Non‐cultivated grass hosts of yellow dwarf viruses in Ethiopia and their epidemiological consequences on cultivated cereals

The yellow dwarf (YD) disease complex epidemics in cultivated cereals grown in a specific period of the year mainly depend on the presence of potential reservoir alternative hosts harbouring both the viruses and the vectors over the off‐season and serve as a source of inoculum in subsequent cropping season, further spread being supported by efficient aphid vectors. As such, an extensive and intensive exploration to generate base line information on the identity and prevalence of YD viruses [barley yellow dwarf virus (BYDV)‐PAV, BYDV‐MAV and BYDV‐SGV; cereal yellow dwarf virus (CYDV)‐RPV; and maize yellow dwarf virus (MYDV)‐RMV] on wild annual and perennial grasses and forage cereals alternative hosts was conducted consecutively during 2013–2015 main‐ and short‐rainy seasons in cereals growing belts of Ethiopia. Random sampling was employed to collect the samples that were tested by the tissue blot immunoassay (TBIA) to identify the YDVs associated with the hosts using a battery of virus‐specific polyclonal antibodies. Of 13,604 samples analysed, YDVs were detected in 392 (2.9%) samples, which consisted of various wild grasses, forage cereals and three cultivated crops. YDVs were identified from at least 26 grass species and forage cereals, some of them are new records, and some are previously documented hosts. To our knowledge, this is the first report of YDV infection of Andropogon abyssinicus (FresenR.Br. ex Fresen.) (BYDV‐PAV), Avena abyssinica Hochst (BYDV‐PAV), Bromus pectinatus Thunb. (BYDV‐PAV and BYDV‐MAV), Eragrostis tef (Zuccagni) Trotter (BYDV‐PAV), Eragrostis sp. (BYDV‐PAV), Hyparrhenia anthistrioides Stapf. (BYDV‐PAV), Panicum coloratum L. (BYDV‐PAV), Polypogon monspeliensis (L.) Desf. (BYDV‐PAV), Setaria pumila (Poir.) Roem & Schult (BYDV‐PAV, BYDV‐SGV and MYDV‐RMV), Setaria australiensis (Scribn. & Merrill) Vickery (BYDV‐PAV, BYDV‐MAV and CYDV‐RPV) and Snowdenia polystachya (Fresen.) Pilg (BYDV‐PAV, BYDV‐MAV, BYDV‐SGV, CYDV‐RPV and MYDV‐RMV).     

Nucleotide sequence of coat protein gene for GPV isolate of barley yellow dwarf virus and construction of expression plasmid for plant

GPV is a Chinese serotype isolate of barley yellow dwarf virus (BYDV) that has no reactionwith antiserum of MAV, PAV, SGV, RPV and RMV. The sequence of the coat protein (CP) of GPV isolate of BYDV was identified and its amino acid sequence was deduced. The coding region for the putative GPV CP is 603 bases nucleotides and encodes a Mr 22218 (22 ku) protein. The same as MAV, PAV and RPV, GPV contained a second ORF within the coat protein coding region. This protein of 17024 Mr (17 ku) is thought to correspond to the Virion protein genome linked (Vpg). Sequence comparisons of the CP coding region between the GPV isolate of BYDV and other isolates of BYDV have been done. The nucleotide and ammo acid sequence homology of GPV has a greater identity to the sequence of RPV than those of PAV and MAV. The GPV CP sequence shared 83.7% of nucleotide similarity and 77.5% of deduced amino add similarity, whereas that of the PAV and MAV shared 56.9%. 53.2% and 44.1%. 43.8% respectively. According to BYDV-GPV CP seque     

Cloning and Phylogenetic Analysis of Coat Protein of Barley yellow dwarf virus Isolates from Different Regions of Pakistan

Barley yellow dwarf virus (BYDVs) is an emerging threat for wheat and may seriously threaten its production, especially as climate change may result in increased infestation by aphids, the insect vectors of the virus. To assess the possibility of using pathogen‐derived resistance against the virus, the genetic diversity of BYDVs originating from different wheat‐growing areas of Pakistan where its incidence has been higher was investigated. Wheat samples with suspected symptoms of BYDVs were screened for the presence of Barley yellow dwarf and Cereal yellow dwarf viruses (B/CYDVs) subgroup 1 (Barley yellow dwarf virus‐PAV, BYDV‐MAV, BYDV‐SGV) and subgroup II (BYDV‐RPV, CYDV‐RPV, BYDV‐GPV) by PCR using basic multiplex oligonucleotides designed on coat protein (CP) of the virus. Of 37 samples tested, 13 were positive for BYDV subgroup I and only one sample was positive for BYDV subgroup II. Samples positive for subgroup I were further tested by PCR, and results showed that 10 samples were positive for BYDV‐PAV and three for BYDV‐MAV. DNA sequences of CP region of nine isolates (BYDV‐PAV) were determined and compared with available sequences in databases. Sequence analysis showed that three isolates (from Fatehjang, Nowshera and Attock districts) had maximum identity (92.8–94.6%) to BYDV‐PAS, and six isolates (from Peshawar, Islamabad Swabi and Faisalabad districts) had maximum identity (99.3–99.7%) to BYDV‐PAV. Thus BYDV‐PAV species may be dominant in northern wheat‐growing areas of Pakistan. The conserved nature of the BYDVs suggests that pathogen‐derived resistance strategies targeting the coat protein of the virus are likely to provide protection under field conditions.     

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

Plants 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.     

Distribution of Cereal Luteoviruses and Molecular Diversity of BYDV‐PAV Isolates in Central and Southern Iran: Proposal of a New Species in the Genus Luteovirus

During a survey , 148 wheat, 70 barley and 24 wild grass samples of plants showing symptoms of yellowing or reddening of leaves and general stunting were collected in central and southern provinces of Iran and tested for Barley yellow dwarf virus (BYDV) and Cereal yellow dwarf virus (CYDV) infection by enzyme‐linked immunosorbent assay (ELISA) and tissue print immunoassay (TPIA). The results showed the presence of the viruses in most regions. Positive reactions to BYDV‐PAV, BYDV‐MAV, CYDV‐RPV and BYDV‐SGV antisera were recorded. BYDV‐PAV was the most prevalent virus. The genetic diversity of BYDV‐PAV isolates in central and southern provinces was studied by analysing ORF1 (903 nt) and read through domain (RTD) (575 nt) of 13 and nine isolates respectively. Sequence analysis of RTD at nucleotide and amino acid levels revealed a high identity (91.8–97.2% and 91.4–100% respectively) between Iranian and other available isolates in the GenBank. However, in regards to ORF1, a high genetic diversity among Iranian and other known PAV isolates at both amino acid (2–16.9%) and nucleotide (4.1–16.5%) levels were detected. Based on phylogenetic analysis of ORF1, two major groups of BYDV‐PAV isolates were distinguished. The Iranian isolates were divided between the two clusters. Our results suggest that the occurrence of two genetically distinct groups of PAV isolates in central and southern Iran, from which according to the ICTV criteria for species demarcation in the family Luteoviridae, four isolates from central parts of the country, qualify for designation as new species.     

Occurrence of barley yellow dwarf virus (BYDV) isolates in different farmland habitats in western France and south-west England

The incidence and distribution of the three principal isolates of barley yellow dwarf virus (PAV, RPV and MAV) are described in winter cereal crops, cereal (stubble) regrowth and grasses from 11 sites in western France and south-west England during 1987 and 1988. Isolates were identified by indirect ‘sandwich’ ELISA using the monoclonal antibodies MAC91, MAC92 and MAFF2. More virus infection occurred in all localities and in most of the plant communities sampled, with the exception of perennial grass leys, in 1987 than in 1988. All three isolates were widespread. MAV was associated more with sites further north and PAV more with those further south. The geographical distribution of RPV was less variable. Underlying these trends, the relative abundance of isolates differed considerably between habitats. RPV always predominated in perennial grass leys and MAV in most cereal crops, although in the latter MAV was less prevalent in 1987 than in 1988. The greatest regional difference was found in stubble regrowth where PAV predominated in France but MAV predominated in England. Grasses from field margins (only sampled in England) were mainly infected by MAV and RPV. The implications of these findings for the epidemiology of BYDV are discussed, especially the roles of different host plant communities or habitats in the annual infection cycle of small-grain cereals.     

Serological and biological characterisation of isolates of barley yellow dwarf virus in Sweden in 1983

In 1983, cereal plants showing symptoms of barley yellow dwarf virus (BYDV), collected from 15 localities in Sweden, were tested for BYDV using enzyme-linked immunosorbent assay (ELISA). Antisera against two Swedish isolates of BYDV were used, a mild isolate (27/77) transmitted specifically by Sitobion avenae and a severe one (39/78) transmitted mainly by Rhopalosiphum padi. No virus was detected in 57 of 607 plants of oats and barley tested. Of the 550 plants in which virus was detected, 366 were infected with viruses similar to isolate 27/77, 116 with viruses similar to 39/78 and the remaining 68 reacted strongly with both antisera. When tested, the latter isolates were shown to be mixtures. Thirty-nine selected samples were also tested with antisera against the USA isolates RPV, RMV, MAV and PAV, and for transmission by S. avenae and R. padi. Twenty-six of these samples were transmitted specifically by S. avenae, one was transmitted only by R. padi and the remaining 12 samples were shown to be infected with a mixture of an S. avenae-specific isolate and one transmitted mainly by R. padi. Antisera against PAV and MAV each detected all isolates tested and the results were very similar to those with the antisera to the 39/78 and 27/77 isolates, respectively. None of the field isolates reacted with antisera against RMV or RPV. It was concluded that 1983 was an epidemic year for BYDV in Sweden and that isolates specifically transmitted by S. avenae predominated. Symptoms of infection by these isolates on oat plants ranged from mild to severe.     

Biological Characterization of an Italian Isolate of Barley Yellow Dwarf Luteovirus from Barley

An isolate of BYDV (BYDV-OC), from barley in Northwest Italy with typical symptoms of yellowing and dwarfing, was transmitted by Rhopalosiphum padi, Sitobion fragariae. S. avenae, Metopolophium festucae, R. maidis and M. dirhodum , but not by Myzus persicae or Schizaphis graminum . It reacted in DAS-ELISA with monoclonal and polyclonal antisera to PAV, but not with antibodies to MAV, RPV and RMV. A polyclonal antiserum prepared to BYDV-OC did not react with MAV-like, RPV-like, or RMV-like isolates of BYDV in ELISA or in Western blots. The concentration of BYDVOC in Avena byzantina plants decreased from weeks 1 to 10 after inoculation, but the total virus content per plant increased up to weeks 7 to 8, following the increase of plant weight.     

A single wheatgrass chromosome reduces the concentration of barley yellow dwarf virus in wheat

Seedlings of a series of addition or substitution lines of wheat containing different Thinopyrum intermedium chromosomes were inoculated with the PAV and RPV serotypes of barley yellow dwarf virus (BYDV). Reduced virus titres in infected plants were ascribed to a single pair of homoeologous group 7 chromosomes from Th. intermedium in the disomic addition lines L1 and TAF 2. The group 7 chromosome is associated with red pigmentation of coleoptiles, which was also observed in two lines ditelosomic for the α arm of the chromosome. However, when infected with the PAV serotype of BYDV, the ditelosomic lines had normal virus titres and it is concluded that potential determinants of BYDV resistance are located on the β arm of the Group 7 chromosome.     

Introduced Plant Viruses and the Invasion of a Native Grass Flora

Weed and native grasses from the South Island of New Zealand were surveyed for virus infection. Cocksfoot mottle virus (CfMV) and Ryegrass mosaic virus (RgMV) were restricted to a few introduced species; however, Barley yellow dwarf viruses (BYDVs) have invaded native grasses in New Zealand. Virus incidence was significantly lower in the native species (2%) than in the introduced species (12%). Four different serotypes (RMV, RPV, PAV, MAV) were detected in the introduced grass flora but only two (RMV, PAV) were detected in native species. In experimental transmission tests the aphid vector Rhopalosiphum padi's survival was variable on the 20 native species tested but this was not due to the presence or absence of endophytic fungi as none were detected in the New Zealand species. Aphid numbers increased and plants were killed when R. padi fed on Agrostis muelleriana and Festuca multinodis. R. padi transmitted a PAV isolate to these and six other native species. BYDVs infected 4/5 of the subfamilies tested. Virus incidence in native Arundinoideae and Pooideae was significantly lower than in introduced Pooideae and Panicoideae. One species of Bambusoideae collected from the field was not infected but was found susceptible in glasshouse tests. Agrostis capillaris, Dactylis glomerata and Lolium perenne were identified as the most likely reservoirs of infection for the native flora. Anthoxanthum odoratum was not infected but if the SGV serotype and its vector Schizaphis graminum were ever introduced, A. odoratum could form an effective reservoir from near sea level into alpine areas. This revised version was published online in July 2006 with corrections to the Cover Date.     

Aerial flow of barley yellow dwarf viruses and of their vectors in western France

During the years 1989–1992 cereal aphids were caught alive in a low level (1.5 m high) suction trap operated in Le Rheu (Brittany, France) and tested for BYDV transmission. In most cases comparisons with data collected simultaneously by a 12.2 m suction trap operating in the same site resulted in good relationships between weekly catches at both heights. Results from transmission tests showed that: (i) the two main BYDV vectors were Rhopalosiphum padi and Metopolophium dirhodum during the years of experiment; (ii) PAV and MAV were the commonest viruses and RPV was relatively scarce; (iii) during spring M. dirhodum appeared to be the most important MAV vector and nearly as good a PAV vector as R. padi; (iv) during autumn R. padi was the only vector of the three viruses with mixed transmission allowing it to transmit also MAV probably by heteroencapsidation. To give an indication of the risk of infection, infectivity indices were calculated by multiplying the numbers of aphids caught by the 12.2 m suction trap by the proportion that were infective. These infectivity indices agreed with field records of primary infections.     

Mapping quantitative and qualitative disease resistance genes in a doubled haploid population of barley (Hordeum vulgare)

Stripe rust, leaf rust, and Barley Yellow Dwarf Virus (BYDV) are important diseases of barley (Hordeum vulgare L). Using 94 doubled-haploid lines (DH) from the cross of Shyri x Galena, multiple disease phenotype datasets, and a 99-marker linkage map, we determined the number, genome location, and effects of genes conferring resistance to these diseases. We also mapped Resistance Gene Analog Polymorphism (RGAP) loci, based on degenerate motifs of cloned disease resistance genes, in the same population. Leaf rust resistance was determined by a single gene on chromosome 1 (7H). QTLs on chromosomes 2 (2H), 3 (3H), 5 (1H), and 6 (6H) were the principal determinants of resistance to stripe rust. Two- locus QTL interactions were significant determinants of resistance to this disease. Resistance to the MAV and PAV serotypes of BYDV was determined by coincident QTLs on chromosomes 1 (7H), 4 (4H), and 5 (1H). QTL interactions were not significant for BYDV resistance. The associations of molecular markers with qualitative and quantitative disease resistance loci will be a useful information for marker-assisted selection. Received: 2 February 1999 / Accepted: 30 December 1999     

Some characteristics of monoclonal antibodies to a British M A V-like isolate of barley yellow dwarf virus

Rat monoclonal antibodies (MAbs) specific for a British F (MAV-like) isolate of barley yellow dwarf virus (BYDV) were produced and studied. In indirect ELISA using an antiserum to BYDV-F to trap virus from infected sap, the MAbs were shown to be specific for MAV-like isolates of BYDV from Britain, USA and Sweden but, in this test, they did not detect PAV-, RPV-, SGV- or RMV- like isolates of BYDV. In similar tests using homologous antisera to trap the viruses, the MAbs did not detect BYDV-PAV or -RPV or two other luteoviruses (potato leafroll and beet western yellows). One of the MAbs (MAFF 2) was partially purified from ascitic fluid, and used successfully in ELISA as a coating antibody and when conjugated to the enzyme alkaline phosphatase. Also, MAFF 2 successfully trapped BYDV-F particles when used to coat electron microscope grids. In indirect ELISA using three MAbs (MAFF 2, MAC 91 and MAC 92) it was possible to type the three major strain groups of BYDV, viz. MAV, PAV and RPV-like strains from Britain, USA and Europe.     

High Levels of Resistance in Agropyron Species to Barley Yellow Dwarf and Wheat Streak Mosaic Viruses

Several Agropyron species were tested for new sources of resistance to barley yellow dwarf virus (Bydv ) and wheat streak mosaic virus (WSMV). With BYDV strain PAV, 11 of the 17 Agropyron species showed no virus transmission when plants were given access feed by viruliferous Rhopalosiphum padi. Similar trials with BYDV strain RMV (vectored by R. maidis) indicated that all plants, except susceptible control plants, remained virus free. Virus status was confirmed by enzyme-linked immunosorbent assays. When plants were mechanically inoculated with WSMV, 11 Agropyron species failed to express symptoms, while five other species showed a segregating response or had some accessions segregating and some resistant. Test results suggest that resistance to BYDV and WSMV in Agropyron species does not appear to be correlated with any specific genome of Agropyron species although most of the Agropyron species containing S genome were resistant to BYDV and WSMV.     

Detection of BMYV and BWYV isolates using monoclonal antibodies and radioactive RNA probes, and relationships among luteoviruses

In order to discriminate between sugar beet infecting beet mild yellowing virus (BMYV) and other isolates of beet western yellows virus (BWYV), monoclonal antibodies (MAbs) and radioactive riboprobes were used. With MAbs prepared against BMYV or potato leafroll virus (PLRV) no distinction could be established between BMYV and BWYV. Seven probes were synthesised from a lettuce infecting BWYV isolate; their localisation in the genome is known and they cover almost its entire length. Probes from the '3 part of the genome hybridised with all BMYV and BWYV isolates whereas those from the '5 part did not recognise BMYV isolates, showing that a divergent '5 region exists in the genomes of BMYV and BWYV. Probes also readily detected the virus in single aphids. The relevance of this finding for epidemiological studies is discussed.
MAbs and riboprobes were also tested against other luteoviruses (PLRV; barley yellow dwarf virus (BYDV) MAV, PAV and RPV strains). The serological relationship between BMYV and PLRV was confirmed and an epitope common to PLRV and BYDV-RPV was found. Using probes, PLRV and BYDV-RPV were found to share domains of homology with BWYV. BYDV-PAV showed weak homology with BWYV, while BYDV-MAV showed none.     

Barley Yellow Dwarf Luteovirus (BYDV) Infectivity of Alate Aphid Vectors in Northeast Spain

Rhopalosiphum padi and Sitobion avenae alates were collected from colonised winter cereals and maize in N.E. Spain and fed on young wheat plants for 7–10 days in the glasshouse. Then, aphids were killed and the plants on which aphids reproduced were kept in the glasshouse for 30–40 days. ELISA of infested plants was made using polyclonal and monoclonal antisera against PAV-, RPV- and MAV-like isolates. In autumn and spring, MAV serotypes were transmitted by S. avenae and R. padi , mainly in mixed infections with PAV serotypes. This possibly explains the high frequency of MAV-like isolates and their previously recorded year-to-year stability in maize, grain and forage winter cereals and cereal volunteers. PAV-like isolates were rarely transmitted by S. avenae and its spread thus depends almost exclusively on R. padi. These results confirm the importance of forage cereals and cereal volunteers as virus sources for winter cereal infection in the autumn, and the latter as a source of BYDV for maize in spring.     

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

RPV 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.     

向普通小麦导入纤毛鹅观草抗黄矮病基因的研究──Ⅰ.F_1和BC_1的产生及其细胞遗传学

为了将纤毛鹅观草Z1010对黄矮病毒株系PAV和RPV的抗性基因转入普通小麦,通过幼胚拯救,获得了纤毛鹅观草Z1010×普通小麦品种莱州953的杂种F1,以及用5个普通小麦品种（系）回交的BC1衍生系。对杂种F1及BC1植株的细胞学分析表明,纤毛鹅观草Z1010不仅对Ph基因具有很强的抑制作用,而且能使杂种F1形成未减数配子,对细胞遗传学资料的进一步分析认为,通过部分同源染色体间的交换将纤毛鹅观草Z1010的抗黄矮病基因转入小麦是可能的。     

RT-PCR-RFLP在大麦黄矮病毒检测中的应用

The universal primer of Luteovirus was designed and synthesized.An experimental system of RT PCR RFLP was developed in barley yellow dwarf virus (BYDVs).BYDVs can be distinguished qualitatively by RT PCR method.It was seen that different serotypes of BYDVs have critical different RFLP patters when the PCR producs were digested by restriction enzyme HinfI.The RFLP patterns of 7 isolates of PAV serotype were greatly different.These results indicate there existed sequence variations among different serotypes of BYDVs and vector phenotypes of PAV serotype.There is no difference between MAV serotypes in RFLP analysis.The slight distinction in the segment of coat protein gene of BYDVs can be revealed by RT PCR RFLP system.     

Identification, Distribution and Vector Population Dynamics of Barley Yellow Dwarf Virus in Three Cereal-Producing Areas of Spain

ELISA-based surveys during 1985–87 in three major cereal-growing areas of Spain confirmed the presence of barley yellow dwarf virus (BYDV). Samples of small grain cereals and grasses with and without BYDV-like symptoms were collected in the central, southwestern, and northeastern Spain. Infections were found in all cereal species sampled and in some grasses. About 37 % of the samples collected in 1985 were infacted with isolates of the PAV serotype. Isolates of the RPV serotype were less common, and were detected only in samples from the central region at El Encin, Madrid. Only a single sample, collected from El Encin in 1987, was unequivocally diagnosed as containing an isolate of the MAV serotype. Aphid vector population dynamics was monitored during fall and winter of 1984–87 in the central region. Rhopalosiphum padi L. appeared to be the most abundant species during fall and winter months, infesting grasses and volunteer wheat. Other species present were Sitobion avenae (F.), Metopolophium dirhodum (Walker) and Rhopalosiphum maidis (Fitch). Both R. padi and S. avenae seem to be anholocyclic in the central region of Spain, and are able to remain and reproduce on wheat volunteers and grasses until the beginning of spring. S, avenae populations increase quickly on wheat volunteers in April, while populations of R. padi remain low. Therefore, spread of S. avenae-transmitted BYDV types to neighbouring cereal fields seem more likely to occur than spread of other types. Other possible virus reservoirs, such as maize, also need investigation for a better understanding of BYDV epidemiology in the central and other cercal-growing areas of Spain.