Molecular mapping of a fertility restoration locus (Rfm1) for cytoplasmic male sterility in barley (Hordeum vulgare L.)

The Rfm1a gene restores the fertility of msm1 cytoplasmic male-sterile lines in barley. We identified three RAPD markers linked to the Rfm1 locus (CMNB-07/800, OPI-18/900, and OPT-02/700) using isogenic lines and segregating BC₁F₁ and F₂ populations. Using a previously developed linkage map of barley, we located CMNB-07/800 and OPT-02/700 beside MWG2218 on chromosome 6HS. The linkage between MWG2218 and the Rfm1 locus was demonstrated using the segregating BC₁F₁ and F₂ populations. To confirm the chromosomal locations of these markers, we converted them to STSs and tested against two sets of wheat–barley chromosome addition lines. These STS markers, CMNB-07/800, OPT-02/700, and MWG2218, were amplified only in the addition lines possessing the chromosome 6H, thereby providing additional evidence the Rfm1 locus is located on chromosome 6H. Homoeologous relationships among fertility restoration genes in Triticeae are discussed. Received: 27 March 2000 / Accepted: 25 June 2000     

RFLP mapping of BaYMV resistance gene rym3 in barley (Hordeum vulgare)

The rym3 (formerly designated ym3) gene conferring resistance to barley yellow mosaic virus (BaYMV) is effective against all strains of the virus but up to now has not been mapped to any chromosome. We performed a linkage analysis, using DNA extracted from individually harvested mature leaves of 153 F₂ plants derived from a cross between BaYMV-resistant cv ’Ishuku Shirazu’ carrying rym3 and susceptible cv ’Ko A’. Additionally, the F₃ lines derived from F₂ plants were grown in the BaYMV-infested field and examined for their reaction to BaYMV. Our results indicated that rym3 is located on the short arm of chromosome 5H and flanked by RFLP markers MWG28and ABG705A at distances of 7.2 and 11.7 cM, respectively. The chromosomal configuration estimated by DNA markers around rym3 and the utilization of these molecular markers for pyramiding with the BaYMV resistance genes in barley breeding programs are discussed. Received: 24 August 1998 / Accepted: 30 January 1999<@head-com-p1a.lf>Communicated by F. Salamini     

Molecular mapping of novel resistance genes against Barley Mild Mosaic Virus (BaMMV)

 In the present study three novel genes from barley accessions 10247 (ym8), Bulgarian 347 (ym9), and Russia 57 (ym11), which confer resistance to Barley Mild Mosaic Virus (BaMMV), were mapped using molecular markers. Bulked segregant analysis of four progenies segregating for resistance to BaMMV was followed by fine-scale mapping of the resistance genes using individual F₂ or BC₁F₂ plants. The resistance genes are inherited recessively and are located on the long arm of barley chromosome 4HL. A series of closely linked molecular markers are available for marker-assisted breeding programs. A marker (MWG2134) linked with resistance gene ym11 from Russia 57 was identified, which is diagnostic for the resistance gene. Received: 25 July 1997 / Accepted: 22 August 1997     

Genetic and physical mapping of blast resistance gene <Emphasis Type="Italic">Pi-42(t)</Emphasis> on the short arm of rice chromosome 12

We have identified, genetically mapped and physically delimited the chromosomal location of a new blast resistance gene from a broad spectrum resistant genotype ‘DHR9’. The segregation analysis of an F₂ progeny of a cross between a susceptible cv. ‘HPU741’ and the resistant genotype ‘DHR9’ suggested that the resistance was conditioned by a single dominant gene. A RAPD marker, OPA8₂₀₀₀, linked to the resistance gene was identified by the linkage analysis of 109 F₂ individuals. By chromosomal landing of the sequence of RAPD marker on the sequence of reference cv. Nipponbare, the gene was mapped onto rice chromosome 12. Further linkage analysis with two polymorphic simple sequence repeat (SSR) markers, RM2529 and RM1337 of chromosome 12, confirmed the chromosomal localization of the resistance gene. Based on linkage analysis of 521 susceptible F₂ plants and comparative haplotype structure analysis of the parental genotypes with SSR and sequence tagged site (STS) markers developed from the Nipponbare PAC/BAC clones of chromosome 12, the resistance gene was delimited within a 2 cM interval defined by STS marker, STS5, on the telomeric side and SSR marker, RRS6 on the centromeric side. By aligning the sequences of linked markers on the sequence of cv. Nipponbare, a ~4.18 Mb cross-over cold region near the centromere of chromosome 12 was delineated as the region of blast resistance gene. In this region, six putatively expressed NBS-LRR genes were identified by surveying the equivalent genomic region of cv. Nipponbare in the TIGR Whole Genome Annotation Database (http://www.tigr.org). NBS-LRR locus, LOC_Os12g18374 situated in BAC clone OJ1115_G02 (Ac. No. AL772419) was short-listed as a potential candidate for the resistance gene identified from DHR9. The new gene was tentatively designated as Pi-42(t). The markers tightly linked to gene will facilitate marker-assisted gene pyramiding and cloning of the resistance gene.     

Identification of a STS marker linked to the Aegilops speltoides-derived leaf rust resistance gene Lr28 in wheat

 A sequence-tagged-site (STS) marker is reported linked to Lr28, a leaf rust resistance gene in wheat. RAPD (random amplified polymorphic DNA) analysis of near-isogenic lines (NILs) of Lr28 in eight varietal backgrounds was carried out using random primers. Genomic DNA enriched for low-copy sequences was used for RAPD analysis to overcome the lack of reproducibility due to the highly repetitive DNA sequences present in wheat. Of 80 random primers tested on the enriched DNA, one RAPD marker distinguished the NILs and the donor parent from the susceptible recurrent parents. The additional band present in resistant lines was cloned, sequenced, and STS primers specific for Lr28 were designed. The STS marker (Indian patent pending: 380 Del98) was further confirmed by bulk segregation analysis of F₃ families. It was consistently present in the NILs, the resistant F₃ bulk and the resistant F₃ lines, but was absent in recurrent parents, the susceptible F₃ bulk and the susceptible F₃ lines. Received: 20 February 1998 / Accepted: 4 March 1998     

Conversion of an amplified fragment length polymorphism marker into a co-dominant marker in the mapping of the<Emphasis Type="Italic"> Rph15</Emphasis> gene conferring resistance to barley leaf rust,<Emphasis Type="Italic"> Puccinia hordei</Emphasis> Otth.

Leaf rust, caused by Puccinia hordei, is an important disease afflicting barley (Hordeum vulgare) in many production regions of the world. The leaf rust resistance gene Rph15 was identified in an accession of wild barley (Hordeum vulgare subsp. spontaneum) and is one of the most broadly effective resistance genes known. Using amplified fragment length polymorphism (AFLP) and simple sequence repeat markers, Rph15 was mapped to chromosome 2HS in an F₂ population derived from a cross between Bowman (Rph15), a Bowman backcross-derived line carrying Rph15, and the susceptible cultivar Bowman. AFLP marker P13M40 co-segregated with Rph15 in this mapping population and two others involving Bowman (Rph15) and cultivars Proctor and Nudinka. The dominant AFLP marker P13M40 was converted to a co-dominant PCR-based marker that may be useful in breeding programs employing marker-assisted selection. The allelic relationship between Rph15 and the gene Rph16, also mapping to chromosome 2HS, was studied. The lack of segregation in F₂ progeny derived from the two resistance sources indicates that Rph15 and Rph16 are alleles of the same locus.Communicated by F. Salamini     

High-resolution mapping of the Rym4/Rym5 locus conferring resistance to the barley yellow mosaic virus complex (BaMMV, BaYMV, BaYMV-2) in barley (Hordeum vulgare ssp. vulgare L.)

Soil-borne barley yellow mosaic virus disease – caused by a complex of at least three viruses, i.e. Barley mild mosaic virus (BaMMV), Barley yellow mosaic virus (BaYMV) and BaYMV-2 – is one of the most important diseases of winter barley in Europe. The two genes rym4, effective against BaMMV and BaYMV, and rym5, additionally effective against BaYMV-2, comprise a complex locus on chromosome 3HL, which is of special importance to European barley breeding. To provide the genetic basis for positional cloning of the Rym4/Rym5 locus, two high-resolution maps were constructed based on co-dominant flanking markers (MWG838/Y57c10 - MWG010/Bmac29). Mapping at a resolution of about 0.05% rec., rym4 has been located 1.07% recombination distal of marker MWG838 and 1.21% recombination proximal to marker MWG010. Based on a population size of 3,884 F₂ plants (0.013% recombination) the interval harbouring rym5 was delimited to 1.49±0.14% recombination. By testing segmental recombinant inbred lines (RILs) for reaction to the different viruses at a resolution of 0.05% rec. (rym4) and 0.019% rec. (rym5), no segregation concerning the reaction to the different viruses could be observed. AFLP-based marker saturation for rym4, using 932 PstI+2/MseI+3 primer combinations only resulted in three markers with the closest one linked at 0.9% recombination to the gene. Two of these markers detected epialleles arising from the differential cytosine methylation of PstI sites. Regarding rym5, profiling of 1,200 RAPD primers (about 18,000 loci) and 2,048 EcoRI+3/MseI+3 AFLP primer combinations (about 205,000 loci) resulted in one RAPD marker and seven AFLP markers tightly linked to the resistance gene. Flanking markers with the closest linkage to rym5 (0.05% and 0.88% recombination) were converted into STS markers. These markers provide a starting point for chromosomal walking and may be exploited in marker-assisted selection for virus resistance based on rym5.     

Mapping of powdery mildew resistance genes in a newly determined accession of Hordeum vulgare ssp. spontaneum

The accession PI466197 of wild barley (Hordeum vulgare ssp. spontaneum) with a newly identified resistance to powdery mildew caused by Blumeria graminis f.sp. hordei was studied with the aim to localise the genes determining resistance on a barley genetic map using DNA markers. Molecular analysis was performed in the F₂ population of the cross between the winter variety ‘Tiffany’ and the resistant accession PI466197, consisting of 113 plants. DNA markers, 17 simple sequence repeats (SSRs), four sequence-tagged sites (STSs) and one cleaved amplified polymorphic sequence (CAPS) marker developed from the Mla locus sequence were used for genetic mapping and a two-locus model of resistance was shown. One of the resistance genes originating from H. vulgare ssp. spontaneum PI466197 was localised between the markers RGH1aE1 and Bmac0213 on the short arm of chromosome 1H, which is the position consistent with the Mla locus. The other gene was proven to be highly significantly linked with GBMS247, Bmac0134 and MWG878 on the short arm of chromosome 2H. The flanking markers were Bmac0134 and MWG878, assigned 4 and 8 cM from the resistance gene, respectively. Until now, no gene conferring powdery mildew resistance originating from H. vulgare has been located on the short arm of barley chromosome 2H.     

RFLP mapping of the Ha 2 cereal cyst nematode resistance gene in barley

 The cereal cyst nematode (CCN), Heterodera avenae Woll., is an economically damaging pest of barley in many of the world’s cereal-growing areas. The development of CCN-resistant cultivars may be accelerated through the use of molecular markers. A number of resistance genes against the pest are well known; one of them, the single dominant Ha 2 resistance gene, has been shown to be effective against the Australian pathotype and maps to chromosome 2 of barley. Segregation analysis identified two restriction fragment length polymorphism (RFLP) markers flanking the resistance gene in two doubled-haploid populations of barley. AWBMA 21 and MWG 694 mapped 4.1 and 6.1 cM respectively from the Ha 2 locus in the Chebec×Harrington cross and 4.0 and 9.2 cM respectively in the Clipper×Sahara cross. Analysis of a further seven sources of CCN resistance in the form of near-isogenic lines (NILs) indicates that all available sources of resistance to the Australian pathotype of CCN in barley represent the Ha 2 locus. Received: 5 December 1996 / Accepted: 20 December 1996     

Chromosome landing at the Mla locus in barley (Hordeum vulgare L.) by means of high-resolution mapping with AFLP markers

 The complex Mla locus of barley determines resistance to the powdery mildew pathogen Erysiphe graminis f. sp. hordei. With a view towards gene isolation, a population consisting of 950 F₂ individuals derived from a cross between the near-isogenic lines ‘P01’ (Mla1) and ‘P10’ (Mla12) was used to construct a high-resolution map of the Mla region. A fluorescence-based AFLP technique and bulked segregant analysis were applied to screen for polymorphic, tightly linked AFLP markers. Three AFLP markers were selected as suitable for a chromosome-landing strategy. One of these AFLP markers and a closely linked RFLP marker were converted into sequence-specific PCR markers. PCR-based screening of approximately 70 000 yeast artificial chromosome (YAC) clones revealed three identical YACs harbouring the Mla locus. Terminal insert sequences were obtained using inverse PCR. The derived STS marker from the right YAC end-clone was mapped distal to the Mla locus. Received: 17 July 1998 / Accepted: 9 August 1998     

Molecular mapping of a new gene in wild barley conferring complete resistance to leaf rust (Puccinia hordei Otth)

 A dominant gene conferring resistance to all known races of Puccinia hordei Otth was identified in two accessions of Hordeum vulgare ssp. spontaneum. Using restriction fragment length polymorphism (RFLP) markers the gene was mapped on chromosome 2HS in doubled-haploid populations derived from crosses of both accessions to the susceptible cultivar L94. Until now, complete leaf rust resistance was not known to be conditioned by genetic factors on this barley chromosome. Therefore, the designation Rph16 is proposed for the gene described in this study. A series of sequence tagged site (STS) and cleaved amplified polymorphic sequence (CAPS) markers were generated by conversion of RFLP probes which originate from the chromosomal region carrying the resistance gene. Two PCR-based markers were shown to co-segregate with the Rph16 gene in both populations thus providing the basis for marker-assisted selection. Received: 20 May 1998 / Accepted: 9 June 1998     

High-resolution mapping of the barley leaf rust resistance gene Rph5 using barley expressed sequence tags (ESTs) and synteny with rice

The rapidly growing expressed sequence tag (EST) resources of species representing the Poacea family and availability of comprehensive sequence information for the rice (Oryza sativa) genome create an excellent opportunity for comparative genome analysis. Extensive synteny between rice chromosome 1 and barley (Hordeum vulgare L.) chromosome 3 has proven extremely useful for saturation mapping of chromosomal regions containing target genes of large-genome barley with conserved orthologous genes from the syntenic regions of the rice genome. Rph5 is a gene conferring resistance to the barley leaf rust pathogen Puccinia hordei. It was mapped to chromosome 3HS, which is syntenic with rice chromosome 1S. The objective of this study was to increase marker density within the sub-centimorgan region around Rph5, using sequence-tagged site (STS) markers that were developed based on barley ESTs syntenic to the phage (P1)-derived artificial chromosome (PAC) clones comprising the distal region of rice chromosome 1S. Five rice PAC clones were used as queries in a blastn search to screen 375,187 barley ESTs. Ninety-four non-redundant EST sequences were identified from the EST database and used as templates to design 174 pairs of primer combinations. As a result, 9 barley EST-based STS markers were incorporated into the ‘Bowman’ × ‘Magnif 102’ high-resolution map of the Rph5 region. More importantly, six markers, including five EST-derived STS sequences, were found to co-segregate with Rph5. The results of this study demonstrate the usefulness of rice genomic resources for efficient deployment of barley ESTs for marker saturation of targeted barley genomic regions.     

Genetic and physical mapping of <Emphasis Type="Italic">Pi36</Emphasis>(t), a novel rice blast resistance gene located on rice chromosome 8

Blast resistance in the indica cultivar (cv.) Q61 was inherited as a single dominant gene in two F₂ populations, F₂-1 and F₂-2, derived from crosses between the donor cv. and two susceptible japonica cvs. Aichi Asahi and Lijiangxintuanheigu (LTH), respectively. To rapidly determine the chromosomal location of the resistance (R) gene detected in Q61, random amplified polymorphic DNA (RAPD) analysis was performed in the F₂-1 population using bulked-segregant analysis (BSA) in combination with recessive-class analysis (RCA). One of the three linked markers identified, BA1126₅₅₀, was cloned and sequenced. The R gene locus was roughly mapped on rice chromosome 8 by comparison of the BA1126₅₅₀ sequence with rice sequences in the databases (chromosome landing). To confirm this finding, seven known markers, including four sequence-tagged-site (STS) markers and three simple-sequence repeat (SSR) markers flanking BA1126₅₅₀ on chromosome 8, were subjected to linkage analysis in the two F₂ populations. The locus was mapped to a 5.8 cM interval bounded by RM5647 and RM8018 on the short arm of chromosome 8. This novel R gene is therefore tentatively designated as Pi36(t). For fine mapping of the Pi36(t) locus, five additional markers including one STS marker and four candidate resistance gene (CRG) markers were developed in the target region, based on the genomic sequence of the corresponding region of the reference japonica cv. Nipponbare. The Pi36(t) locus was finally localized to an interval of about 0.6 cM flanked by the markers RM5647 and CRG2, and co-segregated with the markers CRG3 and CRG4. To physically map this locus, the Pi36(t)-linked markers were mapped by electronic hybridization to bacterial artificial chromosome (BAC) or P1 artificial chromosome (PAC) clones of Nipponbare, and a contig map was constructed in silico through Pairwise BLAST analysis. The Pi36(t) locus was physically delimited to an interval of about 17.0 kb, based on the genomic sequence of Nipponbare.     

Development of an STS marker tightly linked to <Emphasis Type="Italic">Yr26</Emphasis> against wheat stripe rust using the resistance gene-analog polymorphism (RGAP) technique

The gene Yr26 confers resistance to all races of Puccinia striiformis f. sp. tritici (PST), the casual pathogen of wheat stripe rust in China. Here, we report development of a molecular marker closely linked to Yr26 using a resistance gene-analog polymorphism (RGAP) technique. A total of 787 F₂ plants and 165 F₃ lines derived from the cross Chuanmai 42/Taichung 29 were used for linkage analysis. Eighteen near-isogenic lines (NILs) and 18 Chinese wheat cultivars and advanced lines with different genes for stripe rust resistance were employed for the validation of STS markers. A total of 1,711 RGAP primer combinations were used to test the parents and resistant and susceptible bulks. Five polymorphic RGAP markers were used for genotyping all F₂ plants. Linkage analysis showed that the five RGAP markers were closely linked to Yr26 with genetic distances ranging from 0.5 to 2.9 cM. These markers were then converted into STS markers, one, CYS-5, of which was located 0.5 cM to Yr26 and was closely associated with the resistance gene when validated over 18 NILs and 18 Chinese wheat cultivars and lines. The results indicated that CYS-5 can be used in marker-assisted selection targeted at pyramiding Yr26 and other genes for stripe rust resistance.     

Identification of an RFLP marker tightly linked to theHt1 gene in maize

Summary We have identified tight linkage of an RFLP marker to theHt1 gene of maize that confers resistance to the fungal pathogenHelminthosporium turcicum race 1. This was accomplished by the use of four pairs of near isogenic lines (NILs; B73, A619, W153R, and CM105), each differing by the presence or the absence of the geneHt1. SinceHt1 maps to chromosome 2, 26 clones already mapped to this chromosome were labeled and probed against Southern blots of these NILs DNA digested with three restriction enzymes:EcoRI,BamHI, andHindIII. Six markers exhibited an RFLP for at least one pair of NILs. Presumptive linkage was further tested by analyzing the segregation of five of the six markers (one was monomorphic in the cross studied) and resistance toH. turcicum race 1 on 95 F₂ individuals from the cross DF20 × LH146Ht. The results indicate a tight linkage between one of the DNA markers,UMC150B, and theHt1 gene.     

RFLP mapping of the ym4 virus resistance gene in barley

RFLP (restriction fragment length polymorphism) mapping of a recessive gene (ym4) conferring resistance to barley yellow mosaic and barley mild mosaic virus was performed using progeny of 86 F₁ anther-derived doubled haploid lines. Two closely linked RFLP markers that flank the gene at a distance of 1.2 centiMorgans were identified. Using one of these markers (MWG10) we obtained a clear differentiation between resistant and susceptible German cultivars. An analysis of a series of unrelated barley lines with probe MWG10 did not reveal additional RFLP fragments. The use of this probe for both marker-assisted selection and the generation of a high-density map around the resistance locus is discussed.     

Molecular mapping of powdery mildew resistance gene <Emphasis Type="Italic">Eg-3</Emphasis> in cultivated oat (<Emphasis Type="Italic">Avena sativa</Emphasis> L. cv. Rollo)

Powdery mildew is a prevalent fungal disease affecting oat (Avena sativa L.) production in Europe. Common oat cultivar Rollo was previously shown to carry the powdery mildew resistance gene Eg-3 in common with cultivar Mostyn. The resistance gene was mapped with restriction fragment length polymorphism (RFLP) markers from Triticeae group-1 chromosomes using a population of F₃ lines from a cross between A. byzantina cv. Kanota and A. sativa cv. Rollo. This comparative mapping approach positioned Eg-3 between cDNA-RFLP marker loci cmwg706 and cmwg733. Since both marker loci were derived from the long arm of barley chromosome 1H, the subchromosomal location of Eg-3 was assumed to be on the long arm of oat chromosome 17. Amplified fragment length polymorphism (AFLP) marker technology featured as an efficient means for obtaining markers closely linked to Eg-3.     

A transgressive segregation factor (RKN2) in Gossypium barbadense for nematode resistance clusters with gene rkn1 in G. hirsutum

Host plant resistance is an important strategy for managing root-knot nematode (Meloidogyne incognita) in cotton (Gossypium L.). Here we report evidence for enhanced resistance in interspecific crosses resulting from transgressive segregation of clustered gene loci. Recently, a major gene, rkn1, on chromosome 11 for resistance to M. incognita in cv. Acala NemX was identified using an intraspecific G. hirsutum cross with susceptible cv. Acala SJ-2. Using interspecific crosses of Acala NemX × susceptible G. barbadense cv. Pima S-7, F₁, F₂, F_2:3, backcross, and testcross Acala NemX × F₁ (Pima S-7 × SJ-2), parental entries and populations were inoculated in greenhouse tests with M. incognita. Genetic analyses based on nematode-induced root galling and nematode egg production on roots, and molecular marker analysis of the segregating interspecific populations revealed that gene rkn1 interacted with a gene (designated as RKN2) in susceptible Pima S-7 to produce a highly resistant phenotype. RKN2 did not confer resistance in Pima S-7, but when combined with rkn1 (genotype Aa or aa), high levels of resistance were produced in the F₁ and segregating F₂, F₃, and BC₁F₁ populations. One SSR marker MUCS088 was identified tightly linked to RKN2 within 4.4 cM in a NemX × F₁ (Pima S-7 × SJ-2) testcross population. Using mapped SSR markers and interspecific segregating populations, MUCS088 linked to the transgressive gene from the susceptible parent and was located in the vicinity of rkn1 on chromosome 11. Diverse genome analyses among A and D genome diploid and tetraploid cottons revealed that marker MUCS088 (165 and 167 bp) is derived from G. arboreum, A₂ diploid genome. These results demonstrated that a highly susceptible parent contributed to nematode resistance via transgressive segregation. Derived highly resistant lines can be used as improved resistance sources in cotton breeding, and MUCS088 can be used to monitor RKN2 introgression in diverse populations. The close genomic location of the transgressive resistance determinants provides an important model system for studying transgressive segregation and epistasis in plants.     

Identification and mapping of pm2026: a recessive powdery mildew resistance gene in an einkorn (Triticum monococcum L.) accession

Triticum monococcum accession TA2026 showed resistance to wheat powdery mildew. To identify the resistance gene and transfer it to common wheat, genetic analysis and molecular mapping were conducted using an F₂ population and derived F₃ families from the cross of TA2026 × M389. The results indicated that TA2026 possessed a recessive powdery mildew resistance gene. This gene was mapped to the terminal portion of chromosome 5A^mL and flanked by SSR marker loci Xcfd39 and Xgwm126. Eight RFLP markers previously mapped to the terminal chromosome 5A^mL were converted into STS markers. Three loci, detected by MAG1491, MAG1493 and MAG1494, the STS markers derived from RFLP probes CDO1312, PSR164 and PSR1201, respectively, were linked to this resistance gene with Xmag1493 only 0.9 cM apart from it. In addition, the STS marker MAG2170 developed from the tentative consensus wheat cDNA encoding the Mlo-like protein identified a locus co-segregating with Xmag1493. This is the first recessive powdery mildew resistance gene identified on chromosome 5A^m, and is temporarily designated pm2026. We have successfully transferred it to a tetraploid background, and this resistance stock will now be used as the bridge parent for its transfer to common wheat.     

Inheritance and mapping of a powdery mildew resistance gene introgressed from Avena macrostachya in cultivated oat

The powdery mildew resistance from Avena macrostachya was successfully introgressed into hexaploid oat (A. sativa). Genetic analysis of F₁, F₂, F₃ and BC₁ populations from two powdery-mildew resistant introgression lines revealed that the resistance is controlled by a dominant gene, tentatively designated Eg-5. Molecular marker analysis was conducted using bulked-segregant analysis in two segregating F₃ populations. One codominant simple sequence repeats (SSR) marker AM102 and four AFLP-derived PCR-based markers were successfully developed. The SSR marker AM102 and the STS marker ASE41M56 were linked to the gene Eg-5, with genetic distances of 2 and 0.4 cM, respectively, in both mapping populations. Three STS markers (ASE45M56, ASE41M61, ASE36M55) co-segregated with Eg-5 in one population while two (ASE45M56, ASE36M55) of them linked to Eg-5 with a genetic distance of 1 cM in another population. The gene was further mapped to be in a region corresponding to linkage group 22_44+18 in the Kanota × Ogle (KO) hexaploid oat map by comparative mapping. To our knowledge, this is the first report of mapping powdery-mildew resistance in hexaploid oat. The new resistance source of A. macrostachya, together with the tightly linked markers identified here, could be beneficial in oat breeding programmes.