Antje Habekuß

Ryd4 Hb : a novel resistance gene introgressed from Hordeum bulbosum into barley and conferring complete and dominant resistance to the barley yellow dwarf virus

Barley yellow dwarf virus (BYDV) causes high yield losses in most of the major cereal crops worldwide. A source of very effective resistance was detected within the tetraploid wild species of Hordeum bulbosum. Interspecific crosses between a resistant H. bulbosum accession and H. vulgare cv. ‘Igri’ were performed to transfer this resistance into cultivated barley. Backcrosses to H. vulgare resulted in offspring which carried a single subterminal introgression of H. bulbosum chromatin on barley chromosome 3HL and proved to be fully resistant to BYDV-PAV, as inferred by ELISA values of zero or close to zero and lack of BYDV symptoms. Genetic analysis indicated a dominant inheritance of the BYDV-PAV resistance factor, which we propose to denote Ryd4Hb. The identity and effect of Ryd4Hb are discussed in relation to other known genes for BYDV resistance or tolerance, as well as the relevance of this gene for resistance breeding in barley.

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.

Gene-based high-density mapping of the gene rym7 conferring resistance to Barley mild mosaic virus (BaMMV)

Barley yellow mosaic virus (BaYMV) disease seriously affects winter barley (Hordeum vulgare L.) production. Improvement of resistance to this disease can prevent yield losses. Based on previous reports, the gene rym7 (rmm7), conferring partial resistance to BaMMV, was assigned to chromosome 1H, closely linked to the centromere. In this study, newly developed barley genomic resources were applied to saturate the genetic map at the rym7 locus. Out of a set of 350 gene-based markers of chromosome 1H, we genetically assigned 23 to the rym7 region, delimiting the resistance locus to a 9.9-cM interval close to the centromere by genetic mapping in 53 doubled haploid progeny of a bi-parental mapping population. Nine gene-derived co-dominant markers co-segregated with the resistance locus. Among these, we identified the eukaryotic translation initiation factor Hv-eIF(iso)4E. Its homolog in Arabidopsisthaliana confers resistance to potyviruses. However, sequencing the entire open reading frame of resistant and susceptible genotypes could not reveal any sequence variation in exons of the gene. These results demonstrate how to combine newly developed barley genomic resources for rapid gene-based marker saturation. As a result, several easy-to-handle co-dominant markers have been identified for marker-assisted selection of rym7 in barley breeding.

Analysis of bymovirus resistance genes on proximal barley chromosome 4HL provides the basis for precision breeding for BaMMV/BaYMV resistance

Key messageUnlocking allelic diversity of the bymovirus resistance generym11located on proximal barley chromosome 4HL and diagnostic markers provides the basis for precision breeding for BaMMV/BaYMV resistance.AbstractThe recessive resistance gene rym11 on barley chromosome 4HL confers broad-spectrum and complete resistance to all virulent European isolates of Barley mildmosaic virus and Barley yellow mosaic virus (BaMMV/BaYMV). As previously reported, rym11-based resistance is conferred by a series of alleles of naturally occurring deletions in the gene HvPDIL5-1, encoding a protein disulfide isomerase-like protein. Here, a novel resistance-conferring allele of rym11 is reported that, in contrast to previously identified resistance-conferring variants of the gene HvPDIL5-1, carries a single non-synonymous amino acid substitution. Allelism was confirmed by crossing to genotypes carrying previously known rym11 alleles. Crossing rym11 genotypes with a cultivar carrying the recessive resistance gene rym1, which was reported to reside on the same chromosome arm 4HL like rym11, revealed allelism of both loci. This allelic state was confirmed by re-sequencing HvPDIL5-1 in the rym1 genotype, detecting the haplotype of the rym11-d allele. Diagnostic PCR-based markers were established to differentiate all seven resistance-conferring alleles of the rym11 locus providing precise tools for marker-assisted selection (MAS) of rym11 in barley breeding.

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.

Genetic fine mapping of a novel leaf rust resistance gene and a Barley Yellow Dwarf Virus Tolerance (BYDV) Introgressed from Hordeum Bulbosum by the Use of the 9K iSelect Chip

Leaf rust and barley yellow dwarf, caused by Puccinia hordei Otth and barley yellow dwarf virus (BYDV)/cereal yellow dwarf virus (CYDV), are important diseases of barley (Hordeum vulgare L.) worldwide. Screening of spring barley landraces from Serbia led to the identification of the accession ‘MBR1012’ carrying resistance to the most widespread virulent leaf rust pathotypes in Europe, while a barley line carrying an introgression derived from H. bulbosum on chromosome 2HL was found to be highly tolerant to BYDV-PAV. In a population of 91 doubled haploid lines, derived from the cross MBR1012 (R) × Scarlett (S), the resistance gene against leaf rust was mapped in the telomeric region of chromosome 1HS by using simple sequence repeats (SSR). In parallel, the population was genotyped on the newly developed Illumina iSelect custom 9K BeadChipQ1, resulting in the identification of closer linked markers. To exploit BYDV tolerance, DH lines derived from the cross (Emir x H. bulbosum) x Emir have been analysed in three steps. In a first step, out of 221 DH lines, 27 plants carrying a recombination event in the H. bulbosum fragment were selected based on nine markers specific for chromosome 2HL. In a next step, selected recombinant plants were analysed on a custom-made Illumina BeadXpress Array (384 SNPs) and on the 9k iSelect BeadChip. Finally, artificially inoculated DH lines carrying introgressions of different sizes will be screened for BYDV virus tolerance by artificial inoculation in order to map this tolerance. Results obtained revealed the presence of novel resistance/tolerance genes and in parallel provide the tools for their efficient deployment in barley breeding

Sequence diversification in recessive alleles of two host factor genes suggests adaptive selection for bymovirus resistance in cultivated barley from East Asia.

Key messageTwo distinct patterns of sequence diversity for the recessive alleles of two host factorsHvPDIL5-1andHvEIF4Eindicated the adaptive selection for bymovirus resistance in cultivated barley from East Asia.AbstractPlant pathogens are constantly challenging plant fitness and driving resistance gene evolution in host species. Little is known about the evolution of sequence diversity in host recessive resistance genes that interact with plant viruses. Here, by combining previously published and newly generated targeted re-sequencing information, we systematically analyzed natural variation in a broad collection of wild (Hordeum spontaneum; Hs) and domesticated barleys (Hordeum vulgare; Hv) using the full-length coding sequence of the two host factor genes, HvPDIL5-1 and HvEIF4E, conferring recessive resistance to the agriculturally important Barley yellow mosaic virus (BaYMV) and Barley mild mosaic virus (BaMMV). Interestingly, two types of gene evolution conferred by sequence variation in domesticated barley, but not in wild barley were observed. Whereas resistance-conferring alleles of HvEIF4E exclusively contained non-synonymous amino acid substitutions (including in-frame sequence deletions and insertions), loss-of-function alleles were predominantly responsible for the HvPDIL5-1 conferred bymovirus resistance. A strong correlation between the geographic origin and the frequency of barley accessions carrying resistance-conferring alleles was evident for each of the two host factor genes, indicating adaptive selection for bymovirus resistance in cultivated barley from East Asia.

Marker assisted separation of resistance genes Rph22 and Rym16 Hb from an associated yield penalty in a barley: Hordeum bulbosum introgression line

Key messageThe resistance genesRph22andRym16Hbtransferred into barley fromHordeum bulbosumhave been separated from a large yield penalty locus that was present in the original introgression line ‘182Q20’.AbstractThe Hordeum bulbosum introgression line ‘182Q20’ possesses resistance to barley leaf rust (Rph22) and Barley mild mosaic virus (Rym16Hb) located on chromosome 2HL. Unfortunately, this line also carries a considerable yield penalty compared with its barley genetic background ‘Golden Promise’. Quantitative trait locus (QTL) mapping of the components of yield (total yield, thousand grain weight, hectolitre weight, percentage screenings and screened yield) was performed using 75 recombinant lines derived from the original ‘182Q20’ introgression line. A QTL for the yield penalty was located in the proximal region of the introgressed segment. Marker assisted selection targeting intraspecific recombination events between overlapping H. bulbosum introgression segments was used to develop the lines ‘372E’ and ‘372H’ which feature genetically small introgressions around Rph22. Further yield trials validated the separation of both Rph22 and Rym16Hb from the proximal yield penalty. These results, combined with molecular markers closely linked to Rph22 and Rym16Hb, make these resistance genes more attractive for barley breeding.

Linkage mapping of Barley yellow dwarf virus resistance in connected populations of maize

BackgroundWith increasing winter temperatures, Barley yellow dwarf virus (BYDV) is expected to become an increasing problem in maize cultivation in Germany. Earlier studies revealed that BYDV has a negative impact on maize performance. Molecular markers would accelerate the development of BYDV resistant maize. Therefore, the objectives of this study were (i) the identification of quantitative trait loci (QTL) for BYDV resistance in five connected segregating maize populations in a field experiment and (ii) their comparison with the QTL detected under greenhouse conditions.ResultsIn linkage analyses of the traits virus extinction, infection rate, and the symptom red edges, a highly associated major QTL was identified on chromosome 10. This QTL explained 45% of the phenotypic variance for the traits virus extinction and infection rate and 30% for the symptom red edges.ConclusionWe could show that BYDV resistance traits are oligogenically inherited. The QTL on chromosome 10 could be observed in the connected linkage analyses and in the single population analyses. Furthermore, this QTL could also be confirmed in the greenhouse experiment. Our results let suggest that this QTL is involved in multiple virus resistance and the markers are promising for marker assisted selection.

High resolution mapping of resistance genes against barley mosaic disease and Barley yellow dwarf virus

Ryegrass (Lolium spec.) is the most important cool-season forage crop in temperate regions. Though, the seed production is considerably affected by several fungal and bacterial obligate biotrophic pathogens. The overall purpose of this study is directed to developing ryegrass cultivars with multiple pathogen resistance and agronomic adaption to Germany’s agricultural conditions. This aim shall be achieved by combining genes for resistances to stem rust, crown rust and bacterial wilt. The pyramidisation shall be accomplished by the use of specific molecular markers which will be derived by bulked segregant analysis combined with next generation sequencing based massive analysis of cDNA ends (MACE) transcriptome profiling. RNA was isolated from bulks of infected and noninfected leaf segments from susceptible and resistant genotypes of various fullsibling mapping populations (n ≥ 200) and their respective parental lines for every investigated pathogen. After MACE was performed, bioinformatic analysis detects SNPs and transcripts that were exclusively expressed in the resistant bulk. Thus, 30 molecular markers were genetically mapped to a 50.8 cM spanning region surrounding the stem rust resistance locus LpPg1. The development of this high efficient molecular selection tool marks MACE as a fast and reliable method that detects polymorphisms for genetic mapping of candidate genes and obtains to be the method of choice for investigating the molecular and genetic base of resistances to stem rust, crown rust and bacterial wilt.The current production systems in arable farming have reached their limits. Sizes of machinery are continuously increasing. Compaction and limits on the road are the consequences. Productionrelated restrictions like nitrogen pressure and development of resistances against plant protection products are further problems. Last but not least, the sociopolitical acceptance of crop production is questioned in public opinion. Due to these circumstances the question arises if the system of crop farming which has been adapted to the machinery available on the market is the right strategy for the future. Why not going the other way round and decide what a plant production system has to look like to be at an optimum and then decide what kind of machinery is needed to cultivate? Following this idea the plants must be in the focus.