes. The tactical and basic directions for control of harmful organisms in the ecosystem of the rose garden are discussed.

Immune status of flower-ornamental plants in the collections of the Main Botanical Garden (Viral and Fungal Pathogens)

The article presents the results of studies to assess the resistance of a number of ornamental crops to viral and fungal pathogens. The objects were collections of Phlox L., Paeonia L., Dahlia L.; pathogens of powdery mildew phlox (Erysiphe cichoracearum D. C. f. phlogis Jacz.), cladosporiosis (Cladosporium paeoniae Pass.) and rust (Cronartium fl accidum (Alb. et Schw.) Wint.) peony, dominant viruses in the gene pool of these cultures. As a result of the conducted studies, it was found that the nature of interaction with pathogens at the level of plant varieties and genotypes is realized differentially. Phlox L. varieties have been isolated. with a medium and high level of resistance, and two immune varieties ‘Bright Eyes’ and ‘Karl Furst’ in conditions of a severe infectious background to Erysiphe cichoracearum D. C. f. phlogis Jacz., however, not all varieties have retained this property over the past 5 years. Two varieties have a decrease in the level of resistance, four varieties have lost this property, and three varieties have increased this property. Fife varieties with a high level of resistance to the complex of dominant viruses (Cucumber mosaic cucumovirus (CMV), Tobacco mosaic tobamovirus (TMV), Alfalfa mosaic alfamovirus (AMV), Arabis mosaic nepovirus (ArMV)) were identifi ed and 38 varieties were ranked according to the index of resistance to individual pathogens. In the Dahlia L. collection no virus-resistant varieties were found. Two out of five known viruses have been identifi ed within the Paeonia L. gene pool, to which 65% of varieties are resistant. Most varieties of Paeonia L. had weakly expressed resistance to the causative agent of Cladosporium paeoniae Pass. No varieties with a high level of resistance have been identified. Only 10 varieties susceptible to Cronartium flaccidum (Alb. et Schw.) Wint. were registered in the gene pool, 16 – medium-resistant and 30 – highly resistant. The article emphasizes the importance of finding sources of resistance and cultivating resistant varieties to harmful organisms as the safest method from the point of view of greening plant protection.

Mapping of the exchangeable and dispensable domains of the RNA 2-encoded 2AHP protein of arabis mosaic nepovirus

The N-terminal domains of the RNA 2-encoded 2AHP proteins of the arabis mosaic (ArMV) and grapevine fanleaf (GFLV) nepoviruses were shown to be highly variable and a hotspot for intra- and inter-species recombination events. Chimeric ArMV-NW clones in which the N-terminal domain of 2AHP or the entire 2AHP of GFLV isolates replaced the corresponding domains of ArMV retained their infectivity, showing that the 2AHP proteins of ArMV-NW and GFLV are exchangeable. ArMN-NW clones with deletions of the N-terminal, core, or C-terminal domains of the ArMV-NW 2AHP were infectious in Chenopodium quinoa although viral RNA (especially RNA 2) accumulated at reduced levels. In contrast, deletion of the entire 2AHP protein or of the C-terminal two thirds of the protein abolished infectivity of the ArMV-NW clones. These results suggest that multiple functional domains are distributed throughout the 2AHP protein and are essential for the accumulation of viral RNA 2.

In vitro and in vivo evidence for differences in the protease activity of two arabis mosaic nepovirus isolates and their impact on the infectivity of chimeric cDNA clones

Regulated processing of nepovirus polyproteins allows the release of mature proteins and intermediate polyproteins. Infectious cDNA clones of the mild NW isolate of arabis mosaic virus (ArMV) and chimeric clones incorporating RNA1 segments of Lv, a severe isolate, were generated. Clones containing the Lv X2–NTB cleavage site were not infectious unless the Lv protease was present. The Lv and NW X2–NTB cleavage sites differ at positions P6, P4 and P2. In vitro, processing at the X2–NTB site was undetectable or reduced in chimeric polyproteins containing the Lv X2–NTB site and the NW protease but was restored when both the Lv protease and X2–NTB site were present. In contrast, cleavage at this site was increased in polyproteins that contained the NW X2–NTB site and the Lv protease. These results show that the ArMV-Lv protease has greater activity and is active on a greater range of cleavage sites than that of ArMV-NW.

DETECTION AND ELIMINATION OF VIRUSES IN USDA HOP (HUMULUS LUPULUS) GERMPLASM COLLECTION

The United States Department of Agriculture (USDA), Agricultural Research Service (ARS) maintains a collection of Humulus germplasm at its National Clonal Germplasm Repository (NCGR) in Corvallis, Oregon, for the conservation and improvement of hop genetic resources. About 268 clonal accessions and seedlings are maintained as potted plants in a screen house. A ‘core’ subset of 84 genotypes is also maintained in vitro under cold storage. Clonal accessions were tested by ELISA for Apple mosaic ilarvirus (ApMV), Arabis mosaic nepovirus (ArMV), Hop latent carlavirus (HpLV), American hop latent carlavirus (AHLV), Hop mosaic carlavirus (HpMV), and Prunus necrotic ringspot ilarvirus (PNRV). Ninety-eight hop clones out of 200 were found to be virus infected. HpMV was the virus most commonly detected (67% of infected plants), followed by HpLV (51%), AHLV (50%), and ApMV (28%). ArMV and PNRV were not detected. More than 60% of infected accessions contained 2 or more viruses, and more than 25% contained 3 or more. Cultivars ‘Wye Target’, ‘Vojvodina’, ‘Shinsuwase’, ‘Cascade’ and ‘USDA 21119’ were infected with all 4 viruses. Alternating temperature heat-therapy and apical meristem culture were used to eliminate viruses from infected plants. Infected plants were grown for 2 weeks at temperatures alternating between 38°C and 30°C every 4 hours. Apical meristems 0.5mm or smaller were dissected and grown in vitro until large enough to transfer to soil in the glasshouse. Following a natural dormant period, plants were retested by ELISA. Of 182 plants regenerated from heat treated meristems, none tested positive in subsequent virus assays. Presently, the NCGR maintains 125 unique hop genotypes that have tested negative for all of these hop viruses.

Occurrence of nepoviruses in small fruits and fruit trees in Slovakia

A survey of nepoviruses in small fruits and fruit trees in thirteen localities of Slovakia was undertaken during the last three years. The samples of spontaneously infected small fruits and fruit trees with symptoms such as leaf yellowing, mottling, chlorotic spotting, vein clearing, chlorosis, dwarfing, and in some cases even plant dying, were analysed. Virus identification in collected samples from affected crops was performed by ELISA using polyclonal antibodies. The following quarantine nepoviruses were detected: Tobacco ringspot nepovirus, Tomato ringspot nepovirus, Tomato black ring nepovirus, Raspberry ringspot nepovirus, Cherry leafroll nepovirus and Arabis mosaic nepovirus. Screening of virus vector nematodes in the rhizosphere of infected plants was also undertaken. Three Longidorus (L. elongatus, L. picenus and L. leptocephalus) and four Xiphinema phytonematode species (X. vuittenezi, X. diversicaudatum, X. taylori and X. pachtaicum) were recorded in localities tested.

Complete nucleotide sequences of the RNAS 2 of German isolates of Grapevine fanleaf and Arabis mosaic nepoviruses

The RNAs 2 of an Arabis mosaic virus (ArMV) and a grapevine fanleaf virus (GFLV) isolate, originating from South West of Germany near Neustadt an der Weinstrasse (NW), were sequenced. They are 3820 and 3775 nucleotides long respectively, and both contain one open reading frame encoding a polypeptide of 1110 amino acids. Their 5′ non-coding regions contain conserved and repeated sequences, which are able to form stem-loop structures. Nucleotide sequence comparisons between the full-length RNAs 2 revealed homology levels of 84 and 82% between the ArMV-NW and the ArMV-L and -U, respectively, 90% between GFLV-NW and GFLV-F13, and 72% between ArMV-NW and GFLV-NW. Amino acid sequence comparisons showed that the greatest difference was found between the 2A proteins of the different ArMV isolates, the 2A protein of the ArMV-NW showing more similarity to the 2A protein of GFLV-NW than to those of ArMV-L2 or -U2.

Analysis of transgenic grapevine ( Vitis rupestris) and Nicotiana benthamiana plants expressing an Arabis mosaic virus coat protein gene

A disarmed LBA4404 strain of Agrobacterium tumefaciens harboring a binary vector which contained chimeric genes encoding the neomycin phosphotransferase ( npt II) and the coat protein (CP) of Arabis mosaic nepovirus (ArMV) was used in co-cultivation experiments with leaf discs of Nicotiana benthamiana and somatic embryos of the grapevine rootstock cultivar Vitis rupestris. Transgenic N. benthamiana expressing the ArMV CP gene were regenerated and six independent lines were characterized. Enzyme-linked immunosorbent assay (ELISA) performed on leaf tissue demonstrated the accumulation of the ArMV CP in five of the six lines analyzed. Immunosorbent electron microscopy (ISEM) studies revealed the presence of virion-like isometric particles (VLPs) reacting to a rabbit antiserum specific to ArMV virions. ArMV-CP expressing transgenic N. benthamiana lines showed protection against ArMV expressed as a delay in infection and a reduction of the percentage of infected plants. Four independent transgenic lines of V. rupestris transformed with the ArMV CP gene were regenerated and characterized. In contrast to N. benthamiana, transgenic V. rupestris did not accumulate the ArMV CP at levels detectable by ELISA and no VLPs could be observed by ISEM. Northern blot analysis showed that the ArMV CP mRNA was expressed at lower level in V. rupestris compared with N. benthamiana. The reason for this difference in transgene expression and/or mRNA stability between grapevine and N. benthamiana is unclear, but the genetic state of the transgene(s) (homozygous in N. benthamiana versus hemizygous in V. rupestris) may have an effect on gene expression.

003 Viruses Associated to Alstroemeria Varieties and Epidemiology of Tomato Spotted Wilt in the Cultivar Rosario

Viruses associated to eight Alstroemeria varieties and the relationship of thrips density and environmental factors with Tomato Spotted Wilt (TSW) intensity as well as the TSW effect on yield were studied in `Rosario' in Central Mexico. Using hosts range the viruses detected were Tomato Spotted Wilt Tospovirus (TSWV), Impatiens Necrotic Spot Tospovirus (INSV), Alstroemeria Mosaic Potyvirus (AlMV), Alstroemeria Streak Potyvirus (ASV), Arabis Mosaic Nepovirus (ArMV) and Cucumber Mosaic Cucumovirus (CMV). With serology, the presence of TSWV was confirmed in `Jubilee', `Rosario', and `Regina'; INSV in `Anabel', `Jubilee', and `Red Sunset'; and AlMV in `Rosario', `Red Sunset', `Rosita', `Yellow King', `Jubilee', and `Rojo Sangria'. TSWV and AlMV were found coinfecting `Rosario' plants. Five percent of plants were serologically positive to TSWV in the first flower harvest (25 Jan.-5 Apr.), 10% in the second (12 Apr.-21 June), and third (5 July-13 Sept.) and 18% in the last harvest (24 Sept.-6 Dec.). The highest peak density of thrips (520 to 630 individuals per sticky trap) were registered when the maximum temperature was higher than 35 °C and the relative humidity was between 40% to 60%. However, such peak density was not correlated with a significant increase of TSW incidence. Number and quality of inflorescences and the stem growth rate were significantly higher (P = 0.05) in plots with asymptomatic plants than that with plants showing putative symptoms of TSW.

001 Viruses Associated to Alstroemeria Varieties and Epidemiology of Tomato Spotted Wilt in cv. `Rosario'

Viruses associated to eight Alstroemeria varieties and the relationship of thrips density and environmental factors with Tomato Spotted Wilt (TSW) intensity as well as the TSW effect on yield were studied in `Rosario' in Central Mèxico. Using hosts range the viruses detected were Tomato Spotted Wilt Tospovirus (TSWV), Impatiens Necrotic Spot Tospovirus (INSV), Alstroemeria Mosaic Potyvirus (AlMV), Alstroemeria Streak Potyvirus (ASV), Arabis Mosaic Nepovirus (ArMV), and Cucumber Mosaic Cucumovirus (CMV). With serology it was confirmed the presence of TSWV in `Jubilee', `Rosario', and `Regina' varieties; INSV in `Anabel', `Jubilee', and `Red Sunset'; and AlMV in `Rosario', `Red Sunset', `Rosita', `Yellow King', `Jubilee'. and `Rojo Sangria'. TSWV and AlMV were found coinfecting `Rosario' plants. Five percent of plants were serologically positive to TSWV in the first flower harvest (25 Jan.-5 Apr.), 10% in the second (12 Ap.-21 June), and third (5 July-13 Sept.), and 18% in the last harvest (23 Sept.-6 Dec.). The highest peak density of thrips (520 to 630 individuals per sticky trap) were registered when the maximum temperature was higher than 35 °C and the relative humidity was between 40% to 60%. However, such peak density was not correlated with a significant increase of TSW incidence. Number and quality of inflorescences and the stem growth rate were significantly higher (P = 0.05) in plots with asymptomatic plants than that with plants showing putative symptoms of TSW.

Improved RNA Extraction from Woody Plants for the Detection of Viral Pathogens by Reverse Transcription-Polymerase Chain Reaction.

An efficient procedure for the extraction of high-quality RNA from woody plants without the use of phenol, organic solvents, or alcohol precipitation is described. The method employs commercially available spin-column matrices and mitigates the inhibitory effects of plant polysaccharides and polyphenolic compounds commonly observed on subsequent polymerase chain reaction amplification when conventional extraction methods are applied to woody plant species. The method described has been successfully used in the development of highly sensitive reverse transcription-polymerase chain reaction (RT-PCR) techniques for the detection of a number of viruses in their woody hosts. The viruses detected included apple stem grooving capillovirus (ASGV), apple stem pitting virus, Prunus necrotic ringspot ilarvirus (PNRSV), grapevine fanleaf and Arabis mosaic nepoviruses, and grapevine leafroll-associated closterovirus type 3. The method described was equally effective for the extraction of viral RNA from either budwood, leaves, or flower blossoms as determined by the equivalent RT-PCR detection of ASGV and PNRSV from these tissues. Detection of viral RNA in samples of total plant RNA prepared using this method was found to be as sensitive as was previously described for the immunocapture RT-PCR technique.

A damaging outbreak of arabis mosaic nepovirus in blackcurrant, the occurrence of other nepoviruses in Ribes species, and the demonstration that alfalfa mosaic virus is the cause of interveinal white mosaic in blackcurrant

Summary.In a crop of blackcurrant (Ribes nigrum), cv. Baldwin in Eire, chlorotic mottling and ringspot symptoms in leaves on plants and severe crop loss was associated with infection with arabis mosaic nepovirus (ArMV) and the presence in the soil of its nematode vector, Xiphinema diversicaudatum. This is only the second report of ArMV damaging a crop of blackcurrant. Tomato black ring (TBRV) and raspberry ringspot nepoviruses were detected in single plants of redcurrant (R. rubrum) in England and flowering currant (R. sanguineum) in Scotland respectively; each of these infected plants showed foliar chlorotic line‐pattern symptoms. This is the first record of TBRV in redcurrant. A single blackcurrant plant in New Zealand showing symptoms typical of those described for interveinal white mosaic disease, contained alfalfa mosaic virus (AMV). When AMV particles were purified and concentrated from herbaceous test plants and mechanically inoculated to young blackcurrant plants, several became infected with AMV and most infected plants developed systemic symptoms typical of the original disease. This provides the strongest evidence to date that AMV is the causal agent of interveinal white mosaic disease.

The 119 kDa and 124 kDa polyproteins of arabis mosaic nepovirus (isolate S) are encoded by two distinct RNA2 species.

Arabis mosaic virus (ArMV) is a nepovirus that is serologically distantly related to grapevine fanleaf virus (GFLV). Both ArMV and GFLV induce grapevine degeneration disease. Several ArMV isolates, unlike isolates of GFLV, produce upon in vitro translation of RNA2 a polyprotein (P2) that forms a double band in polyacrylamide-SDS gels. Cloning of full-length copies of RNA2 of an ArMV isolate from grapevine (ArMV-S) revealed that this isolate contained two RNA2s of different length, called RNA2-U and RNA2-L. The two species were not readily separated by electrophoresis of the virion RNA under denaturing gel electrophoresis conditions but could be distinguished by analysis of primer extension and in vitro translation products. The size difference of the two RNA2s is due mostly if not exclusively to differences in their coding regions. The 124 kDa RNA2-U-encoded polyprotein P2' and the 119 kDa RNA2-L-encoded polyprotein P2", which co-migrate, respectively, with the upper and lower polyprotein bands produced by RNA2 of ArMV-S, were more than 95% identical except in their N-terminal domains. In vitro maturation experiments and sequence comparisons indicate that the N-terminal products of P2' and P2" have a molecular mass of 31 kDa and 26 kDa. The genomic organization proposed is similar to that of GFLV RNA2.

The persistence and spread of Xiphinema diversicaudatum in cultivated and uncultivated biotopes

SummaryThe distribution of Xiphinema diversicaudatum in an uncultivated woodland habitat in England and a cultivated soil in Scotland, was re‐investigated in 1991 after an interval of 30 and 24 years, respectively. In the undisturbed habitat, nematodes had a distribution similar to that in 1961 but with a lower population density. In the cultivated habitat, nematodes were aggregated in several discrete populations associated with the cultivation and change of cropping in the intervening years but had spread little further horizontally into the raspberry crop, planted in 1982. Although strawberry latent ringspot and arabis mosaic nepoviruses were present in 1966, only the latter virus was found in crop and weed plants in 1991.The X. diversicaudatum populations from the two locations were morphologically similar to each other and to other populations, including those used for a redescription of the species.

Transgenic resistance genes from nepoviruses: Efficacy and other properties

Abstract Evidence of RNA‐RNA recombination or transcapsidation was sought in transgenic tobacco (Nicotiana tabacum L. ‘Xanthi‐nc') containing the 3'‐non coding sequence (1.3 kb) from a birch isolate of cherry leaf roll nepovirus (CLRV). Following mechanical inoculation with a rhubarb isolate of the virus, no evidence of recombination was obtained using polymerase chain reactions whether the transgenic gene produced transcripts in the sense or the antisense orientation. Transgenic tobacco containing the CLRV‐derived sequence (in either orientation) did not lessen the pathological effects of the rhubarb isolate of the virus althdugh there was amelioration of the disease caused by the birch isolate. When expressed as a transgenic gene in tobacco, the capsid coding sequence of arabis mosaic nepovirus (ArMV) lessened infectibility by nematodes carrying that virus. This construct did not influence the pathogenicity of potato virus Yo(PVY0), tobacco rattle tobravirus (PRN), alfalfa mosaic ilarvirus (A1MV), or CL...

The multiplication in plants of arabis mosaic virus satellite RNA requires the encoded protein.

Oligonucleotide-directed mutagenesis was used to create two mutations at each of three positions within the open reading frame (ORF) of a cDNA clone representing a satellite RNA from a lilac isolate of arabis mosaic nepovirus (ArMV). Three of the six mutants, in which stop codons were introduced at three different sites, did not direct synthesis of a translation product. The other three mutants, in which stop codons were not introduced, directed synthesis of a translation product (39K) although, in two of these, the mutation led to a single amino acid substitution. When Chenopodium quinoa plants were inoculated with in vitro transcripts from each of the six mutants together with the genomic RNA molecules (RNA-1 and RNA-2) of ArMV, progeny RNA was detected only with two of the three mutants in which the nucleotide changes did not introduce a stop codon to the coding region. To look for complementation, two deletion mutants were made. In these, 113 or 117 nucleotides were removed from two consecutive regions within the ORF. Two insertion mutants (in which the deleted sequences were replaced with a 130 nucleotide sequence from RNA-2 of cherry leaf roll nepovirus) were also made. Transcripts from none of these mutants retained messenger activity and none was detected either in C. quinoa plants or in virions, even in the presence of wild-type satellite RNA.

Cross-reacting and heterospecific monoclonal antibodies produced against arabis mosaic nepovirus.

Monoclonal antibodies (MAbs) were produced against arabis mosaic nepovirus (AMV). A hybridoma screening procedure was applied which involved the testing of culture supernatants, before the hybridomas were cloned to single cell lines, for their reaction with eight nepoviruses [AMV, cherry leafroll virus (CLRV), grapevine fanleaf virus (GFLV), peach rosette mosaic virus, raspberry ringspot virus (RRSV), tobacco ringspot virus, tomato black ring virus (TBRV) and tomato ringspot virus]. In addition to AMV-specific MAbs, this screening technique has allowed the selection of two cross-reacting MAbs: one reacting with AMV and GFLV, and one reacting with AMV and RRSV. This is the first report of MAbs cross-reacting with these nepoviruses. In addition, five heterospecific MAbs (HS-MAbs) could be selected: two reacting with RRSV, two with CLRV and one with TBRV. The usefulness of the screening technique that was applied for the selection of cross-reacting MAbs and HS-MAbs, and the potential use of such antibodies are discussed.

Arabis mosaic nepovirus coat protein in transgenic tobacco lessens disease severity and virus replication

SummaryTobacco plants expressing the coat protein of a lilac isolate of arabis mosaic virus (ArMV) poorly supported the replication of this virus and did not display any of the signs of systemic invasion produced in their untransformed counterparts or in transgenic plants expressing a different gene (β‐glucuronidase). These effects, were manifest whether the inoculum was virions or RNA. This is the first report of such coat protein protection with a nepovirus.

Biologically Active Transcripts of a Large Satellite RNA from Arabis Mosaic Nepovirus and the Importance of 5' End Sequences for its Replication

Synthetic transcripts of a satellite RNA associated with a lilac isolate of arabis mosaic nepovirus (ArMV) were made from cDNA clones. Transcripts having either six (M1R) or 29 (M3R) extra nucleotides at their 5' ends replicated in the presence of ArMV genomic RNA in manually inoculated Chenopodium quinoa plants, even though M1R also differs from the native sequence at nucleotide position 2. Transcript 12R, which has 11 guanosyl residues and 27 other nucleotides not present in the natural satellite RNA at its 5' end, and also lacks the two 5'-terminal nucleotides (UA), replicated inefficiently, both in transformed tobacco plants and in plants that had been manually inoculated. Transcripts from another construct (M2R) lacking eight 5'-terminal bases of the native sequence did not multiply in plants. Each of these transcripts directed the in vitro synthesis of a protein (Mr 39K) encoded by satellite RNA, although 12R was the least efficient message. Analysis of the 5'-terminal sequences in progeny RNA from M1R showed that the non-native bases were removed and the second nucleotide corrected, suggesting that VPg plus a few initial 5'-terminal bases might serve as a primer for plus-strand synthesis of this satellite RNA. When M1R was inoculated with genomic RNAs from ArMV of ash or ivy, the transcripts replicated and were encapsidated. However, when the same amounts of M1R were inoculated with genomic RNAs of ArMV from hop or sugar-beet, progeny of the transcripts were not detected either in virions or in plants. Less surprisingly, this RNA transcript did not multiply in the presence of dogwood mosaic, strawberry latent ringspot, grapevine fanleaf or cherry leaf roll nepoviruses.

A satellite RNA of arabis mosaic nepovirus and its pathological impact

SUMMARYThree RNA species were encapsidated in arabis mosaic nepovirus from lilac (ArMV‐L): the two genomic RNAs, RNA‐1 and ‐2, and an RNA‐3, Mr. 0.4 × 106. The genomic RNAs from ArMV‐L separated by gel electrophoresis from RNA‐3 were infectious and, during ten passages of this isolate (ArMV‐SF) RNA‐3 was not produced; only RNA‐1 and RNA‐2. When inoculated with the genomic species of ArMV‐L, or with those of other ArMV isolates, RNA‐3 replicated but did not do so in the absence of RNA‐1 and RNA‐2. The RNA‐3 did not share extensive regions of nucleotide sequences with the genomic RNAs but, like them, was polyadenylated and was linked to a protein (VPg) which did not seem essential for replication.When the pathogenicity of ArMV‐L and ArMV‐SF was compared in 42 plant species/cultivars representing 36 genera and 14 families, the following differences were observed: in three species of legume, disease progressed more rapidly when RNA‐3 was present but in species from five families, the presence of RNA‐3 was correlated with symptom amelioration. When RNA‐3 was present, the amounts of ELISA detected antigen were not consistently different in tip leaves of Nicotiana megalosiphon, Chenopodium amaranticolor, C. quinoa or Pisum sativum from those in leaves where RNA‐3 was absent.