Multigene Families of Powdery Mildew Resistance Genes in Locus Mla on Barley Chromosome 5

A review of data on powdery mildew resistance genes in the Mla locus of barley reveals that there are at least 12 clusters of genes present, each comprising one Mla gene and one or more closely linked, additional resistance genes. Tentative designations are listed for 16 additional resistance genes. Many sources of powdery mildew resistance in barley appear to harbour multigene families in the Mla region, not single ‘superior’genes.     

New molecular markers linked to qualitative and quantitative powdery mildew and scald resistance genes in barley for dry areas

A partial genetic linkage map was constructed on 71 doubled-haploid lines derived from a cross between the barley lines Tadmor and WI2291 with 181 molecular markers. The segregating population was used to detect markers linked to the gene Mlg conferring resistance to powdery mildew (Erysiphe graminis f. sp. hordei) and to genes for quantitative resistance to scald (Rhynchosporium secalis). The gene Mlg on chromosome 4H was flanked by two AFLP markers at a distance of 2.0 and 2.4 cM, respectively. QTLs for resistance to scald were detected on chromosomes 2H and 3H. This association of molecular markers with qualitative and quantitative disease resistance loci represents a valuable starting-point for marker-assisted selection. This revised version was published online in July 2006 with corrections to the Cover Date.     

Candidate markers for powdery mildew resistance genes from wild barley PI284752

PI284752, an accession of wild barley (Hordeum vulgare ssp. spontaneum) resistant to powdery mildew caused by Blumeria graminis f.sp. hordei, was studied with the aim of identifying genes involved in powdery mildew resistance. An F₂ population (456 plants) was established from a cross between the winter barley variety ‘Tiffany’ and PI284752. This cross demonstrated a two-locus model of resistance. Linkage analysis using polymorphic DNA markers was carried out on 180 plants. The RGH1a gene sequence from the Mla locus was used as a source for developing the RGH1aE2I2 marker. By interval mapping on chromosome 1HS, one resistance gene was found to be tightly linked with RGH1aE2I2 and it was found to be located 2 cM from GBMS062. In F₂ plants exhibiting resistance reaction type (RT) 0, specific DNA fragments for the RGH1aE2I2 marker were amplified. In plants with RT1 to RT2-3, the resistance was conferred exclusively by the second R gene that we identified, which is linked with Bmac0134 and GBMS247 on chromosome 2HS. The aforementioned markers may be valuable candidates for marker-assisted selection of resistant genotypes conferred by one or both genes.     

Search for novel genes for resistance to powdery mildew (Sphaerotheca fuliginae) in cucumber (Cucumis sativus)

Summary The current powdery mildew (Sphaerotheca fuligninea) resistant cucumber varieties suffer from leaf chlorosis during autumn, winter and early spring cultivation in the Netherlands. Therefore screening was carried out for novel powdery mildew resistance genes. From 177 accessions, derived from different sources, 108 accessions proved to be partially resistant to S. fuliginea. Crosses were made with 53 resistant accessions to distinguish the presence of novel genes. It is likely that the accessions C. sativus 2145, C. sativus LV 41, PI 188807, Vladivostokij, White and Yellow 1 have one or more recessive powdery mildew resistance genes, different from powdery mildew resistance genes of the line NPI, which was used for variety breeding. Powdery mildew resistance tests with S. fuliginea give similar results in different regions of the world.Abbreviations pmr powdery mildew resistance     

Molecular mapping of powdery mildew resistance genes in wheat: A review

Powdery mildew, caused by Blumeria graminis f. sp. tritici (syn. Erysiphe graminis f. sp. tritici), is one of the most important diseases of common wheat (Triticum aestivum L.) worldwide. Molecular mapping and cloning of genes for resistance to powdery mildew in hexaploid wheat will facilitate the study of molecular mechanisms underlying resistance to powdery mildew diseases and help understand the structure and function of powdery mildew resistance genes, and permit marker-assisted selection in breeding programs. So far, 48 genes/alleles for resistance to powdery mildew at 32 loci have been identified and located on 16 different chromosomes, of which 21 resistance genes/alleles have been tagged by restriction fragment length polymorphisms (RFLPs), random-amplified polymorphic DNAs (RAPDs), amplified fragment length polymorphisms (AFLPs), sequence characterized amplified regions (SCARs), sequence-tagged sites (STS) or simple sequence repeats (SSRs). Several quantitative trait loci (QTLs) for adult plant resistance (APR) to powdery mildew have been associated with molecular markers. The detailed information on chromosomal location and molecular mapping of these genes has been reviewed. Isolation of powdery mildew resistance genes and development of valid molecular markers for pyramiding resistance genes in breeding programs is also discussed.     

EcoTILLING for the identification of allelic variation in the powdery mildew resistance genes mlo and Mla of barley

In this investigation the successful implementation of a CEL I‐based mutation detection technique for the discovery and detection of DNA polymorphism in the genes mlo and Mla of barley is described. The technique is called EcoTILLING, which is a high‐throughput method to detect and discover new point mutations and small insertions/deletions in DNA. That the method not only reveals polymorphism between different alleles but can also be used as a powerful genetic marker is demonstrated. The genes mlo and Mla are involved in the defence of barley against the fungal pathogen powdery mildew. The powdery mildew resistance gene mlo is a single copy gene, whereas multiple alleles exist at the Mla locus. With EcoTILLING it was possible to identify point mutations and deletions in each of the 11 mlo mutants tested. For Mla 25 natural barley variants were tested, and although the identification was complex due to the presence of highly similar paralogues of Mla, most of the recently identified alleles from Hordeum vulgare ssp. spontaneum were identified. This method offers the possibility to combine different mlo alleles with different Mla alleles from wild barley to obtain cultivars with more durable resistance.     

Isolation, chromosomal location, and expression analysis of putative powdery mildew resistance genes in wheat (Triticum aestivum L.)

Special and degenerate primers are designed according to the conservative sequence of barley powdery mildew resistance genes Mla1, Mla6, and Mla13. Two wheat Mla-like orthologs, TaMla-2 and TaMla-3 are cloned and sequenced from the cDNA of wheat resistant-powdery mildew line TAM104R by RT-PCR method. TaMla-2 and TaMla-3 encode distinct but highly related coiled-coil nucleotide-binding site leucine-rich repeat type (NBS-LRR) resistant disease proteins and both reveal about 74 and 81% identity with amino acid sequence of Mla1, respectively. They are multiple copies in wheat genomes, one copy of them is mapped on wheat chromosome 1AL and two on 1BL using Chinese Spring nulli-tetra-somic lines and ditelosomic lines of 1A, 1B and 1D in southern analysis. This result suggests that may be the two Mla-like genes originated from the two diploid ancestral genomes, respectively. The expression pattern analysis of semi-quantitative PCR shows the TaMla genes are mainly expressed in leaf and sheath, and expression level is enhanced in organs infected by Erysiphe graminis, suggesting that TaMla-2 and TaMla-3 are powdery mildew resistance related-genes in wheat. Electronic Supplementary Material Supplementary material is available for this article at     

A new resistance gene to powdery mildew identified in <Emphasis Type="Italic">Solanum neorossii</Emphasis> has been localized on the short arm of potato chromosome 6

A new resistance (R) gene to powdery mildew has been identified and characterized in a population derived from the wild potato species, Solanum neorossii under natural infection in the greenhouse. The segregation of resistance has revealed that this R gene is controlled by a single monogenic and dominant gene designated Rpm-nrs1. Analysis of the DNA sequence on an internal transcribed spacer (ITS) region of the pathogen genome suggests that the pathogen causing the powdery mildew disease is either Golovinomyces orontii or G. cichoracearum. The resistance locus was localized to the short arm of chromosome 6 where several disease R genes already identified in potato and tomato are known to reside. The resistance locus cosegregated in 96 progeny with three AFLP markers and one PCR marker. The sequences of the two cosegregating AFLP markers are highly homologous to Mi-1 conferring resistance to nematode, potato aphid and whitefly and Rpi-blb2 conferring resistance to late blight. The results in this study will facilitate the cloning of this gene conferring resistance to powdery mildew.     

Resistance to powdery mildew in selections from Tunisian landraces of barley

Two-hundred and thirty-two accessions of barley landraces collected from Tunisia were screened for resistance to powdery mildew. A number of race-specific genes were detected using the detached leaf technique. Among the 232 accessions tested, 169 were susceptible to powdery mildew, 20 were resistant and 43 showed differential reactions to the three isolates of powdery mildew used. An attempt was made to determine the number of genes, the types of gene, the types of gene action and the gene loci in 20 resistant accessions. Three types of cross were made: (1) the accessions were crossed to the susceptible variety ‘Pallas’, (2) the accessions were crossed with ‘Pallas’ isolines, and (2) accessions with identical powdery mildew reaction patterns were intercrossed. Three isolates of Erysiphe graminis f. sp. hordei were used: Bzm-1, KM 18-75, R13C. A number of different resistance genes were detected among the 19 resistant accessions. Surprisingly, segregation indicating single genes only were detected with the isolates used. Some of these genes could be associated with loci already known. In 19 cases a dominant and in one a recessive mode of inheritance was detected. The recessive gene was not located at the mlo locus. This investigation represents the first systematic study of race-specific genes for powdery mildew resistance in Tunisian landraces. The newly identified sources of resistance may be used in many strategies of breeding for disease resistance.     

Hordeum chilense resistance to powdery mildew and its potential use in cereal breeding

Summary Hordeum chilense is a wild barley with high crossability with Triticum, Hordeum and Secale. Its amphiploid with wheat, tritordeum, has potential as a new crop. H. chilense is highly resistant to the powdery mildew diseases of both wheat and barley. Whereas tritordeum is resistant to barley powdery mildew, its reaction to wheat powdery mildew is similar to that of its wheat parent. However H. chilense contributes to a reduced density of mildew colonies. This quantitative resistance of tritordeum is diluted at higher ploidy levels.     

Spectrum of resistance conferred by ML-O powdery mildew resistance genes in barley

Summary Ten barley mutants and five Ethiopian barley lines representing 11 independently arisen powdery mildew resistance genes in the ml-o locus were tested at the seedling stage to cultures of the powdery mildew fungus from Europe, Israel, USA. Canada, and Japan. They were resistant with infection type 0/(4) in all tests. They were also resistant to field populations of the pathogen when scored in disease nurseries at more than 78 locations in 29 countries in Europe, the Near East, North and South America. New Zealand, and Japan. This indicates that the 11 genes confer the same, world-wide spectrum of powdery mildew resistance. They have no effect on several other barley diseases such as stripe rust and leaf rust.Part of the research reported here was carried out under IAEA Research Agreement No 1043 and Research Contract No 139-74-1 BIO DK with the European Atomic Energy Community.     

Discovery,characterization and exploitation of Mlo powdery mildew resistance in barley

Summary Mlo resistance to barley powdery mildew is a relatively new kind of resistance. It was originally described in a powdery mildew resistant barley mutant in 1942 and has been mutagen-induced repeatedly since then. About 1970 it was also recognized in barley landraces collected in Ethiopia in the 1930s. It is unique in that 1) Mlo resistance does not conform to the gene-for-gene system; 2)mlo genes originating from different mutational events map as non-complementing recessive alleles in one locus; 3) all alleles confer the same phenotype, though with small quantitative differences; 4) it is effective against all isolates of the pathogen; and 5) the resistance is caused by rapid formation of large cell wall appositions at the encounter sites preventing penetration by the fungus. Powdery mildew isolates with elevated Mlo aggressiveness have been produced on barley in the laboratory, but have not been found in nature. Mlo resistance is considered very durable. The exploitation of Mlo resistance has been hampered by pleiotropic effects of themlo genes, vix. necrotic leaf spotting and reduced grain yield, but they have been overcome by recent breeding work. During the 1980s Mlo-resistant spring barley varieties have become cultivated extensively in several European countries, in 1990 on about 700,000 ha.     

Genetic linkage of the Yr1 and Pm4 genes for stripe rust and powdery mildew resistances in wheat

Summary Genes Yr1 for resistance to stripe rust and Pm4a for resistance to powdery mildew showed linkage of 2.0±0.6 cM. Close repulsion linkage probably accounts for the absence in European wheats of genes Yr1 and Pm4b in combination.     

Genes for scald resistance from wild barley (Hordeum vulgare ssp spontaneum) and their linkage to isozyme markers

Summary Accessions of Hordeum vulgare ssp. spontaneum, the wild progenitor of barley, collected in Israel (70), Iran (15) and Turkey (6) were screened for seedling response to four isolates of Rhynchosporium secalis, the pathogen causing leaf scald in barley. Resistance was very common in the collection (77%) particularly among accessions from the more mesic sites (90%). The genetics of this resistance were investigated in fifteen backcross (BC₃) lines that contained an isozyme variant from H.v. ssp. spontaneum in a H.v. ssp. vulgare (cv. Clipper) background and were resistant to scald. Segregation in the BC₃F₂ families conformed with a single dominant resistance gene in 9 of the 15 lines. Scald resistance and the isozyme marker were closely linked in three of the BC₃-lines, loosely linked in four and unlinked in the remaining eight. Scald resistance genes were identified on barley chromosomes 1, 3, 4 and 6. Crosses between several of the scald resistant BC-lines together with the linkage data indicated that at least five genetically independent resistances are available for combining together for deployment in barley. The linkage of scald resistance in several BC₃-lines to the isozyme locus Acp2 is of special interest as this locus is highly polymorphic in wild barley.     

Sources of resistance to diseases of sugar beet in related <Emphasis Type="Italic">Beta</Emphasis> germplasm: I. Foliar diseases

Resistance to four foliar diseases of sugar beet (Beta vulgaris ssp. vulgaris), virus yellows caused by Beet mild yellowing virus (BMYV) and Beet yellows virus (BYV), powdery mildew (Erysiphe betae) and Cercospora leaf spot (Cercospora beticola), was assessed in up to 600 accessions of closely related wild and cultivated Beta species. Most accessions were from the Section Beta, a taxon containing types most closely related to, and sexually compatible with, sugar beet and therefore most valuable for use in crop improvement. Between 1–12% of accessions were highly resistant (resistance scores of 2 on an international standardised resistance scale of 1–9) to these diseases. These levels, however, underestimate the potential number of resistant sources available from this section as some accessions with intermediate mean resistance scores contained a significant proportion of highly resistant plants within segregating populations. Variation in resistance to all diseases except BYV was observed within the Section Beta. Much higher levels of resistance were observed, and more frequently, in more distantly related sections of the genus Beta. Accessions of the Section Corollinae were highly resistant to both viruses (>62% of accessions tested), but less so to Cercospora (15%) and they were very susceptible to powdery mildew. Section Procumbentes accessions were highly resistant to BMYV and Cercospora (100%) but less so to powdery mildew (50%) and BYV (20%). However, sexual incompatibility between these sections and sugar beet make utilisation of these sources impractical using conventional breeding methods.     

Identification of QTLs for powdery mildew and scald resistance in barley

A population of 103 recombinant inbred lines (RILs, F₉-derived lines) developed from the two-row spring barley cross L94 × ‘Vada’ was evaluated under field conditions for resistance against powdery mildew (Blumeria graminis f.sp. hordei) and scald (Rhynchosporium secalis). Apart from the major resistance gene mlo on chromosome 4 (4H), three QTLs (Rbgq1, Rbgq2 and Rbgq3) for resistance against powdery mildew were detected on chromosomes 2 (2H), 3 (3H), and 7 (5H), respectively. Rbgq1 and Rbgq2 have not been reported before, and did not map to a chromosome region where a major gene for powdery mildew had been reported. Four QTLs (Rrsq1, Rrsq2, Rrsq3 and Rrsq4) for resistance against scald were detected on chromosomes 3 (3H), 4 (4H) and 6 (6H). All four mapped to places where QTLs for scald resistance had been reported before in different populations.     

Associations of simple sequence repeats with quantitative trait variation including biotic and abiotic stress tolerance in Hordeum spontaneum

A total of 33 simple sequence repeats (SSRs) was analyzed in 52 genotypes of Hordeum spontaneum originally collected from two different soil types (Terra rossa and Basalt) at Tabigha in Israel. Data on the performance of developmental, morphological, and yield‐related traits under well‐watered control and water‐stress conditions were available from previous experimentation, and powdery mildew susceptibility was scored. Regression analyses based on SSR allele class differences were performed. Highly significant associations were detected at the SSR loci Bmac181 (on chromosome 4H) and Bmac316 (6H) for water ‐stress tolerance and powdery mildew resistance, respectively. The study shows that association mapping using SSRs and genetically diverse germplasm provides an effective means of relating genotypes to complex quantitative phenotypes.     

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.     

The resistance of Hordeum bulbosum and its hybrids with H. vulgare to common fungal pathogens

Summary Two tetraploid and two diploid clones of Hordeum bulbosum were screened for resistance to five isolates of powdery mildew which are virulent on cultivated barley. All were resistant and this resistance was also expressed in hybrids with H. vulgare. The tetraploid genotypes were also resistant to isolates of yellow rust and brown rust. These results show that H. bulbosum contains useful genes for resistance to these diseases and that there is a potential to transfer these into cultivated barley.     

The oat line Pc54 as a source of resistance to crown rust,stem rust and powdery mildew in Europe

Summary The oat line Pc54 was found to be resistant to powdery mildew under both field and glasshouse conditions. The ratio of resistant to susceptible F₂ and F₂ progeny of a cross between a selection from the Pc54 line (Cc7422) and a susceptible cultivar (Selma) showed that, in addition to carrying the crown rust resistance gene Pc54 and the pg15 gene for stem rust resistance, the mildew resistance of the Pc54 line was conditioned by a single incompletely dominant gene along with additional factors which modified the expression of resistance. Previous results, that there was no linkage between genes Pc54 and Pg15, were confirmed. In addition, there was no evidence of linkage between the mildew resistance gene and gene Pc54. Evaluation of selections from within the Pc54 line showed that the expression of both stem rust and mildew resistance was modified by, or linked to, plant height. The effectiveness of genes Pc54 and Pg15, as measured by virulence frequencies, in central and eastern Europe is described.