Resistance to the Barley Yellow Mosaic Virus Complex — Differential Genotypic Reactions and Genetics of BaMMV-Resistance of Barley (Hordeum vulgare L.)

Barley yellow mosaic disease is caused by several viruses, i.e. barley yellow mosaic virus (BaYMV), barley mild mosaic virus (BaMMV) and BaYMV-2. The reaction of different barley germplasms to the barley mosaic viruses was studied in field and greenhouse experiments. The results show a complex situation; some varieties are resistant to all the viruses, while others are resistant to one or two of them only. Crosses between different barley germplasms were earned out in order to test whether genetic diversity of resistance against mosaic viruses does exist, particularly, BaMMV. A total of 45 foreign barley varieties were crossed to German cultivars carrying the resistance gene ym4. In F₂ of 27 crosses, no segregation could be detected, leading to the conclusion that the resistance genes of the foreign parents are allelic with ym4 e.g. Ym1 (‘Mokusekko 3’) and Ym2 (‘Mihori Hadaka 3’). A total of 18 crosses segregated in F₂ indicating that foreign parents, like ‘Chikurin Ibaraki 1’, ‘Iwate Omugi 1’, and “Anson Barley”, carry resistance genes different from the gene of German cultivars, e.g. ‘Asorbia’ or ‘Franka’. By means of statistical evaluation (Chi²-test), the observed segregation ratios were analyzed in order to obtain significant information on the heredity of resistance. All the resistance genes described here as being different from the gene ym4, act recessively. Most of the exotic varieties seem to carry only one resistance gene. In a few cases, more than one gene may be present.     

Localisation and combination of resistance genes against soil-borne viruses of barley (BaMMV,BaYMV) using doubled haploids and molecular markers

Barley yellow mosaic virus disease caused by different strains of BaYMV and BaMMV is a major threat to winter barley cultivation in Europe. Different resistance genes against these viruses have been mapped and suitable PCR-based markers have been developed. In this respect doubled haploid (DH) populations proved to be advantageous as they facilitate a repeated test for resistance against all agents of the barley yellow mosaic virus complex and besides this, dominant marker systems are as informative as co-dominant ones in DHs due to the lack of heterozygous genotypes. Using DH populations resistance genes rym4, rym5, rym11, rym13, rym15 and the BaYMV/BaYMV-2 resistance of the barley cultivar ‘Chikurin Ibaraki 1’ have been mapped. DHs are also well suited to pyramiding resistance genes against BaMMV and BaYMV. Since homozygous recessive genotypes are more frequent in DHs than in segregating F₂ populations, DHs can be efficiently used to create broad-spectrum resistance and to extend the usability of partly overcome resistance genes. Results from employing two different strategies for pyramiding, based on one and two DH-steps, respectively, combining three recessive resistance genes, i.e. rym4/rym5, rym9 and rym11, are presented. The faster strategy based on one haploidy step resulted in the identification of all three and two-way combinations of the respective resistance genes.     

RAPD-mapping of the distal portion of chromosome 3 of barley, including the BaMMV/BaYMV resistance gene ym4

Experiments were carried out in order to identify RAPD-markers for the BaMMV/BaYMV resistance gene ym4 to facilitate efficient marker-based selection in practical breeding programmes. Linkage analysis was carried out with 283 doubled haploid (DH) barley lines out of a cross between the BaMMV/BaYMV susceptible cv. ‘Igri’ and the resistant cv. ‘Franka’. Using bulked segregant analysis, 310 RAPD-primers were screened for polymorphism between the parents. Four of these primers gave rise to specific bands linked to the resistance gene ym4.     

Investigating resistance to Barley mild mosaic virus

There are claims that at least 11 genes confer resistance in barley ( Hordeum vulgaris ) to one or more components of the soilborne barley mosaic virus complex but, apart from the immunity conferred by the widely used gene rym4 , little is known about their mode of action. This study used mechanical (sap) and plasmodiophorid vector-inoculation techniques combined with ELISA, RT-PCR, symptom development and virus transmission to investigate the response of different genotypes to Barley mild mosaic virus (BaMMV). Barley genotypes were grown at 20 and 12°C to test for temperature sensitivity. Plants with the genes rym3 or rym6 were fully susceptible to the virus, whereas those with genes rym1 , Rym2 , rym5 or rym11 appeared to be immune, as BaMMV was never detected in any tissue type nor was the virus transmitted from them to susceptible genotypes. The remaining genotypes could all be infected to some extent by BaMMV using one or both inoculation methods, and virus could be transmitted from their roots by the plasmodiophorid vector Polymyxa graminis . Plants with the rym7 gene had delayed symptoms compared to susceptible controls at 12°C. Plants with the rym8 gene could be infected by both inoculation methods, but there was no virus in the leaves at 12°C. Plants with the rym9 gene could be infected only by vector inoculation, and virus remained localized in the roots. Plants with the rym10 gene appeared susceptible by mechanical inoculation at both temperatures, but after vector inoculation virus moved to leaves only at 20°C. This suggests the operation of translocation resistance in plants with the rym8 , rym9 or rym10 genes, which is temperature-sensitive in rym8 and rym10 and perhaps tissue-specific in rym9 . No resistance to P. graminis was observed in any of the genotypes.     

The complete nucleotide sequence of RNA2 of barley mild mosaic virus (BaMMV)

Barley mild mosaic virus is a member of theBymoviruses, a genus of the familyPotyviridae. The virus consists of two types of flexuous rod-shaped particles. Each of them contains one single-stranded polyadenylated RNA in plus orientation of approximately 7.6 kb (RNA1) and 3.6 kb (RNA2). Complementary DNAs of both RNAs have been synthesised and cloned. The nucleotide sequence of RNA2 has been determined. It is 3524 nucleotides in length, excluding the 3 poly(A) tail, and contains one large open reading frame (2679 nts), coding for a polyprotein of approximately 98 kDa. There are indications that a putative proteolytic activity in the N-terminal part can cleave the polyprotein autocatalytically into a 25 kDa protein (putative proteinase) and a 73 kDa polypeptide of unknown function.     

Exotic barley germplasms in breeding for resistance to soil-borne viruses

Summary Soil-borne mosaic inducing viruses, i.e., barley mild mosaic virus (BaMMV), barley yellow mosaic virus (BaYMV), and BaYMV-2, cause one of the most important diseases of winter barley in Western Europe. Since resistance of all commercial European barley cultivars is due to a single recessive gene (ym4) which is not effective against BaYMV-2, exotic barley germplasms (Hordeum vulgare L., H. spontaneum Koch) were screened for resistance to the different viruses and analyzed for genetic diversity concerning BaMMV resistance. In these studies it turned out that resistance to BaMMV is entirely inherited recessively and that a high degree of genetic diversity concerning resistance is present within the barley gene pool at least to BaMMV. Therefore, exotic barley germplasms are a very useful source for the incorporation of different resistance genes into barley breeding lines, thereby enabling the breeder to create cultivars adapted to cultivation in the growing area of fields infested by soil-borne viruses. Furthermore, in order to obtain more information on these germplasms they were evaluated for agronomic traits and isozyme, RFLP and RAPD analyses were carried out on these varieties to detect markers linked to the respective resistance genes and to obtain information on the genetic similarity between yellow mosaic resistant barley accessions derived from different parts of the world. Actual results of these studies are briefly reviewed.     

Potential and limitations of isozymes for chromosomal localization of resistance genes against barley mild mosaic virus (BaMMV)

Summary To assess the possibilities offered by isozymes to locate resistance genes against barley mild mosaic virus (BaMMV), the isozyme patterns of 19 barley (Hordeum vulgare L.) genotypes carrying genes different from ym4 were determined. Of the 15 isozyme systems tested, only three were polymorphic, namely aconitate hydratase, esterase, phosphogluconate dehydrogenase, providing markers on four of the seven barley chromosomes. Studies of F₂ progenies derived from three crosses between resistant genotypes and susceptible varieties failed to reveal linkage between resistance genes and isozymes. Another goal of the experiment was to study the linkage relationships between ym4 and the esterase locus (Est1-Est2-Est4). Our estimates of the recombination rate between these two loci (3.41 and 8.32%) were in the range of those reported between these esterases and one of the resistance genes of the Chinese variety Mokusekko 3.     

Gene for Resistance to Barley Mild Mosaic Virus in German Winter Barley Located on Chromosome 3L

In order to identify the chromosome arm carrying a gene for resistance to barley mild mosaic virus (BaMMV) in German winter barley cultivars, a line trisomic for the long arm of chromosome 3 (telo-trisomic 3L) was crossed to the resistant cvs. ‘Sonate’ and ‘Ogra’. Results of tests for BaMMV reaction in the F2 indicate that the gene for resistance in German cultivars is located on the long arm of chromosome 3.     

大麦黄花叶病抗性遗传与育种研究进展

大麦黄花叶病是欧亚冬大麦区的主要病害之一。随着国内外对大麦黄花叶病抗病品种培育的重视,大麦黄花叶病抗性遗传与育种研究也在不断深入。本文综述了国内外大麦黄花叶病病毒株系的分类、病害的发生与传播、抗性遗传、抗病基因的定位以及抗黄花叶病育种等方面的研究进展,同时就大麦黄花叶病遗传育种中存在的一些问题及今后的育种策略进行了探讨,以期为今后我国大麦黄花叶病抗病育种提供参考。