Barley Yellow Dwarf Disease Research Articles

Molecular Characteristics of Barley Yellow Dwarf Virus-PAS-The Main Causal Agent of Barley Yellow Dwarf Disease in Poland.

Barley yellow dwarf is a threat to cereal crops worldwide. Barley yellow dwarf virus-PAS (BYDV-PAS) was detected for the first time in Poland in 2015, then in 2019. In the spring of 2021, in several locations in Poland, winter wheat and barley plants with dwarfism and leaf yellowing were collected. Reverse transcription-polymerase chain reaction results revealed BYDV presence in 47 samples and excluded wheat streak mosaic virus infections. Next, immuno-captured polymerase chain reactions confirmed only one case of co-infection caused by BYDV and wheat dwarf virus. Moreover, restriction fragment length polymorphism analysis showed that BYDV-PAS was predominant. The preliminary results were confirmed using sequencing. Infected cereal plants originated mainly from northwestern Poland. The complete coding sequence of coat protein (CP) and a fragment of RNA-dependent RNA polymerase (RdRp) genes of 14 Polish isolates were determined and deposited in the GenBank database. The nucleotide and deduced amino acid sequences of local isolates were compared with others reported to date, indicating their high similarity, from 75.4% to 99.5% and from 81.1% to 100% nucleotide sequence identity, in RdRp and CP, respectively. Phylogenetic analysis, based on the CP gene, revealed the presence of 3 main groups. The Polish isolates clustered together within the Ia group.

First report of barley virus G infecting wheat (Triticum aestivum) in Japan.

Barley virus G (BVG) is a single stranded, positive sense RNA virus and tentative species of the genus Polerovirus in the family Solemoviridae. BVG was first identified in barley (Hordeum vulgare) in Korea with symptoms that were similar to those of barley yellow dwarf disease (Zhao et al. 2016). It has also been identified from proso millet (Park et al. 2017), barley (Erickson and Falk, 2021; Nancarrow et al. 2019; Svanella-Dumas et al. 2022), maize (Gavrili et al. 2021), wheat (Nancarrow et al. 2019), and oats (Nancarrow et al. 2019) in various countries. In the spring of 2019, wheat (Triticum aestivum) plants that exhibited symptoms of yellow leaves, necrosis, and stunting were observed in a few fields of the Chugoku region (western main island) in Japan. The four soil-borne viruses, wheat yellow mosaic virus (WYMV), Chinese yellow mosaic virus (CWMV), Japanese soil-borne wheat mosaic virus (JSBWMV), and soil-borne wheat mosaic virus (SBWMV), that often occur in winter wheat in Japan, were not detected by DAS-ELISA for WYMV, CWMV, and JSBWMV (Netsu et al. 2011) and ELISA Reagent Set for SBWMV (Agdia, IN, USA). To identify the pathogen, total RNA was isolated from the leaves and petioles using the PureLink RNA Mini kit (Thermo Fisher Scientific, MA, USA), and RT-PCR was performed using the PrimeScript One Step RT-PCR Kit Ver.2 (Dye plus) (Takara Bio Inc, Shiga, Japan). Based on the symptoms, luteoviruses and poleroviruses, which are transmitted by aphids, were suspected and RT-PCR was performed using known primers (Malmstrom and Shu, 2004; Mustafayev et al. 2013). This resulted in an amplicon of approximately 300 bp being obtained from RT-PCR using the Luteo2F/YanR-new primers (Mustafayev et al. 2013). The amplicon was directly sequenced by Sanger sequencing and a nucleotide BLAST search of the database revealed that the sequence was highly similar (99% identity, query coverage 95%) to the genome of BVG. In samples of a single field, four out of six plants that were showing necrosis and stunting were positive by RT-PCR using the primers BVG-CP-F (5´- GCGGGAAACATTTGTATTTTCG-3´)/BVG-CP-R (5´- GATTTTGGGTTAGAACATCCATCG-3´). In addition, five out of six plants with some yellowing of the leaves in the same field were also positive. Other luteoviruses and poleroviruses were not detected by RT-PCR using known primers. The full-length genome sequence of the Chugoku isolate was amplified using the primers BVG-F (5´-ACAAAAGGGACCCAGAGGG-3´)/BVG-R (5´-TACCAAGGATACTAGAGAGAGA-3´), which were designed from the 5´ and 3´ end sequences of the known BVG sequence. The resultant amplicon was directly sequenced by Sanger sequencing and the sequence was deposited into the DNA Data Bank of Japan (Chugoku isolate, LC649801). The sequence comprised of 5,620 bp and the genomic structures were consistent with that of BVG. The sequence showed more than 97% nucleotide identity with the BVG Gimji (KT962089), Uiseong (LC259081), NL1 (MF960779), and California (LC259081) isolates by pairwise comparisons. This is the first report of BVG in wheat in Japan to the best of our knowledge. The correlation between BVG and the observed symptoms and the impact of BVG on wheat production in Japan requires further investigation. Reference Erickson, A. C. and Falk, B. 2021. Plant Dis. doi:10.1094/PDIS-03-21-0478-PDN Gavrili, V. et al. 2021. J. Plant Pathol. 103:1331. doi:10.1007/s42161-021-00903-4 Malmstrom, C. M. and Shu, R. 2004. J. Virol. Methods. 120:69. doi:10.1016/j.jviromet.2004.04.005 Mustafayev, E. S. et al. 2013. Plant Dis. 97:849. doi:10.1094/PDIS-07-12-0656-PDN Nancarrow, N. et al. 2019. Plant Dis. 103:1799. doi: 10.1094/PDIS-01-19-0166-PDN Netsu, O. et al. 2011. Plant Dis. 58:13. doi.org/10.11337/ktpps.2011.13 Park, C.Y. et al. 2017. Plant Dis. 101:393. doi: 10.1094/PDIS-07-16-0952-PDN Svanella-Dumas, L. et al. 2022. Plant Dis. doi: 10.1094/PDIS-06-22-1294-PDN Zhao, F. et al. 2016. Arch. Virol. 161: 2047. doi:10.1007/s00705-016-2881-0.

First report of barley virus G infecting winter barley (Hordeum vulgare L.) in France.

As part of a cereals virome project high throughput sequencing (HTS)-based viral indexing was performed on plants with symptoms of barley yellow dwarf disease collected in June (2017-2020) in the main French cereals production areas. Total RNAs from 32 individual plants were purified (RNeasy Plant Mini Kit, Qiagen, Courtaboeuf, France) and Illumina sequenced (2x150 nt) following ribodepletion (Genewiz-Azenta, Leipzig, Germany). Following quality trimming, reads for each sample were de novo assembled (CLC Genomics Workbench 21, Qiagen) [1] and contigs annotated by BlastX analysis. In four winter barley samples collected in 2018 (18-58, 18-325 and 18-326) and 2019 (19-30A), besides contigs representing diverse viruses such as barley yellow dwarf viruses-PAV and PAS, Hordeum vulgare endornavirus, cereal yellow dwarf virus-RPV (18-326), wheat dwarf virus (18-325 and 18-326) and a novel Polerovirus (18-58 and 18-326), large contigs with high identity to barley virus G (BVG) were identified. BVG, a tentative Polerovirus, was initially reported in barley in South Korea in 2016 [2] and has so far been identified in a few other hosts including wheat, oat, maize, proso and foxtail millets as well as switchgrass. It has been reported from the USA and Australia [3] and, in Europe, from the Netherlands, Germany, Hungary and Greece [4]. Large BVG scaffolds representing near complete genomes could be reconstructed for each sample, integrating a total of 128.339, 7.188, 8.078 and 20.073 reads, for samples 19-30A, 18-58, 18325 and 18-326 respectively. Given that between 17.2 and 20.5 million reads had been obtained per sample, these values translate into between 0.04% (18-58 and 18-325) and 0.6% (19-30A) of total reads, and to average coverages of between 158x (18-58) and 2866x (19-30A) for the genomic scaffolds. The four assembled sequences (5584-5610 nt) have been deposited in GenBank (ON419453-ON419456). They are nearly identical (98.4 to 99.5% nt identity) and share between 97.7% and 98.5% nt identity with a barley reference isolate from the South Korea (NC_029906). To confirm the presence of BVG, a primer pair was designed based on available BVG sequences. Primers BVG-F(5'-CTAGCCCAACGAGTTGCGGG-3') and BVG-R(5'-GGTACAGAAGCTCTACGGTTC-3') amplifying a 394 nt were used in a two-step RT-PCR on new RNA extracts obtained from the 18-325 and 18-326 infected plants. The amplicons were directly sequenced and showed respectively 99.2% (ON419457, 18-325) and 100% (18-326) nt identity with the corresponding de novo scaffolds. The four analyzed samples have been collected respectively in 2018 (18-58, 18-325, 18-326) and 2019 (19-30A) in three different regions of France (Auvergne-Rhône-Alpes, Occitanie and Centre-Val de Loire), indicating a wide distribution and a persistence over time of BVG in France. To our knowledge, this represents the first report of a natural infection of BVG in cultivated winter barley in France. Presence of BVG may have been overlooked in a range of situation, as indicated by its retrospective discovery in a 34 years old Australian sample [3], possibly explaining its broad distribution in France. While the mixed infection status of the analyzed plants precludes any conclusion on its pathogenicity in French cereals, BVG has been reported to be associated with a range of symptoms in various hosts so that further studies to evaluate its prevalence and impact in France and to begin to understand its epidemiology are clearly warranted by the present results.

Barley yellow dwarf virus-PAV is the dominant species causing Barley yellow dwarf disease in South Dakota and Minnesota

Barley yellow dwarf (BYD), caused by ten different species of viruses from the Luteoviridae family, is an economically important viral disease of small grains in the US Northern Great Plains. Identification of virus species in the region associated with BYD is critical to deployment of specific effective resistance genes. However, a comprehensive survey of virus species using modern diagnostic tools has not been done before in the US Northern Great Plains. In this study, species composition of viruses associated with BYD in small grains of Minnesota and South Dakota were determined by sampling BYD infected tissue from a large geographical area over three years. Whole genomic RNA was extracted from leaf tissue and reverse transcription polymerase chain reaction (RT-PCR) was conducted to detect infection of BYD and classify into species using primers from a two-step multiplex PCR protocol. Out of 463 samples collected from Minnesota and South Dakota from 2013 to 2015, about 50% (n = 222) of the samples tested positive for BYD. The majority of virus infected samples (n = 146) were identified as the Barley yellow dwarf virus PAV. These results indicate that the RT-PCR protocol used in this study is a viable molecular diagnostic tool for detection of BYD causing viruses in field collected samples. Moreover, the results indicate that Barley yellow dwarf virus PAV is most the dominant species associated with BYD in the US Northern Great Plains. Due to the species-specific nature of resistance to BYD these results can also guide breeding strategies in small grains for BYD management.

Effects of barley yellow dwarf disease on wheat grain quality traits

AbstractBackground and objectivesBarley yellow dwarf (BYD) is an important aphid‐vectored viral disease of wheat. Grain samples were obtained from a previously reported integrated pest management (IPM) field plot experiment that was designed to test the effects of planting dates, cultivars, and insecticide treatments on BYD incidence and wheat yields over 4 years in Kansas, USA. In the current study, the effect of BYD on grain quality traits was estimated by comparing untreated plots that had varying levels of BYD to healthy control plots that received repeated insecticide treatments. Additional grain samples were compared from Tagged Tillers of visually healthy and symptomatic plants.FindingsFor IPM Plots, interactions between insecticide treatments and cultivars were not significant (α = 0.05). The effect of BYD on protein content (PC), starch content (SC), average kernel weight (AKW), and yield was a relative percent gain or loss of +3.7%, −1.0%, −6.4%, and −12.6%, respectively, averaged over all experimental factors and years. Linear critical point models were developed to estimate the percent gain or loss relative to healthy controls as a function of BYD incidence. For each percentage of BYD incidence, BYD increased PC by 0.284%, decreased SC by 0.063%, decreased AKW by 0.314%, and decreased grain yield by 0.664%. Similar magnitudes of effects of BYD were estimated from Tagged Tiller samples. There were distinct, non‐overlapping distributions for healthy versus symptomatic Tagged Tillers for PC and SC for four of six cultivars. However, two cultivars had overlapping distributions for healthy versus symptomatic samples, suggesting they had resistance or physiological tolerance to BYD.ConclusionsNatural infection with BYD significantly increased PC and decreased SC, AKW, and yields of wheat. The increase in PC was probably due to the concentrating effect of decreased SC and AKW. Critical point models were developed to predict the impact of varying levels of BYD on these parameters. Near‐infrared spectroscopy (NIRS) measurement of PC and SC of diseased versus healthy samples has potential to identify wheat lines with resistance or tolerance to BYD.Significance and noveltyThis is the first report of the effect of BYD on wheat starch content and confirms the effect on average kernel weight and protein content. This is the first report of simple models to predict grain quality changes as a function of BYD incidence. Near‐infrared spectroscopy (NIRS) measurement of grain PC and SC from plants with BYD may offer wheat breeding programs a rapid and objective selection method for improved resistance or physiological tolerance to BYD.

Selected Early-Season Insect Pests of Wheat in the United States and Factors Affecting Their Risks of Infestation

Abstract The Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae); cereal aphids (Hemiptera: Aphididae); and wireworms (Coleoptera: Elateridae) are three common and important insect pests of seedling wheat, Triticum aestivum L., in the United States. Though less common as pests, false wireworms (Coleoptera: Tenebrionidae) may also be problematic in situations that favor wireworms. In addition, cereal aphids vector viruses that cause barley yellow dwarf, a serious and widespread wheat disease. Scientific journal publications, review articles, and management guidebooks on wheat insect pests were consulted to determine the extent and intensity that these pests impose on wheat production in the United States. Widespread outbreaks occur infrequently, but local outbreaks happen nearly every year for the three major pests and cause several millions of dollars in crop losses annually. Hessian fly perennially threatens wheat in the southeastern United States, and wireworms are persistent pests in northwestern wheat-production systems. Otherwise, the particular location and severity of outbreaks vary yearly and are largely unpredictable. However, particular agronomic practices can greatly reduce risk of infestation such as elimination of volunteer wheat and weedy hosts and planting wheat during periods of reduced pest abundance. In addition, resistant cultivars can limit Hessian fly and Russian wheat aphid (Diuraphis noxia [Kurdjumov]) damage in some areas, but virulent biotypes of each pest complicate their management. Although several preemptive tactics reliably suppress infestations and barley yellow dwarf severity, they are not compatible in all agricultural systems. Consequently, insecticides are necessary in certain areas and within particular production systems to manage major early-season insect pests of wheat.

Aphid Oat Rhopalosiphum padi (L.) as an Economic Aphid Insect Vectors of Barley Yellow Dwarf Virus in Wheat Fields.

In the course of the transmission experiment carried out in the present work, the author pointed out a Rhopalosiphum padi (L.) transmitting the virus causing barley yellow dwarf disease (BYDV) from infect wheat plants to celery plants and from infected celery plants to healthy ones. It plays an important role in spreading the barley yellow dwarf virus in wheat cultivations in Sharkia Governorate, Egypt. The results of insect transmission experiment could be summarized as follows: The acquisition threshold feeding periods ranged between 1 hr and 24 hr. Incubation periods in insects ranged between 48 - 73 hr. , while in the host plants were 18 to 22 days in celery plants.

Molecular characterization of barley yellow dwarf virus in Tunisia.

Barley yellow dwarf disease is a worldwide ubiquitous virus disease of cereal crops. In order to characterize the B/CYDV isolates occurring in Tunisia, 240 barley leaves were randomly sampled from 6 fields following a North-South trend and analyzed by serological and molecular tests. DAS-ELISA results showed 40 positive samples with a prevalence of barley yellow dwarf virus (BYDV)-PAV (77.5%), followed by cereal yellow dwarf virus (CYDV)-RPV (25%) and BYDV-MAV (15%). Studies of the geographic distribution showed a high incidence of B/CYDV in the Tunisian Southern provinces. RT-PCR assays were performed to amplify the viral coat protein gene (CP) and sequence analyses revealed six BYDV-PAV haplotypes named PAV-TN1 to PAV-TN6. Phylogenetic analysis showed that the six Tunisian haplotypes were close to BYDV-PAV-II subspecies and had a strong similarity with Moroccan, Czech, French and German haplotypes. Although PAV-TN2 and PAV-TN5 showed up to 10% divergence from BYDV-PAV-II at the amino acid level, it seems to belong to the same subspecies but in a separated cluster. Our results will be important in developing appropriate control measures against BYDV disease in Tunisia.

High-resolution mapping of the barley Ryd3 locus controlling tolerance to BYDV

Barley yellow dwarf disease (BYD) is transmitted by aphids and is caused by different strains of Barley yellow dwarf virus (BYDV) and Cereal yellow dwarf virus (CYDV). Economically it is one of the most important diseases of cereals worldwide. Besides chemical control of the vector, growing of tolerant/resistant cultivars is an effective way of protecting crops against BYD. The Ryd3 gene in barley (Hordeum vulgare L.) confers tolerance to BYDV-PAV and BYDV-MAV and the locus was previously mapped on the short arm of barley chromosome 6H near the centromere. We applied a strategy for high-resolution mapping and marker saturation at the Ryd3 locus by exploiting recent genomic tools available in barley. In a population of 3,210 F2 plants, 14 tightly linked markers were identified, including 10 that co-segregated with Ryd3. The centromeric region where Ryd3 is located suffers suppressed recombination or reduced recombination rate, suggesting potential problems in achieving (1) map-based cloning of Ryd3 and (2) marker selection of the resistance in breeding programmes without the introduction of undesirable traits via linkage drag.

Phylogenetic analysis of coat protein gene of BYDV-MAV strain from wheat

Barley yellow dwarf disease is globally the most important viral disease of wheat. The full-length nucleotide sequence of coat protein (CP) gene of 12 isolates revealed the presence of three distinct clusters. Pakistani isolate of MAV (MAV-PK) has maximum similarity of 99.23% with MAV isolate of Morocco and PAV-Australia following 99.22 and 99.22% with PAV-France. Similar degree of similarity was found in comparison of amino acid sequence. The finding of this study is that MAV-PK has similarity with both MAV-France and PAV-Australia, which is due to the reason that both MAV and PAV belong to the same group and both share maximum nucleotide homology. Low genetic diversity was found not only between MAV isolates but also between MAV and PAV isolates because phylogenetic analysis was done on the CP gene which is highly conserved region in genome of Barley yellow dwarf viruses (BYDVs). Divergence in MAV-PK was due to this recombination which is now most prevalent in Pakistan. MAV-PK has maximum similarity with MAV-Morocco followed by MAV-Sweden and MAV-Cz, which seems to indicate that Pakistani isolate of MAV evolved as the result of recombination between MAV isolates of the USA and PAV isolates of Australia and France. At the same time, recombination of MAV-CZ and MAV-Sweden also occur. This work can be successfully utilised in epidemiological studies of MAV isolate in Pakistan. Further analysis of variation level in these isolates will help scientists to formulate appropriate management strategies like incorporation of BdV 2 gene in wheat against BYDVs.

Barley yellow dwarf disease as a target of breeding for resistance (short review)

The aim of this work was to give a brief review of some points of wide knowledge of barley yellow dwarf (BYD) disease and its breeding for resistance program.<i>Yd2</i> gene has been shortly characterised. Current situation in Poland has been underlined.

First Report of Barley yellow dwarf virus-MAV in Oat, Wheat, and Barley Grown in the Czech Republic.

Barley yellow dwarf disease, a ubiquitous virus disease of cereal crops worldwide, is caused by a group of related, single-stranded RNA viruses assigned to Luteovirus (Barley yellow dwarf virus [BYDV] spp. PAV, PAS, MAV, and GAV) or Polerovirus (Cereal yellow dwarf virus-RPV) genera or unassigned to a genera (BYDV-SGV, BYDV-RMV, and BYDV-GPV) in the family Luteoviridae (1). Incidence of BYDV in cereal crops (e.g., barley, wheat, and oats) was high, and in recent years, reached epidemic levels in many regions of the Czech Republic. BYDV-PAV and BYDV-PAS have been identified in Czech cereal crops (2,4). Surveys of the incidence of BYDV were carried out using ELISA (SEDIAG SAS, Longvic, France) and one-step reverse transcription (RT)-PCR (Qiagen, Hilden, Germany) (2) during 2007 and 2008. Samples (125) were collected from different fields around the Czech Republic and 96 were BYDV positive. Three of the field isolates, CZ-6815, CZ-1561, and CZ-10844, from oat (Avena sativa; cv. Auron), winter wheat (Triticum aestivum; cv. Apache), and winter barley (Hordeum vulgare; cv. Merlot), respectively, were identified as BYDV-MAV by sequencing of the RT-PCR product (641-bp fragment) used to identify BYDV, which spanned 2839-3479 of the BYDV genome (GenBank Accession Nos. EF043235 and NC_002160) (2). The partial coat protein gene sequence of 483 nt was compared with the available sequences of 12 BYDV-PAV isolates (PAV-JP, PAV-NY, PAV-ILL, PAV-AUS, PAV-WG2, PAV-whG4y3, PAV-on21-4, Tahoe1, CA-PAV, HB3, FH3, and MA9501); nine BYDV-PAS isolates (PAS-129, PAS-64, WS6603, WG13, PAS-Tcb4-1, PASwaw5-9, FL2, PAS-Vd29, and PAS-MA9516); and six BYDV-MAV isolates (MAV-CA, MAV-PS1X1, MAV-Alameds268, LMB2a, SI-o4, and MAV-CN) by MEGA4 (3). Nucleotide and amino acid sequence identities for the three isolates ranged from 92.9 to 99.4% and 88.0 to 95.8%, respectively, for available BYDV-MAV isolates; 76.8 to 78.2% and 62.7 to 67.6%, respectively, for available BYDV-PAS isolates; and 77.6 to 79.3% and 65.5 to 70.4%, respectively, for available PAV isolates. The sequence data indicates that these isolates (CZ-6815, CZ-1561, and CZ10844; GenBank Accession Nos. FJ645747, FJ645758, and FJ645746, respectively) are BYDV-MAV. To my knowledge, this is the first record of BYDV-MAV in the Czech Republic.

First Report of Barley yellow dwarf virus-PAS in Wheat and Barley Grown in the Czech Republic.

Barley yellow dwarf disease, an important, ubiquitous virus disease of cereal crops worldwide, is caused by a group of related single-stranded RNA viruses assigned to luteovirus (Barley yellow dwarf virus (BYDV) spp. PAV, PAS, MAV, and GAV) or polerovirus (Cereal yellow dwarf virus-RPV) genera or unassigned to a genera (BYDV-SGV, BYDV-RMV, and BYDV-GPV) in the family Luteoviridae (2). Incidence of BYDV in cereal crops (e.g., barley, wheat, and oats) was high and reached epidemic levels in recent years in many regions of the Czech Republic. Previously, only PAV isolates have been identified here on the basis of serological detection (4), although antibodies to differentiate between PAV, PAS, and MAV are not widely available. Field samples of cereal crops were routinely tested in 2006 and 2007 and BYDVs were detected by ELISA. One-step-reverse transcription (RT)-PCR (Qiagen, Hilden, Germany) was adapted for BYDV detection using primer pairs BYcpF (5'-CCACTAGAGAGGTGGTGAATG-3') and BYcpR (5'-CCGGTGTTGAGGAGTCTACC-3') designed from conserved sequences identified by aligning multiple BYDV sequences available in public databases. These primers amplify a 641-bp fragment spanning nucleotides 2839-3479 from PAV (GenBank Accession No. EF043235) or PAS (GenBank Accession No. NC_002160) that includes a region of the coat protein gene and the intergenic region. RT-PCR amplicons were generated from two field isolates, PS-RuJK (spring wheat isolate, cv. Granny, collected in July 2007 from experimental plots at the CRI in Prague) and JE-120JK (winter barley isolate, cv. Merlot, collected in January 2008 from a barley field in Rychnov), both of which induced severe BYD symptoms. Amplicons were sequenced in both directions in a CEQ2000XL sequencer (Beckman Coulter, Fullerton, CA). The partial coat protein gene sequence of 483 nt of PS-RuJK and JE-120JK was analyzed and compared with available sequences of 26 PAV, 17 PAS, and 13 MAV isolates by MEGA4 (3). PS-RuJK (GenBank Accession No. EU863652) nucleotide and amino acid sequence identities ranged from 96.3 to 99.2% and 93.7 to 98.7%, respectively, for available PAS isolates, and 89.9 to 90.5% and 85.5 to 86.9%, respectively, for available PAV isolates, and 78.3 to 79.5% and 70.0 to 72.5%, respectively, for available MAV isolates. Similarly, nucleotide and amino acid sequence identities JE-120JK (GenBank Accession No. EU863653) ranged from 95.2 to 98.6% and 90.6 to 96.9%, respectively, for PAS isolates, 88.8 to 90.1% and 83.1 to 84.4%, respectively, for PAV isolates, and 77.6 to 78.7% and 67.5 to 70.0%, respectively, for MAV isolates. Also, both of these isolates have the conserved amino acid motif "SIPGS" that is usually present in a variable region of the coat protein gene on the surface of virion (1) at position 52 to 56 of amino acid sequences of all published PAS-like isolates, including Vd29:AY167109, FH1:AJ223588, MA9516:AJ007926, FL2:AJ223586, ASL-1:AJ810418, and WS6603:DQ285680, contrary to "PVFRP" or "LISGP" motif in PAV or MAV, respectively. Therefore, the sequence data clearly confirm that these two isolates belong to the PAS species. To our knowledge, this is the first record of PAS detected in the Czech Republic.

Recent advances in breeding of cereals for resistance to barley yellow dwarf virus

The review focuses on recent progress in the breeding of small grain cereals (barley, wheat, oats) for resistance to the barley yellow dwarf virus (BYDV). First, the symptomatology of barley yellow dwarf (BYD) disease is briefly described and the genome of BYDV, its serotypes and mechanisms of its replication and translation in host plants are characterized. Great attention is paid to the description of resistance genes and sources of BYDV resistance that are currently used in some breeding programmes of barley, wheat and oats. In barley, the introduction of the Ryd2 gene into high-yielding cultivars is still desirable. An example of recent success reached in a European programme aimed at a pyramiding of resistance genes is the registration of the Italian feeding barley cultivar Doria, carrying resistance genes Ryd2, rym4 and Rdg1. The release of this cultivar resulted from the cooperation between EICR, Fiorenzuola d’Arda and CRI in Prague-Ruzyně in the field of virus resistance. Finally, some experiments employing transgenic techniques in the construction of resistant plants are mentioned. In conclusion, the advantages and disadvantages of classical breeding methods using crossing and transgenic techniques are compared and newly arising approaches are discussed.

Transmission of two viruses that cause Barley Yellow Dwarf is controlled by different loci in the aphid, Schizaphis graminum.

Clonal populations of the aphid, Schizaphis graminum, have been separated into biotypes based on host preference and their ability to overcome resistance genes in wheat. Recently, several biotypes were found to differ in their ability to transmit one or more of the viruses that cause barley yellow dwarf disease in grain crops, and vector competence was linked to host preference. The genetics of host preference has been studied in S. graminum, but how this may relate to the transmission of plant viruses is unknown. Sexual morphs of a vector and nonvector S. graminum genotype were induced from parthenogenetic females and reciprocal crosses made. Eighty-nine hybrids were generated and maintained by parthenogenesis. Each hybrid was evaluated for its ability to transmit Barley yellow dwarf virus-PAV and Cereal yellow dwarf virus-RPV, and for its ability to colonize two wheat genotypes each expressing a different gene that confers resistance to S. graminum. The F1 genotypes were genetically variable for their ability to transmit virus and to colonize the aphid resistant wheat, but these traits were not genetically correlated. Individual F1 genotypes ranged in transmission efficiency from 0–100% for both viruses, although the overall mean transmission efficiency was similar to the transmission competent parent, indicating directional dominance. The direction of the cross did not significantly affect the vector competency for either virus, suggesting that maternally inherited cytoplasmic factors, or bacterial endosymbionts, did not contribute significantly to the inheritance of vector competency in S. graminum. Importantly, there was no genetic correlation between the ability to transmit Barley yellow dwarf virus and Cereal yellow dwarf virus-RPV in the F1 genotypes. These results taken together indicate that multiple loci are involved in the circulative transmission, and that the successful transmission of these closely related viruses is regulated by different sets of aphid genes.

Biometrical genetic analysis of luteovirus transmission in the aphid Schizaphis graminum

The aphid Schizaphis graminum is an important vector of the viruses that cause barley yellow dwarf disease. We studied the genetic architecture of virus transmission by crossing a vector and a non-vector genotype of S. graminum. F1 and F2 hybrids were generated, and a modified line-cross biometrical analysis was performed on transmission phenotype of two of the viruses that cause barley yellow dwarf: Cereal yellow dwarf virus (CYDV)-RPV and Barley yellow dwarf virus (BYDV)-SGV. Our aims were to (1) determine to what extent differences in transmission ability between vectors and non-vectors is due to net additive or non-additive gene action, (2) estimate the number of loci that determine transmission ability and (3) examine the nature of genetic correlations between transmission of CYDV-RPV and BYDV-SGV. Only additive effects contributed significantly to divergence in transmission of both CYDV-RPV and BYDV-SGV. For each luteovirus, Castle-Wright's estimator for the number of effective factors segregating for transmission phenotype was less than one. Transmission of CYDV-RPV and BYDV-SGV was significantly correlated in the F2 generation, suggesting that there is a partial genetic overlap for transmission of these luteoviruses. Yet, 63% of the F2 genotypes transmitted CYDV-RPV and BYDV-SGV at significantly different rates. Our data suggest that in S. graminum, the transmission efficiency of both CYDV-RPV and BYDV-SGV is regulated by a major gene or set of tightly linked genes, and the transmission efficiency of each virus is influenced by a unique set of minor genes.

Genetic analysis of a novel Alaska barley yellow dwarf virus in the family Luteoviridae

A new plant virus belonging to the family Luteoviridae and isolated from diseased oat (Avena sativa L.) plants was discovered in Alaska in 2003. Even though plants with red/orange leaves were indicative of barley yellow dwarf disease, they were not reactive to specific antibodies corresponding to barley yellow dwarf virus (BYDV)-MAV, -PAV, -SGV, and cereal yellow dwarf virus-RPV from enzyme-linked immunosorbent assays (ELISA). An alternative RT-PCR assay that incorporated Shu-F/Yan-R primers for detection of BYDV-MAV, -PAS, -PAV, and SGV was effective in producing approximately 830-nt fragments that contained genomic sequences to the 3'-terminus of the polymerase gene (ORF 2), the intergenic region ( approximately 113 nt), the coat protein gene (ORF 3), and the putative movement gene (ORF 4). The Alaskan isolates were most similar to BYDV-MAV with only about 77 and 80% amino acid identity in the CP and ORF 4, respectively. The Alaska isolates coat protein gene sequences differed in several regions that otherwise are conserved among BYDV-MAV isolates, and may be important in serological variations, accounting for the negative ELISA results. Based upon sequence and serological differences, we concluded that the Alaskan BYDV-MAV-like isolates formed a novel species tentatively in the genus Luteovirus, and propose the name BYDV-ORV (oat red-leaf virus).

Occurrence of barley yellow dwarf virus and cereal yellow dwarf virus in pasture grasses and spring cereals in Latvia

The relative frequency of three viruses causing barley yellow dwarf disease (BYD) was assessed in spring cereals and pasture grasses at two regions in Latvia in 2000–2002. A total of 2589 leaf samples (367 from spring oats, 743 from spring barley, 1479 from predominant grass species) were collected from 44 fields of spring oats, 84 fields of spring barley, and 26 pastures. We found that isolates of barley yellow dwarf virus-PAV (BYDV-PAV), barley yellow dwarf virus-MAV (BYDV-MAV) and cereal yellow dwarf virus-RPV (CYDV-RPV) were present in these samples of spring cereals and pasture grasses. The most common isolates of barley yellow dwarf virus were BYDV-PAV and BYDV-MAV in both grasses and cereals, but there was a great difference between years and regions. The proportion of BYD symptomatic cereal samples that reacted positively in TAS-ELISA test was 9 to 15%. The overall BYDV/CYDV incidence in pasture grasses ranged from 2 to 19%. The incidence of BYDV/CYDV infection was higher in Festuca elatior than in other grass species. Isolates of CYDV-RPV were rather rare: only found in Lolium perenne and Dactylis glomerata among six grass species tested and more frequently in barley than oats. This paper reports the first quantitative survey of selected BYD-causing viruses in spring cereals and pasture grasses in Latvia and in the Baltic states. We conclude that three selected virus species are prevalent in spring cereals and pasture grasses in Latvia, although with great variation between years. Further studies are needed to obtain knowledge of the most critical factors that determine these fluctuations.

Genetic Regulation of Polerovirus and Luteovirus Transmission in the Aphid Schizaphis graminum

ABSTRACT Sexual forms of two genotypes of the aphid Schizaphis graminum, one a vector, the other a nonvector of two viruses that cause barley yellow dwarf disease (Barley yellow dwarf virus [BYDV]-SGV, luteovirus and Cereal yellow dwarf virus-RPV, polerovirus), were mated to generate F1 and F2 populations. Segregation of the transmission phenotype for both viruses in the F1 and F2 populations indicated that the transmission phenotype is under genetic control and that the parents are heterozygous for genes involved in transmission. The ability to transmit both viruses was correlated within the F1 and F2 populations, suggesting that a major gene or linked genes regulate the transmission. However, individual hybrid genotypes differed significantly in their ability to transmit each virus, indicating that in addition to a major gene, minor genes can affect the transmission of each virus independently. Gut and salivary gland associated transmission barriers were identified in the nonvector parent and some progeny, while other progeny possessed only a gut barrier or a salivary gland barrier. Hemolymph factors do not appear to be involved in determining the transmission phenotype. These results provide direct evidence that aphid transmission of luteoviruses is genetically regulated in the insect and that the tissue-specific barriers to virus transmission are not genetically linked.

Relationships of Barley yellow dwarf virus-PAV and Cereal yellow dwarf virus-RPV from Iran with viruses of the family Luteoviridae

Barley yellow dwarf disease is one of the most important problems confronting cereal production in Iran. Barley yellow dwarf virus-PAV (BYDV-PAV) and Cereal yellow dwarf virus-RPV (CYDV-RPV) are the predominant viruses associated with the disease. One isolate of BYDV-PAV from wheat (PAV-IR) and one isolate of CYDV-RPV from barley (RPV-IR) were selected for molecular characterisations. A genome segment of each isolate was amplified by PCR. The PAV-IR fragment (1264 nt) covered a region containing partial genes for coat protein (CP), read through protein (RTP) and movement protein (MP). PAV-IR showed a high sequence identity to PAV isolates from USA, France and Japan (96–97%). In a phylogenetic analysis it was placed into PAV group I together with PAV isolates from barley and oats. The fragment of RPV-IR (719 nt) contained partial genes for CP, RTP and MP. The sequence information confirmed its identity as CYDV. However, RPV-IR showed 90–91% identity with both RPV and Cereal yellow dwarf virus-RPS (CYDV-RPS). Phylogenetic analyses suggested that it was more closely related to RPS. These data comprise the first attempt to characterise BYD-causing viruses in Iran and southwest Asia.