Plant Virus

Plant viruses have evolved a wide array of strategies to ensure efficient transfer from one host to the next. Any organism feeding on infected plants and traveling between plants can potentially act as a virus transport device. Such organisms, designated vectors, are found among parasitic fungi, root nematodes and plant-feeding arthropods, particularly insects. Due to their extremely specialized feeding behavior – exploring and sampling all plant tissues, from the epidermis to the phloem and xylem – aphids are by far the most important vectors, transmitting nearly 30% of all plant virus species described to date. Several different interaction patterns have evolved between viruses and aphid vectors and, over the past century, a tremendous number of studies have provided details of the underlying mechanisms. This article presents an overview of the different types of virus-aphid relationships, state-of-the-art knowledge of the molecular processes underlying these interactions, and the remaining black boxes waiting to be opened in the near future.Les virus de plantes ont développé une grande diversité de stratégies pour assurer leur transmission efficace d’un hôte malade vers un nouvel hôte sain. Tout organisme se nourrissant sur une plante infectée, et capable de se déplacer vers d’autres plantes, peut potentiellement transporter des virus. De tels organismes sont dénommés « vecteurs » et se trouvent parmi les champignons phytopathogènes, les nématodes des racines, et les arthropodes, en particulier les insectes. Du fait de leur comportement alimentaire très particulier, explorant et échantillonnant différents tissus végétaux (épiderme, mésophylle et tissus vasculaires), les pucerons sont de loin les vecteurs de virus les plus performants, transmettant près de 30 % des espèces de virus de plantes décrites à ce jour. Plusieurs mécanismes d’interaction virus-puceron très différents ont évolué et, depuis plus d’un siècle, un effort de recherche très important a permis de les décortiquer, au moins pour certaines espèces virales modèles. Cet article présente une synthèse de ces connaissances, les trajets des virus dans leurs pucerons vecteurs, les mécanismes cellulaires et moléculaires de leurs interactions et les grandes inconnues qui persistent et qui devront être élucidées dans les années à venir.

BBTD or Banana Bunchy Top Disease caused by BBTV known as Banana Bunchy Top Virus belongs to the genus Babuvirus and family Nanoviridae affects Musa genus and generally transmitted through aphid vectors on a worldwide pandemic basis. Due to BBTV there are heavy significant loss to Bananas worldwide with various infectious symptoms such as stunted growth, Bunchy appearance on leaves, yield loss etc. BBTV has its integral genome that comprises of a total of six circular ss-DNA genomic components and its isolates are known worldwide. The genomic pathway of BBTV has been studied in great details and molecular approaches has been compared to other single stranded plant viruses as well. Several detection and disease management methods are there some of these are very new approach. So, in this review I discuss spread and effect of a popularized vector born Banana Bunchy Top Virus and its different detection and management approach. Recently searches are going on to enumerate protein function and host viral interaction in a better way for prevention.

In eukaryotes, RNA silencing is a regulatory mechanism that controls gene expression and genome stability through the synthesis of small RNAs (sRNAs) of 20 to 25 nts from inductor RNA molecules with double stranded features (dsRNA). sRNAs bind multienzymatic complexes and provide them with the ability to recognize and silence highly complementary DNA or RNA sequences by transcriptional or post-transcriptional silencing, respectively. This process is activated naturally in plant tissues in the presence of viruses through the formation of viral dsRNAs. As a result, the viral infection is coupled to the synthesis of virus-derived sRNAs (vsRNAs) whose potential regulatory activity is associated not only with the function of RNA silencing as an antiviral defense mechanism but also with phenomena such as viral pathogenesis or host range. In this thesis, we used different sequencing techniques and molecular hybridization methods in the model system Tobacco rattle virus (TRV)-Arabidopsis thaliana and other plant-virus systems to infer the composition and structure of the vsRNA populations formed in infected tissues. We also investigated the genetic components and structural requirements of the plant RNA silencing machinery to produce vsRNAs. Finally, we analyzed the role of RNA silencing as an antiviral mechanism in plants and its potential to reprogramme the transcriptome of infected cells through functional interactions between vsRNAs and messenger RNAs (mRNA).
Our results reveal that vsRNA populations are abundant, diverse and share common features in all plant-virus systems investigated. Thus vsRNAs show an obvious bias in size distribution (21 and 22 nts are the most abundant classes) and often in their polarity (positive polarity tends to dominate). Another common feature is the generation of vsRNAs from any position along the entire viral genome. Nevertheless, their distribution is heterogeneous, with genomic regions where vsRNAs are poorly represented alternating with more enriched regions in the form of accumulation peaks or larger regions with high sequence densities.
Our work shows that RNase type III Dicer-like, DCL4, DCL3 and DCL2 process, alone or in combination with others, viral dsRNAs to produce vsRNAs of both polarities throughout the TRV genome. Even so, the three DCL enzymes slice viral substrates hierarchically (DCL4> DCL2> DCL3) producing vsRNAs of 21, 22 and 24 nts, respectively. Our data suggest that these enzymes act on inductor dsRNA molecules such as replicative intermediates or imperfect-folded viral RNAs to generate primary vsRNAs. Nevertheless, our results confirm that the majority of the vsRNAs in infected tissues are secondary and result from the activity of DCL on dsRNAs produced by the activity of plant RNA-dependent RNA polymerases (RDR). These enzymes amplify the initial silencing responses by converting viral RNAs into dsRNAs.
The analysis of sequenced libraries suggests that vsRNAs have an affinity for different ARGONAUTE (AGO) proteins that act as silencing effector molecules on RNA or DNA targets. This indicates that vsRNAs could mediate different regulatory pathways that control the expression of virus and host genes. Our data confirm the role of various components of the silencing machinery in antiviral immunity since the genetic inactivation or DCL2, DCL4 and RDR1, RDR6 and RDR2 results in hypersusceptibility to TRV. This phenomenon is not associated with DCL processing of viral dsRNAs but rather likely with vsRNA activity generated from viral dsRNAs. Using bioinformatics we have identified arabidopsis genes that are highly complementary to vsRNAs, which could serve as potential targets of negative regulation during viral infection.

Plant viruses are inducers and targets of RNA
silencing. Viruses counteract with RNA silencing
by expressing silencing-suppressor proteins. Many
of the identified proteins bind siRNAs, which prevents assembly of silencing effector complexes,
and also interfere with their 3’ methylation, which
protects them against degradation. Here, we investigated the 3’ modification of silencing-related small
RNAs in Nicotiana benthamiana plants infected with
viruses expressing RNA silencing suppressors, the
p19 protein of Carnation Italian ringspot virus (CIRV)
and HC-Pro of Tobacco etch virus (TEV). We found
that CIRV had only a slight effect on viral siRNA 3’
modification, but TEV significantly inhibited the 3’
modification of si/miRNAs. We also found that p19
and HC-Pro were able to bind both 3’ modified and
non-modified small RNAs in vivo. The findings suggest that the 3’ modification of viral siRNAs occurs
in the cytoplasm, though miRNA 3’ modification
likely takes place in the nucleus as well. Both silencing suppressors inhibited the 3’ modification of
si/miRNAs when they and small RNAs were transiently co-expressed, suggesting that the inhibition
of si/miRNA 3’modification requires spatial and temporal co-expression. Finally, our data revealed that
a HEN1-like methyltransferase might account for the
small RNA modification at the their 3’-terminal
nucleotide in N. benthamiana.

Insect pests, pathogens, and other types of plant attackers cause great losses and uncertainties to agriculture, increasing economic costs for producers. Apart from decreasing the yield, they lower crop quality by releasing toxins and viruses; insects in fact transmit approximately 80% of all plant viruses. Insecticidal solutions may have detrimental effects on the ecosystem by damaging non-target organisms and pests may quickly develop resistance to such practice. Hence, host plant resistance, via both conventional and transgenic breeding of R genes, is an essential measure for eco-friendly integrated pest management. Yet, R genes are occasionally a scarce resource in some crops’ gene pools; in such cases, other transgenic approaches have been developed to increase crop endurance against insects. Exploring R genes, specifically the tomato Mi-1 gene, will review current knowledge and technological advance in this field. Moreover, insight into other transgenic approaches used for coffee plants will give an appreciation of other available options to confer resistance.

Tomato Yellow Leaf Curl Virus (TYLCV) is currently the most devastating virus of cultivated tomatoes in tropical and subtropical regions, accounting for significant yield losses in cultivated tomato in Ghana. Severe population outbreaks of the whitefly vector (Bemisia tabaci), are usually associated with high incidence of the disease. Resistance breeding is the surest solution to TYLCV in developing viable seeds for increased tomato production in Ghana. The Wild tomato (Solanum pimpinellifolium L.) is a recognised crop Wild species (CWS) with resistance genes to different diseases including the TYLCV disease and possesses good fruit quality traits in Ghana. Three (3) cultivated tomato varieties and seven breeding lines developed from crosses between the Wild tomato and three hybrids, three backcrossed lines and the Wild tomato were evaluated with their parents against TYLCV disease under local field conditions. Field appraisal of whitefly populations, disease incidence and severity, agronomic and yield characteristics of the tomato varieties/breeding lines were undertaken to hasten selection of tolerant/ resistant varieties or breeding lines in the breeding programme. Wild tomato (ISSAP = 0.31 and ISSDP = 0.76) and Woso (ISSAP = 1.90 and ISSDP = 2.27) recorded the least and highest average symptom severity on all plants (ISSAP) and diseased plants only (ISSDP); while the least and highest disease incidence was recorded by the Wild tomato (11.10 %) and Roma (43.05 %). Roma which recorded the highest population of whiteflies in the dry season also exhibited the highest symptom severity on all plants as well as diseased plants during the study period. There was a significant symptom relapse in Wild tomato and Woso x Wild in 6-8 WAT for both ISSAP and ISSDP. Number of fruits per plant, ISSAP  and ISSDP  were positively and/or inversely correlated (r = 0.98, 0.93, -0.83) with average whitefly count, percent disease incidence and yield (t/ha).

Luteovirus is a phytopathogenic monopartite virus of global importance. Re-assortment and recombination by exchanging genome segments play vital role in the virus evolution. Differences in the breadth and specificity of host range, serology and divergence of >10 % amino acids in any gene product (ORF) are the basis of Luteovirus species distinction. To confirm taxonomic status, single ORF that may not accommodate / represent occurrence of genetic recombination (may be of polythetic nature), therefore, may not be sufficient. Instead inference from the whole genome is required. We analyzed distribution of a total of 94 available whole genome Luteovirus sequences in a consistent classification based on pairwise sequence comparison. The adjustment of the two outlier sequences, being recognized, is also discussed

The first biologically active infectious clones of tomato torrado virus (ToTV) were generated and delivered into Nicotiana benthamiana and Solanum lycopersicum plants via Agrobacterium tumefaciens. The engineered constructs consisted of PCR-amplified complementary DNAs derived from the ToTV RNA1 and RNA2 compo

Onion (Allium cepa L.), an important edible species of genus Allium cultivated both in rabi and kharif season in Indian Punjab. It is planted directly by seeds or by bulb sets for table purpose and seed production. Onion is reported to be attacked by many viruses among these, Onion yellow dwarf virus (OYDV), Leek yellow stripe virus(LYSV),Garlic common latent virus, Shallot latent virus and Garlic virus X have been reported from India. These virus(es) attack onion either singly or in combination and causes severe losses. Present study was carried out to study the effect of virus (es) on symptoms and yield parameter. Serological and molecular detection from infected samples confirmed the association of OYDV and LYSV in onion. The virus symptoms associated with onion were categorized in three category (i) Symptomless plant with flattened older leaves (ii) Yellow stripping on leaves, flattening and stunting of plant        (iii )Severe twisting, thinning, partial and complete yellowing of leaves, stunting of plant and such plant did not bolt. The first category symptoms are more prominent in crops raised by seeds, whereas, the other two categories are prominent in crop raised by bulb sets. Growth parameter such as plant height, leaf diameter, number of leaves were recorded both in infected and healthy control. Severe reduction in growth parameter i.e. 16.89, 12.24, 1.50 per cent reduction in height of plant, no of leaves per plant and diameter of leaves, respectively, were recorded over healthy control. Yield parameter viz. bulb weight, seed weights were also recorded. Reduction in bulb weight by 56.16% and seed weight by 7.50% over healthy control was observed. This data revealed that virus complex of onion is responsible for drastic reduction in bulb and seed production in north-western part of India.

We describe a droplet-vitrification cryotherapy method for the eradication of grapevine leafroll-associated virus-3 (GLRaV-3) from diseased in vitro shoots of Vitis plants. The procedure involved pre-culture of 1.0-mm shoot tips containing five to six leaf primordia (LPs) for 3 days with a pre-culture medium containing 0.3 M sucrose, 0.16 mM glutathione and 0.14 mM ascor-bic acid, treatment of the pre-cultured shoot tips for 20 min at room temperature with a loading solution composed of 2 M glycerol and 0.4 M sucrose and exposure to plant vitrification solution 2 (PVS2), prior to freezing in liquid nitrogen of dehydrated shoot tips contained in 2.5-μL PVS2 droplets on aluminium foil strips. Virus localisation showed GLRaV-3 was not present in apical dome (AD) and LPs 1-4, but it was detected in the basal shoot tip region, approximately 0.5 mm from the AD, as well as in LP 5 and more mature tissues. Histological observations identify that only freezing in liquid nitrogen results in the death of all cells in areas of shoot tips harbouring virus, whereas PVS2 treatment does not. Thus, freezing in liquid nitrogen is a necessary step that eradicates GLRaV-3. This cryotherapy procedure produced shoot regrowth levels that ranged from 43% to 59%, and all plants recovered after cryotherapy were free of GLRaV-3 in two wine, one table and one rootstock cultivars. Thus, this procedure can be considered to be efficient and wildly applicable for eradication of GLRaV-3 from Vitis spp. K E Y W O R D S cryotherapy, grapevine leafroll disease, histological study, shoot tip, virus localisation, Vitis

تعد  زراعة الأنسجة أو الخلايا أو الأعضاء النباتية علم به تقنيات حديثة و أساليب تجارى متطلبات الزراعة الحديثة و التى تتطور بإستمرار لتصبح أكثر ملائمة لطبيعة الإنتاج الكبير المتميز و لتحقيق أكبر عائد ممكن من الوحدة الإنتاجية وتتميز طرق الإكثار فيها بأن نباتاتها بقوتها و مطابقتها للصنف و خلوها من الأمراض و خاصة الفيروسية دون التقيد بالمواسم المناخية، كما أمكن باستخدام  هذا العلم الحصول على المواد الطبية و العطرية الفعالة داخل المعامل دون تكلفة الزراعة فى الأرض و الحصاد. كما مكن من إنتخاب و إنتاج سلالات نباتية تتحمل الجفاف و البرودة و الأملاح و الأمراض و سمية المبيدات و العناصر الثقيلة و الحفاظ عليها لفترات مختلفة.

Euphorbia milii cv. splendens plants with leaf mosaic and flower colour breaking symptoms in Caracas, Venezuela, were shown to contain potyvirus-like particles. Degenerate Potyviridae primers were used in a reverse transcription-polymerase chain reaction (RT-PCR) to amplify and sequence the 3′-terminal region of the virus. Nucleotide sequence of the obtained amplicons was 99% identical to that of Euphorbia ringspot virus (EuRV) isolates deposited in the GenBank database. A simple step RT-PCR assay with degenerate primers was used to readily identify the virus in field samples. This is the first report of EuRV infecting E. milii in Venezuela.

Potato viruses such as Potato virus Y (PVY) cause diseases that affect potato quality and thus damage potato production worldwide. Current tests for viral infection use double-antibody sandwich enzyme linked immunosorbent assays (DAS ELISA) or reverse transcription polymerase chain reaction (RT-PCR)/real-time RT-PCR. Despite many advantages, these assays have a number of drawbacks that affect cost and time of diagnosis. Reverse transcription loop-mediated isothermal amplification (RT-LAMP) allows fast detection of target RNA. Here, we developed a closed-tube real-time RT LAMP assay for fluorescent detection of PVY. Specific RT-LAMP primers were designed to target the conserved region of the sequence encoding the PVY coat protein. The assay was specific and facilitated sensitive PVY detection in a single tube at 65 °C. The time-to positive values depended on the PVY concentration in tested samples. The effectiveness of RT LAMP in testing field-grown plants compared favorably with DAS ELISA and RT-PCR; under the tested conditions, RT-LAMP was about 1000-fold more sensitive than DAS ELISA and lateral flow assay (LFA) and about 10-fold more sensitive than RT PCR. Thus, this fluorescent RT-LAMP assay has great potential for routine detection of PVY.

Use of resistant varieties is a proven way of controlling the tomato yellow leaf curl virus (TYLCV), which causes a devastating disease of tomato in tropical and warm temperate regions, resulting in significant yield losses. However, breeding for resistant varieties is slow due to lack of effective methods of virus detection that will lead to efficient selection of desired varieties. A study was conducted to evaluate the susceptibility or otherwise of ten tomato genotypes to TYLCV under field conditions. The ten (10) tomato genotypes were planted in the field and left to natural infection by whitefly vectors. Leaf samples were collected from symptomatic as well as asymptomatic plants at five weeks after transplanting (5WAT) for analysis by serological and nucleic acid-based techniques. Triple antibody sandwich enzyme-linked immunosorbent assay (TAS-ELISA) detected TYLCV in five out of ten genotypes while polymerase chain reaction using six primers (virus-specific and degenerate) det...

Plant virus diseases are significant threats to modern agriculture and their control remains a challenge to the management of cultivation. The plant virus diseases can be controlled to some extent by the use of biotechnological methods. Biotechnology is the genetic manipulation and multiplication of any living organism through novel technologies and technologies such as tissue culture and genetic engineering in order to produce new organisms and/or products that can be used in a variety of ways. The virus resistance strategies are based on either natural resistance or engineered resistance. The recombinant DNA technology play a great role to makes it possible to isolate individual genes and incorporate resistance genes into otherwise agronomically acceptable cultivars.  The biotechnological methods have to be used for accurate identification to distinguish between virus strains, isolation, and purification of viruses to obtain pathology free mother plants and control of plant disease by inserting resistance genes into plants by genetic engineering techniques.

The botanical product RD-Repelin, was highly repellent to pea aphids at 1%, 4%, or 10% concentrations. Repellency occurred prior to leaf contact by aphids at all concentrations. RD-Repelin delayed symptom expression of ZYMV in 81% of plants treated with 1% concentrations, although virus transmission was not prevented. The effects of RD-Repellin on aphid settling behavior, symptom expression and potenital for pest management are discussed.

Antisera to the nucleoprotein of maize yellow stripe tenui-like virus (MYSV) were produced and used for detection of this virus in several host plants and vector leafhoppers in Egypt. Dot-blot and direct antigen coating (DAC) ELISA were used to detect MYSV in naturally or experimentally infected maize, wheat, barley, oats, and the graminaceous weeds #Bromus wildenowii$, #Cenchrus biflorus$, #Dichanthium annulatum$, #Digitaria sanguinalis$, #Echinochloa colonum$, #Setaria verticillata$ and #S. viridis$. In maize leaves, differences in virus titer appeared to be correlated with leaf age and with MYSV symptom-types. Dot-blot and DAC-ELISA were used also to detect MYSV in naturally or experimentally infective leafhoppers (#Cicadulina chinai$). (Résumé d'auteur)

The study was conducted at Department of Plant Pathology, Bangladesh Agricultural University, Mymensingh to find out virus-vector relationship in JLMV of jute during 2010-2011. So far, 12 different diseases have been recorded on jute in Bangladesh. Among these diseases jute leaf mosaic is considered as the most devastating one. The minimum acquisition feeding period of 30 min was required for whitefly on a JLMV source that resulted in 12.5% transmission and for cent percent transmission 48 h AFP was required. A minimum feeding period of 15 min was required by a viruliferous whitefly to cause infection on jute test plants; this gave 10% transmission. With inoculation access of 48 h on jute test plants, the transmission rose to 100%. Starving the vector for 30 min and 5 h pre-acquisition resulted 10 and 100% transmission of JLMV respectively. Extending the fasting period beyond 5 h resulted in a reduced transmission level. Starving the vector for 30 min and 4 h post-acquisition result...

Banana streak viruses (BSVs) are double-stranded DNA pararetroviruses causing banana streak disease. Recently, numerous outbreaks of the disease occurred in many banana-producing areas in interspecific hybrids (#Musa acuminata# × #Musa balbisiana#) originating from virus-free parents. These infections correlated with the presence of endogenous banana streak viruses (eBSVs), viral DNA sequences integrated in the #M. balbisiana# genome only. Although integration is not needed for the viral replication cycle, some viral integrants are infectious under stress conditions by reconstituting a replication-competent genome after possible homologous recombination events. Even though the wild #M. balbisiana# Pisang Klutuk Wulung (PKW) harbours infectious eBSVs, it is resistant to BSVs. We characterised the genetic and genomic endogenous viral organisation of three BSV species in PKW in order to determine the species responsible for the viral expression in the interspecific F1 progeny. (Resume d'auteur)

For the first time in Ukraine, a virus disease of elderberry (Sambucus nigra L.) was found. Plants with symptoms of a viral infection were found in 2015-2016 in the Poltava region, in 2016 the same symptoms on elder plants were disfigured in the Kiev region. The symptoms of the disease and the morphological properties of the virus were studied. We found plants with chlorotic symptoms, mosaic and chain mail, plants rolling on the tops of leaves, and twisting the edges. In the leaves of infected plants, filamentous virions with a particle length of 650 ± 50 nm were detected by the method of electron microscopy. Based on the scientific literature data, viruses that can infect elder plants in Ukraine are screened. The levels of lipid peroxidation in older plants under conditions of viral infection and heat stress were studied. It is shown that a viral infection significantly reduces the content of TBA-active products in elder plants. The content of malonic dialdehyde significantly incre...