Faba Bean Necrotic Yellows Virus Research Articles

Identification of New Chickpea Virus and Control of Chickpea Virus Disease

Objective The objective of the study was to discuss the classification, virus characteristics, detection methods, and control measures of chickpea virus, with an aim to provide a theoretical basis for identification of new chickpea virus and control of chickpea virus disease. Methods The domestic and foreign studies were reviewed, and the virus coat protein or nucleic acid sequence was identified by immunological and molecular diagnostic techniques. Results There were 14 main types of chickpea viruses attacking, and seven Luteoviridae viruses were reported, namely, chickpea chlorotic stunt virus (CpCSV), bean leafroll virus (BLRV), beet western yellows virus (BWYV), soybean dwarf virus (SbDV), cotton leafroll dwarf virus (CLRDV), cucurbit aphid-borne yellows virus (CABYV), and phasey bean mild yellows virus (PhBMYV). The family Geminiviridae includes chickpea chlorotic dwarf virus (CpCDV), chickpea chlorosis virus (CpCV), chickpea redleaf virus (CpRLV), chickpea yellows virus (CpYV), and mastrevirus. The family Nanoviridae is dominated by the faba bean necrotic yellows virus (FBNYV). The family Bromoviridae includes cucumber mosaic virus (CMV) and alfalfa mosaic virus (AMV). Conclusion At present, there are mainly 12 types of viruses infecting chickpeas, which are transmitted by leafhoppers or aphids and are associated with symptoms such as yellowing, chlorosis, and stunted pod development, resulting in serious yield loss. Correct use of various molecular diagnostic tools to detect and identify chickpea virus can accurately assess chickpea virus infection and provide a basis for the prevention and treatment of chickpea virus disease.

Distribution and identification of luteovirids affecting chickpea in Sudan

In Sudan yellowing viruses are key production constraints in pulse crops. Field surveys were carried out to identify luteovirids affecting chickpea crops in the major production regions (Gezira Scheme and River Nile State). A total of 415 chickpea plant samples with yellowing and stunting symptoms were collected during the 2013, 2015 and 2018 growing seasons. Serological results (Tissue-blot immunoassays) showed that Luteoviridae and Chickpea chlorotic dwarf virus (CpCDV, genus Mastrevirus, family Geminiviridae) were the most common viruses, with rare infections with Faba bean necrotic yellows virus (FBNYV, genus Nanovirus, family Nanoviridae). Some samples reacted only with a broad-spectrum luteovirid monoclonal antibody (5G4-MAb), and others showed cross reactions between the specific monoclonal antibodies, suggesting the occurrence of new luteovirid variants. Serological results were confirmed by amplification with reverse transcription-polymerase chain reaction (RT-PCR) and sequencing of the partial coat protein gene. Molecular analyses provided a basic, sufficient and reliable characterization for four viruses affecting chickpea that belong to Polerovirus (family Luteoviridae). These were Cucurbit aphid-borne yellows virus (CABYV), Pepper vein yellows virus (PeVYV), Pepo aphid-borne yellows virus (PABYV) and Cotton leafroll dwarf virus (CLRDV), that shared high similarity with the type sequences. Phylogenetic analyses also revealed high similarity to luteovirid species. This study has established reliable, rapid and sensitive molecular tools for the detection of luteovirid species.

Recent advances in understanding the replication initiator protein of the ssDNA plant viruses of the family Nanoviridae.

The families of viruses possessing single-stranded (ss) circular genome employ a dedicated replication initiator protein (Rep) for making copies of their genome through the process of rolling circle replication. The replication begins at conserved nonanucleotide sequence at the intergenic region. The Rep protein seems to be the most conserved amongst the available proteins of the nanovirids and comprises of the N-terminal endonuclease domain and the C-terminal helicase domain. The structural studies of Faba bean necrotic yellows virus endonuclease domain suggests a α + β fold comprising of central β sheet built from five antiparallel β strands surrounded by outer short α helices. The catalysis is mediated by a conserved Tyr residue and employs divalent metal ions (Mn2+). On one hand, the Reps associate with each other and oligomerize and on the other hand interact with varied host and vector associated proteins for successful infection. The sequence analysis of Reps from previously known nanovirids and the newly found ones from metagenomics data shed light on the evolutionary pattern of nanovirids in comparison to other plant infecting ssDNA viruses.

Molecular characterization of faba bean necrotic yellows viruses in Tunisia.

Faba bean necrotic yellows virus (FBNYV) (genus Nanovirus; family Nanoviridae) has a genome comprising eight individually encapsidated circular single-stranded DNA components. It has frequently been found infecting faba bean (Vicia faba L.) and chickpea (Cicer arietinum L.) in association with satellite molecules (alphasatellites). Genome sequences of FBNYV from Azerbaijan, Egypt, Iran, Morocco, Spain and Syria have been determined previously and we now report the first five genome sequences of FBNYV and associated alphasatellites from faba bean sampled in Tunisia. In addition, we have determined the genome sequences of two additional FBNYV isolates from chickpea plants sampled in Syria and Iran. All individual FBNYV genome component sequences that were determined here share>84% nucleotide sequence identity with FBNYV sequences available in public databases, with the DNA-M component displaying the highest degree of diversity. As with other studied nanoviruses, recombination and genome component reassortment occurs frequently both between FBNYV genomes and between genomes of nanoviruses belonging to other species.

Virus surveys of process vegetable crops pea beetroot and dwarf bean

In a survey of 14 processing crops and 7 pea seed crops throughout Canterbury Cucumber mosaic virus (CMV) was the most widespread with crop incidences of up to 20 Alfalfa mosaic virus (AMV) up to 11 Pea seedborne mosaic virus (PSbMV) up to 9 Soybean dwarf virus (SDV) up to 2 Turnip yellows virus (TuYV) up to 2 and Bean yellow mosaic virus (BYMV) up to 35 Red clover vein mosaic virus (RCVMV) was detected in peas for the first time in New Zealand with incidences of up to 35 Pea necrotic yellow dwarf virus (PNYDV) Faba bean necrotic yellows virus (FBNYV) and Broad bean stain virus (BBSV) were not detected In a survey of 8 beetroot crops TuYV was detected in Auckland at 1 incidence but not in Hawkes Bay Beet mosaic virus was detected at 1 incidence in both regions Fungal leaf spotting pathogens appear a greater concern in beetroot In 12 dwarf bean processing crops throughout Canterbury virus was only detected in early sown crops AMV and RCVMV were most widespread with incidences of up to 9; CMV with up to 7 incidence; then BYMV TuYV and SDV each with 1 incidence No Bean common mosaic virus was detected

The RXL motif of the African cassava mosaic virus Rep protein is necessary for rereplication of yeast DNA and viral infection in plants

Geminiviruses, single-stranded DNA plant viruses, encode a replication-initiator protein (Rep) that is indispensable for virus replication. A potential cyclin interaction motif (RXL) in the sequence of African cassava mosaic virus Rep may be an alternative link to cell cycle controls to the known interaction with plant homologs of retinoblastoma protein (pRBR). Mutation of this motif abrogated rereplication in fission yeast induced by expression of wildtype Rep suggesting that Rep interacts via its RXL motif with one or several yeast proteins. The RXL motif is essential for viral infection of Nicotiana benthamiana plants, since mutation of this motif in infectious clones prevented any symptomatic infection. The cell-cycle link (Clink) protein of a nanovirus (faba bean necrotic yellows virus) was investigated that activates the cell cycle by binding via its LXCXE motif to pRBR. Expression of wildtype Clink and a Clink mutant deficient in pRBR-binding did not trigger rereplication in fission yeast.

Genome diversity and evidence of recombination and reassortment in nanoviruses from Europe

The recent identification of a new nanovirus, pea necrotic yellow dwarf virus, from pea in Germany prompted us to survey wild and cultivated legumes for nanovirus infections in several European countries. This led to the identification of two new nanoviruses: black medic leaf roll virus (BMLRV) and pea yellow stunt virus (PYSV), each considered a putative new species. The complete genomes of a PYSV isolate from Austria and three BMLRV isolates from Austria, Azerbaijan and Sweden were sequenced. In addition, the genomes of five isolates of faba bean necrotic yellows virus (FBNYV) from Azerbaijan and Spain and those of four faba bean necrotic stunt virus (FBNSV) isolates from Azerbaijan were completely sequenced, leading to the first identification of FBNSV occurring in Europe. Sequence analyses uncovered evolutionary relationships, extensive reassortment and potential remnants of mixed nanovirus infections, as well as intra- and intercomponent recombination events within the nanovirus genomes. In some virus isolates, diverse types of the same genome component (paralogues) were observed, a type of genome complexity not described previously for any member of the family Nanoviridae. Moreover, infectious and aphid-transmissible nanoviruses from cloned genomic DNAs of FBNYV and BMLRV were reconstituted that, for the first time, allow experimental reassortments for studying the genome functions and evolution of these nanoviruses.

Application of Motif-Based Tools on Evolutionary Analysis of Multipartite Single-Stranded DNA Viruses

Multipartite viruses contain more than one distinctive genome component, and the origin of multipartite viruses has been suggested to evolve from a non-segmented wild-type virus. To explore whether recombination also plays a role in the evolution of the genomes of multipartite viruses, we developed a systematic approach that employs motif-finding tools to detect conserved motifs from divergent genomic regions and applies statistical approaches to select high-confidence motifs. The information that this approach provides helps us understand the evolution of viruses. In this study, we compared our motif-based strategy with current alignment-based recombination-detecting methods and applied our methods to the analysis of multipartite single-stranded plant DNA viruses, including bipartite begomoviruses, Banana bunchy top virus (BBTV) (consisting of 6 genome components) and Faba bean necrotic yellows virus (FBNYV) (consisting of 8 genome components). Our analysis revealed that recombination occurred between genome components in some begomoviruses, BBTV and FBNYV. Our data also show that several unusual recombination events have contributed to the evolution of BBTV genome components. We believe that similar approaches can be applied to resolve the evolutionary history of other viruses.

Three Distinct Nanoviruses, One of Which Represents a New Species, Infect Faba Bean in Ethiopia.

In all, 70 of 296 leaf samples (23.6%) collected from faba bean (Vicia faba) plants showing leaf yellowing and stunting in Ethiopia gave nanovirus-positive reactions when studied by triple-antibody sandwich enzyme-linked immunosorbent assay using broad-spectrum monoclonal antibodies (MAbs) specific to nanoviruses. Further analysis of these samples with seven discriminating MAbs revealed contrasting epitope profiles that were categorized into roughly three serogroups, designated A, B, and C. Serogroup A was found in 89% of the nanovirus-positive samples whereas serogroups B and C were infrequently encountered. Sequence analysis of DNA-S and DNA-U1 of serogroup A, B, and C isolates suggested that each represents a distinct nanovirus species. Serogroup A comprised isolates of Faba bean necrotic stunt virus reported earlier only from Ethiopia and Morocco. The DNA-R, -S, -U1, and -U2 sequences of a serogroup B isolate closely resembled those of Faba bean necrotic yellows virus, providing first molecular evidence for its occurrence in Ethiopia. Sequence analysis of the eight genomic DNAs of a representative serogroup C isolate (Eth-231) showed that it shared overall nucleotide and amino acid sequence identities of only ≤70 and ≤74%, respectively, with other nanoviruses. This suggests that Eth-231 represents a new nanovirus species, for which the name faba bean yellow leaf virus is proposed.

Chapter 11 - Virus Diseases of Peas, Beans, and Faba Bean in the Mediterranean Region

In the Mediterranean region, pea, bean, and faba bean production is affected by around 17 major viruses. These viruses do not have the same ecology and consequently require a variety of different preventive measures to control them. Some of these viruses have a narrow host range, such as Faba bean necrotic yellows virus (FBNYV), and others, such as Alfalfa mosaic virus (AMV) and Cucumber mosaic virus (CMV), a very wide host range. Such features are important when identifying sources of virus inoculum in a region, and the vectors can transmit viruses from natural reservoirs to the crop plants. Some of these viruses are seed borne and, consequently, can be disseminated long distances through infected seeds. Crop losses caused by these viruses are variable, depending on the sensitivity and susceptibility of the crop to infection. Host resistance genes have been identified for some of these viruses, but in others, such as FBNYV, no resistance genes in faba bean have been identified yet. Significant progress was made in developing precise methods for the identification of these viruses, and new virus problems are being identified every year. This chapter is not intended to be a review for pea, bean, and faba bean viruses, but rather focuses on the major viruses which affect these crops in the Mediterranean basin with focus on the progress made over the past two decades.

Viruses infecting chickpea and lentil crops in Azerbaijan

A survey was conducted to identify viruses affecting chickpea and lentil crops in the major production areas of Azerbaijan during June 2007 and May 2008. The survey covered randomly selected 16 farmers’ fields (13 chickpea and three lentil) and one lentil field in research station during 2007, and 14 fields (nine chickpea and five lentil fields) during 2008. Infection incidences were determined for 11 legume viruses by tissue blot immunoassays (TBIA) on 50–200 randomly samples collected from each field. The TBIA and confirmatory nucleic acid analyses indicated that Luteoviridae species [Beet western yellows virus (BWYV), Bean leafroll virus (BLRV) and Chickpea chlorotic stunt virus (CpCSV)] were collectively the most common viruses in chickpea and lentil fields followed by Faba bean necrotic yellows virus (FBNYV). Pea seed-borne mosaic virus (PSbMV) was not detected in chickpea but reached high incidences in lentil fields. This is the first survey of legume viruses in Azerbaijan and first record of FBNYV, BWYV, BLRV and CpCSV naturally infecting chickpea and lentil crops, and PSbMV infecting lentil crop in Azerbaijan.

Purification, Serological and Molecular Studies on an Egyptian Isolate of Faba Bean Necrotic yellows Virus (FBNYV) Infecting Faba Bean Plants

Purification, Serological and Molecular Studies on an Egyptian Isolate of Faba Bean Necrotic yellows Virus (FBNYV) Infecting Faba Bean Plants

First Report of Beet mosaic virus Infecting Chickpea (Cicer arietinum) in Tunisia.

Chickpea plants with severe yellowing and tip wilting were observed in the Cap-Bon Region of Tunisia in 2006. The viral-like symptoms resulted in yield loss of approximately 25% in some fields. A total of 110 symptomatic chickpea plants was collected from nine chickpea fields and tested at the Virology Laboratory of ICARDA, Syria for eight legume viruses using tissue-blot immunoassay (TBIA) (3). Polyclonal antisera produced at the ICARDA Virology Laboratory were used to test for Chickpea chlorotic dwarf virus (genus Mastrevirus, family Geminiviridae), Broad bean stain virus (genus Comovirus, family Secoviridae), Broad bean mottle virus (genus Bromovirus, family Bromoviridae), and Bean yellow mosaic virus and Pea seed borne mosaic virus (genus Potyvirus, family Potyviridae). Antiserum to Beet mosaic virus (BtMV; genus Potyvirus, family Potyviridae) (AS-0143) was provided by the German Collection of Microorganisms and Cell Cultures (DSMZ, Braunschweig, Germany). In addition, three monoclonal antibodies (MAb) were used to detect Faba bean necrotic yellows virus (FBNYV; genus Nanovirus, family Nanoviridae) (MAb 3-2E9) (1), potyviruses (PVAS-769 [MAb PTY 3 Potyvirus Group] American Type Culture Collection, Manassas, VA), and luteoviruses (MAb B-2-5G4) (2). Twenty-two of the plants tested positive with MAb PTY 3 and BtMV antisera, 56 samples reacted with MAb B-2-5G4, and eight plants with the FBNYV MAb, whereas 24 plants tested negative with all antisera. Because reactions with the BtMV antiserum were unexpected, detection of BtMV was confirmed by reverse transcription-(RT)-PCR assays using BtMV-specific primers (LN26 and LN27) (4), which produced an amplicon of expected size (1,050 bp) from all plants that reacted with BtMV antiserum but not from plants that were serologically negative. Leaf tissue from a BtMV-infected plant was ground in 0.01 M potassium phosphate buffer, pH 7.2 (1:20, wt/vol), mixed with 0.5% celite, and used for mechanical inoculation of chickpea seedlings (cv. Beja 4). In addition, adults of three legume aphid species (Aphis craccivora, A. fabae, and Acyrthosiphon pisum) were starved for 1 h before feeding on BtMV-infected chickpea leaves for an acquisition access period of 5 min. Fifteen aphids of each species were placed on each chickpea plant, allowed to feed for 24 h, and then sprayed with an insecticide. Tip wilting symptoms appeared on plants 15 to 20 days after mechanical and aphid inoculations but not on plants used as negative control treatments (inoculated mechanically with healthy leaf tissue or with aphids that had fed on noninfected chickpea plants). Use of BtMV antiserum for TBIA analysis of inoculated plants revealed systemic BtMV infections in 35 of 92 plants inoculated mechanically and 15 of 75 plants inoculated with viruliferous A. fabae only. To our knowledge, this is the first record of BtMV infecting chickpea in Tunisia.

Advances in Small Isometric Multicomponent ssDNA Viruses Infecting Plants.

Multicomponent ssDNA plant viruses were discovered during 1990s. They are associated with bunchy top, yellowing and dwarfing diseases of several economic plants under family Musaceae, Leguminosae and Zingiberaceae. In the current plant virus taxonomy, these viruses are classified under the family Nanoviridae containing two genera, Nanovirus and Babuvirus. The family Nanoviridae was created with five members in 2005 and by 2010, it has expanded with four additional members. The viruses are distributed in the tropical and subtropical regions of Asia, Australia, Europe and Africa. The viruses are not sap or seed transmissible and are naturally transmitted by aphid vector in a persistent manner. The genome is consisted of several circular ssDNAs of about 1kb each. Up to 12 DNA components have been isolated from the diseased plant. The major viral proteins encoded by these components are replication initiator protein (Rep), coat protein, cell-cycle link protein, movement protein and a nuclear shuttle protein. Each ssDNA contains a single gene and a noncoding region with a stable stem and loop structure. Several Rep encoding components have been reported from each virus, only one of them designated as master Rep has ability to control replication of the other genomic components. Infectivity of the genomic DNAs was demonstrated only for two nanoviruses, Faba bean necrotic yellows virus and Faba bean necrotic stunt virus (FBNSV). A group of eight ssDNA components of FBNSV were necessary for producing disease and biologically active progeny viruses. So far, infectivity of genomic components of Babuvirus has not been demonstrated.

First Report of a Nanovirus Disease of Pea in Germany.

During the growing season of 2009, a disease consisting of leaf rolling, top yellows, and plant stunting affected pea (Pisum sativum) in fields near Aschersleben, Saxony-Anhalt, Germany. Samples from symptomatic plants collected in July 2009 were analyzed at the JKI in Braunschweig for infections by various legume viruses by ELISA, immunoelectron microscopy, and transmission assays by sap and aphids. Of 23 samples, 9 were shown to contain Pea enation mosaic virus and three samples each contained Bean leafroll virus and Soybean dwarf virus. From two further samples that had tested negative for the aforementioned viruses, we succeeded in transferring a disease agent to faba bean (Vicia faba) seedlings by giving 50 to 100 individuals of the pea aphid (Acyrthosiphon pisum) acquisition and inoculation access feedings each of ~48 h. Following vector transmission, the agent caused severe yellowing and stunting in pea and faba bean, sometimes followed by necrosis. Attempts at mechanical transmission of the agent failed, and isolation of double-stranded RNA from infected tissue was not successful. Therefore, we considered the possible presence of a nanovirus (4). When using polyclonal antibodies (PAbs) against Faba bean necrotic yellows virus (FBNYV) for double-antibody sandwich (DAS)-ELISA analysis of the two isolates of the disease agent we observed weak but clearly positive reactions. To confirm these weak DAS-ELISA reactions, we used all available monoclonal antibodies (MAbs) raised against FBNYV (1) and faba bean necrotic stunt virus (FBNSV) (3) individually in triple-antibody sandwich (TAS)-ELISA in combination with the FBNYV PAbs for plate coating. Six of 26 MAbs reacted from weak to strong with the two pea isolates, with MAbs FBNYV-3-1F7 and FBNSV-5-1G8 giving the strongest reactions and none of the MAbs giving a differential reaction with the two pea isolates. Employing rolling circle amplification of total DNA extracted from symptomatic leaves of one of the pea isolates yielded a substantial amount of high molecular weight DNA, whereas little or no amplification occurred when using DNA from noninoculated pea leaves. Restriction of the amplified DNA in a nanovirus iteron-specific manner by AatII endonuclease yielded a predominant and abundant product of ~1 kb (3). Sequence comparisons of eight cloned DNAs of 1,002 nucleotides long unequivocally identified them as complete DNA-R component of a new member of the genus Nanovirus (2,4). Its DNA-R sequence (GenBank No. GU553134) is nearly equidistant from the DNA-R sequences of FBNYV (Y11405), FBNSV (GQ150778), Milk vetch dwarf virus (MDV) (AB027511) and Subterranean clover stunt virus (SCSV) (AJ290434), sharing with them respective sequence identities of 79, 78, 79, and 73%. Moreover, it is more distinct from the DNA-R sequences of FBNYV, FBNSV, and MDV than the three latter are from each other (86 to 91%). This together with the serological data relating to the capsid protein properties of this virus strongly suggest that it is distinct from the hitherto described nanoviruses FBNYV, MDV, FBNSV, and SCSV. Therefore, we propose the name pea necrotic yellow dwarf virus (PNYDV) for this new nanovirus naturally infecting pea in Germany.

Two distinct nanovirus species infecting faba bean in Morocco.

Using monoclonal antibodies raised against a Faba bean necrotic yellows virus (FBNYV) isolate from Egypt and a Faba bean necrotic stunt virus (FBNSV) isolate from Ethiopia, a striking serological variability among nanovirus isolates from faba bean in Morocco was revealed. To obtain a better understanding of this nanovirus variability in Morocco, the entire genomes of two serologically contrasting isolates referred to as Mor5 and Mor23 were sequenced. The eight circular ssDNA components, each identified from Mor5- and Mor23-infected tissues and thought to form the complete nanovirus genome, ranged in size from 952 to 1,005 nt for Mor5 and from 980 to 1,004 nt for Mor23 and were structurally similar to previously described nanovirus DNAs. However, Mor5 and Mor23 differed from each other in overall nucleotide and amino acid sequences by 25 and 26%, respectively. Mor23 was most closely related to typical FBNYV isolates described earlier from Egypt and Syria, with which it shared a mean amino acid sequence identity of about 94%. On the other hand, Mor5 most closely resembled a FBNSV isolate from Ethiopia, with which it shared a mean amino acid sequence identity of approximately 89%. The serological and genetic differences observed for Mor5 and Mor23 were comparable to those observed earlier for FBNYV, FBNSV, and Milk vetch dwarf virus. Following the guidelines on nanovirus species demarcation, this suggests that Mor23 and Mor5 represent isolates of FBNYV and FBNSV, respectively. This is the first report not only on the presence of FBNSV in a country other than Ethiopia but also on the occurrence and complete genome sequences of members of two nanovirus species in the same country, thus providing evidence for faba bean crops being infected by members of two distinct nanovirus species in a restricted geographic area.

Detection and Characterization of Chickpea Chlorotic Stunt Virus in Syria

AbstractField surveys were conducted in Syria during the 2005/2006 and 2006/2007 growing seasons to identify viruses which affect cool‐season food legumes, volunteer crops, and weeds with yellowing, reddening and/or stunting symptoms. Serological tests (tissue blot immunoassay) showed that Faba bean necrotic yellows virus and luteoviruses including, Beet western yellows virus, Bean leafroll virus and Soybean dwarf virus were the main viruses identified. In addition, a large number of samples reacted positively with the broad spectrum legume luteovirus (5G4) monoclonal antibody but not with any other specific luteovirus monoclonal antibodies suggesting the occurrence of new luteovirus species/strains. RT‐PCR assay of 27 of such samples revealed the presence of Chickpea chlorotic stunt virus (CpCSV; genus Polerovirus, family: Luteoviridae). The coat protein nucleotide sequence analysis of the Syrian CpCSV isolate from chickpea showed a high homology (98%) to that of the Ethiopian CpCSV isolate. However, there were some differences in host range and aphid transmission characteristics between the Syrian and Ethiopian isolates. This is the first report of CpCSV naturally affecting eight legume species (Cicer arietinum L., Lens culinaris Medik., Pisum sativum L., Vicia faba L., Vicia sativa L., Vicia ervilia L. Willd., Vicia narbonensis L. and Medicago sp.) and four wild non‐legume plant species [Apium sp. (Apiaceae), Euphorbia sp. (Euphorbiaceae), Physalis longifolia Nutt. (Solanaceae) and Sinapis arvensis L. (Brassicaceae)] in Syria.

First Report of Faba bean necrotic yellows virus Affecting Legume Crops in Azerbaijan.

A total of 482 chickpea (Cicer arietinum L.), 182 lentil (Lens culinaris Medik.), 12 vetch (Vicia sativa L.), 5 field pea (Pisum sativum L.), and 3 faba bean (Vicia faba L.) samples were collected from plants with symptoms suggestive of a viral infection (leaf rolling, yellowing, and stunting) from the major legume-production areas of Azerbaijan in the 2007 and 2008 growing seasons. All samples were tested by the tissue-blot immunoassay (3) at the Virology Laboratory of ICARDA, Syria using 11 specific legume virus antisera including a monoclonal antibody (2-5H9) (1) for Faba bean necrotic yellows virus (FBNYV). Laboratory tests showed that FBNYV was detected in 73, 61, 11, 3, and 2 samples of chickpea, lentil, vetch, field pea, and faba bean, respectively. Total DNA was extracted from six FBNYV-positive samples (two chickpea, two lentil, and two vetch) and tested by PCR with the following four primer sets (FBNYV, Milk vetch dwarf virus [MDV], Subterranean clover stunt virus [SCSV], and nanovirus DNA-R primers [F103 and R101]) (2). All six Azeri samples as well as the reference nanovirus isolates (SCSV-Australia, MDV-Japan, and FBNYV-Syria) generated amplicons of the expected size (~770 bp) using the nanovirus DNA-R primers (F103 & R101). In addition, Azeri samples and FBNYV-Syria yielded a PCR amplicon of the expected size (666 bp) with the FBNYV primer pair. The MDV- and SCSV-specific primers did not generate amplicons with these six samples. Sequence analysis of the FBNYV amplicons from two isolates (AzL 282-07 from lentil [GenBank Accession No. GQ351600] and AzV 277-07 from vetch [GenBank Accession No. GQ371215]) showed that they were 99% identical with each other. Comparing the sequence of AzL 282-07 with that of other nanoviruses revealed identities of 97% (FBNYV-Spain; DQ830990), 96% (FBNYV-Iran; AM493900), 92% (FBNYV-Syria; Y11408), 92% (FBNYV-Egypt; AJ132183), 78% (MDV; AB044387) and 69% (SCSV-Australia; U16734). FBNYV has been reported to infect food legumes in many countries in West Asia and North Africa and cause economic losses on faba bean in Egypt, Jordan, and Syria. To our knowledge, this is the first record of FBNYV infecting legume crops in Azerbaijan.

Viral diseases affecting chickpea crops in Eritrea

A survey to identify virus diseases affecting chickpea crops in the major production areas of Eritrea was conducted during November 2005. The survey covered 31 randomly selected chickpea fi elds. Virus disease incidence was determined on the basis of laboratory testing of 100–200 randomly collected samples from each fi eld against antisera of 9 legume viruses. Serological tests indicated that the Luteoviruses were the most common, with an overall incidence of 5.6%, followed by Faba bean necrotic yellows virus (FBNYV, genus Nanovirus, family Nanoviridae) (4.1%) and Chickpea chlorotic dwarf virus (CpCDV, genus Mastrevirus, family Geminiviridae) (0.9%). The reverse transcription polymerase chain reaction (RT-PCR) test showed that the most common luteoviruses in Eritrea are Chickpea chlorotic stunt virus (CpCSV) followed by Beet western yellows virus (BWYV, genus Polerovirus, family Luteoviridae). Based on the fi eld symptoms observed, 29 fi elds had, at the time of the survey, a virus disease incidence of 1% or less and only two fi elds had an incidence of about 5%, whereas on the basis of laboratory testing, 19 fi elds had more than 6% virus incidence (three of these had an incidence of 29.5, 34.5 and 40.5%). This is the fi rst survey of chickpea viruses in Eritrea and the fi rst report of BWYV, CpCDV, CpCSV and FBNYV naturally infecting chickpea in Eritrea.

Transcripts encoding the nanovirus master replication initiator proteins are terminally redundant

The multicomponent single-stranded DNA plant nanoviruses encode unique master replication initiator (Rep) proteins. We have mapped the 5' and 3' termini of the corresponding polyadenylated mRNAs from faba bean necrotic yellows virus (FBNYV) and subterranean clover stunt virus and found that these are terminally redundant by up to about 160 nt. Moreover, the origin of viral DNA replication is transcribed into RNA that is capable of folding into extended secondary structures. Other nanovirus genome components, such as the FBNYV DNA encoding the protein Clink or an FBNYV DNA encoding a non-essential para-Rep protein, are not transcribed in such a unique fashion. Thus, terminally redundant mRNAs and the resulting transcription of the replication origin appear to be restricted to nanovirus master Rep DNAs. We speculate that this may be a way to regulate the expression of the essential master Rep protein.