Isolates Of Barley Yellow Dwarf Virus Research Articles

Barley Yellow Dwarf Virus Influences Its Vector's Endosymbionts but Not Its Thermotolerance.

The barley yellow dwarf virus (BYDV) of cereals is thought to substantially increase the high-temperature tolerance of its aphid vector, Rhopalosiphum padi, which may enhance its transmission efficiency. This is based on experiments with North American strains of BYDV and R. padi. Here, we independently test these by measuring the temperature tolerance, via Critical Thermal Maximum (CTmax) and knockdown time, of Australian R. padi infected with a local BYDV isolate. We further consider the interaction between BYDV transmission, the primary endosymbiont of R. padi (Buchnera aphidicola), and a transinfected secondary endosymbiont (Rickettsiella viridis) which reduces the thermotolerance of other aphid species. We failed to find an increase in tolerance to high temperatures in BYDV-infected aphids or an impact of Rickettsiella on thermotolerance. However, BYDV interacted with R. padi endosymbionts in unexpected ways, suppressing the density of Buchnera and Rickettsiella. BYDV density was also fourfold higher in Rickettsiella-infected aphids. Our findings indicate that BYDV does not necessarily increase the temperature tolerance of the aphid transmission vector to increase its transmission potential, at least for the genotype combinations tested here. The interactions between BYDV and Rickettsiella suggest new ways in which aphid endosymbionts may influence how BYDV spreads, which needs further testing in a field context.

Incidence and Distribution of Barley yellow dwarf virus Infecting Oats in Korea

A survey of Barley yellow dwarf virus (BYDV) was conducted in major oat-growing areas of Korea in 2020. BYDV is an economically important pathogen of cereal crops that can be transmitted by aphids. The present study evaluated the genetic composition of BYDV in oat from eight geographical areas in Korea. Multiplex reverse transcription-polymerase chain reaction was used to screen 322 oat leaf samples for six BYDV strains (PAV, MAV, SGV, PAS, RPV, and RMV). The 125 samples (~39%) tested positive for BYDV. BYDV-PAV, BYDV-SGV, BYDV-PAS, and BYDV-RPV were detected from oat in different areas. Most of the BYDV-infected samples were assigned to subgroup I (n=112). The results indicate that BYDV-PAV could be dominant throughout Korea. Also, the phylogenetic analysis of coat protein sequences indicated that 23 BYDV isolates from Korea could be separated into two clades, which exhibited high nucleotide sequence similarity. In conclusion, the present survey provides a BYDV infection assessment for domestic oat varieties in Korea and basic information for the development of BYDV control measures in Korea’s oat industry.

Identification of Viruses Infecting Oats in Korea by Metatranscriptomics.

Controlling infectious plant viruses presents a constant challenge in agriculture. As a source of valuable nutrients for human health, the cultivation of oats (Avena sativa L.) has recently been increased in Korea. To date, however, few studies have been undertaken to identify the viruses infecting oats in this country. In this study, we carried out RNA-sequencing followed by bioinformatics analyses to understand the virosphere in six different geographical locations in Korea where oats are cultivated. We identified three different virus species, namely, barley yellow dwarf virus (BYDV) (BYDV-PAV and BYDV-PAS), cereal yellow dwarf virus (CYDV) (CYDV-RPS and CYDV-RPV), and rice black-streaked dwarf virus (RBSDV). Based on the number of virus-associated reads and contigs, BYDV-PAV was a dominant virus infecting winter oats in Korea. Interestingly, RBSDV was identified in only a single region, and this is the first report of this virus infecting oats in Korea. Single nucleotide polymorphisms analyses indicated that most BYDV, CYDV, and RBSDV isolates show considerable genetic variations. Phylogenetic analyses indicated that BYDVs and CYDVs were largely grouped in isolates from Asia and USA, whereas RBSDV was genetically similar to isolates from China. Overall, the findings of this study provide a preliminary characterization of the types of plant viruses infecting oats in six geographical regions of Korea.

Investigation of the mechanism of adult-stage resistance to barley yellow dwarf virus associated with a wheat–Thinopyrum intermedium translocation

Barley yellow dwarf virus (BYDV) can infect wheat (Triticum aestivum L.), leading to yield loss. Among four BYDV strains (GAV, GPV, PAV, and RMV) identified in China, BYDV-GAV is the prevailing isolate. YW642, a wheat–Thinopyrum intermedium translocation line, is resistant to BYDV isolates at both seedling and adult stages. Zhong 8601 is the wheat recurrent parent of YW642 and is susceptible to BYDV. In this study, we investigated the adult-stage resistance mechanism of YW642, measured BYDV titer and hydrogen peroxide (H2O2) in adult-stage leaves of YW642 and Zhong 8601 inoculated with BYDV-GAV, and identified transcriptional differences between YW642 and Zhong 8601 using microarray-based comparative transcriptomics. Enzyme-linked immunosorbent assay and H2O2 assay showed that both BYDV titer and H2O2 content were markedly lower in YW642 than in Zhong 8601 at 21, 28, 35, and 40days post-inoculation (dpi). The transcriptomic comparison revealed that many types of genes were significantly up-regulated at 35dpi in adult-stage leaves of YW642 compared to Zhong 8601. The important up-regulated genes associated with the adult-stage resistance encoded 15 resistance-like proteins, pathogenesis-related proteins (such as defensin and lipid transfer proteins), protein kinase homologs, transcription factors, reactive oxygen species scavenging-related proteins, and jasmonic acid and gibberellic acid biosynthesis enzymes. These results suggest that precise expression regulation of these proteins plays a crucial role in adult-stage resistance of YW642 against BYDV infection.

Sequencing and validation of reference genes to analyze endogenous gene expression and quantify yellow dwarf viruses using RT-qPCR in viruliferous Rhopalosiphum padi.

The bird cherry-oat aphid (Rhopalosiphum padi), an important pest of cereal crops, not only directly sucks sap from plants, but also transmits a number of plant viruses, collectively the yellow dwarf viruses (YDVs). For quantifying changes in gene expression in vector aphids, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) is a touchstone method, but the selection and validation of housekeeping genes (HKGs) as reference genes to normalize the expression level of endogenous genes of the vector and for exogenous genes of the virus in the aphids is critical to obtaining valid results. Such an assessment has not been done, however, for R. padi and YDVs. Here, we tested three algorithms (GeNorm, NormFinder and BestKeeper) to assess the suitability of candidate reference genes (EF-1α, ACT1, GAPDH, 18S rRNA) in 6 combinations of YDV and vector aphid morph. EF-1α and ACT1 together or in combination with GAPDH or with GAPDH and 18S rRNA could confidently be used to normalize virus titre and expression levels of endogenous genes in winged or wingless R. padi infected with Barley yellow dwarf virus isolates (BYDV)-PAV and BYDV-GAV. The use of only one reference gene, whether the most stably expressed (EF-1α) or the least stably expressed (18S rRNA), was not adequate for obtaining valid relative expression data from the RT-qPCR. Because of discrepancies among values for changes in relative expression obtained using 3 regions of the same gene, different regions of an endogenous aphid gene, including each terminus and the middle, should be analyzed at the same time with RT-qPCR. Our results highlight the necessity of choosing the best reference genes to obtain valid experimental data and provide several HKGs for relative quantification of virus titre in YDV-viruliferous aphids.

Pyramiding of Ryd2 and Ryd3 conferring tolerance to a German isolate of Barley yellow dwarf virus-PAV (BYDV-PAV-ASL-1) leads to quantitative resistance against this isolate

Barley yellow dwarf virus (BYDV) is an economically important pathogen of barley, which may become even more important due to global warming. In barley, several loci conferring tolerance to BYDV-PAV-ASL-1 are known, e.g. Ryd2, Ryd3 and a quantitative trait locus (QTL) on chromosome 2H. The aim of the present study was to get information whether the level of tolerance against this isolate of BYDV in barley can be improved by combining these loci. Therefore, a winter and a spring barley population of doubled haploid (DH) lines were genotyped by molecular markers for the presence of the susceptibility or the resistance encoding allele at respective loci (Ryd2, Ryd3, QTL on chromosome 2H) and were tested for their level of BYDV-tolerance after inoculation with viruliferous (BYDV-PAV-ASL-1) aphids in field trials. In DH-lines carrying the combination Ryd2 and Ryd3, a significant reduction of the virus titre was detected as compared to lines carrying only one of these genes. Furthermore, spring barley DH-lines with this allele combination also showed a significantly higher relative grain yield as compared to lines carrying only Ryd2 or Ryd3. The QTL on chromosome 2H had only a small effect on the level of tolerance in those lines carrying only Ryd2, or Ryd3 or a combination of both, but the effect in comparison to lines carrying no tolerance allele was significant. Overall, these results show that the combination of Ryd2 and Ryd3 leads to quantitative resistance against BYDV-PAV instead of tolerance.

Molecular mapping of genomic regions underlying barley yellow dwarf tolerance in cultivated oat (Avena sativa L.).

Barley yellow dwarf (BYD) is one of the most important viral diseases in small grains, including oat (Avena sativa L.). Breeding for BYD tolerance is an effective and efficient means to control the disease. Characterization of major sources of tolerance, and identification of marker and the trait associations, will directly benefit breeding for BYD tolerance. Genomic regions underlying BYD tolerance were mapped and characterized in an oat population consisting of 152 recombinant inbred lines from the cross of 'Ogle' (tolerant)/MAM17-5 (sensitive). Tolerance was evaluated in replicated field trials across 2 years under artificial inoculation with viruliferous aphids harboring BYD virus isolate PAV-IL. Composite interval mapping was used for quantitative trait loci (QTLs) analysis with a framework map consisting of 272 molecular markers. Four QTLs, BYDq1, BYDq2, BYDq3 and BYDq4, for BYD tolerance were identified on linkage groups OM1, 5, 7 and 24, respectively. All but BYDq2 were consistently detected across both years. Significant epistasis was found between some QTLs. The final model including the epistatic effect explained 50.3 to 58.2% of the total phenotypic variation for BYD tolerance. Some QTLs for BYD tolerance were closely linked to QTLs for plant height and days to heading. Potential problems with QTL mapping for BYD tolerance have been discussed. The identified association of markers and tolerance should be useful to pyramid favorable alleles for BYD tolerance into individual oat lines.

Effect of Barley yellow dwarf virus Infection on Yield and Malting Quality of Barley.

Barley yellow dwarf virus (BYDV) infection occurs frequently in barley in the Upper Midwest region of the United States; however, the impact of this disease on the yield and quality of malting cultivars has not been adequately addressed. Studies were conducted at Fargo, North Dakota (from 1989 to 1990) to determine the effect of BYDV infection on yield and malt quality parameters in barley. Three malting cultivars varying in yield potential and malting characteristics were artificially inoculated at the seedling stage with a North Dakota BYDV isolate of the PAV serotype. Overall yields were reduced 32.5 to 38% in 1989 and 8.5 to 19.8% in 1990 by BYDV infection. Thousand-kernel weight (3.2 to 14.9%) and kernel plumpness (11.9 to 38.9%) also were reduced. Kernel color and three malt quality parameters (α-amylase, malt recovery, and wort viscosity) were not affected by BYDV infection. Increases in wort protein (2.5 to 14.5%) and diastatic power (3.8 to 12.6%), and decreases in malt extract (1.1 to 5.6%) were found. Most notably, total protein increased 4.6 to 17.5% with BYDV infection. Higher proportions of thin seed, as a result of BYDV infection, contributed to the effects on several quality parameters. In summary, the negative effect of BYDV infection on overall quality is significant and should be considered when assessing the impact of this disease. Although annual BYD disease-related losses are typically not extensive in the Midwestern malting barley region, the incorporation of host resistance into recommended cultivars would ameliorate the negative effects of BYD disease on crop quality as well as on yield.

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.

Expression of Thinopyrum intermedium-Derived Barley yellow dwarf virus Resistance in Elite Bread Wheat Backgrounds

ABSTRACT Resistance to Barley yellow dwarf virus (BYDV) is not found in wheat but is available in a Thinopyrum intermedium translocation (Ti) carried on chromosome 7DL of bread wheat recombinant lines. We used one of those lines (TC14/2*Spear) to introgress the Ti into bread wheat cultivars and to determine the influence of wheat backgrounds, with and without known tolerance to BYDV, on the expression of resistance. Two single and three backcross populations, segregating for the presence of the alien fragment, were tested under field conditions and artificial inoculation with BYDV isolates MAV-Mex and PAV-Mex. Lines containing the fragment were identified using the microsatellite marker gwm37. Tillering, biomass, grain yield, thousand-kernel weight, and seed quality were evaluated in inoculated and noninoculated plots. Resistance was assessed by enzyme-linked immunosorbent assay. In early generations, the alien fragment followed expected Mendelian segregation, whereas in the advanced ones a slight bias against its transmission was observed. No positive nor negative effects of Ti on agronomic performance and quality were found. A significant optical density reduction in individuals carrying the fragment was observed after PAV infection in crosses with lines Anza and Baviacora but not with Milan. In addition, the fragment was associated with a lower frequency of infected plants for both PAV and MAV isolates. The reduced yield loss associated with the presence of the translocation was due largely to the lower infection rate.

Yield Effects of Barley yellow dwarf virus in Soft Red Winter Wheat

ABSTRACT Three cultivars of soft red winter wheat were evaluated to determine the relationship between the incidence and time of infection by Barley yellow dwarf virus (BYDV) and yield. Wheat was planted in 1995, 1996, and 1997 in a split-plot design with six replicates at sites in Indiana and Illinois. Yield plots were infested with different amounts of viruliferous aphids, and the incidence of BYDV in each plot was measured. In a 2-year study in Illinois with cv. Clark and the PAV-IL isolate of BYDV, yields were assessed following aphid infestation in fall, early spring, and late spring. Early spring infections resulted in larger yield reductions than late spring infections in both years and larger than fall infections in one year. Regression analyses to relate incidence of infection and yield with data from fall and early spring infections provided R(2) values of 0.89 and 0.51 for the 1996 to 1997 and 1997 to 1998 seasons, respectively. An additional study at the same site in the 1996 to 1997 season compared the yield responses of cvs. Clark, Y88-3e, and PT8935b. Increases in the incidence of BYDV correlated with decreases in yield, with R(2) values of 0.80, 0.78, and 0.90 for the three cultivars, respectively. Estimated yield losses in both studies and all cultivars ranged from 27 to 45 kg/ha or 0.34 to 0.55% for each percent increase in virus infection. In a third study over a 2-year period in Indiana with the same three wheat genot ypes and a second BYDV isolate (PAV-P), BYDV treatments resulted in significant reductions in yield, but yield loss and the incidence of BYDV were not linearly correlated. Given the differences in yield reductions caused by the two BYDV isolates, PAV-P may be an attenuated strain of BYDV and may cross-protect plants from naturally occurring strains of the virus.

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.

Coat protein-mediated resistance to isolates of barley yellow dwarf in oats and barley.

Tissue cultures of GAF30/Park oats were biolistically co-transformed with constructs containing the coat protein (CP) genes of the P-PAV, MAV-PS1 or NY-RPV isolates of barley yellow dwarf virus (BYDV), together with a construct containing the bar gene for herbicide resistance and the uidA reporter gene. Transformed, herbicide-resistant tissue cultures were screened by PCR for the presence of the CP genes. Fertile regenerated plants were recovered from some CP-transformed tissue cultures. T1 progeny of these plants were screened for resistance to the BYDV isolate corresponding to the introduced gene by inoculation with viruliferous aphids followed by ELISA tests. Variation in ELISA values for GAF30/Park control plants made interpretation of the data difficult, but oat plants resistant to each of the three isolates of BYDV (ELISA values less than 0.3; virus titers equivalent to less than 25% of infected controls) were identified in T1 generations. Further testing of MAV-PS1 CP-transformed lines to the T2 generation, NY-RPV CP-transformed lines to the T3 generation and P-PAV CP-transformed lines to the T4 generation identified further resistant plants. Similarly, immature embryos and calli of the barley cultivar Golden Promise were biolistically bombarded with constructs containing the CP gene of the P-PAV isolate of BYDV and the bar and uidA reporter genes, lines of self-fertile P-PAV CP-transformed barley plants were developed, and T1plants were screened for resistance to P-PAV. Eight plants from six lines showed moderate to high levels of resistance to P-PAV that correlated with the presence of the CP gene. Plants giving low ELISA values were also found in other lines, even though the CP gene was not detected in these plants. Some T2 plants derived from resistant parents that contained the CP gene were themselves highly resistant.

Diversity Among Isolates Within the PAV Serotype of Barley Yellow Dwarf Virus

Several barley yellow dwarf virus (BYDV) isolates collected from viruliferous aphids in upstate New York were identified as PAV serotypes, based on their reaction with a polyclonal antiserum to NY-PAV. Four of six isolates examined were distinguished from the NY-PAV type isolate of BYDV by their failure to react with a PAV-specific monoclonal antibody in enzyme-linked immunosorbent assay (ELISA) and by restriction fragment length polymorphisms of polymerase chain reaction-amplified viral sequences. The capsid protein amino acid sequence of one of these four isolates, designated PAV-129, was less similar to that of NY-PAV (86.5% similar) than NY-PAV is to two other isolates, serotyped as PAV, from Indiana (98% similar) or Australia (97% similar). In biological comparisons of PAV-129 and NY-PAV, the efficiency of transmission by two aphid species, Rhopalosiphum padi and Sitobion avenae, was not significantly different; however, PAV-129 caused more severe symptoms when inoculated to a variety of oat genotypes. In addition, the growth and grain yield of 'Ogle', a spring oat considered resistant to the BYDV PAV serotype was significantly reduced when infected with PAV-129.

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.

トウモロコシ及び数種イネ科植物から分離されたオオムギ黄萎ウイルス（ｂａｒｌｅｙ ｙｅｌｌｏｗ ｄｗａｒｆ ｖｉｒｕｓ，ＢＹＤＶ）について

Barley yellow dwarf virus (BYDV) distributed widely in barley, wheat, rye, oat, maize, teosinte and foxtail millet showing a yellowing, redding or dwarfing in Kanto area. Wheat, rye, maize, teosinte and foxtail millet were newly recorded natural host plants of BYDV in Japan. New diseases named yellow dwarf or yellows for them. Two BYDV isolates from maize and oat were characterized by the aphid transmission, host range, physicochemical properties, serology and intracellular appearance. These two isolates were regularly transmitted by Rhopalosiphum padi and R. maidis, respectively, indicating that the isolates may be differ from other known isolates of BYDV.

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.

Barley Yellow Dwarf Virus Resistance in Triticum aestivum×Leymus angustus Hybrids

AbstractThe enzyme‐linked immunosorbent assay (ELISA) was used to determine the concentration of barley yellow dwarf virus (BYDV) in leaves of spring wheat Triticum aestivum L. cv. ‘Fukuhokomugi’, Leymus angustus (Trin.) Pilger (Altai wild rye) and their F1 hybrids inoculated at the 2‐ to 3‐leaf stage. The BYDV isolate “Cloutier” (serotype PAV) was used. The results showed that L. angustus confers immunity or strong resistance to the virus. Significant multiplication of the virus occurred in ‘Fukuhokomugi’ which expressed an intermediate level of tolerance to the disease under field conditions. The F1 haploid hybrids of ‘Fukuhokomugi’×L. angustus expressed a level of resistance almost equal to that of their wild parent, with a low concentration of virus appearing 16 days after inoculation and no more afterwards. The discovery of BYDV resistance in L. angustus and the expression of this character in the F1 hybrids provide new opportunities for the enlargement of the gene pool for BYDV resistance in wheat.

Aphid Vectors of Barley Yellow Dwarf Virus in West‐Central Morocco

AbstractThe ability of seven aphid species, collected in west‐central Morocco, to transmit barley yellow dwarf virus (BYDV) was determined. Aphids were either collected from grasses showing symptoms of BYDV infection or were allowed acquisition access to plants infected with a PAV‐like isolate of BYDV before transfer to oat test plants. BYDV transmission by six of the seven aphid species was confirmed by ELISA test; only Melanaphis donacis failed to transmit. The six newly defined BYDV vector species brings the total known to occur in Morocco to ten.

Heterologous encapsidation in mixed infections among four isolates of barley yellow dwarf virus

We used immunohybridization and ELISA to investigate heterologous encapsidation (transcapsidation and phenotypic mixing) between paired isolates of barley yellow dwarf virus (BYDV) in doubly infected oat plants, Avena sativa L. cv. Clintland 64. Virons in samples extracted from plants doubly infected with two viruses were trapped with an antibody specific to one virus, and the nucleic acids of the trapped virions were identified with a cDNA probe specific to the other. Heterologous encapsidation was found in mixed infections between isolates NY-RPV and NY-MAV-PS1, NY-RPV and P-PAV, NY-RMV and NY-MAV-PS1, P-PAV and NY-MAV-PS1, and NY-RPV and NY-RMV. Heterologous encapsidation between NY-RPV and P-PAV, and between NY-RPV and NY-MAV-PS1, occurred in one direction, while the heterologous encapsidation between P-PAV and NY-MAV-PS1 occurred in both directions. Further analysis by heterologous ELISA and immunohybridization assays with immunoprecipitated samples demonstrated that transcapsidation was the predominant type of heterologous encapsidation in mixed infections of NY-RPV and P-PAV, NY-RPV and NY-MAV-PS1, and NY-RMV and NY-MAV-PS1; phenotypic mixing was the predominant type of heterologous encapsidation in mixed infections of P-PAV and NY-MAV-PS1. Phenotypic mixing was also detected in mixed infections of NY-RPV and NY-RMV. These results suggest that among BYDV isolates transcapsidation is more common between distantly related isolates than between more closely related isolates, and phenotypic mixing is more common between more closely related isolates than distantly related isolates.