Cereal and grass viruses II
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Alice: Johnsongrass mosaic virus infecting sorghum in Brazil.

Alice: Johnsongrass mosaic virus infecting sorghum in Brazil. | Cereal and grass viruses II | Scoop.it
Sorghum bicolor (L.) Moench is cultivated in several tropical and subtropical regions in the world. Among the diseases, the mosaic caused by potyvirus is an important constraint for the agricultural production causing reduction in grain and forage sorghum production. In Brazil, only Sugarcane mosaic virus (SCMV) had previously been reported as the potyvirus species causing mosaic in sorghum and maize. A survey was carried out in sorghum plantations of the State of Minas Gerais, Brazil, during the 2014/2015 crop season for monitoring mosaic disease. Samples of sorghum plants expressing virus disease symptoms were collected for molecular analyzes. Molecular characterization of coat protein (CP) of the potyviruses naturally infecting sorghum, allowed us to identify the Johnsongrass mosaic virus (JGMV) as a new causal agent of mosaic disease in sorghum in Brazil. The sequences of the Brazilian JGMV sorghum-infecting (JGMV-Sr) isolates were deposited in the GenBank under the accession numbers KY952241, KY952242, and KY952243. Comparisons of the CP gene sequences of these Brazilian JGMV-Sr isolates revealed high nucleotide (nt) and amino acid (aa) sequence identities, ranging from 97.93 to 98.23%, and 99.12 to 99.20%, respectively, with the U07218.1 (JGMV-MDKS1) isolate. The Brazilian JGMV-Sr isolates were distinct from the Brazilian forage grasses-infecting (JGMV-Fg) isolates (KT833782 and KT289893). Transmission evaluations showed susceptibility of the teosinte, Sorghum verticilliflorum and Sorghum bicolor (L.) Moench, except line QL3.Maize and sugarcane genotypes were not infected by the Brazilian JGMV-Sr isolate. However, it is important to test more genotypes. This is the first report showing the identification and molecular characterization of the JGMV species naturally infecting sorghum at field conditions, expanding the knowledge about the dynamic and range of the mosaic causal agent for this crop in Brazil.
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Wheat streak mosaic virus: a century old virus with rising importance worldwide - Singh - - Molecular Plant Pathology - Wiley Online Library

SUMMARY
Wheat streak mosaic virus (WSMV) causes wheat streak mosaic, a disease of cereals and grasses that threatens wheat production worldwide. It is a monopartite, positive‐sense single stranded RNA virus and the type member of the genus Tritimovirus in the family Potyviridae. The only known vector is the wheat curl mite (WCM, Aceria tosichella), recently identified as a species complex of biotypes differing in virus transmission. Low rates of seed transmission have been reported. Infected plants are stunted and have a yellow mosaic of parallel discontinuous streaks on the leaves. In the fall, WCMs move from WSMV‐infected volunteer wheat and other grass hosts to newly emerged wheat and transmit the virus which survives the winter within the plant and the mites survive as eggs, larvae, nymphs or adults in the crown and leaf sheaths. In the spring/summer, the mites move from the maturing wheat crop to volunteer wheat and other grass hosts and transmit WSMV, completing the disease cycle. WSMV detection is by ELISA, RT‐PCR, or RT‐qPCR. Three types of WSMV are recognized: A (Mexico), B (Europe, Russia, Asia), and D (USA, Argentina, Brazil, Australia, Turkey, Canada). Resistance genes Wsm1, Wsm2, and Wsm3 have been identified. The most effective, Wsm2, has been introduced into several wheat cultivars. Mitigation of losses caused by WSMV will require enhanced knowledge of the biology of WCM biotypes and WSMV, new or improved virus detection techniques, development of resistance through traditional and molecular breeding, and adaptation of cultural management tactics to account for climate change. This article is protected by copyright. All rights reserved.
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Frontiers | Barley yellow dwarf virus Infection Leads to Higher Chemical Defense Signals and Lower Electrophysiological Reactions in Susceptible Compared to Tolerant Barley Genotypes | Plant Science

Frontiers | Barley yellow dwarf virus Infection Leads to Higher Chemical Defense Signals and Lower Electrophysiological Reactions in Susceptible Compared to Tolerant Barley Genotypes | Plant Science | Cereal and grass viruses II | Scoop.it
Barley yellow dwarf virus (BYDV) is a phloem limited virus that is persistently transmitted by aphids. Due to huge yield losses in agriculture, the virus is of high economic relevance. Since the control of the virus itself is not possible, tolerant barley genotypes are considered as the most effective approach to avoid yield losses. Although several genes and quantitative trait loci are known and used in barley breeding for virus tolerance, little is known about molecular and physiological backgrounds of this trait. Therefore, we compared the anatomy and early defence responses of a virus susceptible to those of a virus-tolerant cultivar.One of the very early defence responses is the transmission of electrophysiological reactions. Electrophysiological reactions to BYDV infection might differ between susceptible and tolerant cultivars, since BYDV causes disintegration of sieve elements in susceptible cultivars. The structure of vascular bundles, xylem vessels and sieve elements was examined using microscopy. All three were significantly decreased in size in infected susceptible plants where the virus causes disintegration of sieve elements. This could be associated with an uncontrolled ion exchange between the sieve-element lumen and apoplast. Further, a potential reduced electrophysiological isolation would negatively affect the propagation of electrophysiological reactions. To test the influence of BYDV infection on electrophysiological reactions, electropotential wave
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Simultaneous Detection of Barley Virus Diseases in Korea - ScienceCentral

Abstract
Barley mild mosaic virus (BaMMV), Barley yellow mosaic virus (BaYMV) and Barley yellow dwarf virus (BYDV) have been identified as an important causative agents for an economically important disease of winter barley in Korea. In this study, a multiplex reverse transcription polymerase chain reaction (mRT-PCR) method was used for the simultaneous detection. Three sets of virus-specific primers targeted to the capsid protein coding genes of BaMMV, BaYMV and BYDV were used to amplify fragments that were 594 bp, 461 bp, and 290 bp, respectively. Several sets of primers for each target virus were evaluated for their sensitivity and specificity by multiplex RT-PCR. The optimum primer concentrations and RT-PCR conditions were determined for the multiplex RT-PCR. The mRT-PCR assay was found to be a better and rapid virus diagnostic tool of specific barley diseases and potential for investigating the epidemiology of these viral diseases.


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Combined Effects of Barley yellow dwarf virus (BYDV) Infection and Salinity Stress on Barley Growth and Yield Parameters

Najar, A., Abassi, M., Ben Ghanem, H., and Debez, A. 2017.Combined effects of Barley yellow dwarf virus (BYDV) infection and salinity stress on barley growth and yield parameters. Tunisian Journal of Plant Protection 12: 121-133.

ABSTRACT
Following the current climate changes, Tunisia climate is characterized by less and more irregular rainfall together with milder and shorter winter, resulting in increased soil salinity and higher incidence of Barley yellow dwarf virus (BYDV). The selection of productive cultivars adapted to both abiotic and biotic constraints is crucial for crop breeders, and especially for cereal breeding. In this study, the behavior of two genotypes (G1 and G2) obtained from a cross breeding (QB813-2/3/Lignee527/NK1272//JLB70-63) and the most commonly grown cultivar Rihane were compared for their responses to the combined effects of various salinity levels (0 to 150 mMNaCl) and BYDV virus infection. Rihane was the most sensitive cultivar under biotic and abiotic stress combination whereas growth and yield parameters were significantly improved in G1 and G2 genotypes under BYDV+50 mMNaCl treatment. In addition, these two genotypes were less affected by the virus infection and high salinity (100 and 150 mMNaCl) combination than Rihane. Interestingly, stress tolerance index was higher in G2, followed by G1 and Rihane, suggesting that this parameter could be a useful trait to discriminate genotypes for their performance under multiple stress conditions.
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Temperature affected Transmission, Symptom Development and Accumulation of Wheat Dwarf Virus

Abstract
One of the biotic agents of yellowing and stunting in wheat and barley cultivations is Wheat dwarf virus (WDV) which is naturally transmitted by the leafhopper Psammotettix alienus (Dahlbom). WDV-Wheat and WDV-Barley isolates of WDV were transmitted to wheat and barley, respectively, using the leafhoppers under four temperature regimes of constant 20, 25, 30, and 35°C. Infection rate, symptom development and virus content of the virus-inoculated plants were determined and the data was statistically analysed. The results showed that the temperature of 25°C was associated with the highest infection rate caused by the viruses. Moreover, P. alienus nymphs were found to be more efficient vectors of WDV than adults, highlighting the importance of nymphs in the epidemiology of wheat dwarf disease. WDV-infected plants incubated at 35°C showed less symptoms than those kept at 20, 25, and 30°C. ELISA results showed that these plants had comparatively low virus content. However, there was no significant difference between the infection rate, symptom development and virus content in plants infected by WDV-Wheat or WDV-Barley.
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Frontiers | Identification and Characterization of Wheat Yellow Striate Virus, a Novel Leafhopper-Transmitted Nucleorhabdovirus Infecting Wheat | Microbiology

Frontiers | Identification and Characterization of Wheat Yellow Striate Virus, a Novel Leafhopper-Transmitted Nucleorhabdovirus Infecting Wheat | Microbiology | Cereal and grass viruses II | Scoop.it
A new wheat viral disease exhibiting unusual symptoms - yellow stripes on leaves and slight dwarfism -was found in China. The bullet-shaped viral particles within the nucleus of the infected wheat leave cells, which possessed 180-210 nm length and 35-40 nm width, were observed under transmission electron microscopy. The putative wheat-infecting rhabdovirus vectored by the leafhopper Psammotettix alienus was tentatively named wheat yellow striate virus (WYSV). The full-length nucleotide sequence of WYSV was determined using transcriptome sequencing and RACE analysis of both wheat samples and leafhoppers P. alienus. The negative-sense RNA genome of WYSV contains 14,486 nucleotides (nt) and seven open reading frames (ORFs) encode deduced proteins in the order N-P-P3-M-P6-G-L on the antisense strand. In addition, WYSV genome has a 76-nt 3′ leader RNA and a 258-nt 5′ trailer, and the ORFs are separated by conserved intergenic sequences. The entire genome sequence shares 58.1% and 57.7% nucleotide sequence identity with two strains of rice yellow stunt virus (RYSV-A and RYSV-B) genomes, respectively. The highest amino acid sequence identity was 63.8% between the L proteins of the WYSV and RYSV-B, but the lowest was 29.5% between the P6 proteins. Phylogenetic analysis firmly established WYSV as a member of the genus Nucleorhabdovirus. Collectively, this study provided evidence that WYSV is likely the first nucleorhabdovirus described infecting wheat via leafhopper P. alienu
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Vector mediated transmission of persistently transmitted plant viruses

Highlights

• Persistently transmitted propagative plant viruses use viral inclusions to overcome the transmission barriers of insect vectors
 • Insect antiviral pathways are induced to modulate viral persistent infection.
 • Insect vitellogenin-mediated viral entry into the oocyte may be a common mechanism of transovarial transmission.
 • Binding of viral particles to endosymbionts facilitates transovarial transmission in insect vectors.

Many vector-borne plant viruses of agricultural importance are persistently transmitted from plant to plant by sap-sucking insects. So far, the mechanisms for vector-mediated horizontal transmission of the viruses to plant hosts and for vertical transmission to insect offspring have been poorly understood. During horizontal transmission, intact virions or virus-induced inclusions are exploited by persistently transmitted viruses to overcome the midgut and salivary gland barriers. The existing oocyte entry paths used by vitellogenin or symbiont bacteria can mediate the vertical transmission of viruses by female insects. We hypothesize that the viruses may also be vertically transmitted by male insects via attachment to the surface of sperm. Inhibiting vertical transmission of the viruses by insect vectors in the overwintering season unfavorable for horizontal transmission may open new perspectives for viral control. Previous article in issue N
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So What Have Plant Viruses Ever Done for Virology and Molecular Biology?

Abstract
The discovery of a new class of pathogen, viruses, in the late 19th century, ushered in a period of study of the biochemical and structural properties of these entities in which plant viruses played a prominent role. This was, in large part, due to the relative ease with which sufficient quantities of material could be produced for such analyses. As analytical techniques became increasingly sensitive, similar studies could be performed on the viruses from other organisms. However, plant viruses continued to play an important role in the development of molecular biology, including the demonstration that RNA can be infectious, the determination of the genetic code, the mechanism by which viral RNAs are translated, and some of the early studies on gene silencing. Thus, the study of plant viruses should not be considered a “niche” subject but rather part of the mainstream of virology and molecular biology.
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Sélection de lignées d’orge (Hordeum vulgare L.) pour leur résistance au barley yellow dwarf virus (BYDV) et évaluation de leurs performances agronomiques

Sélection de lignées d’orge (Hordeum vulgare L.) pour leur résistance au barley yellow dwarf virus (BYDV) et évaluation de leurs performances agronomiques | Cereal and grass viruses II | Scoop.it

Barley yellow dwarf virus (BYDV) is the most important virus affecting grain crops. Over 40% of barley grown in Tunisia may be contaminated in some regions. Selection of resistant genotypes is the best way to fight BYDV. Ten F2 barley populations with some parents carrying the resistance gene Yd2 provided by ICARDA have been the subject of a breeding program. In total 198 F2 to F5 advanced lines were selected for their resistance. The lines’ resistance was evaluated at the symptomatic, serological, and molecular levels with the Ylp (CAPS) marker linked to the target gene (Yd2). The lines’ agronomic performance was evaluated during the 2006–2007 crop year in Béja (a subhumid region) and Kef (a semi-dry region). Twenty-five lines were selected for their grain yield and all were superior to the susceptible cultivar “Rihane”, but only eight lines did better than the susceptible cultivar “Manel”. Sixteen of those lines could be grown for both grain and straw production, and two lines present adaptation capability to semi-dry and subhumid growing conditions


A. Najar, H. Ben Ghanem, S. Kumari, H. Sayed, S. Rezgui, and M. Baum (2017) Sélection de lignées d’orge (Hordeum vulgare L.) pour leur résistance au barley yellow dwarf virus (BYDV) et évaluation de leurs performances agronomiques. Canadian Journal of Plant Science: Vol. 97, No. 2, pp. 277-285. https://doi.org/10.1139/cjps-2016-0170

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Curr ent Status Of Rice Yellow Mottle Disease In Western Kenya

Rice yields in Kenya remain very low due to several constraints with Rice Yellow Mottle Disease (RYMD) caused by Rice Yellow Mottle Virus (RYMV) being the greatest challenge. However, information on pattern of distribution and diversity still remain scanty and hence a hindrance in designing most suitable control measures. A research study was carried out determine the occurrence and distribution of RYMV in rice growing areas of Western Kenya. A survey was conducted in rice growing schemes and farms in five Counties in July 2015 and June 2016 and symptomatic and some asymptomatic leaf samples were collected. Visual RYMD incidence ranged between 2-100%. Serological detection of RYMV in the leaf samples was done by DAS- ELISA. Results showed that 54% and 96% of the 2015 and 2016 samples, respectively were RYMV positive. Selected ELISA positive samples were subjected to molecular analysis. Extraction of total RNA was done using GeneJET Plant RNA Purification Mini Kit. PCR was done using RYMV specific primers and a product of approximately 1000 bp obtained. The coat protein gene was sequenced and sequences (720 bp) were established which identified strain S4 of RYMV. This is useful in monitoring diversity of RYMV in Western Kenya and to assist plant breeders develop resistant rice varieties. n
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Organelle luminal dependence of (+)strand RNA virus replication reveals a hidden druggable target

Organelle luminal dependence of (+)strand RNA virus replication reveals a hidden druggable target | Cereal and grass viruses II | Scoop.it
Positive-strand RNA viruses replicate their genomes in membrane-bounded cytoplasmic complexes. We show that endoplasmic reticulum (ER)–linked genomic RNA replication by brome mosaic virus (BMV), a well-studied member of the alphavirus superfamily, depends on the ER luminal thiol oxidase ERO1. We further show that BMV RNA replication protein 1a, a key protein for the formation and function of vesicular BMV RNA replication compartments on ER membranes, permeabilizes these membranes to release oxidizing potential from the ER lumen. Conserved amphipathic sequences in 1a are sufficient to permeabilize liposomes, and mutations in these sequences simultaneously block membrane permeabilization, formation of a disulfide-linked, oxidized 1a multimer, 1a’s RNA capping function, and productive genome replication. These results reveal new transmembrane complexities in positive-strand RNA virus replication, show that—as previously reported for certain picornaviruses and flaviviruses—some alphavirus superfamily members encode viroporins, identify roles for such viroporins in genome replication, and provide a potential new foundation for broad-spectrum antivirals.
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AgriLife Research survey: Triticum a major player in wheat crop diseases | AgriLife Today

AgriLife Research survey: Triticum a major player in wheat crop diseases | AgriLife Today | Cereal and grass viruses II | Scoop.it
Writer: Kay Ledbetter, 806-677-5608, skledbetter@ag.tamu.edu Contact: Dr. Charlie Rush, 806-354-5804, crush@tamu.edu AMARILLO – Knowing what diseases are turning wheat fields yellow is half the battle, according to a Texas A&M AgriLife Research plant pathologist in Amarillo. And sometimes, t
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Phylogenetic and recombination analysis of sorghum isolates of Sugarcane yellow leaf virus

Phylogenetic and recombination analysis of sorghum isolates of Sugarcane yellow leaf virus | Cereal and grass viruses II | Scoop.it

Abstract

Recombination has played an important role in evolution and genetic diversity of Sugarcane yellow leaf virus (SCYLV) isolates sequenced to date. This study found that three newly sequenced SCYLV sorghum isolates from the USA underwent intraspecies recombination. No statistical significance on probable progeny–parent relationships involving SCYLV sorghum isolates were found in possible interspecies recombination with 18 members of the Luteoviridae family. Sorghum isolates deposited in the GenBank database under accession numbers KT960995, KT960996 and KT960997 were phylogenetically closely related to SCYLV genotypes IND, CUB and CHN1, all members of phylogroup II. Networked relationships among the sorghum isolates showed that numerous incompatibilities occurred in the sequences. These conflicting signals were probably due to recombination, especially in KT960997, which was heavily impacted by recombination. The KT960997 accession was positioned on a distinct branch compared to other members of phylogroup II, suggesting that it has probably emerged as a new genotype. Future studies on molecular evolution may reveal further insights into the adaptation capacity of these SCYLV lineages to new environments.

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Agronomical, biochemical and histological response of resistant and susceptible wheat and barley under BYDV stress [PeerJ Preprints]

Barley yellow dwarf virus-PAV (BYDV-PAV) is one of the major viruses causing a widespread and serious viral disease affecting cereal crops. To gain a better understanding of plant defence mechanisms of BYDV resistance genes ( Bdv2 and Yd2 ) against BYDV-PAV infection, the differences in agronomical, biochemical and histological changes between susceptible and resistant wheat and barley cultivars were investigated. We found that root growth and total dry matter of susceptible cultivars showed greater reduction than that of resistant ones after infection. BYDV infected leaves in susceptible wheat and barley cultivars showed a significant reduction in photosynthetic pigments, an increase in the concentration of reducing sugar. The protein levels were also low in infected leaves. There was a significant increase in total phenol contents in resistant cultivars, which might reflect a protective mechanism of plants against virus infection. In phloem tissue, sieve elements (SE) and companion cells (CC) were severely damaged in susceptible cultivars after infection. It is suggested that restriction of viral movement in the phloem tissue and increased production of phenolic compounds may play a role in the resistance and defensive mechanisms of both Bdv2 and Yd2 against virus infection.
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The genus Luteovirus from infection to disease

The genus Luteovirus from infection to disease | Cereal and grass viruses II | Scoop.it
Abstract
Luteoviruses are economically important plant viruses. Specifically, barley yellow dwarf virus is epiphytotic to almost all small-grain cereal growing areas. The disease cycle is complex. This luteovirus has evolved several intelligent mechanisms to communicate with both plant and phloem-feeding insect-vector aphid. Environmental cues influence disease severity, aphid infestation and viral load. Within an aphid, virus circulates persistently in a non-propagative manner and is transmitted selectively to the host plants. Selection of viruses within aphids has a role in virus isolate prevalence over a specific area. In the host-plant system, the virus has to release its single sense-strand RNA genome (approx. 5.6 to 6 kb), translate and subsequently replicate its genome using its own replicase and host machinery. This review summarizes our current understanding of disease epidemiology and reviews the current literature encompassing viral infectivity, economic impact and control measures.

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Barley stripe mosaic virus infection requires PKA‐mediated phosphorylation of γb for suppression of both RNA silencing and the host cell death response - Zhang - - New Phytologist - Wiley Online Li...

Summary
The Barley stripe mosaic virus (BSMV) γb protein is a viral suppressor of RNA silencing (VSR) and symptom determinant. However, it is unclear how post‐translational modification affects the different functions of γb. Here, we demonstrate that γb is phosphorylated at Ser‐96 by a PKA‐like kinase in vivo and in vitro. Mutant viruses containing a nonphosphorylatable substitution (BSMVS96A or BSMVS96R) exhibited reduced viral accumulation in Nicotiana benthamiana due to transient induction of the cell death response that constrained the virus to necrotic areas. By contrast, a BSMVS96D mutant virus that mimics γb phosphorylation spread similarly to the wild‐type virus. Furthermore, the S96A mutant had reduced local and systemic γb VSR activity due to having compromised its binding activity to 21‐bp dsRNA. However, overexpression of other VSRs in trans or in cis failed to rescue the necrosis induced by BSMVS96A, demonstrating that suppression of cell death by γb phosphorylation is functionally distinct from its RNA silencing suppressor activities. These results provide new insights into the function of γb phosphorylation in regulating RNA silencing and the BSMV‐induced host cell death response, and contribute to our understanding of how the virus optimizes the balance between viral replication and virus survival in the host plants during virus infection.
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Phylogenetic analysis of Wheat dwarf virus isolates from Iran

Phylogenetic analysis of Wheat dwarf virus isolates from Iran | Cereal and grass viruses II | Scoop.it
Abstract
Wheat dwarf virus (WDV) adversely affects cereal production in Asia, Europe, and North Africa. In this study, sequences of several WDV isolates from Iran which is located in the Fertile Crescent were analyzed. Analysis revealed a new geographic cluster for WDV-Wheat from Iran. Recombination analysis demonstrated the existence of several breakpoints in different regions of the viral genome. Data analysis demonstrated that WDV-Barley has an older history and lower diversity than WDV-Wheat. Sequence analysis identified a rare occasion of a co-infection of wheat with WDV-Wheat and WDV-Barley.
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Octapartite negative-sense RNA genome of High Plains wheat mosaic virus encodes two suppressors of RNA silencing

Highlights
• The octapartite genome of HPWMoV encodes two suppressors of RNA silencing.
• Proteins encoded by HPWMoV RNAs 7 (P7) and 8 (P8) suppressed ss- or dsRNA induced silencing.
• Both P7 and P8 efficiently suppressed the transitive pathway of RNA silencing.
• P7 or P8 rescued an RNA silencing suppressor-deficient Wheat streak mosaic tritimovirus in wheat.
• P7 and P8 independently enhanced the pathogenicity of Potato virus X in N. benthamiana.

Abstract
High Plains wheat mosaic virus (HPWMoV, genus Emaravirus; family Fimoviridae), transmitted by the wheat curl mite (Aceria tosichella Keifer), harbors a monocistronic octapartite single-stranded negative-sense RNA genome. In this study, putative proteins encoded by HPWMoV genomic RNAs 2–8 were screened for potential RNA silencing suppression activity by using a green fluorescent protein-based reporter agroinfiltration assay. We found that proteins encoded by RNAs 7 (P7) and 8 (P8) suppressed silencing induced by single- or double-stranded RNAs and efficiently suppressed the transitive pathway of RNA silencing. Additionally, a Wheat streak mosaic virus (WSMV, genus Tritimovirus; family Potyviridae) mutant lacking the suppressor of RNA silencing (ΔP1) but having either P7 or P8 from HPWMoV restored cell-to-cell and long-distance movement in wheat, thus indicating that P7 or P8 rescued silencing suppressor-deficient WSMV. Furthermore, HPWMoV P7 and P8 substantially enhanced the pathogenicity of Potato virus X in Nicotiana benthamiana. Collectively, these data demonstrate that the octapartite genome of HPWMoV encodes two suppressors of RNA silencing.
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Johnsongrass mosaic virus infecting sorghum in Brazil

Sorghum bicolor (L.) Moench is cultivated in several tropical and subtropical regions in the world. Among the diseases, the mosaic caused by potyvirus is an important constraint for the agricultural production causing reduction in grain and forage sorghum production.In Brazil, only Sugarcane mosaic virus (SCMV) had previously been reported as the potyvirus species causing mosaic in sorghum and maize. A survey was carried out in sorghum plantations of the State of Minas Gerais, Brazil, during the 2014/2015 crop season for monitoring mosaic disease. Samples of sorghum plants expressing virus disease symptoms were collected for molecular analyzes. Molecular characterization of coat protein (CP) of the potyviruses naturally infecting sorghum, allowed us to identify the Johnsongrass mosaic virus (JGMV) as a new causal agent of mosaic disease in sorghum in Brazil. The sequences of the Brazilian JGMV sorghum-infecting (JGMV-Sr) isolates were deposited in the GenBank under the accession numbers KY952241, KY952242, and KY952243. Comparisons of the CP gene sequences of these Brazilian JGMV-Sr isolates revealed high nucleotide (nt) and amino acid (aa) sequence identities, ranging from 97.93 to 98.23%, and 99.12 to 99.20%, respectively, with the U07218.1 (JGMV-MDKS1) isolate. The Brazilian JGMV-Sr isolates were distinct from the Brazilian forage grasses-infecting (JGMV-Fg) isolates (KT833782 and KT289893). Transmission evaluations showed susceptibility of the teosinte, Sorghum verticilliflorum and Sorghum bicolor (L.) Moench, except line QL3.Maize and sugarcane genotypes were not infected by the Brazilian JGMV-Sr isolate. However, it is important to test more genotypes. This is the first report showing the identification and molecular characterization of the JGMV species naturally infecting sorghum at field conditions, expanding the knowledge about the dynamic and range of the mosaic causal agent for this crop in Brazil.
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Molecular Variability and Genetic Structure of IYMV in Burkina Faso

Molecular Variability and Genetic Structure of IYMV in Burkina Faso | Cereal and grass viruses II | Scoop.it
Imperata yellow mottle virus (IYMV, Sobemovirus) was first described in 2008 in the south-western region of Burkina Faso (West Africa). The genetic diversity of IYMV was not documented up to day.

In this study, the variability of CP of IYMV was evaluated through the
molecular characterization of 38 isolates collected in the western part of Burkina Faso. Comparison of sequences of these new isolates and one IYMV sequence available in GenBank revealed that the average nucleotide diversity was low. The ratio of non-synonymous over synonymous nucleotide substitutions per site was low, indicating a CP diversification under strong purifying selection. Despite of the low nucleotide diversity, phylogenetic analyses revealed segregation of IYMV isolates into six major clades. There was no correlation of phylogenetic grouping of isolates based on geographical location. This is the first study of the genetic diversity of IYMV.

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Alice: Johnsongrass mosaic virus infecting sorghum in Brazil.

Alice: Johnsongrass mosaic virus infecting sorghum in Brazil. | Cereal and grass viruses II | Scoop.it
Sorghum bicolor (L.) Moench is cultivated in several tropical and subtropical regions in the world. Among the diseases, the mosaic caused by potyvirus is an important constraint for the agricultural production causing reduction in grain and forage sorghum production. In Brazil, only Sugarcane mosaic virus (SCMV) had previously been reported as the potyvirus species causing mosaic in sorghum and maize. A survey was carried out in sorghum plantations of the State of Minas Gerais, Brazil, during the 2014/2015 crop season for monitoring mosaic disease. Samples of sorghum plants expressing virus disease symptoms were collected for molecular analyzes. Molecular characterization of coat protein (CP) of the potyviruses naturally infecting sorghum, allowed us to identify the Johnsongrass mosaic virus (JGMV) as a new causal agent of mosaic disease in sorghum in Brazil. The sequences of the Brazilian JGMV sorghum-infecting (JGMV-Sr) isolates were deposited in the GenBank under the accession numbers KY952241, KY952242, and KY952243. Comparisons of the CP gene sequences of these Brazilian JGMV-Sr isolates revealed high nucleotide (nt) and amino acid (aa) sequence identities, ranging from 97.93 to 98.23%, and 99.12 to 99.20%, respectively, with the U07218.1 (JGMV-MDKS1) isolate. The Brazilian JGMV-Sr isolates were distinct from the Brazilian forage grasses-infecting (JGMV-Fg) isolates (KT833782 and KT289893). Transmission evaluations showed susceptibility of the teosinte, Sorghum verticilliflorum and Sorghum bicolor (L.) Moench, except line QL3.Maize and sugarcane genotypes were not infected by the Brazilian JGMV-Sr isolate. However, it is important to test more genotypes. This is the first report showing the identification and molecular characterization of the JGMV species naturally infecting sorghum at field conditions, expanding the knowledge about the dynamic and range of the mosaic causal agent for this crop in Brazil.
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Pathogenicity of rice yellow mottle virus and screening of rice accessions from the Central African Republic

Pathogenicity of rice yellow mottle virus and screening of rice accessions from the Central African Republic | Cereal and grass viruses II | Scoop.it
Rice yellow mottle virus (RYMV) of the genus Sobemovirus is the most important viral pathogen of rice causing more damage to rice crop in Sub Saharan Africa. The aim of this study was to conduct pathogenic characterization of RYMV isolates from the Central African Republic (CAR) and to screen commonly cultivated rice accessions in the country for resistance/tolerance to the virus. The pathogenicity of RYMV isolates was studied by mechanical inoculation with comparison to differential rice lines highly resistant to RYMV available at the Institute of Environment and Agricultural Research (INERA) in Burkina Faso. To screen commonly cultivated rice accessions in CAR, characterized RYMV isolates from the country were used as inoculum sources. Resistant breaking (RB) isolates were used to prepare RB-inoculum, whereas non-resistant breaking isolates (nRB) were used for nRB-inoculum. Overall 102 isolates used in this study, 29.4% were able to overcome the high resistance genes in the rice cultivars Gigante and Tog7291. All isolates were distributed within three distinct pathogenic profiles. The first profile constituted of 6.9% of the isolates was able to break down the resistance in rice cultivar Gigante only. The second pathogenic profile made of 19.6% of isolates was able to infect Tog7291 only. The third profile, 2.9% of isolates overcame simultaneously resistance genes in both rice cultivars Gigante and Tog7291. Out of isolates able to break down the resistance gene in cultivar Gigante, a single isolate was found to be non-infectious to the susceptible control IR64. Data from screening showed that all accessions were susceptible to RYMV, although IRAT213 was found to be partially resistant to both nRB-inoculum and RB-inoculum. The present study can be considered as the first in the Central African Republic, it gives a caution on the high risk of RYMV damage to rice production in the country. Beside, skills of pathogenic profiles of RYMV isolates will contribute to better disease management.
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Ecological and evolutionary aspects of interactions between microbes coinfecting plants

Ecological and evolutionary aspects of interactions between microbes coinfecting plants | Cereal and grass viruses II | Scoop.it
Coinfections of one host with multiple pathogen species are common, and have important implications for host health and pathogen fitness. In the research reported here, plant virus systems were used to explore the effects of coinfection on pathogen populations and host responses. Chapter 1 addresses the importance of coinfection timing using Barley yellow dwarf virus (BYDV-PAV) and Barley stripe mosaic virus. Coinfection timing significantly influenced viral within-host competition. Additionally, simultaneous coinfections were significantly more severe than sequential coinfections, which were only as severe as the most damaging constituent virus. A mathematical model was used to demonstrate that inaccurate projections of disease impacts on host populations can result when the effects of coinfection timing are not taken onto account. Chapter 2 explores the effects of coinfections of Cereal yellow dwarf virus (CYDV-RPV) and two species of BYDV (PAV and PAS) on pathogen evolution using an experimental evolution approach. Viruses exhibited altered within-host concentrations and transmission after serial passage in coinfections, without altered disease severity. Chapter 3 examines interactions between Bean common mosaic virus (BCMV) and Clover yellow vein virus (ClYVV)), and a microbial mutualist, rhizobia bacteria. The presence of rhizobia allowed ClYVV to reach higher within-host concentrations in coinfections. Viral transmission was also affected by interactions between coinfection and plant nitrogen source. Viral infection significantly reduced the percentage of nitrogen in plant tissues derived from microbial mutualists, with a greater than additive decrease in coinfections. Chapter 4 assesses the effects of BCMV and ClYVV coinfection and rhizobia colonization on plant primary and secondary metabolism. Increased photosynthetic rates were observed in plants colonized by rhizobia, which were driven by increased maximum rates of electron transport. Infection status, inorganic nitrogen fertilizer, and rhizobia had significant effects on components of plant volatile organic compound (VOC) emissions, with nitrogen source significantly affecting overall VOC profile composition. Chapter 5 analyzes how reductions in rhizobial nitrogen fixation caused by viral infection affect soil fertility, and projects substantial monetary losses for farmers when viral prevalence is high in a legume rotation, either due to additional fertilizer costs or reduced yield of a subsequent non-legume crop.
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Frontiers | Barley yellow dwarf virus infection leads to higher chemical defence signals and lower electrophysiological reactions in susceptible compared to tolerant barley genotypes | Plant Science

Barley yellow dwarf virus (BYDV) is a phloem limited virus that is persistently transmitted by aphids. Due to huge yield losses in agriculture, the virus is of high economic relevance. Since the control of the virus itself is not possible, tolerant barley genotypes are considered as the most effective approach to avoid yield losses. Although several genes and quantitative trait loci are known and used in barley breeding for virus tolerance, little is known about molecular and physiological backgrounds of this trait. Therefore, we compared the anatomy and early defence responses of a virus susceptible to those of a virus-tolerant cultivar. One of the very early defence responses is the transmission of electrophysiological reactions. Electrophysiological reactions to BYDV infection might differ between susceptible and tolerant cultivars, since BYDV causes disintegration of sieve elements in susceptible cultivars. The structure of vascular bundles, xylem vessels and sieve elements was examined using microscopy. All three were significantly decreased in size in infected susceptible plants where the virus causes disintegration of sieve elements. This could be associated with an uncontrolled ion exchange between the sieve-element lumen and apoplast. Further, a potential reduced electrophysiological isolation would negatively affect the propagation of electrophysiological reactions. To test the influence of BYDV infection on electrophysiological reactions, electropotential waves (EPWs) induced by leaf-tip burning were recorded using aphids as bioelectrodes. EPWs in infected susceptible plants disappeared already after 10 cm in contrast to those in healthy susceptible or infected tolerant or healthy tolerant plants. Another early plant defence reaction is an increase in reactive oxygen species (ROS). Using a fluorescent dye, we found a significant increase in ROS content in infected susceptible plants but not in infected tolerant plants. Similar results were found for the phytohormones abscisic acid and three jasmonates. Salicylic acid levels were generally higher after BYDV infection compared to uninfected plants. Heat stimulation caused an increase in jasmonates. By shedding light on the plant defence mechanisms against BYDV, this study, provides further knowledge for breeding viral tolerant plants.
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Molecular analysis of barley stripe mosaic virus isolates differing in their biological properties and the development of reverse transcription loop-mediated isothermal amplification assays for the...

Molecular analysis of barley stripe mosaic virus isolates differing in their biological properties and the development of reverse transcription loop-mediated isothermal amplification assays for the... | Cereal and grass viruses II | Scoop.it

Abstract

Barley stripe mosaic virus (BSMV) is an important seed-transmitted pathogen occurring worldwide. Recently, the occurrence of mild BSMV pathotypes has been observed in barley crops in Poland. In this study, the full-length genome sequences of mild and aggressive Polish and German BSMV isolates was established. Phylogenetic and recombination analysis was performed using Polish and other BSMV isolates described to date. The analysis revealed that Polish isolates differed only in 25 nucleotides, which suggests that point mutations might have had a great impact on the biological properties of the virus. The phylogenetic analysis revealed that the closest relationship was that between European and BSMV-CV42, BSMV-ND18 and BSMV-Type isolates, whereas the highest genetic distance was observed for BSMV-Qasr Ibrim and BSMV-China isolates. A recombination event within the αa protein of BSMV-De-M and BSMV-CV42 isolates was also detected. Moreover, a sensitive reverse transcription loop-mediated isothermal amplification (RT-LAMP) method was developed for rapid detection of BSMV isolates. The RT-LAMP assay can be used for routine diagnostics of BSMV in seed and plant material.

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