Beet Western Yellows Luteovirus Research Articles

The prevalence and spatial distribution of viruses in natural populations of Brassica oleracea.

We report a survey of four viruses (beet western yellows luteovirus (BWYV), cauliflower mosaic caulimovirus (CaMV), turnip mosaic potyvirus (TuMV), turnip yellow mosaic tymovirus (TYMV)) in five natural populations of Brassica oleracea in Dorset (UK). All four viruses were common; 43% of plants were infected with BWYV, 60% with CaMV, 43% with TuMV and 18% with TYMV. For each virus there were significant differences in the proportion of infected plants among populations, which were not completely explained by differences in the age of plants. Multiple virus infections were prevalent, with 54% of plants having two or more virus types. There were statistically significant associations between pairs of viruses. The CaMV was positively associated with the other three viruses, and BWYV was also positively associated with TuMV. There was no detectable association between BWYV and TYMV, whereas TuMV and TYMV were negatively associated. We suggest these associations result from BWYV, CaMV and TuMV having aphid vectors in common, as aphids are attracted to plants that already have a virus infection. Infected plants were distributed randomly or were very weakly aggregated within populations. The implications of widespread multiple virus infections in natural plant populations are discussed with respect to the release of transgenic plants expressing virus-derived genes.

Incidence and Effects of Beet Western Yellows Virus in Western Oregon Sugarbeet Seed Crops

A 1986 to 1995 survey of beet western yellows luteovirus (BWYV) in western Oregon crop and weed species demonstrated that BWYV was endemic in at least 30 plant species. Because sugarbeet-seed crops (Beta vulgaris L.) were sometimes perceived as the primary western Oregon source of BWYV inoculum, we sought to examine all components of the inoculum reservoir. The array of BWYV hosts in western Oregon provided a year-round supply of BWYV inoculum comprising three interactive sub-reservoirs : (a) widespread annual, winter annual, and perennial weeds, (b) BWYV-susceptible vegetable crops, including garden beet, lettuce, spinach, Swiss chard, and turnip, and (c) sugarbeet-seed crops. We defined zones of high and low BWYV incidence in sugarbeet-seed fields within western Oregon, and monitored incidence of BWYV in a common weed species, Brassica campestris L. (field mustard). We demonstrated abrupt variations in BWYV incidence in sugarbeet-seed plantings in the vicinity of Corvallis near the Willamette River. BWYV incidence in sugarbeet-seed fields increased in localities where sugarbeet-seed crops were grown successively. Although marked differences in seed yields were observed, no reduction in sugarbeet seed yield was attributable to BWYV infection.

Role of the P74 minor capsid protein of beet western yellows luteovirus in cell to cell movement in plants

Role of the P74 minor capsid protein of beet western yellows luteovirus in cell to cell movement in plants

First Record of Faba Bean Necrotic Yellows Virus and Beet Western Yellows Luteovirus Affecting Lentil and Chickpea in Pakistan.

In an intensive survey of lentil and chickpea fields and Research Station plots in the Punjab province of Pakistan, more than 6,505 samples were collected and tested for presence of 14 different viruses by the tissue-blot immunoassay (TBIA) procedure (2). All antisera used were virus specific, including those for faba bean necrotic yellows virus (FBNYV) (1) and beet western yellows luteovirus (BWYV) (ATCC 647). Counting plants with virus symptoms greatly underestimated virus incidence in lentil crops but was a better guide to virus occurrence in chickpeas. Overall, about 1 in 5 plants of lentil were virus infected with 15% of fields having incidence over 50%. In contrast, levels of infection were mostly low in chickpea. Pea seed-borne mosaic virus (PSbMV) followed by cucumber mosaic virus (CMV), both of which are aphid- and seed-borne, were the most abundant viruses in lentils, but also occurred in chickpea. PSbMV incidence was 17% in lentil and 0.1% in chickpea fields, whereas CMV incidence was 1% in lentil and 0.1% in chickpea fields. The other viruses found on both lentil and chickpea were FBNYV, BWYV, chickpea chlorotic dwarf geminivirus, chickpea luteovirus, and alfalfa mosaic alfamovirus. Because of yield losses associated with PSbMV infection, the high levels of infection in lentils are cause for concern. This is the first record of FBNYV and BWYV affecting lentil and chickpea in Pakistan, but their incidence in the fields where they have been detected was low (less than 1%). FBNYV was detected in three of the 33 lentil and two of the 34 chickpea fields surveyed. BWYV was detected in two of the 33 lentil and three of the 34 chickpea fields surveyed.

Beet Western Yellows Luteovirus in Western Oregon: Pathosystem Relationships in a Vegetable-Sugar Beet Seed Production Region.

uring the 1980s, crisphead lettuce, butterhead lettuce, and spinach crops in western Oregon (Fig. 1) became increasingly damaged by beet western yellows luteovirus (BWYV) (5,8) infection (15), a previously insignificant problem in this area. Utilizing double antibody sandwich enzyme-linked immunosorbent assay (DASELISA) methodology (2), we identified potential BWYV inoculum sources in vicinities of affected lettuce and spinach fields (15) based on the known host range of BWYV (5–9) and prior agroecosystem investigations of BWYV in the Pacific Northwest (20,29,30,32–34,37,38). In current and prior (14,15) studies, we identified three principal subreservoirs of BWYV inoculum in the Willamette Valley: multiseasonal plantings of vegetable crops, biennial plantings of sugar beet seed fields (21), and numerous BWYV-susceptible weed species prevalent in this agroecosystem (14), including native, introduced, and escaped annual and perennial species. We also endeavored to understand beet western yellows (BWY) disease-cycle components in western Oregon and to document the presence and determine the effects of BWYV in representative western Oregon sugar beet seed fields (17). The incidence of potential aphid vectors on one or more of 30 western Oregon plant species or forms commonly infected by BWYV was also separately examined (16). The purpose of this paper is to present interactions within the BWY pathosystem that cause risks to BWYV-susceptible crops in western Oregon.

A Small RNA Resembling the Beet Western Yellows Luteovirus ST9-Associated RNA Is a Component of the California Carrot Motley Dwarf Complex

ABSTRACT Virions were purified from Anthriscus cerefolium or Coriandrum sativum plants infected with the viruses that cause California carrot motley dwarf. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of virion preparations yielded a single prominent protein species of approximately 28,000 molecular weight; however, denaturing agarose gel electrophoresis showed that virions contained three prominent single-stranded RNAs of approximately 5.6, 4.2, and 2.8 kb. Northern hybridization analyses, using transcripts generated from cloned cDNAs that corresponded to each of the virion RNAs, showed that the 5.6- and 4.2-kb RNAs were the genomic RNAs of the carrot red leaf luteovirus (CRLV) and the carrot mottle umbravirus (CMoV), respectively. Virions also contained an approximately 1.3-kb RNA related to the CMoV genomic RNA. The 2.8-kb RNA did not hybridize with CRLV or CMoV cRNA probes. Analysis of naturally infected carrot (Daucus carota) plants showed that CRLV, CMoV, and the 2.8-kb RNA were always present in carrot motley dwarf-affected plants. Greenhouse aphid- and mechanical-transmission experiments showed that the 2.8-kb RNA was consistently present in plants also infected by both CRLV and CMoV, but never in plants infected by only CMoV. Near full-length cloned cDNAs corresponding to the 2.8-kb RNA were prepared, and the complete nucleotide sequence was determined to be 2,835 nucleotides. Two large open reading frames (ORFs), 1a and 1b, were present within the sequence and were separated by an amber (UAG) stop codon. A third ORF (ORF 2), capable of encoding a protein of 4,289 molecular weight, was located near the 3' terminus. BLASTP results showed that the 2.8-kb RNA was most closely related to the beet western yellows luteovirus (BWYV) ST9-associated RNA. Based on its biological and molecular characteristics, we have named the 2.8-kb RNA the CRLV-associated RNA (CRLVaRNA).

Effects of Mutations in the Beet Western Yellows Virus Readthrough Protein on Its Expression and Packaging and on Virus Accumulation, Symptoms, and Aphid Transmission

Virions of beet western yellows luteovirus contain a major capsid protein (P22.5) and a minor readthrough protein (P74), produced by translational readthrough of the major capsid protein sequence into the neighboring open reading frame, which encodes the readthrough domain (RTD). The RTD contains determinants required for efficient virus accumulation in agroinfected plants and for aphid transmission. The C-terminal halves of the RTD are not well conserved among luteoviruses but the N-terminal halves contain many conserved sequence motifs, including a proline-rich sequence separating the rest of the RTD from the sequence corresponding to the major coat protein. To map different biological functions to these regions, short in-frame deletions were introduced at different sites in the RTD and the mutant genomes were transmitted to protoplasts as transcripts and toNicotiana clevelandiiby agroinfection. Deletions in the nonconserved portion of the RTD did not block aphid transmission but had a moderate inhibitory effect on virus accumulation in plants and abolished symptoms. Deletion of the proline tract and the junction between the conserved and nonconserved regions inhibited readthrough protein accumulation in protoplasts by at least 10-fold. The mutants accumulated small amounts of virus in plants, did not induce symptoms, and were nontransmissible by aphids using agroinfected plants, extracts of infected protoplasts, or purified virus as a source of inoculum. Other deletions in the conserved portion of the RTD did not markedly diminish readthrough protein accumulation but abolished its incorporation into virions. These mutants accumulated to low levels in agroinfected plants and elicited symptoms, but could not be aphid-transmitted. A preliminary map has been produced mapping these functions to different parts of the RTD.

Virus Diseases of Broad Bean in Spain.

Broad bean (Vicia faba L.) plants showing symptoms suggestive of viral infection, such as stunting, leaf roll, mosaic, chlorosis, necrosis, and yellowing, were observed in the Andalucia, Baleares, Cataluna, and Murcia regions of Spain. A 4-year field survey showed the presence of five viruses: bean leaf roll luteovirus (BLRV), beet western yellows luteovirus (BWYV), bean yellow mosaic potyvirus (BYMV), tomato spotted wilt tospovirus (TSWV), and cucumber mosaic cucumovirus (CMV). Identity of viruses was first determined by enzyme-linked immunosorbent assay and confirmed by at least one other method, such as inoculation to plant hosts, electron microscopy, molecular hybridization, or immunocapture-reverse transcriptase-polymerase chain reaction. Of the 250 samples assayed, 93 were positive for BYMV, 21 for BLRV, 10 for BWYV, 30 for TSWV, and 2 for CMV. Faba bean necrotic yellow virus (a single-strand DNA virus) and broad bean mottle bromovirus, which are widely distributed in the Mediterranean basin, were not detected in the samples analyzed. BYMV was distributed in all regions, whereas TSWV was restricted only to Mediterranean areas. To our knowledge, this is the first report of viruses infecting broad bean in Spain.

Extraction and aphid transmission of beet western yellows luteovirus from air dried leaf tissue

A protocol is described for the recovery of viable, aphid transmissible beet western yellows luteovirus from air-dried field material. The advantages of the protocol for long-term and cross-border field sampling are discussed.

Production and evaluation of monoclonal antibodies for the detection of beet mild yellowing luteovirus and related strains

A sugar-beet-infecting isolate of beet mild yellowing luteovirus (BMYV), and aBrassica-infecting isolate of beet western yellows luteovirus (BWYV) were used to produce monoclonal antibodies for epidemiological studies with BMYV and related field strains. Thirty-four monoclonal antibodies were tested for their reaction with 9 luteoviruses in triple-antibody-sandwich enzyme-linked immunosorbent assay. One (MAFF 24) is now routinely used in the UK for detecting BMYV and BWYV in plants and aphids, although it does not discriminate between them. Heterologous reactions were detected between some of the monoclonal antibodies and potato leafroll virus (PLRV), bean leafroll virus (BLRV) and barley yellow dwarf virus (BYDV-RPV). 38% of antibodies raised to BWYV reacted with PLRV compared with 4% of those raised to BMYV. Monoclonal antibodies were produced which distinguished a sugar-beet-infecting isolate of BMYV with differing host range and serological properties from the commonly-occurring field strain.

Survey for Beet Western Yellows Luteovirus as a Major Component of the Potato Leaf Roll Disease in Central Brazil

Survey for Beet Western Yellows Luteovirus as a Major Component of the Potato Leaf Roll Disease in Central Brazil

The Coat Protein of Beet Western Yellows Luteovirus is Essential for Systemic Infection but the Viral Gene Products P29 and P19 are Dispensable for Systemic Infection and Aphid Transmission

The Coat Protein of Beet Western Yellows Luteovirus is Essential for Systemic Infection but the Viral Gene Products P29 and P19 are Dispensable for Systemic Infection and Aphid Transmission

Synthesis of a Full-Length Infectious cDNA Clone of Cucurbit Aphid-Borne Yellows Virus and Its Use in Gene Exchange Experiments with Structural Proteins from Other Luteoviruses

A full-length cDNA of cucurbit aphid-borne yellows virus (CABYV) has been constructed and expressed either as anin vitrotranscript, under control of a bacteriophage T7 RNA polymerase promoter, orin vivo,under control of the cauliflower mosaic virus 35S promoter in an agroinfection vector. The biological activity of the cloned cDNA was demonstrated by the ability of itsin vitrotranscript to replicate in protoplasts and of the agroinfection vector to infect agroinoculated plants. Virus in the agroinfected plants could be transmitted by the aphid vectorsMyzus persicaeandAphis gossypii.The specificity of luteovirus RNA packaging was investigated by replacing (1) the CABYV coat protein gene (and the overlapping ORF5) by the corresponding region of potato leafroll luteovirus or (2) the CABYV readthrough domain by the readthrough domain of beet western yellows luteovirus. The resulting chimeric transcripts replicated in protoplasts and produced virions.

Detection of the luteoviruses, beet mild yellowing virus and beet western yellows virus, in aphids caught in sugar‐beet and oilseed rape crops, 1990–1993

SummaryThe incidence of beet mild yellowing luteovirus (BMYV) and non‐beet‐infecting strains of beet western yellows luteovirus (BWYV) in individual winged aphids, caught in yellow water‐traps, in sugar beet during the spring and early summer, and in oilseed rape plots in the autumn, was monitored using monoclonal antibodies in ELISA tests from 1990 to 1993. Between 0% and 8% of the Myzus persicae trapped in sugar beet each year carried BMYV, whereas 0% to 4% caught in oilseed rape in the autumn contained this virus. In 1990, 6.5% of Macrosiphum euphorbiae trapped in sugar beet contained BMYV, but in subsequent years less than 1% were carrying virus. Much higher proportions (26–67%) of the M. persicae tested from sugar beet contained BWYV, and similar proportions tested from oilseed rape (24–45%) also carried this virus in the autumn. In contrast only 3–19% of the M. euphorbiae caught in sugar beet contained BWYV, and none in oilseed rape. In 1991 and 1992 large numbers of Breuicoryne brassicae were caught in the plot of oilseed rape, of which over 50% contained BWYV; none were carrying BMYV.In transmission studies between 1990 and 1992, 1% and 27% of M. persicae transmitted BMYV and BWYV respectively to indicator plants; subsequent ELISA tests on the same aphids showed that 3% and 33% respectively contained the two viruses. One percent of M. euphorbiae transmitted BMYV, but none were found to contain BMYV using ELISA; 15% transmitted BWYV whilst only 5% were found to carry the virus.In 1992 and 1993 the incidence of BMYV‐infection in the sugar‐beet fields in which aphids had been trapped ranged from 1.2%, in a field which had received granular pesticide (aldicarb) at drilling plus three foliar aphicidal sprays, to 39.5% in a field which had received only one foliar spray. In 1992 in a sugar‐beet crop which had received no aphicidal treatments, and where 2.8% of immigrant M. persicae and 2.5% of M. euphorbiae contained BMYV, 11.6% of plants developed BMYV infection. Lowest levels of infection were associated with the use of granular pesticides at drilling.In 1990, 80% of oilseed rape plants in a field plot were infested with a mean of seven wingless M. persicae per plant by mid‐December; 37% of these plants were infected with BWYV. The studies show that M. persicae is the principal vector of BWYV, and large proportions of winged M. persicae carry the virus, in contrast to BMYV, which is consistent with the common occurrence of BWYV in brassica crops such as oilseed rape.

Beet Western Yellows Luteovirus Capsid Proteins Produced by Recombinant Baculoviruses Assemble into Virion-like Particles in Cells and Larvae of Bombyx mori

We subcloned various constructs of the beet western yellows luteovirus (BWYV) 3′ proximal genes into Bombyx mori nuclear polyhedrosis virus (BmNPV) transfer vectors and constructed recombinant BmNPVs. The recombinant BmNPVs were used to infect BmN cells and B. mori larvae. Protein expression was analyzed by SDS-PAGE and immunoblot analysis, and the BWYV-encoded capsid protein (CP), P19, readthrough protein (RT), and a modified capsid-readthrough protein (CPRT*) were detected in BmN cells infected by the respective BmNPVs. However, we detected only the BWYV CP and P19 in BmN cells infected with a recombinant BmNPV containing all three BWYV 3′ proximal genes. BmN cells and fat body cells from B. mori larvae infected with recombinant BmNPVs were analyzed by transmission electron microscopy and immunogold labeling. Particles which morphologically and serologically resembled BWYV virions were detected in the nuclei of BmN cells and B. mori larval fat body cells infected with recombinant BmNPVs producing either the BWYV CP alone or BWYV CP plus a BWYV CP-RT*. Similar particles were not detected in cells infected with a control BmNPV or recombinant BmNPV producing only CP-RT*.

Nucleotide sequence of beet mild yellowing virus RNA.

The complete nucleotide sequence of the genomic RNA of beet mild yellowing virus, isolate 2ITB, is reported. The RNA consists of 5722 nucleotides and contains six long open reading frames which conform to the arrangement characteristic of Subgroup 2 luteoviruses. The three 3'-proximal open reading frames, which encode the viral coat protein, a putative movement protein and the Readthrough Domain, are highly homologous to the corresponding genes of beet western yellows luteovirus while the three 5'-proximal open reading frames are more closely related to the corresponding genes of cucurbit aphid borne yellows luteovirus. The sequence data thus indicate that beet mild yellowing virus should be considered a distinct virus rather than a strain of beet western yellows virus.

A Recombinational Event in the History of Luteoviruses Probably Induced by Base-Pairing between the Genomes of Two Distinct Viruses

Alignments of luteovirus readthrough protein amino acid sequences show they consist of two distinct regions, here named the N domain and the C domain. N domain sequences were classified, and comparison of this gene phylogeny to phylogenies of other luteovirus genes revealed an anomaly in the relationships between beet western yellows luteovirus, cucurbit aphid-borne yellows luteovirus (CABYV), and pea enation mosaic RNA1 (PEMV1). Together with alignments of virion protein and readthrough protein amino acid sequences, these gene phylogenies indicate the anomaly to be the result of two recombinational events, probably between ancestors of CABYV and PEMV1 and leading to the transfer of RNA coding for the N domain to an ancestor of CABYV. Two likely recombination sites were identified from the alignments, one at the 5′ end of the readthrough protein gene and the other at the 5′ end of the sequence coding for the C domain. Alignments of the nucleotide sequences encompassing the probable recombination sites suggest that base-pairing between the genomes of the two ancestral luteoviruses, resulting from local sequence similarity at the 5′ end of the readthrough protein gene, probably induced one of the interspecies recombinational events.

Aphid transmission of beet western yellows luteovirus requires the minor capsid read-through protein P74.

Beet western yellows luteovirus is obligately transmitted by the aphid Myzus persicae in a circulative, non-propagative fashion. Virus movement across the epithelial cells of the digestive tube into the hemocoel and from the hemocoel into the accessory salivary glands is believed to occur by receptor-mediated endocytosis and exocytosis. Virions contain two types of protein; the major 22 kDa capsid protein and the minor read-through protein, P74, which is composed of the major capsid protein fused by translational read-through to a long C-terminal extension called the read-through domain. Beet western yellows virus carrying various mutations in the read-through domain was tested for its ability to be transmitted to test plants by aphids fed on agro-infected plants and semi-purified or purified virus preparations. The results establish that the read-through domain carries determinants that are essential for aphid transmission. The findings also reveal that the read-through domain is important for accumulation of the virus in agro-infected plants.

Detection of Sugar Beet-Infecting Beet Mild Yellowing Luteovirus Isolates with a Specific RNA Probe

A complementary RNA (cRNA) probe, BM1, was prepared by transcription of a 1,061 nucleotide cDNA fragment complementary to nucleotides 1 to 1,061 (open reading frame [ORF] 1) within the sequence of a French sugar beet-infecting beet mild yellowing luteovirus (BMYV) -2ITB isolate. This probe detected specifically the homologous isolate as well as 14 other BMYV isolates collected from sugar beet grown in various areas, mainly in Europe. It did not hybridize with non-beet-infecting isolates of the closely related beet western yellows luteovirus (BWYV) or cucurbit aphid-borne yellows luteovirus (CABYV) -N isolate, but reacted weakly with two English BMYV isolates that do not infect Capsella bursa-pastoris or Montia perfoliata. The probe BMI detected BMYV in single Myzus persicae, giving no reaction with nonviruliferous individuals. As a comparison, a second BMYV probe (BM2) was produced to the coat protein gene (ORF 4) of the French BMYV-2ITB isolate. This probe detected all BMYV, BWYV and CABYV isolates, highlighting the closer sequence homology within this region among Subgroup 2 luteoviruses. The dilution end-point for the detection of virus from infected material by radioactively labeled probes was 1 :500, and about 250 fg of viral RNA could be detected from purified virions preparations. Non-radioactively labeled (digoxigenin [DIG]) probes were found to be 30-fold less sensitive than radioactive cRNA probes. Probe BM1 has potential for large-scale screening with applications in epidemiology and sugar beet-breeding programs. This report shows that heterogeneity at the 5' proximal regions of the genomes of BMYV and BWYV offers the potential for discriminating between the two viruses and identifying the sugar beet-infecting BMYV isolates.

The incidence of three virus diseases of winter oilseed rape in England and Wales in the 1991/92 and 1992/93 growing seasons

The incidence and severity of three diseases of oilseed rape, caused by beet western yellows luteovirus (BWYV), cauliflower mosaic caulimovirus (CaMV) and turnip mosaic potyvirus (TuMV), were assessed in England and Wales in the springs of 1992 and 1993. In 1992, 62% of oilseed rape crops examined were found to contain BWYV, with an average of 28% plants infected; 14% of crops contained CaMV, with an average of 5% plants infected; and TuMV with 3% crops and < 1% plants infected. In 1993, BWYV was found in 42% of crops and 12% of plants infected; CaMV in 25% of crops and 7% of plants infected; and TuMV in 14% of crops and 5% plants infected. The yields of plants showing severe virus symptoms were reduced by an estimated 70 to 79%. The high incidence of CaMV and TuMV in oilseed rape crops could have important consequences for rapeseed production in the UK and also serve as a source of virus for vegetable brassicae.