Alstroemeria yellow spot virus (AYSV): a new orthotospovirus species within a growing Eurasian clade.

An orthotospovirus distinct from all other orthotospoviruses was isolated from naturally infected alstroemeria plants. Disease symptoms caused by this virus mainly consisted of yellow spots on the leaves based on which the name alstroemeria yellow spot virus (AYSV) was coined. A host range analysis was performed and a polyclonal antiserum was produced against purified AYSV ribonucleoproteins which only reacted with the homologous antigen and not with any other (established or tentative) orthotospovirus from a selection of American and Asian species. Upon thrips transmission assays the virus was successfully transmitted by a population of Thrips tabaci. The entire nucleotide sequence of the M and S RNA segments was elucidated by a conventional cloning and sequencing strategy, and contained 4797 respectively 2734 nucleotides (nt). Simultaneously, a next generation sequencing (NGS) approach (RNAseq) was employed and generated contigs covering the entire viral tripartite RNA genome. In addition to the M and S RNA nucleotide sequences, the L RNA (8865 nt) was obtained. The nucleocapsid (N) gene encoded by the S RNA of this virus consisted of 819 nucleotides with a deduced N protein of 272 amino acids and by comparative sequence alignments to other established orthotospovirus species showed highest homology (69.5% identity) to the N protein of polygonum ringspot virus. The data altogether support the proposal of AYSV as a new orthotospovirus species within a growing clade of orthotospoviruses that seem to share the Middle East basin as a region of origin.

Characterization of tomato apical stunt viroid isolated from a 24-year old seed lot of Capsicum annuum.

Tomato apical stunt viroid (TASVd) has been identified in a 24-year old seed lot of Capsicum annuum produced in Taiwan. It is the first finding of TASVd in this plant species. The isolate could be discriminated from all reported isolates of TASVd based on its nucleotide sequence, which showed only 94.8% identity with the most related genotype of TASVd. This discrimination was substantiated by phylogenetic analysis. Inoculation of a RNA extract of contaminated seeds to healthy pepper plants showed that the infectivity of the viroid had remained over time. Nevertheless, no transmission to seedlings was observed.

The complete nucleotide sequence of chrysanthemum stem necrosis virus.

The complete genome sequence of chrysanthemum stem necrosis virus (CSNV) was determined using Roche 454 next-generation sequencing. CSNV is a tentative member of the genus Tospovirus within the family Bunyaviridae, whose members are arthropod-borne. This is the first report of the entire RNA genome sequence of a CSNV isolate. The large RNA of CSNV is 8955 nucleotides (nt) in size and contains a single open reading frame of 8625 nt in the antisense arrangement, coding for the putative RNA-dependent RNA polymerase (L protein) of 2874 aa with a predicted Mr of 331 kDa. Two untranslated regions of 397 and 33 nt are present at the 5' and 3' termini, respectively. The medium (M) and small (S) RNAs are 4830 and 2947 nt in size, respectively, and show 99 % identity to the corresponding genomic segments of previously partially characterized CSNV genomes. Protein sequences for the precursor of the Gn/Gc proteins, N and NSs, are identical in length in all of the analysed CSNV isolates.

Current status of viroid taxonomy.

Viroids are the smallest autonomous infectious nucleic acids known so far. With a small circular RNA genome of about 250-400 nt, which apparently does not code for any protein, viroids replicate and move systemically in host plants. Since the discovery of the first viroid almost forty-five years ago, many different viroids have been isolated, characterized and, frequently, identified as the causal agents of plant diseases. The first viroid classification scheme was proposed in the early 1990s and adopted by the International Committee on Taxonomy of Viruses (ICTV) a few years later. Here, the current viroid taxonomy scheme and the criteria for viroid species demarcation are discussed, highlighting the main taxonomic questions currently under consideration by the ICTV Viroid Study Group. The impact of correct taxonomic annotation of viroid sequence variants is also addressed, taking into consideration the increasing application of next-generation sequencing and bioinformatics for known and previously unrecognized viroids.

First Report of a 16SrIX Group ('Candidatus Phytoplasma phoenicium'-Related) Phytoplasma Associated with a Chrysanthemum Disease.

In November 2010, approximately 2% of the chrysanthemum (Chrysanthemum morifolium) cv. Paniz plants showed numerous small leaves in the top and stunting in a field collection of the National Research Center of Ornamental Plants in Mahallat, Iran. Next to these plants, some plants of the same collection showed leaves with a reddish and/or chlorotic discoloration around the veins. The observed symptoms were believed to represent infection by a phytoplasma and/or a viroid. Two plants with each type of the symptoms were individually analyzed. Using a total RNA extract from diseased leaves, RT-PCR with primer pairs targeting all known pospiviroids, including Chrysanthemum stunt viroid (CSVd) (3), were negative. Purified DNA was examined for the highly conserved phytoplasma 16S rRNA gene by nested-PCR using the universal primer sets P1/P7 and R16F2n/R16R2 (2). Fragments of 1.2 kb, obtained only from the plants with the small leaves and stunting, were sequenced and one of these sequences, which were identical, was deposited in GenBank (Accession No. KC176800). BLAST analysis of the chrysanthemum phytoplasma sequence exhibited 99% identity to Candidatus Phytoplasma phoenicium (Ca. P. phoenicium) species of the 16SrIX group. Subsequently, in silico RFLP analysis of the nested PCR product with the pDRAW32 program using AluI and TaqI restriction sites used for 16SrIX subgroups A, B, C, D, and E indicated that the 16SrIX chrysanthemum isolate belonged to subgroup D (1). Recently, based on GenBank sequences, several strains of Ca. P. phoenicium have been isolated and identified from diverse host species like Lactuca serriola, L. sativa, Solanum lycopersicon, Sonchus sp. [16SrIX-E], Carthamus tinctorius, and Prunus amygdalus [16SrIX-B] (4) in Iran. The vector species transmitting Ca. P. phoenicium to C. morifolium still needs to be identified. The leafhopper Neoaliturus fenestratus may be a potential vector as it is an often encountered efficient transmitter vector of 16SrIX group phytoplasmas in Iran (2). Next to the susceptibility of chrysanthemum to members of aster yellows, stolbur, and Ca. P. aurantifolia phytoplasma groups, this is, to our knowledge, the first report of a 16SrIX group member infecting chrysanthemum. The detection of this phytoplasma in chrysanthemum can form a new threat to this crop and other ornamentals in the Mahallat flower production region. References: (1) R. E. Davis et al. New Dis. Rep. 20:35, 2010. (2) M. Salehi et al. Plant Pathol. 56:669, 2007. (3) J. Th. J. Verhoeven et al. Eur. J. Plant Pathol. 110:823, 2004. (4) M. G. Zamharir. Afr. J. Microbiol. Res. 5:6013, 2011.

Mexican papita viroid and tomato planta macho viroid belong to a single species in the genus Pospiviroid.

Tomato planta macho viroid (TPMVd) and Mexican papita viroid (MPVd) are two closely related (>90% sequence identity) members of the genus Pospiviroid. Their current status as members of separate species is based upon the reported ability of TPMVd to replicate in Gomphrena globosa and the inability of this viroid to evoke flower break in N. glutinosa. Characterization of a viroid recently isolated from diseased tomato plants grown in Mexico (identical to GenBank accession GQ131573) casts doubt on this earlier report and indicates that these viroids should be classified as members of a single species. Giving priority to the older name, we propose including both of these viroids in the current species Tomato planta macho viroid.

High stability of original predominant pospiviroid genotypes upon mechanical inoculation from ornamentals to potato and tomato.

Eleven pospiviroid isolates from ornamental plants and one from pepper were successfully transmitted to potato and tomato by mechanical inoculation. All isolates with characteristic predominant genotypes were inoculated to a series of potato and tomato plants and propagated for up to four passages. In total, 385 nucleotide sequences were determined, in which 17 new predominant genotypes were identified with minimal differences to the original predominant genotype. In addition, in the original ornamental hosts, only one of eleven predominant pospiviroid genotypes had changed during the experiments over a period of 2 years. These results confirm the high stability of predominant pospiviroid genotypes.

A distinct tospovirus causing necrotic streak on Alstroemeria sp. in Colombia.

A tospovirus causing necrotic streaks on leaves was isolated from Alstroemeria sp. in Colombia. Infected samples reacted positively with tomato spotted wilt virus (TSWV) antiserum during preliminary serological tests. Further analysis revealed a close serological relationship to tomato chlorotic spot virus (TCSV) and groundnut ringspot virus (GRSV). A major part of the S-RNA segment, encompassing the nucleocapsid (N) protein gene, the 5' untranslated region and a part of the intergenic region 3' of the N gene, was cloned and sequenced. The deduced N protein sequence showed highest amino acid identity (82%) to that of TCSV, indicating that the virus represents a new tospovirus species, for which the name Alstroemeria necrotic streak virus (ANSV) is coined. Phylogenetic analysis based on the N protein sequence revealed that this Alstroemeria-infecting tospovirus clustered with tospoviruses from the American continent. Frankliniella occidentalis was identified as potential vector species for ANSV.

First Report of Iresine viroid 1 in Celosia plumosa in the Netherlands.

In 2008, in the framework of surveying for pospiviroids, nine symptomless clones of Celosia plumosa (Voss) Burv. (Amaranthaceae) from a Dutch breeding company were tested by reverse transcription (RT)-PCR with primer sets Pospi1-RE/FW and Vid-RE/FW (4). In four samples, amplicons of 227 nt were obtained with primers Pospi1-RE/FW. Sequencing of the amplicons showed identities of more than 99% to the partial sequence of Iresine viroid 1 (IrVd-1) from Alternanthera sessilis, NCBI GenBank Accession No DQ846886 (2). Subsequently, a set of primers was designed to amplify the complete viroid genome, i.e., IrVd-FW1 5'-GCG GAA GAA ACA GGA GCT CGW CT-3' and IrVd-RE1 5'-CGC GWG GAG TTC TCC GGT CTT TA-3' - identical to nt 168 to 190 and 145 to 167 of the complete IrVd-1 sequences in the NCBI GenBank (Nos. DQ094293, DQ094294, NC_003613, and X95734). One isolate from C. plumosa was amplified with this primer pair and amplicons were cloned into the pGEM-T Easy Vector System II. Sequencing of one individual cDNA clone (GenBank Accession No. GU911350) revealed a genome size of 370 nt and 98.1% sequence identity to the IrVd-1 isolate from Vinca major, GenBank Accession No. DQ094293 (1). Hence, the viroid was identified as IrVd-1. The isolate from C. plumosa was also mechanically inoculated to 10 healthy plants of C. plumosa, chrysanthemum (Chrysanthemum × morifolium) cv. White Delianne, potato (Solanum tuberosum) cv. Nicola, and tomato (Solanum lycopersicum) cv. Moneymaker. No symptoms were observed over a 6-week period, and RT-PCR with primers Pospi1-RE/FW on bulked samples of five plants per species only identified IrVd-1 in both samples of C. plumosa. For tomato, these results confirm those of Spieker (3). Therefore, in contrast to the other pospiviroids, it seems unlikely that IrVd-1 poses a threat to potato and tomato. References: (1) X. Nie et al. Can. J. Plant Pathol. 27:592, 2005. (2) R. P. Singh et al. Plant Dis. 90:1457, 2006. (3) R. L. Spieker. J. Gen. Virol. 77:2631, 1996. (4) J. Th. J. Verhoeven et al. Eur. J. Plant Pathol. 110:823, 2004.

First Report of Tomato apical stunt viroid in the Symptomless Hosts Lycianthes rantonnetii and Streptosolen jamesonii in the Netherlands.

In 2009, in the framework of surveying for pospiviroids, samples of various ornamental plants from the Netherlands were tested by reverse transcription (RT)-PCR with the primer pairs Pospi1-RE/FW and Vid-RE/FW (2). With primer pair Pospi1-RE/FW, amplicons of the expected size were obtained in two samples of symptomless plants of Lycianthes rantonnetii and Streptosolen jamesonii. Sequencing of the amplicons, which were expected to correspond with partial pospiviroid genomes, showed identities of 100 and 98% to the sequence of Tomato apical stunt viroid (TASVd), NCBI GenBank Accession No. AM777161 (3). For the amplification of the complete viroid genomes, RT-PCRs were performed with primer pair CEVd-FW/RE (1). Sequencing of these amplicons yielded sequences of 364 nt and identities to TASVd AM777161 of 100 and 98.1%, respectively. Therefore, both isolates were identified as TASVd. The sequence variant from S. jamesonii was submitted to the NCBI GenBank as No. GU911351. In addition, both isolates were mechanically inoculated to four tomato plants (Solanum lycopersicum) of cv. Moneymaker. All inoculated plants developed chlorosis and growth reduction after 4 weeks and TASVd infections were confirmed in a bulked sample by RT-PCR with primer pair CEVd-FW/RE after 6 weeks. Hence, two more ornamental host plant species have been identified that may act as symptomless sources of pospiviroid inoculum. References: (1) N. Önelge. Turk. J. Agric. For. 21:419, 1997. (2) J. Th. J. Verhoeven et al. Eur. J. Plant Pathol. 110:823, 2004. (3) J. Th. J. Verhoeven et al. Plant Dis. 92:973, 2008.

First Report of Tomato chlorotic dwarf viroid in Greenhouse Tomatoes in Arizona.

Tomato chlorotic dwarf viroid (TCDVd), a member of the genus Pospivroid, family Pospiviroidae, was first identified on greenhouse tomato (Solanum lycopersicum) in Canada (2). Since then, it has also been reported elsewhere, e.g., on tomato in Colorado (4). During 2006 in Arizona, tomato plants in a large greenhouse facility with continuous tomato production exhibited viroid-like symptoms of plant stunting and chlorosis of the young leaves. Symptomatic plants were often located along the edge of the row, indicating the presence of a mechanical transmissible agent. Approximately 4% of the plants in this greenhouse were symptomatic in 2008. Symptoms were distinctly different from those caused by Pepino mosaic virus (PepMV), a virus that was generally present in this greenhouse and also in our test samples. Other commonly occurring tomato viruses were ruled out by serological, PCR, or reverse transcription (RT)-PCR tests in multiple laboratories. RT-PCR with two sets of universal pospiviroid primers, PospiI-FW/RE and Vid-FW/RE (4), yielded amplicons of the expected sizes of 196 and 360 bp in three samples collected from symptomatic plants. Direct sequencing of the amplicons revealed that the genome was 360 nt and 100% identical to the type TCDVd from Canada (GenBank Accession No. AF162131) (2). Mechanical inoculation with leaf tissue extract from four samples to plants of the tomato 'Money-Maker' resulted in the same viroid-like symptoms and TCDVd was confirmed in these plants by RT-PCR and sequencing. In both 2007 and 2008, 18 samples were tested using primers PSTVd-F and PSTVd-R (1), which are capable of amplifying the full TCDVd genome. Analysis of the sequences from the amplicons revealed two genotypes of TCDVd. The first genotype (GenBank Accession No. FJ822877) was identical to the type TCDVd and found in 11 samples from 2007 and one from 2008. The second genotype (GenBank Accession No. FJ822878) was 361 nt, differing from the first by nine nucleotide substitutions, 2 insertions, and 1 deletion. This second genotype was found in 7 and 17 samples from 2007 and 2008, respectively, and showed the highest sequence identity (97%) to a Japanese tomato isolate (AB329668) and a much lower sequence identity (92%) to a U.S. isolate previously identified in Colorado (AY372399) (4). The origin of TCDVd in this outbreak is not clear. The genotype identified first could have been introduced from a neighboring greenhouse where the disease was observed before 2006 and where this genotype also was identified in 2007. The second genotype may have been introduced from infected seed since TCDVd has recently been shown to be seed transmitted in tomato (3). To our knowledge, this is the first report of natural occurrence of TCDVd in Arizona. References: (1) A. M. Shamloul et al. Can. J. Plant Pathol. 19:89, 1997. (2) R. P. Singh et al. J. Gen. Virol. 80:2823, 1999. (3) R. P. Singh and A. D. Dilworth. Eur. J. Plant Pathol. 123:111, 2009. (4) J. Th. J. Verhoeven et al. Eur. J. Plant Pathol. 110:823, 2004.

First Report of Potato spindle tuber viroid in Cape Gooseberry (Physalis peruviana) from Turkey and Germany.

Since the recent identification of Potato spindle tuber viroid (PSTVd) in vegetatively propagated ornamental plant species (4), many growers have asked to have their mother plants tested for this viroid. In December of 2007, a grower from Turkey submitted cuttings of cape gooseberry (Physalis peruviana) to be tested for PSTVd. Initial testing by real-time reverse transcription (RT)-PCR according to Boonham et al. (1) indicated the presence of either Mexican papita viroid, PSTVd, or Tomato chlorotic dwarf viroid in four samples. To identify the viroid(s) present, isolated RNA from these samples was used for RT-PCR (2), and products of the expected full genome size for the three viroids were amplified from each sample. One of the PCR products was sequenced (GenBank Accession No. EU862230) and analysis of the 357 nt sequence indicated it was most related to PSTVd sequences belonging to the so-called 'Oceanian' strain of the viroid (3), with 99.7% identity to GenBank Accession No. AY962324. Therefore, the viroid was identified as PSTVd. Pathogenicity of this PSTVd genotype was demonstrated when 4 weeks after mechanical inoculation with sap extracts seedlings of tomato cv. Money-maker showed the expected viroid symptoms of chlorosis and stunting, and the presence of the viroid in these plants was confirmed by RT-PCR (2). In March of 2008, by use of RT-PCR (2) and sequencing of the PCR product (GenBank Accession No. EU862231), PSTVd was identified in young seedlings of P. peruviana from a German grower. The German isolate differed at only three nucleotide positions from the Turkish isolate. The identification of PSTVd in young seedlings indicates that seeds had been source of infection, whereas in the case of the PSTVd infected cuttings from Turkey, the infection originated from infected mother plants. To our knowledge, these are the first reports of PSTVd in P. peruviana. Although infected P. peruviana plants did not show symptoms, they might act as sources of inoculum for crops like potato and tomato, which may suffer serious damage. References: (1) N. Boonham et al. J. Virol. Methods 116:139, 2004. (2) A. M. Shamloul et al. Can. J. Plant Pathol. 19:89, 1997. (3) J. Th. J. Verhoeven et al. Eur. J. Plant Pathol. 110:823, 2004. (4) J. Th. J. Verhoeven et al. Plant Pathol. 57:399, 2008.

First Report of Tomato yellow leaf curl virus in Tomato in the Netherlands.

Tomato yellow leaf curl virus (TYLCV) is an economically important virus with tomato (Solanum lycopersicum L.) as its main host. The virus is widely distributed in subtropical areas and is transmitted by the tobacco whitefly (Bemisia tabaci) in a persistent manner. TYLCV has a quarantine status (IIAII) in the European Union (EU directive 2000/29/EC). It was not previously recorded in the Netherlands. In September 2007, symptoms were observed in tomato crops in a few greenhouses located in close proximity from each other in the western part of the Netherlands. Infected plants showed TYLCV-like symptoms, i.e., stunting, leaf curl, and marginal and interveinal chlorosis. Similar symptoms were evoked after grafting symptomatic tips onto healthy tomato seedlings, whereas no viruses were transmitted by mechanical inoculation to herbaceous test plants. Extracted DNA from symptomatic leaves was used in PCR with two sets of primers for universal detection of begomoviruses (1,2). Analysis of the overlapping amplified products revealed the highest identity to isolate TYLCV-Alm (GenBank Accession No. AJ489258) from Almeria, Spain. To amplify the remaining 60% of the virus genome, three additional primer sets were designed: TYLCV965F 5'-GGCAGCCAAGTACGAGAACC-3' and TYLCV1736R 5'-CCACTATCTTCCTCTGCAATCC-3'; TYLCV1598F 5'-TACTTGCGAACAGTGGCTCG-3' and TYLCV2282R 5'-TCCAAATCGATGGCAGATCAG-3'; TYLCV2229F 5'-ATGCGTCGTTGGCAGATTG-3' and TYLCV68R 5'-CAGTGACGTCTGTGGAACCCT-3'. Analysis of the five overlapping PCR products of one isolate revealed a total virus genome of 2,781 nucleotides. The complete sequence of the Netherlands Isolate (GenBank Accession No. FJ439569) showed 99.3% nucleotide identity to isolate TYLCV-Alm (AJ489258), and therefore, the virus was identified as TYLCV-Alm. After the initial identification, a survey was conducted in all tomato crops in a surrounding area of approximately 40 km2. TYLCV was found in 19 of 27 cultivations. The identity of one isolate per cultivation was confirmed by sequence analysis of the products obtained with the Wyatt and Brown primers (2) occasionally in combination with the Deng primers (with 99.1 to 100% and 99.2 to 100% nucleotide identity to the Netherlands isolate [FJ439569], respectively) (1). As many as 25 symptomatic plants were recorded per greenhouse. A subsequent survey of 34 randomly selected tomato growers in other areas of the country revealed no further infections. Results of the sequence analyses and surveys suggested that the outbreak resulted from a single introduction of the virus, whereas the insect vector B. tabaci accounted for local spread. Measures taken to eliminate the virus included the removal and subsequent destruction of infected tomato plants as well as eradication of B. tabaci. No TYLCV infections were found during surveys in 2008, and therefore, it is believed that the virus was eradicated effectively. References: (1) D. Deng et al. Ann. Appl. Biol. 125:327, 1994. (2) S. D. Wyatt and J. K. Brown. Phytopathology 86:1288, 1996.

First Report of Solanum jasminoides Infected by Citrus exocortis viroid in Germany and the Netherlands and Tomato apical stunt viroid in Belgium and Germany.

Recent identifications of Chrysanthemum stunt viroid (CSVd) and Potato spindle tuber viroid (PSTVd) in Solanum jasminoides (3,4) prompted the testing of this plant species for infections with other pospiviroids. From autumn of 2006 to spring of 2007, samples from symptomless plants of S. jasminoides were collected in Belgium (3 samples ranging from 75 to 150 plants), Germany (3 samples ranging from 1 to 200 plants), and the Netherlands (3 samples ranging from 2 to 200 plants). Samples were tested for pospiviroids by reverse transcription (RT)-PCR assays using the Pospi1-FW/RE and Vid-FW/RE (2) and PSTV-Nb-FW (5'-ggatccccggggaaacctgga-3')/RE (5'-ggatccctgaagcgctcctcc-3') primer sets. Each set amplifies several but not all pospiviroids. The first and last primer sets amplified PCR products from six samples. The full-length genomes of all six isolates were amplified using primer pairs CEVd-FW1/RE1 (1) and CEVd-FW2 (5'-gtgctcacctgaccctgcagg-3')/RE2 (5'-accacaggaacctcaagaaag-3'), which are fully complementary to both Citrus exocortis viroid (CEVd) and Tomato apical stunt viroid (TASVd). Sequence analysis of the PCR products identified CEVd from two samples each from Germany and the Netherlands and TASVd from one sample each from Germany and Belgium (plants were imported from Israel). Although the sequences of the different CEVd isolates from S. jasminoides were not identical, all exhibited more than 95% identity with a CEVd isolate from Vicia faba (GenBank Accession No. EF494687). Both TASVd sequences were identical and showed 99.2% identity to a TASVd isolate from tomato (GenBank Accession No. AY 062121). Two nucleotide sequences of CEVd were submitted to the NCBI GenBank (Accession Nos. EU094207 and EU094208). The two other CEVd sequences and the TASVd sequence were submitted to the EMBL Nucleotide Sequence Database as Accession Nos. AM774356, AM774357, and AM777161. In addition to identification from S. jasminoides by sequence analysis, TASVd infection in the S. jasminoides sample from Germany and CEVd in one sample from the Netherlands was confirmed by mechanical inoculation to tomato followed by RT-PCR using the two CEVd-FW/RE primer pairs and analysis of the sequenced PCR product. Infection by CEVd and TASVd was also confirmed in the German samples by Northern hybridization and TASVd was confirmed in the Belgian sample by return-polyacrylamide gel electrophoresis. To our knowledge, these are the first reports of CEVd and TASVd in S. jasminoides. The viroids do not reduce the quality of S. jasminoides plants; however, the infected plants may act as infection sources for other crops. References: (1) N. Önelge. Turk. J. Agric. For. 21:419, 1997. (2) J. Th. J. Verhoeven et al. Eur. J. Plant Pathol. 110:823, 2004. (3) J. Th. J. Verhoeven et al. Plant Dis. 90:1359, 2006. (4) J. Th. J. Verhoeven et al. Plant Pathol. 57:399, 2008.

First Report of Potato spindle tuber viroid in Tomato in Belgium.

During August of 2006, a sample of a tomato plant (Solanum lycopersicum, formerly Lycopersicum esculentum) from a greenhouse in Belgium was received for diagnosis. The plant showed severe growth reduction and the young leaves were chlorotic and distorted. In the greenhouse, the disease had been spreading slowly along the row. These observations suggested the presence of a viroid infection, and reverse transcriptase (RT)-PCR with two sets of universal pospiviroid primers (Pospi1-RE/FW and Vid-FW/RE; 3) yielded amplicons of the expected size (approximately 196 and 360 bp). Sequence analysis of the larger PCR product revealed that the genome was 358 nt and 100% identical to two isolates of Potato spindle tuber viroid (PSTVd) previously submitted to the NCBI GenBank (Accession Nos. AJ583449 from the United Kingdom and AY962324 from Australia). A pathogen associated with the symptomatic tomato plants was therefore identified as PSTVd. Tracing the origin of the infection revealed the following information: during November of 2005, 8-day-old tomato seedlings raised from seed by a Dutch nursery were transferred to a small part of the greenhouse of the Belgian grower; 7 to 8 weeks later, the plants were transplanted to their final destination; during May of 2006, the grower first observed growth reduction in a single plant; several weeks later, similar symptoms were observed in two more plants in the same row close to the first symptomatic plant; and by September, there were approximately 20 symptomatic tomato plants, all located in two adjacent rows. The viroid outbreak was fully eradicated by destroying all tomato plants in the affected rows as well as in two adjacent rows at both sides. The absence of further infections was confirmed by testing approximately 1,200 tomato plants in pooled samples for PSTVd by RT-PCR (2) and real-time RT-PCR (1). The origin and the method of introduction and spread of the viroid remain unclear. References: (1) N. Boonham et al. J. Virol. Methods 116:139, 2004. (2) R. A. Mumford et al. Plant Pathol. 53:242, 2004. (3) J. Th. J. Verhoeven et al. Eur. J. Plant Pathol. 110:823, 2004.

First Report of Tomato chlorotic dwarf viroid in Petunia hybrida from the United States of America.

In November 2005, 13 accessions of Petunia hybrida from the United States of America entered the post-entry quarantine station of the Plant Protection Service in the Netherlands. The plants were inspected and tested for quarantine organisms according to Directives 95/44 and 97/46 of the European Union. No virus and viroid symptoms were observed in the imported plants or in mechanically inoculated plants of Chenopodium quinoa, Nicotiana benthamiana, and N. occidentalis-P1 (3). Testing for pospiviroids by return-polyacrylamide gel electrophoresis (1) and reverse transcriptase-PCR with universal pospiviroid primers Pospi1-RE/FW (2) indicated the presence of pospiviroids in 3 and 11 P. hybrida accessions, respectively. The 196-bp amplicons of six accessions were sequenced. Sequence analysis showed the highest identity for all amplicons to both isolates of Tomato chlorotic dwarf viroid (TCDVd) in NCBI GenBank, Accession Nos. AF162131and AY372399, from Canada and the United States, respectively. Additional RT-PCRs with the Pospi1-RE/FW primers in opposite order and the semi-universal pospiviroid primers Vid-RE/FW (2) for one isolate, followed by sequence analysis, confirmed the identity as TCDVd. The isolate consisted of 359 nucleotides (GenBank Accession No. DQ859013) and showed sequence identities of 98.6 and 96.1% to the Canadian and American tomato isolates of this viroid, respectively. The next highest sequence identity was 90.0% to two accessions of Potato spindle tuber viroid (GenBank Accession Nos. AJ593449 and AY962324). On the basis of these results, the viroid from P. hybrida was identified as TCDVd. To our knowledge, this is the first report of TCDVd in this plant species. Reference: (1) J. W. Roenhorst et al. EPPO Bull. 30:453, 2000. (2) J. Th. J. Verhoeven et al. Eur. J. Plant Pathol. 110:823, 2004. (3) J. Th. J. Verhoeven and J. W. Roenhorst. EPPO Bull. 33:305, 2003.

First Report of Potato virus M and Chrysanthemum stunt viroid in Solanum jasminoides.

In 2005, a plant of the ornamental crop Solanum jasminoides from the Netherlands was submitted for testing on viruses and viroids because of its intended use for propagation. Sap from this plant was mechanically inoculated to the test plant species Chenopodium quinoa, Nicotiana benthamiana, N. hesperis-67A, and N. occidentalis-P1 (3). N. hesperis-67A showed chlorotic local lesions and rugosity followed by vein necrosis, N. occidentalis-P1 showed necrotic local lesions and systemic leaf distortion, and the two other test plant species remained symptomless. Potato virus M (PVM) was identified by double antibody sandwich enzyme-linked immunosorbent assay using leaves from S. jasminoides and N. hesperis-67A. The plant of S. jasminoides was also tested for the presence of viroids by reverse transcriptase-polymerase chain reaction (RT-PCR) with universal pospiviroid primers Pospi1-RE/FW (2). This reaction yielded an amplicon of the expected size of 198 bp. The sequence showed 100% identity to an isolate of Chrysanthemum stunt viroid (CSVd; NCBI GenBank Accession No. AF394453). Subsequently, the complete sequence of our viroid isolate (GenBank Accession No. DQ406591) was determined from the amplicon obtained after RT-PCR using specific primers for the detection of CSVd (1). The viroid isolate from S. jasminoides consisted of 354 nucleotides and showed the highest identity (98.6%) to a chrysanthemum isolate of CSVd (GenBank Accession No. AB055974). Therefore, the viroid was identified as CSVd. To our knowledge, this is the first report of PVM and CSVd in S. jasminoides. Reference: (1) R. Hooftman et al. Acta Hortic. 432:120, 1996. (2) J. Th. J. Verhoeven et al. Eur. J. Plant Pathol. 110:823, 2004. (3) J. Th. J. Verhoeven and J. W. Roenhorst, EPPO Bull. 33:305, 2003.

First Report of Tomato apical stunt viroid in Tomato in Tunisia.

In May 2005, the Plant Protection Service in the Netherlands received two tomato (Lycopersicon esculentum) plant specimens for diagnosis from a protected crop production facility of 2.5 ha near Kebili in Tunisia. Growth of the plants was reduced and leaves were chlorotic and brittle. Ripening of the fruits was delayed and their storage life was reduced from 3 weeks to 1 week. The grower reported that initially only 5% of plants showed symptoms; however, the number of symptomatic plants increased quickly to 100% as a result of increasing temperatures in the production facility. Test plant species Chenopodium quinoa, Datura stramonium, Nicotiana glutinosa, N. hesperis-67A, N. occidentalis-P1, and L. esculentum 'Money-maker' were mechanically inoculated with sap from the affected plants. Symptoms including chlorosis and stunting were observed only on L. esculentum. Reverse transcriptase-polymerase chain reaction (RT-PCR) with universal pospiviroid primers Pospi1-RE/FW (2) yielded amplicons of the expected size (196 bp) for each of the two samples. One of these amplicons was sequenced and showed the highest identity to the four isolates of Tomato apical stunt viroid (TASVd) in the NCBI Gen-Bank. Subsequently, the complete sequence of the Tunisian isolate (Gen-Bank Accession No. DQ144506) was determined by sequencing the am-plicon obtained after RT-PCR using primers developed for the detection of Citrus exocortis viroid (CEVd) (1). The isolate consisted of 363 nucleotides and showed the highest sequence identity (96.7%) to tomato isolates of TASVd from Indonesia and Israel (GenBank Accession Nos. X06390 and AY062121, respectively), 92.6% to a tomato isolate from the Ivory Coast (GenBank Accession No. K00818), and 87.7% to an isolate from Solanum pseudocapsicum (GenBank Accession No. X95293). The next highest sequence identity was 81.5% to an isolate of CEVd (GenBank Accession No. X53716). On the basis of these results, the viroid was identified as TASVd. To our knowledge, this is the first report of TASVd in Tunisia. Reference: (1) N. Önelge. Turkish J. Agric. For. 21:419, 1997. (2) J. Th. J. Verhoeven et al. Eur. J. Plant Pathol. 110:823, 2004.

A pospiviroid from symptomless portulaca plants closely related to iresine viroid 1.

In symptomless plants of portulaca a potential new pospiviroid was characterized. Analysis by both double and return PAGE showed the presence of a circular RNA. RT-PCR and sequencing revealed a genome of 351 nt with properties characteristic of members of the genus Pospiviroid and with highest sequence identity (circa 80%) with iresine viroid 1 (IrVd-1). The circular RNA from portulaca was shown to replicate independently in its original host, thus showing that it is indeed a viroid. Based on its molecular characteristics, it should be considered a new species. However, since no biological differences have yet been found with its closest relative IrVd-1, the viroid from portulaca does not fulfil all criteria for species demarcation of the ICTV.

First Report of Pepper mottle virus in Tomato.

In 2000, a breeding company submitted a tomato (Lycopersicon esculentum) sample from Guatemala for diagnosis. The plants showed necrotic lesions on leaves surrounded by some chlorosis, necrotic streaks on stems, and large superficial necrotic lesions on fruits. By mechanical inoculation of plant sap to different plant species, symptoms appeared in Capsicum annuum 'Westlandse Grote Zoete', Lycopersicon esculentum 'Money-maker', Nicotiana benthamiana, N. bigelovii, N. glutinosa, N. hesperis-67A, N. occidentalis-P1, N. tabacum 'White Burley', and Physalis floridana. Systemically infected leaves from N. occidentalis-P1 were used for all further experiments. Leaf dip preparations were analyzed by transmission electron microscopy and revealed the presence of filamentous virus particles typical of a potyvirus. Double-antibody sandwich enzyme-linked immunosorbent assay tests for Potato virus A, V, and Y, Tobacco etch virus, and Wild potato mosaic virus were negative. An antiserum (PepMoV/DSMZ As 0186) to Pepper mottle virus (PepMoV), however, gave a positive reaction. To obtain further evidence for the presence of this virus, the nucleotide sequence of the complete 3' nontranslated region (3NTR) and the 3' terminal part of the coat protein gene (3CPG) was determined using the set of degenerate primers P9502/CPUP (1). The obtained nucleotide sequence (approximately 700 bp) was deposited in GenBank under Accession No. AF440801. It showed 93 to 94% 3NTR and 90 to 93% 3CPG homology with the three sequences of PepMoV from pepper already present in GenBank. The two viruses with the next closest nucleotide sequence homology were Potato virus V and Potato virus Y showing up to 80 and 75% homology with the 3CPG and up to 53 and 48% homology with the 3NTR, respectively. Based on these results, we concluded that the virus isolated from the symptomatic tomato plants was PepMoV. Because of the relatively low homologies with the pepper isolates of PepMoV, this tomato isolate might be a separate strain of the virus. To our knowledge, this is the first report of the occurrence of PepMoV in tomato. Reference: (1) R. A. A. van der Vlugt et al. Phytopathology 89:148, 1999.