Potato Virus T Research Articles

Commodity risk assessment of Ullucus tuberosus tubers from Peru.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as ‘High risk plants, plant products and other objects. This Scientific Opinion covers plant health risks posed by tubers of Ullucus tuberosus imported from Peru, taking into account the available scientific information, including the technical information provided by Peru. The relevance of an EU quarantine pest for this opinion was based on evidence that: (i) the pest is present in Peru, (ii) U. tuberosus is a host of the pest and (iii) the pest can be associated with the commodity. The relevance of any other pest, not regulated in the EU, was based on evidence that: (i) the pest is present in Peru (ii) the pest is absent in the EU; (iii) U. tuberosus is a host of the pest; (iv) the pest can be associated with the commodity and (v) the pest may have an impact and can pose a potential risk for the EU territory. There are five pests i.e. one insect (Amathynetoides nitidiventris), two nematodes (Atalodera andina and Nacobbus aberrans) and two viruses (the Andean potato latent virus (APLV) and the potato virus T (PVT)) that fulfilled all relevant criteria were selected for further evaluation. For the five pests, the risk mitigation measures proposed in the technical dossier from Peru were evaluated taking into account the possible limiting factors. For each of the five pests, an expert judgement is given on the likelihood of pest freedom taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. The degree of pest freedom varies among the pests evaluated, with PVT being the pest most frequently expected on the imported commodities. The Expert Knowledge Elicitation indicated, with 95% certainty, that between 9,157 and 10,000 tubers out of 10,000 would be free of PVT.

A novel tepovirus, Agave virus T, identified by the analysis of the transcriptome data of blue agave (Agave tequilana).

The genome sequence of a novel RNA virus was identified by analyzing transcriptome data obtained from the stem sample of a blue agave (Agave tequilana) plant. Sequence comparison and phylogenetic analysis showed that the RNA virus, Agave virus T (AgVT), was a new member of the genus Tepovirus in the family Betaflexiviridae. AgVT genome had three open reading frames: a 1605-amino acid (aa) replicase (REP), 355-aa movement protein (MP), and 220-aa coat protein (CP). Phylogenetic analyses based on the REP, MP, and CP sequences of AgVT, previously reported tepoviruses, and other Betaflexiviridae viruses revealed that tepoviruses could be classified into two subclades: "potato virus T (PVT)-clade" and "Prunus virus T (PrVT)-clade." PVT, the type species and founding member of the genus Tepovirus, belong to "PVT-clade" along with AgVT, while the other five tepoviruses belong to "PrVT-clade." The genome sequence of AgVT may be useful for studying the phylogenetic relationships between tepoviruses and other closely related viruses. Keywords: Agave virus T; Tepovirus; Betaflexiviridae; blue agave; Agave tequilana.

감자T바이러스 검정을 위한 RT-PCR 및 Nested PCR 진단시스템 개발

Potato virus T (PVT) is a plant pathogen in the family Betaflexiviridae, group IV single-stranded positive sense RNA viruses. The major host of PVT is potato, and it has been reported in Ullucus tuberosus, Oxalis tuberosa and Tropaeolum tuberosum. This study aimed at developing reverse transcription (RT)-polymerase chain reaction (PCR) and nested PCR techniques for specific detection of PVT. Finally, Two RT-PCR primer sets were developed and verified. The RT-PCR products were amplified to 734 (PVT RT-PCR primer set 6) and 828 bp (PVT RT-PCR primer set 29) long to detect PVT. The nested PCR primer sets [PVT-N70/C20 (734→315 bp) and PVT-N75/C30 (828→529 bp)] were developed which are high sensitivity and verification for detection of PVT. Furthermore, a modified-positive control plasmid is use to verify contamination of laboratory in PVT detection. This study supported the diagnose PVT in potato or PVT related hosts.

Characterization by Deep Sequencing of Prunus virus T, a Novel Tepovirus Infecting Prunus Species.

Double-stranded RNAs purified from a cherry tree collected in Italy and a plum tree collected in Azerbaijan were submitted to deep sequencing. Contigs showing weak but significant identity with various members of the family Betaflexiviridae were reconstructed. Sequence comparisons led to the conclusion that the viral isolates identified in the analyzed Prunus plants belong to the same viral species. Their genome organization is similar to that of some members of the family Betaflexiviridae, with three overlapping open reading frames (RNA polymerase, movement protein, and capsid protein). Phylogenetic analyses of the deduced encoded proteins showed a clustering with the sole member of the genus Tepovirus, Potato virus T (PVT). Given these results, the name Prunus virus T (PrVT) is proposed for the new virus. It should be considered as a new member of the genus Tepovirus, even if the level of nucleotide identity with PVT is borderline with the genus demarcation criteria for the family Betaflexiviridae. A reverse-transcription polymerase chain reaction detection assay was developed and allowed the identification of two other PrVT isolates and an estimate of 1% prevalence in the large Prunus collection screened. Due to the mixed infection status of all hosts identified to date, it was not possible to correlate the presence of PrVT with specific symptoms.

Tepovirus, a novel genus in the family Betaflexiviridae

Tepovirus is a new monotypic genus of plant viruses typified by potato virus T (PVT), a virus with helically constructed filamentous particles that are 640 nm long, previously classified as unassigned species in the family Betaflexiviridae. Virions have a single-stranded positive-sense polyadenylated RNA genome that is 6.5 kb in size, and a single type of coat protein with a size of 24 kDa. The viral genome contains three slightly overlapping ORFs encoding, respectively, the replication-related proteins (ORF1), a putative movement protein of the 30 K type (ORF2) and the coat protein (ORF3). Its structure and organization (number and order of genes) resembles that of trichoviruses and of citrus leaf blotch virus (CLBV, genus Citrivirus) but has a smaller size. Besides potato, the primary host, PVT can experimentally infect herbaceous hosts by mechanical inoculation. No vector is known, and transmission is through propagating material (tubers), seeds and pollen. PVT has a number of biological, physical and molecular properties that differentiate it from betaflexiviruses with a 30K-type movement protein. It is phylogenetically distant from all these viruses, but least so from grapevine virus A (GVA), the type member of the genus Vitivirus, with which it groups in trees constructed using the sequences of all of the genes.

Infection of capilloviruses requires subgenomic RNAs whose transcription is controlled by promoter-like sequences conserved among flexiviruses

The first open-reading frame (ORF) of apple stem grooving virus (ASGV), of the genus Capillovirus, encodes an apparently chimeric polyprotein containing conserved regions for replicase (Rep) and coat protein (CP). However, our previous study revealed that ASGV mutants with distinct and discontinuous Rep- and CP-coding regions successfully infect plants, indicating that CP expressed via a subgenomic RNA (sgRNA) is sufficient for viability of the virus. Here we identified a transcription start site of the CP sgRNA and revealed that CP translated from the sgRNA is essential for ASGV infection. We mapped the transcription start sites of both the CP and the movement protein (MP) sgRNAs of ASGV and found a hexanucleotide motif, UUAGGU, conserved upstream from both sgRNA transcription start sites. Mutational analysis of the putative CP initiation codon and of the UUAGGU sequence upstream from the transcription start site of CP sgRNA demonstrated their importance for ASGV accumulation. Our results also demonstrated that potato virus T (PVT), an unassigned species closely related to ASGV, produces two sgRNAs putatively deployed for the CP and MP expression and that the same hexanucleotide motif as found in ASGV is located upstream from the transcription start sites of both sgRNAs. This motif, which constituted putative core elements of the sgRNA promoter, is broadly conserved among viruses in the families Alphaflexiviridae and Betaflexiviridae, suggesting that the gene expression strategy of the viruses in both families has been conserved throughout evolution.

The complete nucleotide sequence of potato virus T

Potato virus T (PVT), a member of an unassigned species in the family Flexiviridae, has a genome 6,539 nt in size with three ORFs coding for replication-associated proteins (185 kDa, ORF 1), movement protein (40 kDa, ORF 2) and coat protein (24 kDa, ORF 3), respectively. PVT differs from the type members of all genera of the family Flexiviridae with a 30K-type movement protein and is phylogenetically distant from all of these viruses, least so from grapevine virus A (GVA, genus Vitivirus), with which it groups in all trees. The viral genome resembles that of trichoviruses but is smaller and does not contain the 3' terminal fourth ORF found in some members of this genus. PTV may represent a new genus of plant viruses for which the provisional name of Andesvirus is proposed.

한국에서의 감자 바이러스병 발생과 그 연구에 대한 고찰

The occurrence of potato(Sotanum tuberosum) viral diseases caused by Potato virus X(PVX), Potato virus Y (PVY), Potato leafroll virus(PLRV), Potato vims S(PVS), Potato virus M(PVM), Potato virus A(PVA), Potato virus T(PVT), Alfalfa mosic virus(AIMV), Tobacco mosic virus(TMV), Potato mop top virus(PMTV) Tobacco rattle virus(TRV) and Potato spindle tuber viroid(PSTVd), potato witches` broom phytoplasma, have been identified so far in Korea. Major viral diseases such as PVX, PVY and PLRV had been studied more deeply, however, the others are just identified and only partially characterized since the first study on the relation between PVX nucleic acid and virus protein by Kim in 1961. The most studies on potato viral diseases are mainly focused on the problems of seed potato production. The National Alpine Agricultural Experiment Station(NAAES), since it began its activities in 1961, has given special attention to this problem by doing studies to identify, characterize and control potato virus diseases. This effort resulted in the development of new potato virus detection methods as a basis for elaborating new method of control, such as the production of seed potato free of virus and the selection of new virus-resistant transgenic potatoes. The further studies of potato viral diseases required would be fallowings: the continuous monitoring for the occurrence of identified or not identified potato viruses in Korea, the isolation of resistant viral genes, the development of control method for the non-persistently transmitted viruses like PVY, special vectors such as nematode and fungus transmitted viruses, TRV and PMTV and the development of control methods against potato viral diseases by viral cross protection, therapy, transgenic plant, and the use of the agents or molecules, such as virus inhibitors and antiviral proteins, etc., blocking viral replication.

Other Natural Hosts of Potato virus T.

Potato virus T (PVT), a member of the genus Trichovirus, was isolated from leaves of naturally infected ulluco (Ullucus tuberosus), oca (Oxalis tuberosa), and mashua (Tropaeolum tuberosum). These Andean tuber crops are often grown in small plots in association with potato (Solanum tuberosum) in the Peruvian highlands. PVT isolates from ulluco, oca, mashua, and potato infected virus-free ulluco, oca, and potato genotypes by mechanical inoculation. The incidence of PVT in mashua, oca, and ulluco accessions from the International Potato Center (CIP) in vitro germplasm bank was less than 10%. A polymerase chain reaction (PCR) product of approximately 330 bp was obtained from each of the four isolates using primers designed from the published PVT sequence. Restriction enzyme digestions of the PCR product did not demonstrate variability.

A simple assay system incorporating monoclonal antibodies for the detection of potato virus T

Two monoclonal antibodies (McAbs) which react specifically with potato virus T (PVT) were produced and tested for cross reactivity with potato viruses (A, S, X, Yo, YN, leaf roll), apple stem grooving virus (ASGV) and against healthy sap. They were found to be highly specific for PVT. These two McAbs form the basis of an enzyme-linked immunosorbent assay (ELISA) for the detection of PVT in infected plant material which is of key significance for potato quarantine.

Interactions of the Solanum spp. of the Etuberosa group and nine potato‐infecting viruses and a viroid

SummaryAll 26 accessions of Solanum brevidens, one accession of S. etuberosum and one accession of S. fernandezianum tested were all extremely resistant to potato leafroll virus (PLRV) and potato viruses Y (PVY) and A (PVA). S. brevidens and S. etuberosum were also resistant to Andean potato mottle virus (APMV) and moderately resistant to potato virus X (PVX), whereas S. fernandezianum was susceptible to these viruses. Additionally, S. brevidens was resistant to sap‐inoculated potato viruses M (PVM) and S (PVS). All the Etuberosa accessions were susceptible by graft‐inoculation to PVM, PVS, potato virus T (PVT) and Andean potato latent virus (APLV). Infections by the above mentioned viruses were symptomless in all of the Etuberosa spp. S. etuberosum and S. fernandezianum were infected by mechanical inoculation with potato spindle tuber viroid, S. etuberosum developing severe stunting and leaf‐curl symptoms, but S. brevidens was infected only by graft‐inoculation.The genes conferring resistance to PVY and PVX in S. brevidens and S. etuberosum appeared to be different from those currently utilised by plant breeders.

Nucleotide Sequence of the 3'-Terminal Region of Potato Virus T RNA.

The partial sequence of the capillovirus potato virus T (PVT) RNA containing the 3′-terminal 2392 nucleotides, excluding the poly (A) tail, was determined from cloned cDNA. The sequence contains three open reading frames (ORFs) which encode putative proteins (in the 5′→3′ direction) of Mr>29, 000 (>29K; ORF 1), Mr 40, 451 (40K; ORF 2) and Mr 23, 596 (24K; ORF 3), followed by an untranslated region of 188 nucleotides upstream of the 3′ poly (A) tail. The 5′-proximal ORF 1 encodes a product with significant homologies to the C-terminal portions of the putative polymerase proteins of “alpha-like” supergroup of plant RNA viruses, including apple chlorotic leaf spot virus (ACLSV; closterovirus subgroup A), carlavirus, potexvirus and tymovirus. The PVT 24K protein shared several blocks of conserved amino acids with the coat proteins of filamentous viruses, i.e. ACLSV, beet yellows virus (BYV; closterovirus subgroup B), citrus tristeza virus (CTV; closterovirus subgroup C), potexvirus and carlavirus. The PVT 40K protein had homologies with putative movement proteins encoded by several plant viruses (e.g. ACLSV 50K protein). PVT and ACLSV showed a similar arrangement of three ORFs in the 3′-terminal region of their genomes. However, this arrangement differs significantly from that of BYV. The sequence represented here is the first report on the group capillovirus which was established recently. These results support a close relationship of PVT with ACLSV which is currently classified in the closterovirus subgroup A.

Detection of quarantine viruses of potato by ELISA

According to EC regulations, imported material of tuber‐forming Solarium spp. has to be tested for the absence of defined quarantine viruses. In order to allow an efficient and timesaving application of the quarantine inspection procedure, antisera have been developed and scrutinized for their use by the ELISA technique. The viruses concerned were Andean potato latent virus (APLV), Andean potato mottle virus (APMV), arracacha virus B oca strain (AVB‐O), potato virus T (PVT) and tobacco ringspot virus Andean potato calico strain (TRSV‐Ca). The results show that all viruses can be reliably detected by double‐antibody sandwich (DAS) ELISA. The detection limits were in the range ≤ 1–32 ng ml−1. The strain specificity by DAS‐ELISA of the antisera for APLV and APMV was overcome by mixing antisera from the different strains and strain groups, respectively. Strains C and Lm of APMV seemed to be serologically identical. A comparison of the suceptibility of several wild species of tuber‐forming Solanum with that of several cultivars of Solanum tuberosum showed a higher frequency of infection in the wild species.

Properties of RNAs and Proteins of Apple Stem Grooving and Apple Chlorotic Leaf Spot Viruses

Summary The particles of a Japanese isolate of apple stem grooving virus (ASGV) contained a single coat protein species with a mol. wt. of 27000 and a single RNA species with a mol. wt. of 2.30 × 106. The corresponding values for particles of a Japanese isolate of apple chlorotic leaf spot virus (ACLSV) were 22000 and 2.48 × 106, respectively. RNAs of both ASGV and ACLSV were plus-sense and polyadenylated. Four virus-specific dsRNA species [mol. wt. (× 10-6) 4.8, 4.3, 3.9 and 3.5] were detected in extracts of ASGV-infected plants, whereas three major [mol. wt. (× 10-6) 4.9, 4.3 and 3.9] and two minor (4.5 and 3.1) virus-specific dsRNAs were found in ACLSV-infected plants. The biochemical properties of ASGV closely resemble those of potato virus T (PVT) which supports the proposal that ASGV and PVT should be placed in a new virus group.

Tests for transmission of four potato viruses through potato true seed

SUMMARYThe Andean potato calico strain of tobacco ringspot virus (TRSV‐Ca) was detected in 2–9% of potato seedlings grown from true seed from plants of cv. Cara and clone G5998(6) infected with TRSV‐Ca. Similarly, a potato isolate of the oca strain of arracacha virus B (AVB‐O) was detected in 4–12% of progeny seedlings of cv. Cara and clone D42/8 infected with AVB‐O. Potato virus T (PVT) passed through 33–59% of seed from PVT‐infected cv. Cara, but only 0–2% infection was detected in seedlings from seed of PVT‐infected clone D42/8. By contrast, no infection was detected in seedlings grown from seed from plants of G5998(6), D42/8 or cv. Cara infected with Andean potato latent virus strains Hu (APLV‐Hu) or Caj (APLV‐Caj), although both strains passed through seed of Nicotiana clevelandii.AVB‐O, PVT and TRSV‐Ca were detected in all tests of pollen from flowers of infected potato plants, but APLV‐Hu and APLV‐Caj were detected less frequently. AVB‐O and PVT were transmitted through 2% and 8% respectively, of seed from healthy potato plants pollinated with pollen from infected plants. However, no transmission through seed was detected when pollen from TRSV‐Ca infected plants was used. None of the four viruses were transmitted to healthy potato plants pollinated with pollen from infected plants.APLV‐Hu caused exceptionally severe symptoms in the cv. Cara plants used for seed production, but the Bolivian strain of PVT induced only mild symptoms rather than the severe systemic necrosis previously reported for the type of strain of PVT in this cultivar. No symptoms developed in potato seedlings infected with TRSV‐Ca, AVB‐O or PVT through the seed.

Two previously undescribed potato viruses from South America.

THE proneness of potatoes (Solanum spp.) to virus diseases is well known, and about 20 viruses are recorded in naturally infected potatoes in Europe and North America1,2. Many of these viruses also occur in the Andean region of South America. For example, in Peru several well known viruses were detected3 in ‘basic seed’ stocks by inoculating sap to a range of indicator species and by serological tests. Some indicator plants in these tests, however, developed symptoms unlike those typical of previously described potato viruses. These symptoms were of two main types, necrotic local lesions and systemic necrosis in Chenopodium quinoa, and systemic necrosis and shoot distortion in Phaseolus vulgaris cv. Pinto or Sanilac. We describe here the characterisation of the virus isolates producing these effects. Two previously undescribed viruses were identified: we call them potato black ringspot virus (PBRV) and potato virus T (PVT).