Barley Yellow Dwarf Virus Serotypes Research Articles

Role of winter-active aphids spreading Barley yellow dwarf virus in decreasing wheat yields in a Mediterranean-type environment

In the grainbelt of south-western Australia, which experiences Mediterranean-type climatic conditions, 3 field experiments with wheat were sown in autumn, 2 at Site A over 2 years and 1 at Site B in the first year only. These experiments related both activity of aphid vectors (migration into and colonisation of wheat) and the spread of infection with Barley yellow dwarf virus (BYDV) serotype PAV to wheat grain yield and quality. Incidences of BYDV serotype RMV and Cereal yellow dwarf (CYDV) were mostly low and BYDV serotype MAV was not distinguished. Rhopalosiphum padi was the predominant vector species but small numbers of R. maidis and Sitobion miscanthi were also present. Repeated insecticide spray applications began at different times in the different experimental treatments. These sprays killed or repelled aphid vectors, thereby preventing further virus spread from the time they were first applied. At both sites, migrant aphids were caught flying into the wheat throughout the winter period. Peak numbers of colonising aphids ranged from 0 to 99/0.5-m transect of crop. BYDV-PAV incidence ranged from 0.1 to 58% of plants and yields ranged from 1.9 to 8.6 t/ha. First aphid arrival was earlier, and virus spread and resulting yield losses greater at Site A. At this site, in treatments where repeated insecticide sprays did not start until 8 weeks after crop emergence (WAE), virus incidence and subsequent yield losses were significantly greater than when the regular applications started at emergence. However, delaying the start of sprays beyond 8 weeks had no further effect on virus spread. Since aphid numbers were very low up to 8–10 WAE, yield losses were due entirely to virus infection of plants during this early growth period. Variation in BYDV-PAV incidence explained 81 or 91% of the variation in yield gaps in the 2 years at Site A where, for each 1% increase in virus incidence, there was a yield decrease of 55 or 72 kg/ha. It also explained the variation in seed weight (88%) and protein content (69%), but not in seed screenings. At Site B, virus spread started too late to cause significant yield or quality losses. These results show that wheat yields are decreased substantially in a Mediterranean-type environment, when aphids immigrate early into wheat crops and remain active throughout the winter-growing period, spreading virus infection at young plant growth stages.

Occurrence and distribution of barley yellow dwarf virus (BYDV) isolates in central Ethiopia

A survey for BYDV was carried out in Ethiopia during the main rainy season of 1995 and the short rainy season of 1996 in the major barley-growing areas of the Arsi, North Shewa (Oromiya and Amhara regions) and West Shewa zones. Barley fields were sampled at 5-km intervals, and samples from each field were randomly collected. Samples were tested by the tissue blot immunoassay (TBIA) for the presence of the five BYDV serotypes. Of the 35 fields sampled in Arsi, 20 in North Shewa (Amhara region), 24 in North Shewa (Oromiya region) and 33 in West Shewa, BYDV was detected in 23, 12, 5 and 14 fields, respectively. All five known BYDV serotypes were identified from samples collected in Arsi and West Shewa zones, whereas four isolates (PAV, MAV, RPV and SGV) were detected in North Shewa zone (Amhara region) and two isolates (MAV and RPV) from samples collected from North Shewa zone (Oromiya region). Mixed infections of two or more BYDV serotypes were found in all the survey zones. The BYDV serotypes most frequently detected in Arsi, North Shewa (Amhara region), North Shewa (Oromiya region) and West Shewa were PAV, MAV, RPV, and MAV, respectively. During the short rainy season of 1996, the five BYDV isolates were also detected in samples collected from the two North Shewa zones, where the SGV type was the most common in Oromiya region and PAV in Amhara region.

Molecular and agronomic characterization of wheat‐Agropyron intermedium recombinant chromosomes

AbstractThirty‐six wheat‐Agropyron intermedium (host) Beauv. [Syn. Trichopyrum intermedium (host) A. Love, Elytrigia intermedia (host) Nevski, Thinopyrum intermedium (host) Barkworth and Dewey] 7A/7Ai‐1 recombinant chromosomes were characterized using DNA markers. Analysis of recombinant chromosomes using 15 restriction fragment length polymorphism probes identified the homoeologous crossover products that had varying length of A. intermedium chromatin introgressed onto chromosome 7A of common wheat. The linear order of the probe loci was established along the lengths of the chromosomes. The short arm recombinants that had A. intermedium chromatin distal to the locus Xpsr108 and proximal to the locus Xpsr119 were resistant to wheat stem rust, indicating that the rust resistance gene (Sr44) was located on the distal part of chromosome arm 4Ai‐1s. The barley yellow dwarf virus (BYDV) resistance gene reported to be present on the long arm of chromosome 7Ai‐1 was found to be ineffective against the BYDV serotype used in the present study.

Barley Yellow Dwarf Luteoviruses and Their Predominant Aphid Vectors in Winter Wheat Grown in South Carolina.

Barley yellow dwarf is recognized as an important disease problem in winter wheat production in the southeastern United States, but there is relatively little known about the ecology and epidemiology of barley yellow dwarf virus (BYDV) in this region. From 1991 to 1993, and in 1996 and 1997, winter wheat was sampled for BYDV throughout the principal wheat production areas in South Carolina. In addition, in 1997, a small number of samples were collected from fields in North Carolina and Kentucky. Plant samples were assayed to determine the BYDV serotype and, subsequently, coat protein sequences of isolates within the same serotype were compared using restriction fragment length polymorphisms. Representative BYDV isolates from South Carolina and type isolates from New York were compared in aphid transmission experiments using aphid species collected from South Carolina and laboratory colonies maintained in New York. The predominant BYDV serotype in South Carolina (in all years) was PAV, accounting for 94% of the total BYDV-infected samples analyzed. The RPV serotypes were more abundant in samples collected from western North Carolina and Kentucky. PAV isolates from all regions were identical to the New York BYDV-PAV in terms of serology and restriction fragment patterns. Furthermore, the aphid transmission phenotypes were similar for South Carolina and New York BYDV isolates. The predominant aphids colonizing winter wheat in South Carolina included Schizaphis graminum, Rhopalosiphum rufiabdominalis, R. padi, and Sitobion avenea. The South Carolina clones of R. padi and S. avenae were similar to the New York laboratory clones in their abilities to transmit various BYDV isolates from New York and South Carolina. In contrast to the New York clone of Schizaphis graminum that can vector SGV, PAV, and RPV, the S. graminum clone from South Carolina was not a vector of any BYDV serotype tested. R. rufiabdominalis was found to be an efficient vector of PAV, RPV, and RMV isolates, but did not transmit MAV or SGV.

SGV Serotype Isolates of Barley Yellow Dwarf Virus Differing in Vectors and Molecular Relationships

Two SGV serotype isolates of barley yellow dwarf virus (BYDV), NY-SGV from New York State and TX-SGV from Texas, exhibited differences in aphid transmissibility that could significantly influence their relative occurrence and epidemiology; i.e., TX-SGV was readily transmitted by a range of vector aphids, whereas NY-SGV showed a much greater vector specificity. In serological assays, TX-SGV differed from NY-SGV but resembled an SGV serotype isolate from Idaho that shares similar vector relationships with TX-SGV. Dot blot hybridization assays using cloned cDNA probes distinguished the SGV isolates from the P-PAV, MAV-PS1, NY-RPV, and NY-RMV isolates of BYDV and from each other. Nucleotide sequences were determined for the 22-kDa coat protein gene, the associated 17-kDa internal open reading frame, and a 50-kDa protein gene of the NY-SGV and TX-SGV isolates. The deduced amino acid sequences of these proteins shared approximately 96% similarity between isolates but had only about 71% similarity with comparable regions from the MAV-PSI and P-PAV serotype isolates and approximately 57% similarity with those of the NY-RPV isolate. These comparisons did not identify obvious differences in primary structure that might be related to differences in vector relationships of NY-SGV and TX-SGV. The results demonstrate that the SGV serotype is distinct from other BYDV serotypes and that it includes sequence-distinguishable variants that differ in epidemiologically significant properties, such as transmissibility by various vectors.

Effects of Temperature on BYDV Concentration in Oat Plants and Virus Purification Efficiency, and Detection of a Putative Associated Satellite Virus

AbstractRPV and MAV‐like serotypes of barley yellow dwarf virus (BYDV), designated R‐568 and F, were found during sucrose density gradient centrifugation to suspend at 10 °C and 4 °C but to totally sediment at 15 °C and 12 °C, respectively. These properties were used to purify these serotypes, and antisera were then prepared.Partially purified IgG from antiserum was used in immunosorbent electron microscopy (ISEM) and in enzyme‐labelled immunosorbent (ELISA) tests to detect BYDV RPV‐like serotypes. Using anti‐BYDV R‐568 polyclonal antiserum and the BYDV R‐568 serotype in ISEM tests, isometric virus particles of two sizes were trapped: the 28 nm particles of BYDV R‐568, and others 17 nm in diameter which may be those of a satellite virus.The effects of temperatures on virus concentrations in oat plants infected with BYDV serotypes F and R‐568 were investigated. BYDV F and R‐568 concentrations in the roots and shoots were sensitive to changes in temperature between 10 °C and 25 °C. The concentrations of both viruses in the roots and shoots of infected plants could be manipulated by varying the temperature at which plants were grown. The ELISA absorbance values related to detection of F MAV‐like serotypes were higher in roots and shoots of oats grown at 10 °C than for oats grown at 25 °C. Conversely, cool temperatures reduced the absorbance values for R‐568 RPV‐like serotype in the roots, but less significantly in the shoots.

The occurrence of barley yellow dwarf viruses in CIMMYT bread wheat nurseries and associated cereal crops during 1988–1990

SummaryEnzyme‐linked immunosorbent assay (ELISA)‐based surveys of the occurrence of five barley yellow dwarf virus (BYDV) serotypes (MAV, PAV and SGV in “Group 1”; RPV and RMV in “Group 2”) in CIMMYT bread wheat nurseries and other small grain crops in various locations world‐wide were undertaken in 1988, 1989 and 1990. The objective was to investigate the relative occurrence of BYDV serotypes in areas relevant to CIMMYT cereal breeding programs. Overall, MAV and PAV serotypes predominated in the samples collected, though their relative frequencies depended on the location. SGV serotypes were uncommon in most locations. Group 2 serotypes occurred widely, but RMV serotypes were more common than RPV serotypes.

Occurrence of barley yellow dwarf virus serotypes MAV and RMV in over-summering grasses

Over-summering grasses were collected in the south-west of Western Australia in 1991 and 1992 and tested by ELISA using serotype specific polyclonal antibodies for presence of barley yellow dwarf virus (BYDV) serotypes MAV, PAV and RPV (1991) or MAV, PAV, RPV and RMV (1992). In 1991, 33 samples from 33 sites were tested and MAV was detected in four of 12 samples of Pennisetum clandestinum found infected with BYDV. Presence of MAV was confirmed by retesting these samples using MAV specific monoclonal antibodies. In 1992, 802 samples from 16 grass species were collected from 579 sites in six regions. BYDV was detected in 214 (27%) samples at 178 (31%) sites. MAV was found in 50% and RMV in 38% of infected samples. Both were found either alone or in mixed infections with each other or with PAV and/or RPV; all four serotypes were found in 18 (8%) infected samples. The most important hosts were four perennials: Cynodon dactylon, Eragrostis curvula, Paspalum dilatatum and P. clandestinum. Eight other perennial and five annual grass species were also infected. MAV was most commonly found in C. dactylon and P. clandestinum and RMV in P. dilatatum. All four serotypes were present in the six regions sampled, but the relative proportions of the serotypes found varied from region to region. This paper represents the first extensive survey of MAV and RMV serotypes of BYDV in over-summering grasses in Australia. Aphid species found during this survey infesting over-summering grasses were Rhopalosiphum padi,R. maidis and Hysteroneura setariae. In the Mediterranean type climate of the south-west of Western Australia, BYDV and aphids on over-summering perennial grasses constitute the main reservoir of infection and means of spread to cereal crops. Factors favouring grass survival over summer result in increased cereal crop infection.

Seasonal Occurrence of Barley Yellow Dwarf Virus Serotypes in Small-Grain Cereals in the Valley of Mexico

We assessed the occurrence of serotypes of barley yellow dwarf virus (BYDV) in an area at the International Maize and Wheat Improvement Center (CIMMYT) used to screen germ plasm for field resistance to BYDV. Wheat and barley plants were labeled in the field, and leaves were sampled several times during plant development to monitor BYDV incidence. Samples were tested by enzyme-linked immunosorbent assay with a panel of monoclonal and polyclonal antibodies. Samples from plantings sowed on different dates were tested to investigate seasonal influences on BYDV occurrence. Up to 88% of the plants sowed in winter (November and January) became infected. Fewer infections were detected in summer sowings (May) (.)

Vector specificity of barley yellow dwarf virus serotypes and variants in southwestern Idaho

SummaryPlants with symptoms of barley yellow dwarf virus (BYDV) obtained in infection feeding assays of aphids collected in the field in Idaho between 1986 and 1988 were tested for virus transmissibility by possible aphid vectors. Isolates obtained during 1987–1988 were also tested with a range of polyclonal antisera which distinguished PAV, MAV, SGV, RPV and RMV serotypes. In 1989 some Idaho (ID) BYDV isolates, maintained as standards for comparison, were serotyped and tested for aphid transmissibility, using 11 species of aphids.There was not always the expected correspondence between serotype and vector specificity for ID isolates. For isolates obtained from field‐collected Rhopalosiphum padi, vector transmissibility and serotype corresponded with previous reports; however, 44% of isolates which were serotyped as RMV were also transmissible by species other than Rhopalosiphum maidis. Similarly, the transmissibility of the ID laboratory standards did not always conform to the reported vector specificity of serotypes. The laboratory ID‐MAV culture was transmitted by Metopolophium dirhodum and Myzus persicae as well as by Sitobion avenae. The laboratory ID‐SGV culture was transmitted by R. padi and 5. avenae as well as by Schizaphis graminum. The ID‐RPV culture was transmitted by S. graminum and Rhopalosiphum insertum as well as R. padi. Both of two laboratory ID‐RMV cultures were transmissible by R. insertum and R. padi transmitted one of them. The results indicate that, for isolates collected in Idaho, vector specificity cannot be assumed from their serotypes.

Use of group-specific primers and the polymerase chain reaction for the detection and identification of luteoviruses

A general diagnostic assay for a number of distinct luteoviruses was developed using the polymerase chain reaction (PCR) and restriction enzyme analysis. Two minimally degenerate, group-specific primers were derived from previously published RNA sequences of three luteoviruses. This primer pair generated specific PCR fragments of about 530 bp from extracts of plants infected with potato leafroll virus, beet western yellows virus, or New York barley yellow dwarf virus (BYDV) serotypes MAV, PAV, RMV, RPV and SGV, which span much of the respective viral coat protein gene. Each virus was easily distinguished from the others by restriction enzyme analysis of the amplified DNA products. Samples from BYDV-infected oat and wheat collected in Nebraska were identified as containing PAV-like serotypes; micro-heterogeneity was detected in several samples. This method provides a rapid, sensitive and relatively inexpensive means of luteovirus detection and identification. It is the first test capable of simultaneously detecting all five BYDV serotypes.

Barley Yellow Dwarf Virus Serotypes and Their Vectors in Canterbury, New Zealand.

Barley yellow dwarf virus infections present in cereals at Lincoln, in the Canterbury area of New Zealand, in 1986 and 1987 were identified by ELlSA as PAV-, MAV-, RPVand RMV-like serotypes. Transmission of these serotypes by the aphid vectors Metopolophium dirhodum, Rhopalosiphum maidis, Rhopalosiphum padi and Sitobion Fragariae conformed generally to vector relationships described previously from Australia, but anomalous transmissions also occurred.

Serotype-specific and General Luteovirus Probes from Cloned cDNA Sequences of Barley Yellow Dwarf Virus

Summary Genome fragments from two serotypes of barley yellow dwarf virus (BYDV) were cloned and used as hybridization probes. Dot blot assays using 32P-labelled plasmid probes readily detected BYDV in crude sap extracts from infected plants and were at least as sensitive as ELISA. Some clones were specific for either the RPV or the PAV serotypes. Others hybridized not only with the RNA of both serotypes but also with those of three other luteoviruses (beet western yellows, potato leaf roll and soybean dwarf), but they did not hybridize with the RNA of a tobamovirus or Escherichia coli tRNA. These nucleic acid probes therefore have potential for the general diagnosis of infection by members of the luteovirus group as well as detection of specific BYDV serotype infections. The taxonomic implications of the observation that the genomes of different luteoviruses have some conserved regions are discused.