Tomato Mosaic Virus Infection Research Articles

Evaluation of Tomato (<i>Lycopersicon lycopersicum</i> (L.) Genotypes for their Reaction to <i>Tomato mosaic virus</i> (ToMV) Infection in Kebbi State, Nigeria

Tomato mosaic virus (ToMV) is among the most devastating viral diseases of tomato worldwide and it can cause yield losses of up to 40%. One of the effective managements of plant viral diseases is the use of resistant genotypes. This research was conducted to determine the reaction of tomato genotypes to Tomato mosaic virus (ToMV) infection. The experiment consists of five tomato genotypes which were evaluated for resistance to ToMV infection under screen-house conditions using Completely Randomized Design (CRD) with three replicates. The treatments were Dantaya, Danwarai, Dan-Niko, Dan-Heka, and Hybrid Platinum, which are the five most preferred farmers varieties in Kebbi State. Prior to mechanical inoculation, ToMV-infected leaf samples used as source of inoculum were tested ToMV positive using Direct Antibody Coating-Enzyme Linked Immunoassay (DAC-ELISA). Thirty-six (36) seedlings of each genotype were transplanted into plastic pots containing compost and seedlings recovery were recorded two weeks after transplanting (WAT) before inoculation. Hybrid Platinum has low establishment percentage (72.22%), compared to DanHeka and Dan-Niko with both 100%. All the genotypes evaluated were infected when inoculated with ToMV but with significant variation (P = 0.05) in their reaction to ToMV infection. Dantaya recorded the highest percent disease incidence of 50.00% while, Platinum recorded the lowest percent disease incidence of 31.94%. Three genotypes were susceptible to ToMV while, two were resistant to ToMV. The high incidence of ToMV found on farmers preferred tomato genotypes in Kebbi State is of great management concern. Also, this has implication for tomato productivity and yield in the state.

Molecular and Phenotypic Responses of Rhizobacteria-Treated Tomato Plants to Tomato Mosaic Virus Under Greenhouse Conditions.

Tomato mosaic disease, mainly caused by Tomato mosaic virus (ToMV), is one of the devastating viral diseases which adversely affects tomato yield, globally. Plant growth-promoting rhizobacteria (PGPR) have been recently used as bio-elicitors to induce resistance against plant viruses. The goal of this research was to apply PGPR in the tomato rhizosphere and to determine the response of plants challenged with ToMV infection, under greenhouse conditions. Two different strains of PGPR, Pseudomonas fluorescens SM90 and Bacillus subtilis DR06, in single- and double-application methods applied to evaluate their effectiveness in inducing defense-related genes, viz., NPR1, COI1, and PR1-a before (induced systemic resistance [ISR]-prime) and after (ISR-boost) ToMV challenge. Additionally, to investigate the biocontrol potential of PGPR-treated plants against viral infection, plant growth indices, ToMV accumulation, and disease severity were compared in primed and non-primed plants. Analysis of expression patterns of putative defense-related genes before and after ToMV infection indicated that studied PGPR trigger defense priming through different signaling pathways acting at the transcriptional level and in a species-dependent manner. Moreover, the biocontrol efficacy of consortium treatment did not differ significantly from the single bacteria treatments, even though their mode of action differed in transcriptional changes of ISR-induced genes. Instead, simultaneous application of Pseudomonas fluorescens SM90 and Bacillus subtilis DR06 led to more significant growth indices than the single treatments suggesting that integrated application of the PGPR could additively reduce the disease severity and virus titer and promote the growth of the tomato plant. These results suggested that enhanced defense priming via activation of the expression pattern of defense-related genes is responsible for biocontrol activity and growth promotion in PGPR-treated tomato plants challenged with ToMV compared to non-primed plants, under greenhouse conditions.

Impact of Biochar Soil Amendment on Tomato mosaic virus Infection, Growth and Nutrients Uptake of Tomato Plants

Biochar soil amendment was applied as an eco-friendly approach to control Tomato mosaic virus (ToMV) and improve tomato growth and nutritional status. Three concentrations of biochar, 0.5, 1.0 and 1.5% were used as soil amendments. Using biochar at the rate of 1 and 1.5% reduced the ToMV incidence and delayed symptoms appearance as compared with plants grown in non-amended soil. Infection percentage and disease severity of ToMV were reduced by 33.3 and 50%, respectively, 15 days after inoculation of plants of soil amended with 1.5% biochar. ToMV relative concentration, using indirect ELISA was significantly reduced in plants of biochar 1% and 1.5% treatments. The lowest virus concentration was recorded at 21 days after inoculation in plants of 1.5% biochar amended soil. The shoot fresh weight was increased at biochar rates of 1.5 and 0.5% in non-infected and ToMV infected tomato, respectively. Significant increase was obtained in shoot K content amended with 1.0 and 1.5% biochar treatments of healthy and ToMV-infected tomato plants, respectively. Whereas, shoot Na content was diminished in infected plants grown in biochar amended soil at all tested biochar concentrations. Overall, the biochar application to soil enhanced resistance to ToMV infection, stimulated growth and K content increment and Na content decrement in tomato plants. In conclusion, application of biochar to agricultural soil could be considered a practical tool for minimizing the change effects of climate through carbon sequestration, improve plant productivity and increase diseases tolerance for sustainable agriculture.

Inactivation of plant and animal viruses by proanthocyanidins from Alpinia zerumbet extract.

Alpinia zerumbet (Pers.) B.L. Burtt and R.M. Smith belongs to the Alpinia genus in the Zingiberaceae family. In East Asia, Alpinia zerumbet has been widely used as food and traditional medicine. Previously, we identified proanthocyanidins (PACs), an anti-plant-virus molecule in A. zerumbet, using Nicotiana benthamiana and tomato mosaic virus (ToMV). Here, we found that PACs from A. zerumbet, apple, and green tea effectively inhibited ToMV infection. Additionally, the PACs from A. zerumbet exhibited greater antiviral activity than those from apple and green tea. The PACs from A. zerumbet also effectively inactivated influenza A virus and porcine epidemic diarrhea virus (PEDV), which acts as a surrogate for human coronaviruses, in a dose-dependent manner. The results from the cytopathic effect assays indicated that 0.1 mg/ml PACs from A. zerumbet decreased the titer of influenza A virus and PEDV by >3 log. These findings suggested that the direct treatment of viruses with PACs from A. zerumbet before inoculation reduced viral activity; thus, PACs might inhibit infections by an influenza virus, coronaviruses, and plant viruses.

Comparative Analysis of Host Range, Ability to Infect Tomato Cultivars with Tm-22 Gene, and Real-Time Reverse Transcription PCR Detection of Tomato Brown Rugose Fruit Virus.

Tomato (Solanum lycopersicum L.) is one of the most important vegetables in the world. However, tomato is also susceptible to many viral diseases. Several tobamoviruses, including tomato mosaic virus (ToMV), tomato mottle mosaic virus (ToMMV), and tomato brown rugose fruit virus (ToBRFV), are highly contagious pathogens that could result in significant economic losses if not controlled effectively. Tobamoviruses have been managed relatively well with broad adaptation of tomato cultivars with resistance genes. However, emergence of ToBRFV was shown to break down resistance conferred by the common resistance genes, resulting in serious outbreaks in many countries in Asia, Europe, and North America. The objective of this study was to conduct a comparative analysis of biological properties, including host range and disease resistance of ToMV, ToMMV, and ToBRFV. Results showed that despite many similarities in the host range, there were some unique host plant responses for each of the three viruses. In a comparative evaluation of disease resistance using the same tomato cultivars with or without Tm-22 gene, there was a striking difference in responses from tomato plants with Tm-22 gene inoculated with ToBRFV, ToMV, or ToMMV. Whereas these test plants were resistant to ToMV or ToMMV infection, all test plants were susceptible to ToBRFV. Further, for ToBRFV detection, a sensitive and reliable multiplex real-time reverse transcription (RT)-PCR assay using TaqMan probe with an internal 18S rRNA control was also developed. With simple modifications to RNA extraction and seed soaking, real-time RT-PCR could consistently detect the virus in single infested seed in varied levels of contamination, suggesting its usefulness for seed health assay.

Differential Response of Mycorrhizal Plants to Tomato bushy stunt virus and Tomato mosaic virus Infection.

Tomato bushy stunt virus (TBSV) and Tomato mosaic virus (ToMV) are important economic pathogens in tomato fields. Rhizoglomus irregulare is a species of arbuscular mycorrhizal (AM) fungus that provides nutrients to host plants. To understand the effect of R. irregulare on the infection by TBSV/ToMV in tomato plants, in a completely randomized design, five treatments, including uninfected control plants without AM fungi (C), uninfected control plants with AM fungi (M) TBSV/ToMV-infected plants without AM fungi (V), TBSV/ToMV-infected plants before mycorrhiza (VM) inoculation, and inoculated plants with mycorrhiza before TBSV/ToMV infection (MV), were studied. Factors including viral RNA accumulation and expression of Pathogenesis Related proteins (PR) coding genes including PR1, PR2, and PR3 in the young leaves were measured. For TBSV, a lower level of virus accumulation and a higher expression of PR genes in MV plants were observed compared to V and VM plants. In contrast, for ToMV, a higher level of virus accumulation and a lower expression of PR genes in MV plants were observed as compared to V and VM plants. These results indicated that mycorrhizal symbiosis reduces or increases the viral accumulation possibly via the regulation of PR genes in tomato plants.

Inhibitory effects of Alpinia zerumbet extract against plant virus infection in solanaceous plants.

Tomato mosaic virus (ToMV) and tobacco mosaic virus (TMV) are critical pathogens causing severe crop production losses of solanaceous plants. The present study was undertaken to evaluate the antiviral effects of extracts of Alpinia plants on ToMV and TMV infection in Nicotiana benthamiana. The aqueous extracts of Alpinia zerumbet (Pers.) B.L. Burtt and R.M. Smith and Alpinia kumatake, which grow widely in subtropical and tropical regions including East Asia, were effective in reducing ToMV infection when plants were treated prior to virus inoculation. We also found that the extracts of A. zerumbet isolated from Okinawa (Japan), locally referred to as shima-gettou, strongly inhibited ToMV and TMV infection. To obtain an active fraction, the aqueous extract of A. zerumbet isolate OG1 was separated by ethyl acetate, and the antiviral active compound was found to be present in the water layer. Based on our results, the extract of Alpinia plants has potential as an antiviral reagent for practical application in solanaceous crop production.

MiR403a and SA Are Involved in NbAGO2 Mediated Antiviral Defenses Against TMV Infection in Nicotiana benthamiana

RNAi (RNA interference) is an important defense response against virus infection in plants. The core machinery of the RNAi pathway in plants include DCL (Dicer Like), AGO (Argonaute) and RdRp (RNA dependent RNA polymerase). Although involvement of these RNAi components in virus infection responses was demonstrated in Arabidopsis thaliana, their contribution to antiviral immunity in Nicotiana benthamiana, a model plant for plant-pathogen interaction studies, is not well understood. In this study, we investigated the role of N. benthamiana NbAGO2 gene against TMV (Tomato mosaic virus) infection. Silencing of NbAGO2 by transient expression of an hpRNA construct recovered GFP (Green fluorescent protein) expression in GFP-silenced plant, demonstrating that NbAGO2 participated in RNAi process in N. benthamiana. Expression of NbAGO2 was transcriptionally induced by both MeSA (Methylsalicylate acid) treatment and TMV infection. Down-regulation of NbAGO2 gene by amiR-NbAGO2 transient expression compromised plant resistance against TMV infection. Inhibition of endogenous miR403a, a predicted regulatory microRNA of NbAGO2, reduced TMV infection. Our study provides evidence for the antiviral role of NbAGO2 against a Tobamovirus family virus TMV in N. benthamiana, and SA (Salicylic acid) mediates this by induction of NbAGO2 expression upon TMV infection. Our data also highlighted that miR403a was involved in TMV defense by regulation of target NbAGO2 gene in N. Benthamiana.

Accumulation of salicylic acid in tomato plant under biological stress affects oviposition preference of Bemisia tabaci

ABSTRACT In field, plants are exposed to multiple biological stresses simultaneously; for example, insect damage and pathogenic virus infection. In this study, we constructed a simple tripartite experimental system using tomato plant, their insect pest Bemisia tabaci (whitefly), and infectious tomato mosaic virus (ToMV). In the choice test, whiteflies laid more eggs on uninfected plant than on ToMV-infected plant. Further, whiteflies hatched more and grew better on the uninfected plant. Salicylic acid (SA) accumulated in infected plants, and the expression of genes involved in SA production and SA-related response was significantly induced. These plant responses against ToMV infection were similar to those against whitefly attack or SA-treated plants. To examine the importance of plant endogenous SA for whitefly preference, we repeated the choice test using the NahG transgenic tomato that cannot accumulate SA. Whiteflies did not show oviposition preference between NahG plants with and without ToMV infection or whitefly infestation. Overall, whiteflies prefer healthy plants, and SA accumulation in response to biological stresses is involved in their preference.

Physiological parameters correlated with Tomato Mosaic Virus inducing defensive response in Datura metel.

Programed cell death resembles a real nature active defense in Datura metel against TMV after three days of virus infection. This adaptive plant immune response was quantitatively assessed against Tomato Mosaic Virus infection by the following physiological markers; Chlorophyll-a (mg/g), Chlorophyll-b (mg/g), total protein (mg/g), hydrogen peroxide H2O2 (μmol/100 mg), DNA (μg/100 mg), RNA (μg/100 mg), Salicylic acid (μg/g), and Comet Assays. Parameters were assessed for asymptomatic healthy and symptomatic infected detached leaves. The results indicated H2O2 and Chlorophyll-a as the most potential parameters. Chlorophyll-a was considered the only significant predictor variant for the H2O2 dependent variant with a P value of 0.001 and R-square of 0.900. The plant immune response was measured within three days of virus infection using the cutoff value of H2O2 (⩽1.095 μmol/100 mg) and (⩽3.201 units) for the tail moment in the Comet Assay. Their percentage changes were 255.12% and 522.40% respectively which reflects the stress of virus infection in the plant. Moreover, H2O2 showed 100% specificity and sensitivity in the symptomatic infected group using the receiver-operating characteristic (ROC). All tested parameters in the symptomatic infected group had significant correlations with twenty-five positive and thirty-one negative correlations where the P value was <0.05 and 0.01. Chlorophyll-a parameter had a crucial role of highly significant correlation between total protein and salicylic acid. Contrarily, this correlation with tail moment unit was (r = −0.930, P < 0.01) where the P value was <0.01. The strongest significant negative correlation was between Chlorophyll-a and H2O2 at P < 0.01, while moderate negative significant correlation was seen for Chlorophyll-b where the P value < 0.05. The present study discloses the secret of the three days of rapid transient production of activated oxygen species (AOS) that was enough for having potential quantitative physiological parameters for defensive plant response toward the virus.

First Report of Tomato mosaic virus on Common Sow Thistle in Iran.

The natural incidence of Tomato mosaic virus (ToMV) in common sow thistle (Sonchus oleraceus) from vegetable fields was assessed to determine the role of this weed species as a virus inoculum source. Twenty sow thistle plants with virus-like foliar symptoms including mosaic and malformations were collected from five vegetable fields in Tehran province, Iran, and analyzed by double antibody sandwich (DAS)-ELISA for the presence of ToMV, Tobacco mosaic virus (TMV), and Cucumber mosaic virus (CMV) using specific polyclonal antibodies (Agdia, Elkhart, IN). Six out of the 20 sow thistle plants tested by ELISA were infected with ToMV. This virus was detected in three of five vegetable fields surveyed, while CMV and TMV were not detected. Mosaic symptoms were associated with the ToMV infection, similar to those caused by TMV in common sow thistle in Iran (2). Viral infection was confirmed by RT-PCR using previously described specific primers to amplify a region in the coat protein gene of ToMV (3). The RT-PCR resulted in the amplification of an expected fragment of ~480 bp from ToMV-infected but not from healthy plants. The nucleotide sequence of the amplified DNA fragment was purified (GeneJET Gel Extraction Kit, Fermentas, Germany), directly sequenced, and deposited in GenBank as Accession No. KF527464. BLAST analysis showed 95 to 97% and 98 to 100% identity at the nucleotide and amino acid levels, respectively, with comparable sequences of other ToMV isolates (GenBank AF062519, FN985165, GQ280794, and JX857634). Mechanical inoculation of sow thistle plants with sap of symptomatic sow thistles reproduced symptoms of field-infected sow thistles. The presence of ToMV in the inoculated plants was confirmed by ELISA and RT-PCR. This suggested that ToMV could be the causal agent of the disease on sow thistle. In our earlier studies, the distribution and genetic diversity of ToMV isolates infecting vegetable crops and weed plants were studied (1); however, to our knowledge, this is the first report of ToMV infecting common sow thistle in Iran.

Metabolic fingerprinting of Tomato Mosaic Virus infected Solanum lycopersicum

1H nuclear magnetic resonance (NMR)-based metabolomics has been applied to study the compatible interaction between tomato plants and Tomato Mosaic Virus (ToMV). A detailed time course of metabolic fingerprinting of ToMV-inoculated and non-inoculated systemically infected tomato leaves has provided a fundamental understanding of the metabolic state of the plant not only in response to ToMV infection, but also under various physiological conditions. By this analytical platform a total of 32 metabolites including amino/organic acids, sugars, phenylpropanoids, flavonoids and other miscellaneous compounds were detected. Using multivariate data analysis, we have identified a subset of metabolites induced during the plant defence response and metabolites whose accumulation was dependent on the developmental stage, the position of the leaf on the stem, and the harvesting time. Specifically, a general time-dependent decrease in organic acids, amino acids (excluding asparagine), phenylpropanoids and rutin was observed in individual leaves. In addition, metabolite alterations were also found to correlate with the developmental stage of the leaf: high levels of organic acids, some amino acids, phenylpropanoids, and flavonoids were found in lower leaves while elevated amounts of sugars were present in the upper ones. Moreover, a marked variation in the content of some metabolites was also observed to be associated to the asymptomatic ToMV infection both in inoculated and systemically infected leaves. While flavonoids accumulated in virus-inoculated leaves, increased levels of phenylpropanoids were observed in non-inoculated leaves where ToMV actively replicates. Finally, diurnal changes in the metabolite content were also observed: an increase of amino acids and organic acids (except glutamic acid) were observed in the samples collected in the morning, whereas sugars and secondary metabolite levels increased in the tomato leaves harvested in the evening.

Over‐expression of putative transcriptional coactivator KELP interferes withTomato mosaic viruscell‐to‐cell movement

Tomato mosaic virus (ToMV) encodes a movement protein (MP) that is necessary for virus cell-to-cell movement. We have demonstrated previously that KELP, a putative transcriptional coactivator of Arabidopsis thaliana, and its orthologue from Brassica campestris can bind to ToMV MP in vitro. In this study, we examined the effects of the transient over-expression of KELP on ToMV infection and the intracellular localization of MP in Nicotiana benthamiana, an experimental host of the virus. In co-bombardment experiments, the over-expression of KELP inhibited virus cell-to-cell movement. The N-terminal half of KELP (KELPdC), which had been shown to bind to MP, was sufficient for inhibition. Furthermore, the over-expression of KELP and KELPdC, both of which were co-localized with ToMV MP, led to a reduction in the plasmodesmal association of MP. In the absence of MP expression, KELP was localized in the nucleus and the cytoplasm by the localization signal in its N-terminal half. It was also shown that ToMV amplified normally in protoplasts prepared from leaf tissue that expressed KELP transiently. These results indicate that over-expressed KELP interacts with MP in vivo and exerts an inhibitory effect on MP function for virus cell-to-cell movement, but not on virus amplification in individual cells.

Overexpression of a rice defense‐related F‐box protein gene OsDRF1 in tobacco improves disease resistance through potentiation of defense gene expression†

F-box proteins play important roles in plant growth/development and responses to environmental stimuli through targeting substrates into degradation machinery. A rice defense-related F-box protein gene, OsDRF1, was cloned and identified during a course of study aimed at elucidating the molecular basis of induced immunity in rice. OsDRF1 encodes a protein of 328 amino acids, containing a highly conserved F-box domain. Expression of OsDRF1 was induced upon treatment with benzothiadiazole (BTH), a chemical inducer of defense responses in rice. Moreover, in BTH-treated rice seedlings, expression of OsDRF1 was further induced by infection with Magnaporthe grisea, the rice blast fungus, compared with those in water-treated seedlings. OsDRF1 was also upregulated in rice seedlings after treatment with ABA. Overexpression of OsDRF1 in transgenic tobacco resulted in enhanced disease resistance against tomato mosaic virus (ToMV) and Pseudomonas syringae pv. tabaci and strengthened expression of defense-related genes after salicylic acid treatment or ToMV infection. Root elongation of the OsDRF1-overexpressing transgenic seedlings was significantly inhibited by ABA, indicating that overexpression of OsDRF1 resulted in increased ABA sensitivity. The results suggest that OsDRF1 plays a role in disease resistance via upregulating defense-related gene expression and that OsDRF1 may also be involved in the response to ABA.

Responses of Helicoverpa armigera to Tomato Plants Previously Infected by ToMV or Damaged by H. armigera

We report the comparative inducing effects of a phytopathogen and a herbivorous arthropod on the performance of an herbivore. Tomato, Lycopersicon esculentum Mill., was used as the test plant, and tomato mosaic virus (ToMV) and corn earworm, Helicoverpa armigera Hübner, were used as the phytopathogen and herbivore, respectively. There were decreases in the efficiency of conversion of ingested food and efficiency of conversion of digested food when H. armigera was reared on tomato plants that had been previously inoculated with ToMV. However, virus inoculation did not affect feeding or oviposition preferences by H. armigera. In contrast, approximate digestibility, total consumption, relative growth rate, and relative consumption rate were lower for fourth-instar H. armigera that fed on plants previously damaged by the same herbivore. Feeding and oviposition were both deterred for H. armigera that fed on previously damaged plants. The duration of development of H. armigera was also prolonged under this treatment. Infection by ToMV and feeding damage by H. armigera increased the host plant's peroxidase and polyphenol oxidase activity, respectively, suggesting that the performance of H. armigera may be affected by the induced phytochemistry of the host plant. Overall, this study indicated that, in general, insect damage has a stronger effect than ToMV infection on plant chemistry and, subsequently, on the performance of H. armigera.

Effect of Plant Extracts and Acetone Precipitated Proteins from Six Medicinal Plants Against Tobamovirus Infection

The present study was taken up to evaluate the effect of leaf extracts and acetone-precipitated protein of medicinal plants on seed-borne Tobacco Mosaic Virus (TMV) and Tomato Mosaic Virus (ToMV) infection. The antiviral activity was tested on indicator plant Nicotiana glutinosa. Acetone precipitated proteins and solvent extracts of six medicinal plants were tested for their effect on tobamovirus infection. The aqueous leaf extracts of Guava, Phyllanthus and Thuja were effective in reducing the infection by ToMV. The acetone-precipitated fractions of Tridax, Thuja, Guava and Tulsi were effective in reducing the infection by TMV. The solvent extract of Guava was effective in reducing the ToMV infection. Guava extract was subjected to TLC and the fractions were tested for their antiviral activity. Fraction with RF value of 0.014 proved to be effective in reducing the ToMV infection. The solvent extract of Thuja was effective in reducing TMV infection. TLC fraction of Thuja extract with the R F value of 0.12 reduced the TMV infection. Along with this, effect of aqueous leaf extracts on seed quality parameters of tomato and bell pepper was studied.

Tomato mosaic virus replication protein suppresses virus-targeted posttranscriptional gene silencing.

Posttranscriptional gene silencing (PTGS), a homology-dependent RNA degradation system, has a role in defending against virus infection in plants, but plant viruses encode a suppressor to combat PTGS. Using transgenic tobacco in which the expression of green fluorescent protein (GFP) is posttranscriptionally silenced, we investigated a tomato mosaic virus (ToMV)-encoded PTGS suppressor. Infection with wild-type ToMV (L strain) interrupted GFP silencing in tobacco, coincident with visible symptoms, whereas some attenuated strains of ToMV (L(11) and L(11)A strains) failed to suppress GFP silencing. Analyses of recombinant viruses containing the L and L(11)A strains revealed that a single base change in the replicase gene, which causes an amino acid substitution, is responsible for the symptomless and suppressor-defective phenotypes of the attenuated strains. An agroinfiltration assay indicated that the 130K replication protein acts as a PTGS suppressor. Small interfering RNAs (siRNAs) of 21 to 25 nucleotides accumulated during ToMV infection, suggesting that the major target of the ToMV-encoded suppressor is downstream from the production of siRNAs in the PTGS pathway. Analysis with GFP-tagged recombinant viruses revealed that the suppressor inhibits the establishment of the ToMV-targeted PTGS system in the inoculated leaves but does not detectably suppress the activity of the preexisting, sequence-specific PTGS machinery there. Taken together, these results indicate that it is likely that the ToMV-encoded suppressor, the 130K replication protein, blocks the utilization of silencing-associated small RNAs, so that a homology-dependent RNA degradation machinery is not newly formed.

Yield and fruit quality losses caused by ToMV in pepino (Solanum muricatum L.) and search for sources of resistance

Tomato mosaic virus (ToMV) is a limiting factor for the success of pepino (Solarium muricatum) as a new crop. The effects of ToMV infection on total and marketable yield, fruit weight, length/width ratio and soluble solids content (SSC) have been studied in two commercial clones (`Sweet Long' and `Sweet Round'). ToMV infection depressed total yield in infected plants of `Sweet Long' (43.1%), while it had no effect on this trait in `Sweet Round' . Marketable yield was dramatically reduced by ToMV infection in both clones, 94% in `Sweet Long' and 100% in `Sweet Round'. Infected plants of clone `Sweet Long' had a lower weight than healthy plants. Although no differences in fruit weight were detected in `Sweet Round' between ToMV infected and healthy plants, many fruits from infected plants showed deformities. Changes in fruit length/width ratio and SSC as a result of ToMV infection were not relevant, but fruit quality was lower in infected fruits, most of which had corky-like flesh. Forty-two clones from cultivated (S. muricatum), wild (S. caripense and S. tabanoense) and interspecific hybrids were tested for ToMV resistance. All but seven clones (four from S. muricatum and three from interspecific hybrids S. muricatum × S. caripense) were susceptible. Non-susceptible clones showed variable degrees of resistance and developed hypersensitive local lesions. Among these clones the most promising as sources of variation for resistance to ToMV are those belonging to the cultivated species. Although no immunity was found, plants from these clones remained asymptomatic and absorbance values resulting from the DAS-ELISA tests in these plants were always lower than those of the susceptible control (cv. `Sweet Round'). These sources of resistance may be of great utility in developing commercial clones resistant to this severe disease affecting pepino.

Tomato mosaic virus infection of red spruce on Whiteface Mountain, New York: prevalence and potential impact

Tomato mosaic tobamovirus (ToMV) was detected by enzyme-linked immunosorbent assay in the roots of red spruce (Picearubens Sarg.) on Whiteface Mountain, New York. Both virus incidence and concentration in the roots of red spruce vary by site and were greater in trees with little to moderate crown dieback than in trees with severe dieback. There was no significant association between virus incidence or concentration in the roots of red spruce and elevation on Whiteface Mountain. Multiple regression analysis of virus concentration in the roots, as the dependent variable, was performed against nine selected crown and root variables. In the final regression model, the number of live second-order nonwoody roots per length of first-order nonwoody root and length of the live crown were positively and negatively correlated, respectively, with virus concentration in the roots. These results suggest a complex epidemiology and a potentially significant impact of ToMV infection on the growth of red spruce on Whiteface Mountain.

A cDNA clone of tomato mosaic virus is infectious in plants.

A cDNA clone of tomato mosaic virus (ToMV) genomic RNA was fused to the cauliflower mosaic virus 35S RNA promoter and the nopaline synthase gene polyadenylation signal. The transcriptional initiation site of the 35S RNA promoter was altered by in vitro mutagenesis so that the resulting transcripts start at the first nucleotide of the ToMV sequence. In addition, 12 nucleotides were inserted in the 5' untranslated region of the ToMV genome. This plasmid, pSLN, was used to inoculate several host plants of ToMV. Among five plant species tested, only Chenopodium quinoa accumulated large amounts of viral particles. The infectivities and systemic movements of the resulting viruses were the same as those of virus preparations obtained from a ToMV infection of C. quinoa. Primer extension analyses revealed that the 5' end of the viral genomic RNA was identical to those of RNAs isolated from virus progeny of an infection with T7 transcripts analogous to pSLN. Moreover, the insertion in the 5' untranslated region of the viral genome was stably maintained through several systemic passages of the virus. Thus, inoculation of plants with a plasmid containing a cDNA clone of an RNA virus under the control of a eukaryotic promoter seems to be a convenient alternative to the generation of in vitro transcripts and should facilitate the analysis of viral mutants generated at the DNA level.