ABSTRACT
Viroids are the smallest non-coding infectious RNAs (between 246 and 401 nucleotides) known to be highly structured and replicate autonomously in the host plants. Although they do not encode any peptides, viroids induce visible symptoms in susceptible host plants. This article provides an overview of their physical and biological properties, the diseases they cause and their significance for the plants. The mechanisms underlying the expression of symptoms in host plants, their detection and various strategies employed for diseases prevention are also developed.
Subject(s)
Plant Diseases , Plants , RNA, Viral , Viroids , Viroids/genetics , Viroids/physiology , Plant Diseases/virology , Plant Diseases/prevention & control , RNA, Viral/genetics , RNA, Untranslated/genetics , RNA, Untranslated/physiology , Virus ReplicationABSTRACT
Variations in infection progression with concurrent or prior infections by different viruses, viroids, or their strains are evident, but detailed investigations into viroid variant interactions are lacking. We studied potato spindle tuber viroid intermediate strain (PSTVd-I) to explore variant interactions. Two mutants, U177A/A182U (AU, replication- and trafficking-competent) and U178G/U179G (GG, replication-competent but trafficking-defective) on loop 27 increased cell-to-cell movement of wild-type (WT) PSTVd without affecting replication. In mixed infection assays, both mutants accelerated WT phloem unloading, while only AU promoted it in separate leaf assays, suggesting that enhancement of WT infection is not due to systemic signals. The mutants likely enhance WT infection due to their loop-specific functions, as evidenced by the lack of impact on WT infection seen with the distantly located G347U (UU) mutant. This study provides the first comprehensive analysis of viroid variant interactions, highlighting the prolonged phloem unloading process as a significant barrier to systemic spread.
Subject(s)
Mutation , Phloem , Plant Diseases , RNA, Viral , Viroids , Viroids/genetics , Viroids/physiology , Phloem/virology , Phloem/metabolism , RNA, Viral/genetics , RNA, Viral/metabolism , Plant Diseases/virology , Virus Replication , Nicotiana/virology , Solanum tuberosum/virology , Plant Leaves/virologyABSTRACT
Peach latent mosaic viroid (PLMVd) infects peach trees in China and induces a conspicuous albino phenotype (peach calico, PC) that is closely associated with variants containing a 12-to-14 nucleotide hairpin insertion capped by a U-rich loop. Initially, PC disease distribution was limited to parts of Italy, and it was first detected in the field in China in 2019. To explore the molecular and biological characteristics of PLMVd PC isolates in peach in China, we conducted a comprehensive analysis of disease phenotype development and investigated the data-associated pathogenicity and in vivo dynamics of the Chinese isolate PC-A2 using slash-inoculation into GF-305 peach seedlings. Inoculated seedlings displayed PC symptoms much earlier following topping treatment, and PLMVd infectivity was further assessed using bioassay and semiquantitative RT-PCR experiments. Evolutionary analysis showed that the PC isolate and its progeny variants clustered into a single phylogroup distinct from reference PC-C40 isolates from Italy and PC-K1 and PC-K2 from South Korea. Some PC-A2 progeny variants from green leaves of PC-expressing seedlings showed unbalanced point mutations in hairpin stems compared with the PC-C40 reference sequence and constituted a new stem insertion type. The results reveal associations between the recessive phenotypes of peach albino symptoms and base variation in hairpin stem insertions relative to the PC-C40/chloroplastic heat shock protein 90 reference sequence.
Subject(s)
Plant Diseases , Prunus persica , Viroids , Plant Diseases/virology , Prunus persica/virology , China , Viroids/genetics , Viroids/physiology , Viroids/pathogenicity , Viroids/isolation & purification , Phylogeny , Mutation , Phenotype , RNA, Viral/genetics , Seedlings/virology , Plant Leaves/virologyABSTRACT
Sustainable production of pome fruit crops is dependent upon having virus-free planting materials. The production and distribution of plants derived from virus- and viroid-negative sources is necessary not only to control pome fruit viral diseases but also for sustainable breeding activities, as well as the safe movement of plant materials across borders. With variable success rates, different in vitro-based techniques, including shoot tip culture, micrografting, thermotherapy, chemotherapy, and shoot tip cryotherapy, have been employed to eliminate viruses from pome fruits. Higher pathogen eradication efficiencies have been achieved by combining two or more of these techniques. An accurate diagnosis that confirms complete viral elimination is crucial for developing effective management strategies. In recent years, considerable efforts have resulted in new reliable and efficient virus detection methods. This comprehensive review documents the development and recent advances in biotechnological methods that produce healthy pome fruit plants. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.
Subject(s)
Crops, Agricultural , Fruit , Plant Diseases , Viroids , Plant Diseases/virology , Plant Diseases/prevention & control , Fruit/virology , Crops, Agricultural/virology , Viroids/genetics , Viroids/physiology , Plant Viruses/physiology , Biotechnology/methods , Prunus domestica/virologyABSTRACT
Hop latent viroid (HLVd) is the biggest concern for cannabis and hop growers worldwide. Although most HLVd-infected plants remain asymptomatic, research on hops has demonstrated a decrease in both the α-bitter acid and terpene content of hop cones, which affects their economic value. The HLVd-associated "dudding" or "duds" disease of cannabis was first reported in 2019 in California. Since then, the disease has become widespread in cannabis-growing facilities across North America. Although severe yield loss associated with duds disease has been recorded, little scientific information is available to growers in order to contain HLVd. Consequently, this review aims to summarise all of the scientific information available on HLVd so as to be able to understand the effect of HLVd on yield loss, cannabinoid content, terpene profile, disease management and inform crop protection strategies.
Subject(s)
Cannabis , Carlavirus , Plant Diseases , Viroids , Cannabis/chemistry , Cannabis/virology , Humulus/chemistry , Humulus/virology , North America , Plant Diseases/prevention & control , Plant Diseases/virology , Viroids/pathogenicity , Viroids/physiology , Carlavirus/pathogenicity , Carlavirus/physiology , Host SpecificityABSTRACT
Circular RNAs (circRNAs) are regulatory molecules involved in the modulation of gene expression. Although originally assumed as non-coding RNAs, recent studies have evidenced that animal circRNAs can act as translatable transcripts. The study of plant-circRNAs is incipient, and no autonomous coding plant-circRNA has been described yet. Viroids are the smallest plant-pathogenic circRNAs known to date. Since their discovery 50 years ago, viroids have been considered valuable systems for the study of the structure-function relationships in RNA, essentially because they have not been shown to have coding capacity. We used two pathogenic circRNAs (Hop stunt viroid and Eggplant latent viroid) as experimental tools to explore the coding potential of plant-circRNAs. Our work supports that the analysed viroids contain putative ORFs able to encode peptides carrying subcellular localization signals coincident with the corresponding replication-specific organelle. Bioassays in well-established hosts revealed that mutations in these ORFs diminish their biological efficiency. Interestingly, circular forms of HSVd and ELVd were found to co-sediment with polysomes, revealing their physical interaction with the translational machinery of the plant cell. Based on this evidence we hypothesize about the possibility that plant circRNAs in general, and viroids in particular, can act, under certain cellular conditions, as non-canonical translatable transcripts.
Subject(s)
Plant Diseases/genetics , Plant Viruses/physiology , Plants/metabolism , RNA, Circular/genetics , RNA, Viral/genetics , Viroids/physiology , Virus Replication , Plant Diseases/virology , Plants/genetics , Plants/virology , Solanum melongena/virologyABSTRACT
Viroids are infectious non-coding RNAs that infect plants. During infection, viroid RNAs are targeted by Dicer-like proteins, generating viroid-derived small RNAs (vd-sRNAs) that can guide the sequence specific cleavage of cognate host mRNAs via an RNA silencing mechanism. To assess the involvement of these pathways in pathogenesis associated with nuclear-replicating viroids, high-throughput sequencing of sRNAs and degradome analysis were carried out on tomato and Nicotiana benthamiana plants infected by potato spindle tuber viroid (PSTVd). Both hosts develop similar stunting and leaf curling symptoms when infected by PSTVd, thus allowing comparative analyses. About one hundred tomato mRNAs potentially targeted for degradation by vd-sRNAs were initially identified. However, data from biological replicates and comparisons between mock and infected samples reduced the number of bona fide targets-i.e., those identified with high confidence in two infected biological replicates but not in the mock controls-to only eight mRNAs that encode proteins involved in development, transcription or defense. Somewhat surprisingly, results of RT-qPCR assays revealed that the accumulation of only four of these mRNAs was inhibited in the PSTVd-infected tomato. When these analyses were extended to mock inoculated and PSTVd-infected N. benthamiana plants, a completely different set of potential mRNA targets was identified. The failure to identify homologous mRNA(s) targeted by PSTVd-sRNA suggests that different pathways could be involved in the elicitation of similar symptoms in these two species. Moreover, no significant modifications in the accumulation of miRNAs and in the cleavage of their targeted mRNAs were detected in the infected tomato plants with respect to the mock controls. Taken together, these data suggest that stunting and leaf curling symptoms induced by PSTVd are elicited by a complex plant response involving multiple mechanisms, with RNA silencing being only one of the possible components.
Subject(s)
Host-Pathogen Interactions , RNA Interference , Viroids/physiology , Solanum lycopersicum , RNA, Messenger/metabolism , NicotianaABSTRACT
Viroids are single-stranded circular noncoding RNAs that infect plants. The noncoding nature indicates that viroids must harness their RNA genomes to redirect host machinery for infection. Therefore, the viroid model provides invaluable opportunities for delineating fundamental principles of RNA structure-function relationships and for dissecting the composition and mechanism of RNA-related cellular machinery. There are two viroid families, Pospiviroidae and Avsunviroidae. Members of both families replicate via the RNA-based rolling-circle mechanism with some variations. Viroid replication is generally divided into three steps: transcription, cleavage, and ligation. Decades of studies have uncovered numerous viroid RNA structures with a regulatory role in replication and multiple enzymes critical for the three replication steps. This review discusses these findings and highlights the latest discoveries. Future studies will continue to elucidate regulatory factors and mechanism of host machinery exploited by viroids and provide new insights into host-viroid interactions in the context of pathogenesis.
Subject(s)
Viroids/physiology , Virus Replication/physiology , DNA-Directed RNA Polymerases/metabolism , Host-Pathogen Interactions , Nucleotide Motifs , Plant Diseases/virology , Plant Proteins/genetics , Plant Proteins/metabolism , RNA, Viral/chemistry , RNA, Viral/genetics , RNA, Viral/metabolism , Transcription, Genetic , Viral Proteins/genetics , Viral Proteins/metabolism , Viroids/classification , Viroids/pathogenicityABSTRACT
Members of the family Pospiviroidae have single-stranded circular RNA genomes that adopt a rod-like or a quasi-rod-like conformation. These genomes contain a central conserved region that is involved in replication in the nucleus through an asymmetric RNA-RNA rolling-circle mechanism. Members of the family Pospiviroidae lack the hammerhead ribozymes that are typical of viroids classified in the family Avsunviroidae. The family Pospiviroidae includes the genera Apscaviroid, Cocadviroid, Coleviroid, Hostuviroid and Pospiviroid, with >25 species. This is a summary of the ICTV Report on the family Pospiviroidae, which is available at ictv.global/report/pospiviroidae.
Subject(s)
RNA, Viral/genetics , Viroids/classification , Viroids/genetics , Virus Replication , Genome, Viral , RNA/genetics , RNA, Catalytic/genetics , RNA, Circular , Viroids/physiologyABSTRACT
The initial molecular lesions through which viroids, satellite RNAs and viruses trigger signal cascades resulting in plant diseases are hotly debated. Since viroids are circular non-protein-coding RNAs of â¼250-430 nucleotides, they appear very convenient to address this issue. Viroids are targeted by their host RNA silencing defense, generating viroid-derived small RNAs (vd-sRNAs) that are presumed to direct Argonaute (AGO) proteins to inactivate messenger RNAs, thus initiating disease. Here, we review the existing evidence. Viroid-induced symptoms reveal a distinction. Those attributed to vd-sRNAs from potato spindle tuber viroid and members of the family Pospiviroidae (replicating in the nucleus) are late, non-specific and systemic. In contrast, those attributed to vd-sRNAs from peach latent mosaic viroid (PLMVd) and other members of the family Avsunviroidae (replicating in plastids) are early, specific and local. Remarkably, leaf sectors expressing different PLMVd-induced chloroses accumulate viroid variants with specific pathogenic determinants. Some vd-sRNAs containing such determinant guide AGO1-mediated cleavage of mRNAs that code for proteins regulating chloroplast biogenesis/development. Therefore, the initial lesions and the expected phenotypes are connected by short signal cascades, hence supporting a cause-effect relationship. Intriguingly, one virus satellite RNA initiates disease through a similar mechanism, whereas in the Pospiviroidae and in plant viruses the situation remains uncertain.
Subject(s)
Host-Pathogen Interactions , Plant Diseases/virology , Plants/genetics , Plants/virology , RNA Interference , Viroids/physiology , Viroids/geneticsABSTRACT
Potato spindle tuber viroid (PSTVd) causes systemic infection in plant hosts. There are many studies on viroid-host plant interactions, but they have predominantly focused on the aboveground part of the plant. Here, we investigated transcriptomic profile changes in tomato roots systemically infected with mild or severe PSTVd variants using a combined microarray/RNA-seq approach. Analysis indicated differential expression of genes related to various Gene Ontology categories depending on the stage of infection and PSTVd variant. A majority of cell-wall-related genes were down-regulated at early infection stages, but at the late stage, the number of up-regulated genes increased significantly. Along with observed alterations of many lignin-related genes, performed lignin quantification indicated their disrupted level in PSTVd-infected roots. Altered expression of genes related to biosynthesis and signaling of auxin and cytokinin, which are crucial for lateral root development, was also identified. Comparison of both PSTVd infections showed that transcriptional changes induced by the severe variant were stronger than those caused by the mild variant, especially at the late infection stage. Taken together, we showed that similarly to aboveground plant parts, PSTVd infection in the underground tissues activates the plant immune response.
Subject(s)
Plant Diseases/virology , Plant Proteins/genetics , Solanum lycopersicum/genetics , Solanum lycopersicum/virology , Viroids/physiology , Gene Expression Regulation, Plant , Solanum lycopersicum/immunology , Plant Diseases/genetics , Plant Diseases/immunology , Plant Proteins/immunology , Plant Roots/genetics , Plant Roots/immunology , Plant Roots/virology , Plant Viruses/genetics , Plant Viruses/isolation & purification , Plant Viruses/physiology , Transcriptome , Viroids/genetics , Viroids/isolation & purificationABSTRACT
The Chittering strain of potato spindle tuber viroid (PSTVd) infects solanaceous crops and wild plants in the subtropical Gascoyne Horticultural District of Western Australia. Classical PSTVd indicator hosts tomato cultivar Rutgers (R) and potato cultivar Russet Burbank (RB) and currently widely grown tomato cultivars Petula (P) and Swanson (S) and potato cultivars Nadine (N) and Atlantic (A) were inoculated with this strain to study its pathogenicity, quantify fruit or tuber yield losses, and establish whether tomato strains might threaten potato production. In potato foliage, infection caused spindly stems, an upright growth habit, leaves with ruffled margins and reduced size, and upward rolling and twisting of terminal leaflets (RB, A, and N); axillary shoot proliferation (A); severe plant stunting (N and RB); and necrotic spotting of petioles and stems (RB). Tubers from infected plants were tiny (N) or small and "spindle shaped" with (A) or without (RB) cracking. Potato foliage dry weight biomass was decreased by 30 to 44% in A and RB and 37% in N, whereas tuber yield was diminished by 50 to 89% in A, 69 to 71% in RB, and 90% in N. In tomato foliage, infection caused epinasty and rugosity in apical leaves, leaf chlorosis, and plant stunting (S, P, and N); cupped leaves (S and P); and reduced leaf size, flower abortion, and necrosis of midribs, petioles, and stems (R). Mean tomato fruit size was greatly decreased in all three cultivars. Tomato foliage dry weight biomass was diminished by 40 to 53% (P), 42% (S), and 37 to 51% (R). Tomato fruit yield was decreased by 60 to 76% (P), 52% (S), and 64 to 89% (R), respectively. Thus, the tomato strain studied was highly pathogenic to classical indicator and representative current tomato and potato cultivars, causing major losses in fruit and tuber yields. Tomato PSTVd strains, therefore, pose a threat to tomato and potato industries worldwide.
Subject(s)
Plant Diseases , Solanum lycopersicum , Solanum tuberosum , Viroids , Solanum lycopersicum/virology , Plant Diseases/virology , Solanum tuberosum/virology , Viroids/physiology , Western AustraliaABSTRACT
Characterization of viroid-derived small RNAs (vd-sRNAs) is important to understand viroid-host interactions; however, vd-sRNAs belonging to the genus Coleviroid are yet to be identified and characterized. Herein, we used coleus plants singly infected with coleus blumei viroid (CbVd)-1, -5, or -6 and doubly infected with CbVd-1 and -5 to identify and analyze their vd-sRNAs. We found sense and antisense vd-sRNAs for CbVd-1, -5 and -6, and 22-nt vd-sRNAs were the most abundant; moreover, the 5'-terminal nucleotides (nts) of CbVd-1, -5, and -6 were biased toward U and C, and sRNAs derived from these three viroids were unevenly distributed along their genomes. We also noted that CbVd-5 and -6 share a fragment that forms the right half of the rod-like secondary structure of these viroids, which implied that they generated almost the same type of vd-sRNAs. This finding indicated that vd-sRNA biogenesis is mainly determined by the primary sequence of their substrates. More importantly, we found two complementary vd-sRNAs (22 nt) that were generated from the central conserved region (CCR) of these three viroids, suggesting an important role of CCR in vd-sRNA biogenesis. In conclusion, our results provide novel insight into the biogenesis of vd-sRNAs and the biological roles of CCR.
Subject(s)
Coleus/virology , RNA, Small Untranslated/genetics , RNA, Viral/genetics , Viroids/genetics , Base Sequence , Genome, Viral/genetics , Nucleic Acid Conformation , RNA, Small Untranslated/biosynthesis , Viroids/metabolism , Viroids/physiologyABSTRACT
Viroids are pathogenic agents that have a small, circular noncoding RNA genome. They have been found only in plant species; therefore, their infectivity and pathogenicity in other organisms remain largely unexplored. In this study, we investigate whether plant viroids can replicate and induce symptoms in filamentous fungi. Seven plant viroids representing viroid groups that replicate in either the nucleus or chloroplast of plant cells were inoculated to three plant pathogenic fungi, Cryphonectria parasitica, Valsa mali, and Fusarium graminearum By transfection of fungal spheroplasts with viroid RNA transcripts, each of the three, hop stunt viroid (HSVd), iresine 1 viroid, and avocado sunblotch viroid, can stably replicate in at least one of those fungi. The viroids are horizontally transmitted through hyphal anastomosis and vertically through conidia. HSVd infection severely debilitates the growth of V. mali but not that of the other two fungi, while in F. graminearum and C. parasitica, with deletion of dicer-like genes, the primary components of the RNA-silencing pathway, HSVd accumulation increases. We further demonstrate that HSVd can be bidirectionally transferred between F. graminearum and plants during infection. The viroids also efficiently infect fungi and induce disease symptoms when the viroid RNAs are exogenously applied to the fungal mycelia. These findings enhance our understanding of viroid replication, host range, and pathogenicity, and of their potential spread to other organisms in nature.
Subject(s)
Disease Transmission, Infectious , Fungi/virology , Plant Diseases/microbiology , Plant Viruses/pathogenicity , Viroids/pathogenicity , Fungi/growth & development , Fungi/pathogenicity , Mycelium/virology , RNA, Viral/metabolism , Viroids/physiology , Virus ReplicationABSTRACT
Transcription factors (TFs) play a major role in controlling gene expression by intricately regulating diverse biological processes such as growth and development, the response to external stimuli and the activation of defense responses. The systematic identification and classification of TF genes are essential to gain insight into their evolutionary history, biological roles, and regulatory networks. In this study, we performed a global mining and characterization of hop TFs and their involvement in Citrus bark cracking viroid CBCVd infection by employing a digital gene expression analysis. Our systematic analysis resulted in the identification of a total of 3,818 putative hop TFs that were classified into 99 families based on their conserved domains. A phylogenetic analysis classified the hop TFs into several subgroups based on a phylogenetic comparison with reference TF proteins from Arabidopsis thaliana providing glimpses of their evolutionary history. Members of the same subfamily and subgroup shared conserved motif compositions. The putative functions of the CBCVd-responsive hop TFs were predicted using their orthologous counterparts in A. thaliana. The analysis of the expression profiling of the CBCVd-responsive hop TFs revealed a massive differential modulation, and the expression of the selected TFs was validated using qRT-PCR. Together, the comprehensive integrated analysis in this study provides better insights into the TF regulatory networks associated with CBCVd infections in the hop, and also offers candidate TF genes for improving the resistance in hop against viroids.
Subject(s)
Humulus/immunology , Plant Diseases/virology , Plant Proteins/genetics , Transcription Factors/genetics , Viroids/physiology , Gene Expression Profiling , Humulus/classification , Humulus/genetics , Humulus/virology , Phylogeny , Plant Bark/immunology , Plant Bark/virology , Plant Diseases/genetics , Plant Diseases/immunology , Plant Proteins/immunology , Transcription Factors/immunology , Viroids/geneticsABSTRACT
Viroids are small, non-coding, circular RNA molecules that infect plants. Different hypotheses for their evolutionary origin have been put forward, such as an early emergence in a precellular RNA World or several de novo independent evolutionary origins in plants. Here, we discuss the plausibility of de novo emergence of viroid-like replicons by giving theoretical support to the likelihood of different steps along a parsimonious evolutionary pathway. While Avsunviroidae-like structures are relatively easy to obtain through evolution of a population of random RNA sequences of fixed length, rod-like structures typical of Pospiviroidae are difficult to fix. Using different quantitative approaches, we evaluated the likelihood that RNA sequences fold into a rod-like structure and bear specific sequence motifs facilitating interactions with other molecules, e.g., RNA polymerases, RNases, and ligases. By means of numerical simulations, we show that circular RNA replicons analogous to Pospiviroidae emerge if evolution is seeded with minimal circular RNAs that grow through the gradual addition of nucleotides. Further, these rod-like replicons often maintain their structure if independent functional modules are acquired that impose selective constraints. The evolutionary scenario we propose here is consistent with the structural and biochemical properties of viroids described to date.
Subject(s)
Replicon , Viroids/genetics , Evolution, Molecular , Nucleic Acid Conformation , RNA, Circular/chemistry , RNA, Circular/genetics , RNA, Viral/chemistry , RNA, Viral/genetics , Viral Proteins/genetics , Viroids/chemistry , Viroids/classification , Viroids/physiology , Virus ReplicationABSTRACT
Plant-viroid interactions represent a valuable model for delineating structure-function relationships of noncoding RNAs. For various functional studies, it is desirable to minimize sample variations by using DNA, RNA, and proteins co-purified from the same samples. Currently, most of the co-purification protocols rely on TRI Reagent (Trizol as a common representative) and require protein precipitation and dissolving steps, which render difficulties in experimental handling and high-throughput analyses. Here, we established a simple and robust method to minimize the precipitation steps and yield ready-to-use RNA and protein in solutions. This method can be applied to samples in small quantities, such as protoplasts. Given the ease and the robustness of this new method, it will have broad applications in virology and other disciplines in molecular biology.
Subject(s)
Arabidopsis/cytology , Molecular Biology/methods , Protoplasts/virology , Viroids/physiology , Arabidopsis/genetics , Arabidopsis/virology , Arabidopsis Proteins/genetics , Arabidopsis Proteins/isolation & purification , Arabidopsis Proteins/metabolism , DNA, Plant/genetics , DNA, Plant/isolation & purification , DNA, Plant/metabolism , Genome, Plant , Host-Pathogen Interactions , Protoplasts/metabolism , RNA, Plant/isolation & purification , RNA, Plant/metabolism , RNA, Viral/isolation & purification , RNA, Viral/metabolism , Viroids/genetics , Virus ReplicationABSTRACT
The stunting disease, incited by chrysanthemum stunt viroid (CSVd), has become a serious problem in chrysanthemum production areas worldwide. Here we identified 46 weed species from chrysanthemum fields in two producing regions of the State of São Paulo, Brazil. The mechanical inoculation of these weeds with a Brazilian CSVd isolate revealed that this viroid was able to infect 17 of these species, in addition to chrysanthemum, tomato and potato. Plants of Oxalis latifolia and chrysanthemum naturally infected with CSVd were found in chrysanthemum fields in Colombia, which is the first CSVd report in that country. Therefore, weeds have the potential to act as reservoirs of CSVd in the field. These results are the first reports of experimental CSVd infection in the following species: Amaranthus viridis, Cardamine bonariensis, Chamaesyce hirta, Conyza bonariensis, Digitaria sanguinalis, Gomphrena globosa, Helianthus annuus, Lupinus polyphyllus, Mirabilis jalapa, Oxalis latifolia, Portulaca oleracea and Catharanthus roseus. The phylogenetic analyses of the CSVd variants identified herein showed three groups with Brazilian CSVd variants distributed in them all, which suggests that Brazilian CSVd isolates may have different origins through successive introductions of infected germplasm of chrysanthemum in Brazil.
Subject(s)
Chrysanthemum/virology , Disease Reservoirs/virology , Plant Diseases/virology , Plant Weeds/virology , Viroids/physiology , Animals , Brazil , Colombia , Disease Reservoirs/classification , Genetic Variation , Host Specificity , Solanum lycopersicum/virology , Phylogeny , Plant Weeds/classification , RNA, Viral/genetics , Solanum tuberosum/virology , Viroids/classification , Viroids/genetics , Viroids/isolation & purificationABSTRACT
Rasta is a virus-like disease of unknown etiology affecting tomato (Solanum lycopersicum) plants in Ghana. Symptoms include stunting; epinasty, crumpling, and chlorosis of leaves; and necrosis of leaf veins, petioles, and stems. Leaf samples with rasta symptoms were collected from commercial tomato fields in Ghana in October 2012 and applied to FTA cards, and RNA extracts were prepared. Reverse-transcription polymerase chain reaction (RT-PCR) tests with primers for Columnea latent viroid, which causes rasta-like symptoms in tomato plants in Mali, were negative, whereas tests with degenerate viroid primer pairs were inconclusive. However, tomato seedlings (Early Pak 7) mechanically inoculated with RNA extracts of 10 of 13 samples developed rasta-like symptoms. In RT-PCR tests with RNA from leaves of the 10 symptomatic seedlings and primers for Potato spindle tuber viroid (PSTVd) or Tomato apical stunt viroid (TASVd), the expected size (approximately 360 bp) of DNA fragment was amplified from eight and two seedlings, respectively. Sequence analyses confirmed that these fragments were from PSTVd and TASVd isolates, and revealed a single PSTVd haplotype and two TASVd haplotypes. The PSTVd and TASVd isolates from Ghana had high nucleotide identities (>94%) with isolates from other geographic regions. In a host range study, PSTVd and TASVd isolates from Ghana induced rasta symptoms in the highly susceptible tomato cultivar Early Pak 7 and mild or no symptoms in Glamour, and symptomless infections in a number of other solanaceous species. PSTVd and TASVd isolates were seed associated and possibly seed transmitted.