Turnip mosaic virus in rhubarb grown on farms in Poland

The productivity of cabbage (Brassica oleracea var. capitata) in Ethiopia has been generally low due to several biotic and abiotic constraints among which are several viral diseases. There is a recent report indicating that this economically important vegetable is seriously affected in Ethiopia by cauliflower mosaic virus (CaMV) and turnip mosaic virus (TuMV). However, little information exists on the incidence and distribution of these viruses as the previous report is based on samples only from Addis Ababa. In this study, a total of 370 leaf samples were collected from 75 cabbage growing fields in Central Ethiopia in two rounds of survey. Two cabbage varieties locally known as "Habesha gomen" and "Tikur gomen" with virus-like symptoms were collected and tested with Double Antibody Sandwich Enzyme-Linked Immunosorbent Assay (DAS-ELISA) using polyclonal antibodies specific to CaMV and TuMV. Results from serological diagnosis were confirmed with PCR and Sanger sequencing. The results indicated a high incidence and wide distribution of both viruses in Central Ethiopia with an average of 29.5% infection for CaMV and 40% for TuMV. Biological inoculation tests for CaMV or TuMV or both on healthy cabbage seedlings gave similar symptoms as those observed in the field. Symptom severity was higher with co-infection of CaMV and TuMV followed by TuMV single infection. BLAST analysis showed that TuMV and CaMV isolates from Ethiopia have nucleotide identity of 95-98% and 93-98%, respectively to previously reported isolates. Phylogenetic analysis revealed that CaMV isolates from Ethiopia are closely related to isolates from USA and Italy within Group II clade whereas TuMV isolates have close similarities with isolates from World B clade including isolates from Kenya, UK, Japan and the Netherlands. The identification of the causative agents of the mosaic disease observed on cabbage in Central Ethiopia may lay the foundation for future management studies.

A turnip mosaic virus (TuMV) isolate from asymptomatic Phalaenopsis sp. was detected by indirect ELISA. Its presence was confirmed by RT-PCR with a pair of degenerate primers whose design was based on reported coat protein gene sequences. Further analysis of the genomic sequence of this isolate designated as TuMV-ZH1 (GenBank accession No. KF246570) showed a high nucleotide sequence identity with isolate Lu2 (96.7%) and CHN 12 (96.3%) from China. Phylogenetic analysis indicated that TuMV-ZH1 belongs to the world-B lineage. To the best of our knowledge, the above may be the first indication that TuMV infects orchids in China. In addition, proteins P1 and P3 of TuMV-ZH1 are highly mutated as previously reported for other TuMV isolates.

Turnip mosaic virus (TuMV) is one of the most devastating threats to oilseed rape by causing serious crop losses. A total of 86 leaf samples of oilseed rape from eight different locations in Shaanxi, China, were tested by RT‐PCR for TuMV; the results revealed an infection level of 43% by TuMV. The complete coat protein (CP) gene of 32 TuMV isolates was cloned and sequenced. Analysis of the CP gene with sequences from the database allowed the genetic classification of 170 TuMV isolates or sequences. Four genetic clusters were obtained: MB (mostly Brassica isolates), MR (mostly Radish isolates), IBR (mostly Intermediate between Brassica and Radish clusters) and OBR (mostly outside Brassica and Radish clusters). All subgroups were slightly related to the hosts, but unrelated to geographical origins. Most of Shaanxi TuMV isolates were on separate branches, compared with the 138 known isolates originating from other parts of the world. Our results help provide a better understanding of the genetic diversity of TuMV isolates infecting oilseed rape in Shaanxi, China.

Infectious clones were generated from 17 new Korean radish isolates of Turnip mosaic virus (TuMV). Phylogenetic analysis indicated that all new isolates, and three previously characterized Korean radish isolates, belong to the basal-BR group (indicating that the pathotype can infect both Brassica and Raphanus spp.). Pairwise analysis revealed genomic nucleotide and polyprotein amino acid identities of >87.9 and >95.7%, respectively. Five clones (HJY1, HJY2, KIH2, BE, and prior isolate R007) had lower sequence identities than other isolates and produced mild symptoms in Nicotiana benthamiana. These isolates formed three distinct sequence classes (HJY1/HJY2/R007, KIH2, and BE), and several differential amino acid residues (in P1, P3, 6K2, and VPg) were present only in mild isolates HJY1, HJY2, and R007. The remaining isolates all induced systemic necrosis in N. benthamiana. Four mild isolates formed a phylogenetic subclade separate from another subclade including all of the necrosis-inducing isolates plus mild isolate KIH2. Symptom severity in radish and Chinese cabbage genotypes was not correlated with pathogenicity in N. benthamiana; indeed, Chinese cabbage cultivar Norang was not infected by any isolate, whereas Chinese cabbage cultivar Chusarang was uniformly susceptible. Four isolates were unable to infect radish cultivar Iljin, but no specific amino acid residues were correlated with avirulence. These results may lead to the identification of new resistance genes against TuMV.

Plant viruses account for enormous agricultural losses worldwide, and the most effective way to combat them is to identify genetic material conferring plant resistance to these pathogens. Aiming to identify genetic associations with responses to infection, we screened a large panel of Arabidopsis thaliana natural inbred lines for four disease-related traits caused by infection by A. thaliana-naïve and -adapted isolates of the natural pathogen turnip mosaic virus (TuMV). We detected a strong, replicable association in a 1.5 Mb region on chromosome 2 with a 10-fold increase in relative risk of systemic necrosis. The region contains several plausible causal genes as well as abundant structural variation, including an insertion of a Copia transposon into a Toll/interleukin receptor (TIR-NBS-LRR) coding for a gene involved in defense, that could be either a driver or a consequence of the disease-resistance locus. When inoculated with TuMV, loss-of-function mutant plants of this gene exhibited different symptoms than wild-type plants. The direction and severity of symptom differences depended on the adaptation history of the virus. This increase in symptom severity was specific for infections with the adapted isolate. Necrosis-associated alleles are found worldwide, and their distribution is consistent with a trade-off between resistance during viral outbreaks and a cost of resistance otherwise, leading to negative frequency-dependent selection.

Plant viruses account for enormous agricultural losses worldwide, and the most effective way to combat them is to identify genetic material conferring plant resistance to these pathogens. Aiming to identify genetic associations with responses to infection, we screened a large panel of Arabidopsis thaliana natural inbred lines for four disease-related traits caused by infection by A. thaliana-naïve and -adapted isolates of the natural pathogen turnip mosaic virus (TuMV). We detected a strong, replicable association in a 1.5 Mb region on chromosome 2 with a 10-fold increase in relative risk of systemic necrosis. The region contains several plausible causal genes as well as abundant structural variation, including an insertion of a Copia transposon into a Toll/interleukin receptor (TIR-NBS-LRR) coding for a gene involved in defense, that could be either a driver or a consequence of the disease-resistance locus. When inoculated with TuMV, loss-of-function mutant plants of this gene exhibited different symptoms than wild-type plants. The direction and severity of symptom differences depended on the adaptation history of the virus. This increase in symptom severity was specific for infections with the adapted isolate. Necrosis-associated alleles are found worldwide, and their distribution is consistent with a trade-off between resistance during viral outbreaks and a cost of resistance otherwise, leading to negative frequency-dependent selection.

Plant viruses account for enormous agricultural losses worldwide, and the most effective way to combat them is to identify genetic material conferring plant resistance to these pathogens. Aiming to identify genetic associations with responses to infection, we screened a large panel of Arabidopsis thaliana natural inbred lines for four disease-related traits caused by infection by A. thaliana-naïve and -adapted isolates of the natural pathogen turnip mosaic virus (TuMV). We detected a strong, replicable association in a 1.5 Mb region on chromosome 2 with a 10-fold increase in relative risk of systemic necrosis. The region contains several plausible causal genes as well as abundant structural variation, including an insertion of a Copia transposon into a Toll/interleukin receptor (TIR-NBS-LRR) coding for a gene involved in defense, that could be either a driver or a consequence of the disease-resistance locus. When inoculated with TuMV, loss-of-function mutant plants of this gene exhibited different symptoms than wild-type plants. The direction and severity of symptom differences depended on the adaptation history of the virus. This increase in symptom severity was specific for infections with the adapted isolate. Necrosis-associated alleles are found worldwide, and their distribution is consistent with a trade-off between resistance during viral outbreaks and a cost of resistance otherwise, leading to negative frequency-dependent selection.

Das Turnip mosaic virus (TuMV) ist weltweit verbreitet und gehort zur Gruppe der Potyviren. Es hat einen auserordentlich grosen Wirtspflanzenkreis von uber 300 Arten und wird nicht persistent durch 89 Aphidenarten ubertragen. Bisher sind beim TuMV zwolf Pathotypen bekannt. Im Kohlgemuse verursacht das TuMV die so genannte Kohlschwarzringfleckigkeit. Dabei handelt es sich um eine wirtschaftlich wichtige Virose, die beim Weiskohl bis zu 25 % Ertragsausfall und Gewebenekrotisierungen, insbesondere wahrend der Kuhllagerung, bewirken kann. Zur Sicherung eines hohen Ertrags- und Qualitatsniveaus bei Kohlgemuse wurde begonnen, die Resistenz gegen diese Virose zu verbessern. Mit aktuellen, weitgehend charakterisierten Erregerherkunften des TuMV wurden Resistenzprufmethoden weiterentwickelt und neue Resistenzquellen in der Familie der Brassicaceae erschlossen. Resistenzen gegen mehrere TuMV-Pathotypen liesen sich in B. oleracea-Primitivformen, in Chinakohl (B. rapa ssp. pekinensis), in Meerrettich (Armoracia ru-sticana), in Radies bzw. Rettich (Raphanus sativus) sowie in sexuell erzeugten Raphanobrassica-Hybriden nachweisen. Die evaluierten TuMV-Resistenzen wurden entsprechend der phylogenetischen Distanz zum Kohl durch Kreuzung bzw. durch Protoplastenfusion in Kulturformen des Kohls ubertragen.

The coat protein (CP) gene derived from Turnip mosaic virus (TuMV) isolate JO was introduced into Arabidopsis thaliana and the resulting transgenic progenies were analyzed for resistance to TuMV. Transgenic Arabidopsis plants with no detectable transcripts of the introduced CP gene exhibited complete resistance to TuMV. There was no significant correlation between the resistance and the copy number of the transgene. Instead, small interfering RNAs (siRNAs) were detected in these resistant plants, indicating that the resistance is attributed to RNA silencing. The RNA-mediated resistance was not only inherited over successive generations but also effective against 17 worldwide TuMV isolates with different pathogenicity. Comparative analysis of the CP genes among the 17 TuMV isolates revealed that the 380-nt in the 3' region is highly conserved, suggesting the importance of the 3' conserved region for broad-spectrum resistance. These results indicate that introduction of the TuMV-CP gene into the target Brassicaceae plants followed by selecting transformants that show RNA silencing for the transgenes can be an effective and reliable strategy for developing crucifer crops with a broad spectrum of resistance to TuMV.

HomePlant DiseaseVol. 100, No. 4First Report of White clover mosaic virus and Turnip mosaic virus Mixed Infection on Garlic Mustard in Pennsylvania PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of White clover mosaic virus and Turnip mosaic virus Mixed Infection on Garlic Mustard in PennsylvaniaK. Zhao, P. Margaria, and C. RosaK. ZhaoSearch for more papers by this author, P. MargariaSearch for more papers by this author, and C. RosaSearch for more papers by this authorAffiliationsAuthors and Affiliations K. Zhao P. Margaria C. Rosa , Pennsylvania State University, University Park, PA 16802. Published Online:10 Feb 2016https://doi.org/10.1094/PDIS-09-15-1083-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat In spring 2015, 12 weedy garlic mustard (Alliaria petiolata) plants with mosaic symptoms were found in a garden in State College, PA. The same symptoms are seen on many weedy garlic mustards in the area each spring, as they were in previous years at this location. Incidence was ∼10% in the garden, with 2 of ∼20 groups of 4 to 6 plants infected. Quality of RNA extracted from garlic mustard was poor, so symptomatic leaves were used for mechanical transmission to Nicotiana benthamiana. Seven days after mechanical inoculation, plants showed necrotic spots and leaf deformation on the systemic leaves. Double-stranded RNA was extracted from symptomatic N. benthamiana leaves and electrophoresis was performed on 6% polyacrylamide gel to detect dsRNA, produced in plants infected with RNA viruses (Valverde et al. 1990). A band of high molecular weight confirmed the presence of dsRNA. Total RNA was then extracted from the N. benthamiana plants using Spectrum Plant Total RNA Kit (Sigma-Aldrich). A tobravirus or a potyvirus were suspected as possible causal agents, based on literature search for the potyvirus and on the presence a tobravirus infected ornamental plant in the same garden. Two pairs of degenerate primers (Chen et al. 2001; Jones et al. 2008) were used separately in one tube reverse-transcription PCR (RT-PCR) and 835-bp and 654-bp amplicons were cloned into pGEM-T Easy Vector (Promega) and sequenced by Sanger sequencing. The sequences were deposited as GenBank Accession Nos. KT799530 and KT799528, respectively. BLAST results showed that the first sequence had 96% nucleotide identity with the RNA dependent RNA polymerase (RdRp) of a previously reported White clover mosaic virus (WClMV) sequence (AB669182). The second sequence had 95% nucleotide identity to a Turnip mosaic virus (TuMV) sequence across the NIb and coat protein genes (AB252117). Two newly designed primer pairs W_1F (5′-CAGAACGAGCCATCCGCAGAA), W_1500R (5′-TCAGTGCAGTCAGCATTATGAG) and TuMV_F (5′-TCTTGGACGAAGCATGGAGC), TuMV_R (5′-TCGGACTGCCTCTTTGCCTG) were used to further confirm the presence in N. benthamiana of WClMV and TuMV, respectively. A 1,457-bp amplicon was obtained by using W_1F and W_1500R and sequenced. This sequence (KT799531) had 95 to 96% nucleotide identity with several WClMV RdRp sequences (AB056720, AB669182, and X16636). A 577-bp amplicon was obtained by using the primer pair specific to TuMV sequence. The sequenced amplicon (KT788529) showed 97% nucleotide identity to a TuMV sequence spanning the P3 and 6K1 protein (AB701705). Due to the poor quality of RNA we could not test the original or other garlic mustard plants for the presence of the two viruses, but all weeds had uniform symptoms appearance and severity. To our knowledge, White clover mosaic virus and Turnip mosaic virus have not been previously reported in garlic mustard plants in Pennsylvania. Other potyviruses including TuMV have been reported in garlic mustard and Brassicaceae while WClMV to our knowledge was never reported in Brassicaceae or in garlic mustard before. TuMV is a member of the Potyviridae family, is transmitted by aphids in a nonpersistent manner, and causes a variety of symptoms in many Brassica spp.(Tomlinson and Ward 1978) The presence on garlic mustard of a strain of TuMV very similar to a strain already reported in Europe on arugula (Eruca or Brassica vesicaria subsp. sativa) could indicate that this virus can be transmitted between cultivated and not cultivated Brassicaceae and that wild Brassicaceae can potentially serve as virus reservoir (Lockhart 2012). The mode of transmission of WClMV is not known and reports of its transmission by contact or by dodder (Cuscuta spp.) (probably under experimental conditions) have been controversial; therefore, it is hard to speculate if this virus can move from crops to natural environment and vice versa. This is the first report of infection of garlic mustard with TuMV and WClMV, which have the potential to reduce the fitness of this plant species that is considered invasive in North America.

Concerns about the introduction of genetically modified crops frequently centre on the possibility of gene transfer to wild relatives, resulting either in the disruption of natural patterns of genetic diversity by introgressing into species gene pools or in the addition of traits which may cause wild plants to become more abundant or invasive. This chapter describes a phased approach to the assessment of possible harm in the context of a specific transgenic stress-tolerant trait, namely virus tolerance in inter-breeding species. We assessed the hazard of harm to the 'natural' environment as opposed to agricultural productivity. Our baseline was the distribution and relative abundance in field-grown wild or long-established 'naturalized' Brassica species (B. oleracea, B. nigra and B. rapa) of six viruses, and then glasshouse assessments of components of fitness. Because these observations suggested that generic risk assessment was unlikely to be possible, we focused on the economically significant turnip mosaic virus (TuMV), genus Potyvirus. TuMV is a target for transgenic (capsid-coding sequence-based) approaches to disease management in brassicas as an alternative to natural sources of resistance/tolerance to the virus and because insecticides do not kill the aphid vectors of the virus before they effect inoculation. TuMV was not found in B. rapa growing on the banks of the River Thames in Oxfordshire, UK. Glasshouse tests showed that B. rapa from these populations died within a few days of manual inoculation with some isolates of TuMV, but we found that the pathogenicity of three TuMV isolates from the UK was not uniform. We made crosses in which natural B. rapa lines, genome designation AA, n=10, were the female partners and B. napus, genome designation AACC, 2n=38, were pollen donors, B. napus included untransformed lines and lines that contained a transgenic capsid-coding sequence from a potyvirus. As judged using polymerase chain amplification, 'C' genome transfer frequencies varied from 0 to 84% depending on pollen donor, but there was statistically significant within-population variation among B. rapa, P<0.001 at Culham and P<0.05 at Clifton Hampden, in the efficiency of transgene flow from one B. napus cultivar ('Drakkar'). When manually challenged with TuMV, the transformed B. napus was infectible but the virus was not lethal. In contrast, the untransformed counterparts of these plants were sensitive to the same challenge inocula although two cultivars ('Westar' and 'Drakkar') differed in their absolute infectibility by one of the three isolates of TuMV we assessed. Importantly, when F1 hybrid progeny, identified on the basis of the presence of 'C'-specific sequence and capsid-coding sequence as judged by polymerase chain amplification, were manually challenged with TuMV, these plants tended to be more TuMV tolerant than their maternal parents. Thus, our contained glasshouse-based gene flow and pathogenicity tests, even though done in non-competitive conditions and with an incomplete knowledge of factors regulating the wild populations, provided prima facie evidence of a potential for ecological release from that natural virus constraint following introgression of a resistance trait. The assessments of putative fitness impacts in hybrids between transformed (virus-tolerant) crop plants and wild (virus-sensitive) crop relatives were assembled during an ongoing EU-funded project (VRTP-IMPACT; QLK3-CT-2000-00361).

In recent years, the accumulated molecular data of Turnip mosaic virus (TuMV) isolates from various hosts originating from different parts of the world considerably helped to understand the genetic complexity and evolutionary history of the virus. In this work, four complete TuMV genomes (HC9, PK1, MS04, MS15) were characterised from naturally infected cultivated and wild-growing Papaver spp., hosts from which only very scarce data were available previously. Phylogenetic analyses showed the affiliation of Slovak Papaver isolates to the world-B and basal-B groups. The PK1 isolate showed a novel intra-lineage recombination pattern, further confirming the important role of recombination in the shaping of TuMV genetic diversity. Biological assays indicated that the intensity of symptoms in experimentally inoculated oilseed poppy are correlated to TuMV accumulation level in leaves. This is the first report of TuMV in poppy plants in Slovakia.

Turnip mosaic virus (TuMV) is a single stranded RNA (sRNAs) virus belonging to the genus Potyvirus. Turnip mosaic virus has a wide host range including several important crop plants, making it economically significant. This study investigates the relation between a strain of TuMV and two model plant systems; Arabidopsis thaliana and Nicotiana benthamiana, focusing on the viral sequence, host gene expression and defence mechanisms, and viral derived small RNAs (viRNAs). Turnip mosaic virus has been well studied and characterised with 183 complete genome nucleotide sequences available in GenBank (5 June 2018). The TuMV isolate used in this study was sequenced and submitted to GenBank, as well as the original isolate collected in 1994, under the names TuMV-QLD1b and TuMV-QLD1a, respectively (accession numbers KX641465 and KX641466). The original TuMV isolate was PCR sequenced while the 2015 isolate was sequenced by deep RNA sequencing. A comparison between the two sequences showed minor variations with 18 single-nucleotide-polymorphisms (SNPs). Another aspect of the study involved the sequencing of a Cucumber mosaic virus (CMV) isolate (strain K) as well as an Australian Cauliflower mosaic virus (CaMV) isolate belonging to the genus Cucumovirus and Caulimovirus respectively. This strain of CaMV represents the first Australian isolate to be fully sequenced. Both the CMV and the CaMV isolates were used to study plant defence pathways in Chapter 4 of this thesis. The sequence of both isolates were published and make up Chapter 2.Chapter 3 investigates the early defence response of A. thaliana 6, 24 and 48 hours after TuMV inoculation. Marker gene expression results suggest that the virus upregulated the jasmonic acid (JA) pathway 24 hours after infection. This is significant, as viruses are classified as biotrophic pathogens which usually upregulate the salicylic acid (SA) pathway leading to hyper-sensitive response and programmed cell death, preventing the virus from spreading. It is hypothesised that the upregulation of the JA pathway may favour the virus allowing it to establish more easily and systemically infect its host.The JA and other defence pathways are further researched through studying the interactions between a mediator mutant and four different viruses; TuMV, CMV, CaMV and Alternanthera mosaic virus (AltMV). The mediator complex consists of several subunits and is highly conserved among eukaryotes as it regulates transcription. Previous studies have shown that med18 plants are more resistant to Fusarium oxysporum which was also found to upregulate the JA pathway in WT plants. Results show a similar trend with viral infected med18 plants having less viral RNA than WT plants 14 days after infection, though most were not significant due to large variations of viral load between individual plants. However, med18 plants infected with CMV had significantly less viral load than WT plants.Some of phenotypic symptoms caused by viral infection may be a secondary effect of RNA silencing. It is hypothesised that viRNAs can interfere with the plant’s regulations and development causing phenotypic symptoms. Similar to previous studies, small RNA sequencing of virus infected A. thaliana and N. benthamiana suggested that there was a significant increase in the number of small RNAs (sRNAs), specifically those of 21 nucleotides (nt) in length. This length would also suggest that these are produced through a specific biogenesis pathway. Studies have reported that certain areas of a virus genome, called “hotspots”, are more prone to being acted upon by the plant’s sRNAs biogenesis machinery. Chapter 5 results suggest this to be true, with certain regions producing more sRNAs and causing certain viRNAs to be more abundant.When comparing the most abundant viRNAs to host genes we identified possible targets based on complementarity. As a high degree of complementarity is believed to be required for endogenous small interfering RNAs (siRNAs) directed silencing it was hypothesized that highly abundant and complementary viRNAs had the potential to target and inhibit certain genes. The dual-luciferase report system was used to attempt to quickly validate possible viRNA targeting of host transcript sequences. The quantitative nature of this assay allowed us to determine whether viRNAs interacted with the target transcript based on the expression ratio. A mutated target sequence was included as a control to confirm viRNA interaction. Many targets from both A. thaliana and N. benthamiana were tested, though only one target sequence interaction was repeatedly confirmed using this assay system. The N. benthamiana gene 3160g02007 was confirmed to be targeted by TuMV as there was a clear decrease in the dual LUC expression ratio in the presence of the virus. The expression was restored when the target was mutated. Furthermore, no decrease was apparent when plants were not infected.

Turnip mosaic virus (TuMV) infects many plant species, being the only potyvirus able to infect brassicas. TuMV isolates have been classified into 12 pathotypes according to symptoms induced in lines of Brassica napus, and molecularly clustered into six lineages (basal-B, basal-BR, Asian-BR, world-B, Iranian and OMs). Despite being considered one of the most important viruses infecting brassicas worldwide, there is little information on this virus in the Neotropical region. Aiming to fill in this gap and advance knowledge on occurrence, genetic variability, and biological aspects of TuMV in Brazil, 40 isolates were identified and characterised. Five of these isolates were selected to determine their host range, sequence their genomes, and for phylogenetic, recombination and diversity analyses. Mechanical inoculations performed on plant species from 10 families showed differences in symptom expression among isolates. Inoculations of 13 TuMV isolates in B. napus lines revealed occurrence only of the pathotype 1. According to phylogenetic analyses of the coat protein, TuMV Brazilian isolates clustered into the groups: world-B (subgroups world-B2 and world-B3) and basal-BR. In the latter, there was a formation of a subclade named Brazilian subgroup composed by 31 Brazilian TuMV isolates. Intralineage and interlineage recombination events of world-B, basal-B and basal-BR suggest that Brazilian TuMV isolates had a European origin. Our diversity analysis suggest that a strong negative selection is acting on polyprotein coding region. We confirmed that Brazilian TuMV isolates showed high variability, which together with their ability to infect wild brassicas and to circumvent resistance genes highlight their genetic and epidemiological potential in causing damages in cultivated species of brassicas and other crops in Brazil.

In July 2003, noticeable red lesions were observed on rhubarb leaves (Rheum rhababarum cv. Kerwin) from a plant at the Arctic Plant Germplasm Research and Introduction Project in Palmer, AK. Extracts of leaf tissue tested positive for a potyvirus using indirect enzyme-linked immunosorbent assay (ELISA) and western blots with a monoclonal antibody specific to the potyvirus group (Agdia, Inc., Elkhart, IN). During the following growing season (June 2004), obvious chlorotic ringspots developed into red lesions on the same plant and an adjacent plant of the same cultivar. Partially purified particles that were isolated from the infected rhubarb plants were mechanically inoculated to an experimental host range (number of infected plants per total number of plants), resulting in lesions on leaves of Rheum palmatum (1 of 2) and Chenopodium amaranticolor (3 of 5) but none on C. quinoa (0 of 4). The leaves with local lesions from C. amaranticolor were ground in phosphate buffer (1 g of tissue per 10 ml of buffer), and the extract rubbed onto a set of plants resulting in lesions on R. hybridum (raponticum) (1 of 2), C. amaranticolor (1 of 4), and C. quinoa (1 of 4). The original diseased rhubarb plants and experimental symptomatic plants were confirmed to have a potyvirus using ELISA. Subsequent compound direct ELISA and western blot assays revealed that the virus reacted strongly to monoclonal or polyclonal antibodies to Turnip mosaic virus (TuMV) (Agdia, Inc.). Total RNA was extracted from leaves of the naturally infected rhubarb plants with an RNeasy Plant Mini Kit (Qiagen Sciences, Germantown, Maryland), and used in reverse-transcription-polymerase chain reaction (RT-PCR) with specific primers for TuMV (1) predicted to amplify a 1,134-bp 3'-terminal cDNA fragment encompassing the 3'-end of the nuclear inclusion protein gene (NIb), the coat protein gene, and the 3'-nontranslated region. A PCR product of approximately the expected size was obtained and then sequenced. Sequences (1,077 nt) that corresponded to the TuMV coat protein gene and 3'-terminal noncoding region were submitted to Genbank (Accession No. AY744930). Blast searches against NCBI (National Center for Biotechnology Information) contained high identities to many TuMV isolates with up to 96% (1,043 of 1,077) nucleotide identity (i.e., GenBank Accession No. AF169561). Similar high identities of up to 97% at the amino acid level occurred within the coat protein coding region (i.e., GenBank Accession No. BAC02892.1). Infected rhubarb plants were removed from the site and none of the remaining 109 plants tested positive for TuMV using ELISA. On the basis of the mechanical transmission to plant hosts, the definitive TuMV serology, and the consensus of sequenced regions with TuMV, we concluded that the causal agent of the diseased rhubarb plants was TuMV. Although TuMV has a wide plant host range occurring worldwide (2), to our knowledge, this is the first report of TuMV in rhubarb in Alaska and the first time that TuMV has been detected in Alaska.