Barley Yellow Mosaic Virus Research Articles

Marker-Assisted Selection for Disease Resistance in Wheat and Barley Breeding

Marker-assisted selection (MAS) provides opportunities for enhancing the response from selection because molecular markers can be applied at the seedling stage, with high precision and reductions in cost. About each of 50 genes conferring monogenic resistances and hundreds of quantitative trait loci (QTL) for quantitative disease resistances have been reported in wheat and barley. For detecting single-major gene resistance, MAS could be easily applied, but is often not necessary because the resistances are selected phenotypically. In quantitative disease resistances, MAS would be very useful, but the individual QTL often have small effects. Additionally, only a few monogenic resistances are durable and only a few QTL with high effects have been successfully transferred into elite breeding material. Further economic and biological constraints, e.g., a low return of investment in small-grain cereal breeding, lack of diagnostic markers, and the prevalence of QTL-background effects, hinder the broad implementation of MAS. Examples in which MAS has been successfully applied to practical breeding are the wheat rust resistance genes Lr34 and Yr36, the eyespot resistance gene Pch1, the recessive resistance genes rym4/rym5 to barley yellow mosaic viruses, mlo to barley powdery mildew, and two QTL for resistance to Fusarium head blight in wheat (Fhb1 and Qfhs.ifa-5A). Newly identified broad-spectrum resistance genes/QTL conferring resistance to multiple taxa of pathogens offer additional perspectives for MAS. In the future, chip-based, high-throughput genotyping platforms and the introduction of genomic selection will reduce the current problems of integrating MAS in practical breeding programs and open new avenues for a molecular-based resistance breeding.

Evaluation of host resistance to Barley yellow mosaic virus infection at the cellular and whole‐plant levels

This study analysed the resistance and susceptibility of several barley cultivars harbouring one of six resistance genes (rym1–6) to Japanese Barley yellow mosaic virus (BaYMV) isolate JK05 using infectious RNA transcripts. At the cellular level, the virus replicated efficiently in mesophyll protoplasts from rym3 cultivars, less efficiently in protoplasts from a rym2 cultivar and poorly or not at all in protoplasts from other rym cultivars. None of the rym cultivars was susceptible at the whole‐plant level. These results indicate that rym2 and rym3 cultivars are resistant to this virus isolate at the movement level, whereas the other rym cultivars are resistant at the cellular level. In addition, among five barley cultivars without known resistance genes, it was found that the cv. Haruna Nijo was resistant to this virus isolate at the cellular level. Based on the host responses, it was inferred that the BaYMV isolate JK05 is in the Japanese pathotype II group. A possible mechanism for how resistance‐breaking variants continually emerge in fields is discussed.

Influence of amino acid at position 132 in VPg on replication and systemic infection of Barley yellow mosaic virus

A substitution of Lys with Asn or His at the amino-acid position 132 in VPg (VPg132) correlates with overcoming rym4-gene resistance by European strain 2 of Barley yellow mosaic virus (BaYMV-2). From the full-length cDNA clones for a Japanese BaYMV isolate JK05 (BaYMV-JK05) we generated virus mutants with Tyr, Lys, Asn, and Ala substituted for wild-type His at the VPg132. Only Tyr and Asn mutants replicated efficiently in protoplasts from barley varieties that are susceptible to wild-type virus. The Tyr mutant also infected susceptible barley plants systemically with the emergence of virus populations with partial or complete reversion to His, whereas the Asn mutant did not cause systemic infection. Thus, the VPg132 amino acid is essential for both efficient replication and systemic infection. Neither wild-type virus nor any of the mutants replicated in protoplasts from a rym4 barley genotype. Therefore, substitution of the VPg132 amino acid alone cannot enable breaking rym4-mediated resistance in the BaYMV-JK05 background.

Resistance of cereals to soil-borne virusesOdporność zbóż na wirusy odglebowe

Soil-borne viruses, belonging to the genera Furovirus and Bymovirus, are serious pathogens of winter cereals, transmitted by rootinhabiting fungal-like plasmodiophorid Polymyxa graminis. The vector is widely spread through in Asia, North America and Europe. In Europe there are two main cereal diseases caused by soil-borne viruses: barley yellow mosaic and soil-borne cereal mosaic. Plant protection against this kind of viruses is based exclusively on the cultivation of resistant or tolerant cultivars, as chemical control remains ineffective regarding the biological properties of the vector and unacceptable from the ecological point of view. Symptoms of barley yellow mosaic are caused by two closely related viruses: Barley yellow mosaic virus (BaYMV) and Barley mild mosaic virus (BaMMV), which infect only winter barley. Genetic studies led to the identification of sixteen genes carrying the resistance feature to the barley yellow mosaic viruses in barley. Soil-borne cereal mosaic virus (SBCMV), the causal agent of soil-borne cereal mosaic, can infect different cereal species, including wheat, triticale, rye and barley. Investigations on the resistance of wheat to SBCMV revealed that diverse mechanisms are involved in the reaction of plants and final effect of infection is dependent on many factors including climatic conditions.

Evaluation and Verification of Barley Genotypes with Known Genes for Resistance to Barley yellow mosaic virus and Barley mild mosaic virus Under Field Conditions in South Korea

Soil-borne barley yellow mosaic disease caused by Barley yellow mosaic virus (BaYMV) or Barley mild mosaic virus (BaMMV) gives a serious threat to the winter barley cultivated in the southern regions in Korea. It is important to develop resistant varieties for stable and high-yield production. The objectives of this study were to evaluate 22 genotypes of exotic barley germplasms carrying the resistance genes rym1 through rym12, with the exception of rym10, and to determine the genes that confer resistance to BaYMV or BaMMV in Korea. Using the traditional visual scoring of symptoms at 4 locations over 3 years, average disease rate values differed (P

Identificación y caracterización biológica del Barley yellow striate mosaic virus (BYSMV): nueva enfermedad del trigo en Argentina

Wheat (Triticum aestivum L.) is the most important winter grain in Argentina. Its production is limited by several factors, including viral diseases. The aim of this study was to identify and characterize a recently detected disease of wheat crops in Argentina. Symptomatic plants were collected from different locations from the wheat production area, Miramar and Balcarce (Buenos Aires), Rio Cuarto, Rosales and Marcos Juarez (Cordoba), Parana (Entre Rios) and General Pico (La Pampa). Samples were characterized by: electron microscopy (leaf-dip and ultrathin sections), serological tests (with antiserum reacting against different wheat viruses by DAS-ELISA and indirect ELISA), mechanical, seed and vector transmission assays, differential host range, and susceptibility of different wheat cultivars in natural infections. The results showed that this new disease is caused by Barley yellow striate mosaic virus (BYSMV) (Rhabdoviridae-Cytorhabdovirus), a widely distributed virus that can be transmitted to other crops such as barley, oat and triticale. This work represents the first report of BYSMV in Argentina.

Molecular mapping of Rym17, a dominant and rym18 a recessive barley yellow mosaic virus (BaYMV) resistance genes derived from Hordeum vulgare L.

PK23-2, a line of six-rowed barley (Hordeum vulgare L.) originating from Pakistan, has resistance to Japanese strains I and III of the barley yellow mosaic virus (BaYMV). To identify the source of resistance in this line, reciprocal crosses were made between the susceptible cultivar Daisen-gold and PK23-2. Genetic analyses in the F(1) generation, F(2) generation, and a doubled haploid population (DH45) derived from the F(1) revealed that PK23-2 harbors one dominant and one recessive resistance genes. A linkage map was constructed using 61 lines of DH45 and 127 DNA markers; this map covered 1268.8 cM in 10 linkage groups. One QTL having a LOD score of 4.07 and explaining 26.8% of the phenotypic variance explained (PVE) for resistance to BaYMV was detected at DNA marker ABG070 on chromosome 3H. Another QTL having a LOD score of 3.53 and PVE of 27.2% was located at marker Bmag0490 on chromosome 4H. The resistance gene on chromosome 3H, here named Rym17, showed dominant inheritance, whereas the gene on chromosome 4H, here named rym18, showed recessive inheritance in F(1) populations derived from crosses between several resistant lines of DH45 and Daisen-gold. The BaYMV recessive resistance genes rym1, rym3, and rym5, found in Japanese barley germplasm, were not allelic to rym18. These results revealed that PK23-2 harbors two previously unidentified resistance genes, Rym17 on 3H and rym18 on 4H; Rym17 is the first dominant BaYMV resistance gene to be identified in primary gene pool. These new genes, particularly dominant Rym17, represent a potentially valuable genetic resource against BaYMV disease.

An exceptionally high nucleotide and haplotype diversity and a signature of positive selection for the eIF4E resistance gene in barley are revealed by allele mining and phylogenetic analyses of natural populations

In barley, the eukaryotic translation initiation factor 4E (eIF4E) gene situated on chromosome 3H is recognized as an important source of resistance to the bymoviruses Barley yellow mosaic virus and Barley mild mosaic virus. In modern barley cultivars, two recessive eIF4E alleles, rym4 and rym5, confer different isolate-specific resistances. In this study, the sequence of eIF4E was analysed in 1090 barley landraces and noncurrent cultivars originating from 84 countries. An exceptionally high nucleotide diversity was evident in the coding sequence of eIF4E but not in either the adjacent MCT-1 gene or the sequence-related eIF(iso)4E gene situated on chromosome 1H. Surprisingly, all nucleotide polymorphisms detected in the coding sequence of eIF4E resulted in amino acid changes. A total of 47 eIF4E haplotypes were identified, and phylogenetic analysis using maximum likelihood provided evidence of strong positive selection acting on this barley gene. The majority of eIF4E haplotypes were found to be specific to distinct geographic regions. Furthermore, the eI4FE haplotype diversity (uh) was found to be considerably higher in East Asia, whereas SNP genotyping identified a comparatively low degree of genome-wide genetic diversity in 16 of 17 tested accessions (each carrying a different eIF4E haplotype) from this same region. In addition, selection statistic calculations using coalescent simulations showed evidence of non-neutral variation for eIF4E in several geographic regions, including East Asia, the region with a long history of the bymovirus-induced yellow mosaic disease. Together these findings suggest that eIF4E may play a role in barley adaptation to local habitats.

Polymyxa graminis . [Distribution map

Abstract A new distribution map is provided for Polymyxa graminis Ledingham. Cercozoa: Plasmodiophorida. Hosts: groundnut ( Arachis hypogaea ), oats ( Avena sativa ), barley ( Hordeum vulgare ), rice ( Oryza sativa ), rye ( Secale cereale ), wheat ( Triticum aestivum ), millet ( Panicum miliaceum ) and sorghum ( Sorghum bicolor ). Information is given on the geographical distribution in Europe (Belgium, France, Mainland France, Germany, Greece, Mainland Greece, Italy, Mainland Italy, Netherlands, Spain, Mainland Spain, UK, England and Wales), Asia (China, Anhui, Gansu, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Shaanxi, Shandong, Shanxi, Sichuan, Zhejiang, India, Andhra Pradesh, Gujarat, Punjab, Rajasthan, Iran, Japan, Honshu, Lebanon, Pakistan, Syria, Turkey), Africa (Burkina Faso, Cote d'Ivoire, Mali, Niger, Senegal), North America (Canada, Manitoba, Ontario, Prince Edward Island, USA, Arkansas, Florida, Georgia, Illinois, Iowa, Kansas, Kentucky, Maryland, Missouri, Nebraska, New Mexico, New York, Oklahoma, Pennsylvania, South Carolina, Virginia, Washington), South America (Bolivia, Brazil, Rio Grande do Sul, Colombia), Oceania (New Zealand). Vector of numerous plant viruses, including Soil-borne wheat mosaic virus, Wheat yellow mosaic virus, Wheat spindle streak mosaic virus, Barley yellow mosaic virus, Oat mosaic virus, Rice stripe necrosis virus and Peanut clump virus. Several viruses transmitted by P. graminis cause major widespread diseases on barley, wheat and groundnut. P. graminis is presumed to be present in all fields infested with the viral diseases it transmits, but is also present in virus-free soils. The distribution of the viruses transmitted by P. graminis is greater than the confirmed distribution of P. graminis shown on the map.

First Report of Polymyxa graminis f. sp. temperata, a Vector of Soilborne Cereal Viruses in the Czech Republic.

Polymyxa graminis L. is an eukaryotic, obligate, biotrophic parasite of plant roots (1), which belongs to a poorly studied, discrete, taxonomic unit informally called the 'plasmodiophorids'. P. graminis has the ability to acquire and transmit a range of soilborne viruses that belong to at least three separate genera and can cause economically significant diseases in cereal crops. For example, the winter barley disease caused by Barley yellow mosaic virus (BaYMV) and/or Barley mild mosaic virus (BaMMV) is widespread in Europe, Japan, and China; yield losses of >50% may occur when susceptible barley cultivars are grown on severely infested soils (2). Monitoring for P. graminis was started in the Czech Republic in May 2008. Fifty-six soil samples were collected from different localities of cereal production (wheat and barley) in the Královéhradecký Region (eastern Czech Republic). Soil from each sample was placed in five replicate pots (12 × 12 cm) in a greenhouse at 22 to 25°C. Seeds of barley cv. Florian were sown into the soil (10 seeds per pot). Negative control soil (noninfested soils from the Czech Republic) and positive control soil (known P. graminis-infested soil from Germany) were also planted to barley in five replicate pots. After 90 days, plants were collected and the roots were washed thoroughly in sterilized water and examined with a light microscope without staining. The fungus was identified as P. graminis on the basis of morphology of resting spores (cystosori) and sporangia and the size of individual cystosori (4 to 5 μm in diameter) according to Thouvenel et al. (3). Cystosori of P. graminis were observed in the roots of plants grown in 20 of the 56 soil samples, especially the samples from Ceské Mezirici. The presence of P. graminis in the roots of plants grown in the soil samples and the positive control sample versus the absence of the vector in roots of plants in the negative control soil was verified by PCR assay with DNA extracts and the Psp1 and Psp2rev primers according to Legrève et al. (Page 40 in: Proceedings of the Fifth Symposium of the International Working Group on Plant Viruses with Fungal Vectors, 2003). The PCR assay included denaturation at 94°C for 2 min, then 35 cycles including denaturation of 30 s at 94°C, annealing at 60°C for 1 min, and elongation at 72°C for 35 s. A final elongation was completed at 72°C for 7 min. To characterize the P. graminis isolates, the amplified PCR product (a DNA fragment of 472 bp) was sequenced and blasted for each of the samples that tested positive. These sequences were aligned with a known sequence (GenBank Accession No. AM259276) for P. graminis. The sequences from P. graminis on barley were 100% homologous to the published sequence of P. graminis f. sp. temperata. To our knowledge, this is the first report of P. graminis f. sp. temperata in the Czech Republic.

Breeding of Kirari-mochi: A new two-rowed waxy hull-less barley cultivar with superior quality characteristics

A new, two-rowed, waxy, hull-less barley cultivar, Kirari-mochi, was bred by the pedigree breeding method, and derived from a three-way cross (Shikoku-hadaka 103/Daikei HL107 (ant28.494)) F1/Shikoku-hadaka 97 (wax). Kirari-mochi is both proanthocyanidin-free (ant28.494) and amylose-free (wax), and boiled pearled barley of Kirari-mochi showed lower levels of discoloration after incubation at high temperatures than Ichibanboshi (a standard cultivar of hull-less barley). The polyphenol content of pearled Kirari-mochi is roughly half that of Ichibanboshi and the β-glucan content of Kirari-mochi pearled barley is about 1.5-times higher than that of Ichibanboshi. The broken kernel ratio of Kirari-mochi is lower than that of Ichibanboshi. Although the grain yield of Kirari-mochi is approximately 85% of that of Ichibanboshi, its tolerance to pre-harvest sprouting is lower than that of Ichibanboshi. Kirari-mochi is resistant to both barley yellow mosaic virus and powdery mildew, and is moderately resistant to scab. Kirari-mochi is well adapted to cultivation in the plains of central and western Japan, and it was released in 2010. Kirari-mochi is suitable for pearling and boiling, and has good eating quality.

Investigation of soilborne mosaic virus diseases transmitted by Polymyxa graminis in cereal production areas of the Anatolian part of Turkey

Polymyxa graminis is the vector of several important viruses, including Soilborne cereal mosaic virus, Wheat spindle streak mosaic virus, Barley yellow mosaic virus and Barley mild mosaic virus, of winter cereals worldwide. Surveys were carried out to detect these viruses and their vector P. graminis in 300 soil samples from the main wheat and barley production areas of the Anatolian part of Turkey collected in May 2002, June 2004 and May 2005. For these surveys, various susceptible wheat and barley cultivars were pot grown in the collected soil samples in a greenhouse and then analysed using ELISA and RT-PCR to detect the presence of different virus species. In addition, a combination of light microscopy following roots staining with acid fuchsin and PCR was used for detection of P. graminis. All soil samples analysed were found to be free of these soilborne viruses and their vector.

Development of CAPS marker for identifi cation of rym4 and rym5 alleles conferring resistance to the Barley Yellow Mosaic Virus complex in barley

In barley, soil-borne viruses of the barley mosaic virus complex (BaYMV, BaMMV, BaYMV-2) are of high importance due to their increased spread, yield losses, and the fact that protection with chemicals is not possible. Concerning resistance breeding, simple, cheap, and robust selection methods are required. Markerassisted selection (MAS) has a great potential to meet this demand. A CAPS marker designed directly for SNPs causing mutations responsible for resistance of rym4/rym5 alleles of the Hv-eIF4E gene was developed in this study. Results showed perfect correspondence between the CAPS marker and the allele identified indirectly on the basis of field tests.

Studies on Cereal Soil-Borne Viruses in Poland

Studies on Cereal Soil-Borne Viruses in PolandFour soil-borne cereal viruses have been identified in Poland, so far:Soil-borne cereal mosaic virus(SBCMV),Wheat spindle streak mosaic virus(WSSMV),Barley yellow mosaic virus(BaYMV) andBarley mild mosaic virus(BaMMV). SBCMV was identified in 1993 as a dangerous pathogen of winter cereals and became the object of special interest. Studies on the virus included its biological and molecular characterization, and investigations of the response of winter wheat and winter triticale cultivars on the SBCMV infection. Results of preliminary experiments aiming at the evaluation of the response of winter barley cultivars on barley yellow mosaic viruses were also presented.

Haplotype analysis of the SSRs surrounding rym 11 locus in a set of winter barley

Haplotype analysis of the SSRs surroundingrym 11locus in a set of winter barleyBreeding for Barley Mosaic Virus resistance is of great importance because of yield losses and the impossibility of plant protection using chemicals. Successful breeding of long-term resistant varieties requires widening of the genetic base of resistance, preferably by pyramiding of resistance genes. One of the perspective resistance genes isrym 11, resistant to all strains of Barley Mosaic Virus complex, but which is known to be present only in the cultivar Russia 57. In this work, the identification of potential newrym 11resistance donors on the basis of haplotype analysis of the SSRs surroundingrym 11locus is presented.

작부형태가 보리의 토양전염성 Bymovirus 발생과 매개균(Polymyxa graminis)의 밀도 변화에 미치는 영향

In this study, changes in virus disease occurrence and yield were monitored in conventional cropping system(rice-barley) and soybean-barley double cropping system in virus-prone area for 5 years. Also, changes in the density of Polymyxa graminis, a fungal vector, was investigated. In assay tests, mixed infection of Barley yellow mosaic virus (BaYMV) and Barley mild mosaic virus (BaMMV) was observed. Disease severity was in the range of 7~9 in conventional cropping system. In continuous cropping of soybean-barley and 3-yearfallow land, disease severity also was around 7. However, disease severity was reduced to medium level (5) when barley cultivation was paused for one or two years in soybean-barley cropping. When barley cultivation was paused for a year, the density of P. graminis, a fungal vector for BaYMV and BaMMV, reduced in barley root and soil. Similarly, barley growth was also enhanced by adopting fallow seasons. Compared with the fifth year of conventional cropping, the number of tillers per was increased by 158 when barley cultivation was paused for an year in soybean-barley cropping. When soybean and barley were cultivated continuously or complete fallow period was extended to three years, plant height and the number of tillers of barley were decreased. Yield components of barley in soybean-barley cropping were superior to those in rice-barley cropping. Compared with the fifth year of conventional cropping and soybean-barley cropping, culm length of barley was 1.3~2.3 cm higher and the number of tillers per was 36~90 higher when barley cultivation was paused for one or two years. However, those in continuous cropping of soybean-barley and 3-year-fallow land were lower compared with conventional cropping. Similarly, yield was increased when barley cultivation was paused for one or two years in the third, forth, and fifth years when compared with conventional cropping.

Mapping of resistance against Barley mild mosaic virus‐Teik (BaMMV) – an rym5 resistance breaking strain of BaMMV – in the Taiwanese barley (Hordeum vulgare) cultivar ‘Taihoku A’

With 1 figure AbstractThe Taiwanese barley (Hordeum vulgare L.) cultivar ‘Taihoku A’, which has been described as resistant to Barley mild mosaic virus (BaMMV), Barley yellow mosaic virus (BaYMV) and BaYMV‐2, contains the BaMMV resistance gene rym13 located on chromosome 4HL. Furthermore, ‘Taihoku A’ shows resistance to the newly detected virus strain BaMMV‐Teik, which is able to overcome the resistance gene rym5. By analysing a set of 154 DH‐lines of the cross ‘Taihoku A’ x ‘Plaisant’ it turned out that resistance to BaMMV‐Teik is inherited in a monogenic manner, the gene located on chromosome 4HL. Resistance to BaMMV‐Teik is also encoded by rym13 or an additional gene being closer linked to rym13 than 0.65 centiMorgan (cM). Using bulked segregant analysis employing Simple sequence repeats (SSRs) and Amplified fragment length polymorphisms (AFLPs), a map comprising 39.1 cM was constructed with the closest marker linked to the BaMMV/BaMMV‐Teik resistance at a distance of 1 cM. Respective markers are useful tools to introduce resistance to BaMMV‐Teik into adapted breeding lines carrying other resistance genes, which are not effective against all BaMMV/BaYMV strains known in Europe, e.g. rym4, rym5.

맥류의 토양 전염성 Bymovirus의 감염이 국내 육성 맥주보리의 생육 및 수량에 미치는 영향

우리나라에서 가장 우점하는 BaYMV(Barley yellow mosaic virus)에 의한 국내 육성 맥주보리의 품종의 저항성 정도에 따룬 생육 및 수량 피해를 조사하였다. 바이러스 감염 검정에서 두산 29호는 BaYMV와 BaMMV(Barley mild mosaic virus)에 감염되어 있었으나 진양보리와 호훔보리는 BaYMV에 만 감염된 것으로 나타났다. 월동후 초장과 수확기 간징의 생육을 조사한 결과 폼종별 저항성 정도에 따라 8~29%의 신장 억제율을 보였다. 생육 후기의 간장 단축률은 9~12%로 낮아지는 결과를 보였다. 월동후 경수는 호품에서는 발병포장와 건전포장에서 차이가 없었으나， 감수성인 두산 29호와 진양에서는 10~14%감소되었다. 그러나 수확기경 수수는 BaYMV 감염에 의해 26~33%까지 감소하는 결과를 보였다. 출수기는 발병 포장에서 1~3일까지 지연되는 경향이었다. 수확후 수량구성요소의 피해정도를 조사하였다. 천립중과 l 중도 품종별 저항성 정도에 따라 피해를 받아 각각 4.0~6.6%와1.0~ 4.2% 감소되는 것으로 조사되었다. BaYMV 감염시 6.0~8.6% 정 도의 비립이 발생하였으나 건정포장에서는 2.9~3.6%로 감소되어 두배 이상 비립발생이 증가하였다. 품종간 종실 수량 피해를 조사한 결과 건전한 포장에서의 품종간 평균 수량은 약 509kg~632kg/10a으로 유의성 있는 차이를 보이지 않았다. 발병 포장에서는 품종별 저항성 정도에 따라 유의성 있는 차이를 보였다. 중저항성인 호품의 경우 약 467kg/10a, 중약과 감수성인 진양과 두산29호에서는 각각 390kg과 290kg으로 조사되어 감수성인 두 품종에서는 77~177kg/10a의 수량 감소를 보였다. BaYMV 감염에 의해 수량성은 품종의 저항성 정도에 따라 26~43%의 감소되었다. Viral diseases, especially Barley yellow mosaic virus (BaYMV) and Barley mild mosaic virus (BaMMV) have been most serious in barley fields. In this study, we investigated the effect of different level of resistance to viral diseases on the plant growth and yield in malting barley. In diagnosis of virus infection, BaYMV and BaMMV were detected in 'Doosan 29' (susceptible), however, 'Jinyangbori' (moderate susceptible) and 'Hopumbori' (moderate) was infected by only BaYMV. Plant height was restrained about 8~29% in overwintered plant regeneration stage depending on the resistant of each cultivar. The culm length damaged also to 9~12% by BaYMV infection. The tiller numbers reduced to 10~14% in overwintering season, however, the head numbers in harvest season more decreased to 26~33%. Heading date was delayed to 3~3 days by the infection. In examination of yield components, 1,000 kernel weight and <TEX>$\ell$</TEX> weight reduced according to culrivar's resistant degrees to 4.0~6.4% and 1.0~4.2%, respectively. The yield of abortive grain was doubled in BaYMV infection comparing to non-infested field. Three varieties tested in the non-infected field over two years were not significantly different for yield potential with ranges of 509kg~632kg/10a. However, significant yield reduction was observed in 'Saessalbori' and 'Baegdong' with ranges of 77~177kg/10a as compared to 'Hopumbori' (467 kg/10a) when tested in the virus-infected field. Yield potentials of these cultivars reduced by 26~43%, respectively, in the virus-infected field as compared to those in the non-infected field.

Bymovirus reverse genetics: requirements for RNA2‐encoded proteins in systemic infection

Barley yellow mosaic virus (BaYMV), the type species of the genus Bymovirus in the family Potyviridae in the picornavirus-like superfamily, causes a yellow mosaic disease of winter barley with significant yield losses in Europe and East Asia. Until now, infectious in vitro transcripts for the bipartite plus-sense RNA genome of any bymovirus species have not been available, rendering molecular analyses of bymovirus pathogenicity and the host resistance mechanisms difficult. In this study, we constructed the first cDNA clones of BaYMV RNA1 and RNA2, from which infectious RNA can be transcribed in vitro. Using in vitro transcripts, we showed that RNA1, which encodes eight proteins, including a viral proteinase NIa-Pro, the RNA-dependent RNA polymerase NIb, genome-linked viral protein VPg and the capsid protein CP, replicated autonomously in barley mesophyll protoplasts in the absence of RNA2 optimally at 15 degrees C, a temperature similar to the optimum for causing disease in barley fields. For systemic infection of barley plants, RNA1 alone was not sufficient and RNA2 was also required. Of the two proteins encoded on RNA2 (P1 with cysteine proteinase activity and P2 with unknown functions), P1 was essential and P2 was dispensable for systemic infectivity. The expression of both P1 and P2, but not the precursor polyprotein, together with RNA1 increased systemic infection and caused mosaic leaf symptoms. The infectious cDNA clones of BaYMV will be vital for future studies of bymovirus-host-vector interactions at the molecular level.

The Current and New Strains of Barley Yellow Mosaic Virus (BaYMV) in Tochigi Prefecture.

ビールオオムギ初のオオムギ縞萎縮ウイルス（BaYMV）I，II，III型抵抗性新品種スカイゴールデンの普及にあたり，栃木県におけるBaYMV系統の発生を調査した．その結果，栃木県南地域ではIII型が常発化しており，県中北地域ではI型が発生していることから，これまで普及していた品種では不十分なことが明らかとなった．加えて，栃木県大田原市で既知のI，II，III型と病原性が異なり，BaYMV抵抗性遺伝子rym3を犯す大田原系統を見出した．この大田原系統と，同様にI，II，III型と病原性が異なり未同定であった山口系統について，罹病する品種の差異（病原性）および塩基やアミノ酸配列の相同性や系統樹による分子系統解析を用いて同定を試みた．その結果，それぞれI，II，III型と異なる系統で，大田原系統はIV型，山口系統はV型と判定された．IV型とV型の判別は，早木曽2号または浦項皮麦3と三月を判別品種として用いることにより可能である．また，スカイゴールデン，木石港3は，BaYMV I～V型のいずれにも抵抗性を示し，抵抗性育種に有効である．今後，ビールオオムギ品種育成において，BaYMV抵抗性遺伝子rym1，rym3，rym5の集積が重要と考えられる．