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.     

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.     

A new powdery mildew resistance gene: Introgression from wild emmer into common wheat and RFLP-based mapping

An Israeli accession (TTD140) of wild emmer, Triticum turgidum var. dicoccoides, was found resistant to several races of powdery mildew. Inoculation of the chromosome-arm substitution lines (CASLs) of TTD140, in the background of the Israeli common wheat cultivar ‘Bethlehem’ (BL), with five isolates of powdery mildew revealed that only the line carrying the short arm of chromosome 2B of wild emmer (CASL 2BS) exhibited complete resistance to four of the five isolates. To map and tag the powdery mildew resistance gene, 41 recombinant substitution lines, derived from a cross between BL and CASL 2BS, were used to construct a linkage map at the gene region. The map, which encompasses 69.5 cM of the distal region of chromosome arm 2BS, contains six RFLP markers, a morphological marker (glaucousness inhibitor, W1 ^I), and the powdery mildew resistance gene. Segregation ratios for resistance in F₂ of BL × CASL 2BS and in the recombinant lines, combined with the susceptability of F₁ progeny to all tested isolates, indicate that resistance is controlled by a single recessive allele. This alleleco-segregated with a polymorphic locus detected by the DNA marker Xwg516, 49.4 cM from the terminal marker Xcdo456. The new powdery mildew resistance gene was designated Pm26. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

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.     

Molecular characterization of a novel powdery mildew resistance gene Pm30 in wheat originating from wild emmer

Powdery mildew caused by Erysiphe graminis f. sp. tritici is one of the most important wheat diseases in many regions of theworld. A powdery mildew resistance gene, originating from wild emmerwheat (Triticum dicoccoides) accession `C20', from Rosh Pinna, Israel,was successfully transferred to hexaploid wheat through crossing andbackcrossing. Genetic analysis indicated that a single dominant genecontrols the powdery mildew resistance at the seedling stage. SegregatingBC₁F₂ progenies of the cross 87-1/C20//2*8866 wereused for bulked segregant analysis (BSA). The PCR approach was used togenerate polymorphic DNA fragments between the resistant and susceptibleDNA pools by use of 10-mer random primers, STS primers, and wheatmicrosatellite primers. Three markers, Xgwm159/430,Xgwm159/460, and Xgwm159/500, were found to be linked tothe resistance gene. After evaluating the polymorphic markers in twosegregating populations, the distance between the markers and the mildewresistance gene was estimated to be 5–6 cM. By means of ChineseSpring nullisomic-tetrasomics and ditelosomics, the polymorphic markersand the resistance gene were assigned to chromosome arm 5BS and werephysically mapped on the gene rich regions of fragment length (FL) 0.41–0.43 by Chinese Spring deletion lines. As no powdery mildew resistancegene has been reported on chromosome arm 5BS, the mildew resistancegene originating from C20 should be a new gene and is designated Pm30.     

Identification of RAPD markers closely linked to the mlo-locus in barley

Developing resistance to powdery mildew, Erysiphe graminis f.sp. hordei, is a major goal of many barley breeding programmes. Several resistance genes have been tagged or mapped with molecular markers. The mlo gene confers durable resistance towards all known isolates of the pathogen. In this study, RAPD markers and bulked segregant analysis were used to determine PCR-based markers linked to the mlo-locus. Sixty doubled haploid lines from a cross between an isogenic line of ‘Ingrid’ carrying the mlo11 allele and a susceptible cv. ‘Pokko’ were used as plant material. Seven linked RAPD markers were found, the closest lying 1.6 cM away from the resistance gene. When eight barley varieties were assayed for the presence of this band, F4-980, it was found in the resistant varieties but not in the susceptible ones. The linked marker bands could be amplified from DNA-samples prepared by using three different methods, including a quick squash technique. PCR-based markers linked to the resistance gene can be used as tools for selection in breeding programmes.     

Molecular mapping of QTLs for non-parasitic leaf spot resistance and comparison of half-sib DH populations in spring barley

Quantitative trait loci (QTLs) for resistance against non-parasitic leaf spots (NPLS) were first characterized in a spring barley double haploid population derived from the cross IPZ 24727/Barke (Behn et al., 2004). The aim of the present study was to identify QTLs for NPLS resistance in the half-sibling DH population IPZ 24727/Krona and to compare them with the QTLs of the population IPZ 24727/Barke. An anther culture-derived doubled haploid population of 536 DH lines was developed from the cross IPZ 24727 (resistant)/Krona (susceptible). Field trials were performed over two years in two replications, scoring NPLS and agronomic traits that might interact with NPLS. A molecular linkage map of 1035 cM was constructed based on AFLPs, SSRs and the mlo marker. QTL analyses for NPLS identified three QTLs that accounted for 30% of the phenotypic variation. For comparison of the QTLs from each DH population, a consensus map was generated comprising 277 markers with a length of 1199 cM. In both populations, the QTLs for NPLS mapped to chromosomes 1H, 4H and 7H. A common QTL with a great effect in both populations and over all environments was localized at the mlo locus on chromosome 4H, indicating that the mlo powdery mildew resistance locus has a considerable effect on NPLS susceptibility. The steps necessary to validate the QTLs and to improve the NPLS resistance by breeding were 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.     

Resistance to powdery mildew in selections from Moroccan barley landraces

Seventy-five barley landraces from Morocco were tested for resistance to powdery mildew and a number of different resistance genes were detected. Thirty-five isolates of Blumeria graminis f. sp. hordei and the Pallas isoline differential set were used. Isolates used in the experiment had virulences corresponding to all major resistance genes used in Europe. Forty-four of the tested landraces showed resistant reactions. From each of these landraces, one to five resistant plants were selected and 92 single plant lines were created. Six lines selected from 3landraces were assumed to carry the mlo gene but they were discarded after microscopic investigation. Seventeen lines were tested in the seedling stage with 17isolates and another 69 lines were tested with 23 differential isolates. These lines showed 71 reaction spectra to isolates of powdery mildew. Eight lines (9%), 255-3-3, 282-3-4, 286-1-1, 294-2-3,294-2-4, 295-1-2, 308-1-2 and 327-2-1, selected from 7 landraces showed resistance to all isolates. Seventy-eight lines (90%) showed a resistant infection type 2with more than 50% of the isolates used. In most of the selected lines (86%) unknown genes, alone or in combination with known specific resistance genes, were detected. Four different resistance alleles (Mlat, Mla6, Mla14 and Mla1) were postulated to be present in the tested lines. The most common was Mlat, which was postulated in 35 (41%) lines. The use of newly identified sources of powdery mildew resistance in barley breeding is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

STS markers for powdery mildew resistance gene Pm6 in wheat

The powdery mildew resistance gene Pm6, transferred to common wheat from the tetraploid Triticum timopheevii, is effective in most epidemic areas for powdery mildew in China. RFLP probe BCD135 was previously associated with Pm6. In the present research, four STS primers (NAU/STS_BCD135-1, NAU/STS_BCD135-2, STS003 and STS004) were designed from the sequence data of BCD135. These primers were used for PCR amplification using the genomic DNA of resistant near-isogenic lines with Pm6 and their recurrent parent, cv. Prins. No polymorphic product was observed using primers STS003 and STS004; however, primers NAU/STS_BCD135-1 and NAU/STS_BCD135-2 amplified two and one bands, respectively, polymorphic between the resistant near-isogenic-lines and Prins. The two primers were then used to amplify the F₂ population from the cross IGV1-465 (FAO163b/7*Prins) × Prins. The amplification and the powdery mildew resistance identification data were analyzed using the software Mapmaker 3.0. The results indicated that both NAU/STS_BCD135-1 and NAU/STS_BCD135-2 were closely linked to Pm6 with a genetic distance of 0.8 cM. A total of 175 commercial varieties without Pm6 from different ecological areas of China were tested using marker NAU/STS_BCD135-2 and none of them amplified the 230 bp-specific band. This marker thus has high practicability and can be used in MAS of Pm6 in wheat breeding programs for powdery mildew resistance. Jianhui Ji and Bi Qin contributed equally to this work.     

Mapping powdery mildew resistance gene in V97‐3000 soybean

V97‐3000 is a maturity group (MG) V soybean breeding line derived from SS 516 × V90‐2592 (Vance × V81‐1325) with high stachyose, small seed and powdery mildew resistance. A total of 53 F_2:3 families were derived from a cross between V97‐3000 and a powdery mildew susceptible line V99‐5089. The 53 F_2:3 families, each with 30 plants, were grown in the greenhouse for powdery mildew evaluation, and the corresponding 53 F₂ plants were genotyped using simple sequence repeat (SSR) markers. Results showed that the 53 F_2:3 families segregated in ratio of one resistant : two segregating : one susceptible (13 : 26 : 14) and the 26 segregating F_2:3 families each exhibited a good fit to three resistant : one susceptible, indicating that resistance to powdery mildew is conditioned by a single dominant gene. The gene for powdery mildew resistance in V97‐3000 was mapped on chromosome 16 [linkage group (LG) J] flanked by Satt547 and Sat_396 on one side and Sat_393 on the other side with 3.8 cM and 3.9 cM distance, respectively. This study provides a new source of powdery mildew resistance and information of genetic location of the resistance gene and linked markers, which is useful for breeders selecting powdery mildew resistance through marker‐assisted selection (MAS) in soybean breeding programmes.     

小麦合成种M53抗白粉病基因的RAPD和SSR标记

运用RAPD和SSR技术，采用分离群体分组分析法(BSA)进行了小麦合成种M53抗白粉病基因连锁的分子标记研究。结果表明，M53的抗白粉病基因由显性单基因控制，RAPD标记OPL09-1700与抗病基因连锁，遗传距离为16.8cM。SSR标记Xgwm205也与抗白粉病基因连锁，遗传距离为9.3cM，通过SSR标记将该基因定位于5DS，标记与基因间的排列顺序     

Stability of seed oil quality traits in high and mid-oleic acid sunflower hybrids

Powdery mildew caused by Podosphaera xanthii is an important disease of melon, and race 2F is the predominant race in most areas of China. Resistance to P. xanthii race 2F in melon K7-1 was controlled by a dominant gene, designated Pm-2F, in a 106-member population of recombinant inbred lines derived from K7-1× susceptible K7-2. Using bulked segregant analysis with molecular markers, we have identified two polymorphic simple sequence repeats (SSR) to determine that Pm-2F is located on linkage group II. Comparative genomic analyses using mapped SSR markers and the cucumber genome sequence showed that the melon chromosomal region carrying Pm-2F is homologous to a 288,223 bp genomic region on cucumber chromosome (chr) 1. The SSR markers on chr 1 of cucumber, SSR02734, SSR02733 and CS27 were found linked with Pm-2F. Comparative mapping showed that two SSR markers (SSR02734 and CMBR8) flanked the Pm-2F locus and two nucleotide binding site-leucine-rich repeat resistance genes were identified in the collinear region of cucumber. A cleaved amplified polymorphic sequence (CAPS) marker was developed from the sequence of resistance genes and it delimits the genomic region carrying Pm-2F to 0.8 cM. The evaluation of 165 melon accessions and 13 race differential lines showed that the newly developed CAPS (CAPS-Dde I) marker can be used as a universal marker for effective marker assisted selection in melon powdery mildew resistance breeding. The putative resistance gene cluster provides a potential target site for further fine mapping and cloning of Pm-2F.     

Microsatellite Marker Identification of a Triticum Aestivum -Aegilops Umbellulata Substitution Line with Powdery Mildew Resistance

Summary Aegilops umbellulata acc. Y39 and Triticum carthlicum acc. PS5, immune to many powdery mildew isolates, were crossed to make an amphidiploid line Am9. The powdery mildew resistance of Am9 was transferred to common wheat cultivar Laizhou953 by crossing and backcrossing. In this study, the origin of powdery mildew resistance in a BC₃F_4:5 population derived from a cross of Am9 and Laizhou953 was identified. Microsatellite markers analysis showed that markers Xgwm257, Xgwm296, and Xgwm319, co-segregated with the powdery mildew resistance, whereas markers Xgwm210, Xgwm388/140, Xgwm388/170 and Xgwm526 were related to susceptibility and linked to resistance in repulsion. Of three markers related to resistance, Xgwm257 and Xgwm319 were codominant, whereas Xgwm296 was dominant. All three markers were Ae. umbellulata-specific indicating that resistance in the test population originated from Ae. umbellulata acc. Y39. The chromosome location and mapping of these linked microsatellite markers, the chromosome numbers of derived BC₃F_4:6 families, and chromosome pairing in F₁ plants from a cross of a homozygous resistant BC₃F_4:5 plant and Laizhou953, showed that wheat chromosome 2B was substituted by Ae. umbellulata chromosome 2U. This is the first gene conferring powdery mildew resistance transferred to wheat from Ae. umbellulata, and it should be a novel resistance gene to powdery mildew. It was temporarily designated PmY39.The first two authors made equal contributions     

SCAR and CAPS markers flanking the Brassica oleracea L. Pp523 downy mildew resistance locus demarcate a genomic region syntenic to the top arm end of Arabidopsis thaliana L. chromosome 1

We recently mapped the Pp523 locus that includes a single, dominant gene conferring resistance to downy mildew expressed in adult plants to a 75.1 cm long linkage group on a genetic linkage map of Brassica oleracea L. More recently, we identified a new AFLP marker 2.8 cm downstream from the resistance gene. The five DNA markers within an 8.5 cm region encompassing the Pp523 gene were cloned and sequenced. Three of these markers were transformed into SCARs (sequence characterised amplified regions), however, two among them were monomorphic and were analysed as CAPS (cleaved amplified polymorphic sequence) markers among the mapping population. Searched against genomic databases, the five B. oleracea DNA-marker sequences matched Arabidopsis thaliana L. gene sequences that delimit a conserved syntenic region in the top arm end of chromosome 1 of this last species. Considering the close genetic relatedness between both species, the information on this specific genomic region in A. thaliana is particularly useful for the construction of a fine-scale map of the corresponding genomic region in B. oleracea. The identified SCAR and CAPS markers can be used for marker assisted selection (MAS) in breeding programs aimed at the introgression of the Pp523 resistance locus, allowing the reliable indirect identification of plants harbouring the resistance gene with a margin of error of approximately six in ten-thousand selected plants.     

利用特异PCR引物进行分子标记辅助选择的研究

利用与抗白粉病基因相连锁的RAPD分子标记和控制1 Dy 10基因序列的特异PCR引物对贵农775的杂交组合后代进行了分子标记辅助选择.在50株F2植株中,初步筛选到具有抗白粉病基因标记和5 10亚基特异标记的9株;有抗白粉病基因标记和2 12亚基特异标记的24株;有抗白粉病基因标记,同时具有5 10亚基和2 12亚基特异标记的5株.本研究说明分子标记是检测抗病基因和辅助选择育种的有效手段.     

Identification and genetic mapping of a powdery mildew resistance gene in wild emmer (<Emphasis Type="Italic">Triticum dicoccoides</Emphasis>) accession IW72 from Israel

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a devastating disease of wheat (Triticum aestivum) in China and worldwide, causing severe yield losses annually. Wild emmer (T. dicoccoides) accession IW72 collected from Israel is resistant to powdery mildew at the seedling and adult stages. Genetic analysis indicated that the resistance was controlled by a single dominant gene, temporarily designated MlIW72. The F₂ population and F₃ families derived from a hybrid between IW72 and susceptible durum wheat line Mo75 were used for molecular mapping of the resistance gene. MlIW72 was linked with SSR loci Xgwm344, Xcfa2040, Xcfa2240, Xcfa2257 and Xwmc525 on the long arm of chromosome 7A. In addition, two STS markers, MAG2185 (derived from RFLP marker PSR680) and MAG1759 (developed from EST CD452874), were mapped close to MlIW72. All these markers were physically located in the terminal bin 0.86–1.00 of 7AL. The chromosome location and genetic mapping results suggested that the powdery mildew resistance gene identified in wild emmer accession IW72 might be a new allele at the Pm1 locus or a new locus closely linked to Pm1.     

Molecular and cytogenetic identification of new wheat-Dasypyrum breviaristatum additions conferring resistance to stem rust and powdery mildew

Two cytologically stable wheat-Dasypyrum breviarisatatum addition lines, Y93-1-6-6 and Y93-1-A6-4, were identified by integrated molecular and cytogenetic techniques. C-banding and genomic in situ hybridization (GISH) showed that Y93-1-6-6 and Y93-1-A6-4 were different wheat-D. breviaristatum additions. A total of 51 markers (primer/enzyme combinations), including 6 PCR-based Landmark Unique Gene (PLUG) markers and 45 Sequence-Tagged-Site (STS) markers, were selected from 3,774 primer/enzyme combinations to further characterize these two additions. Marker haploytpes suggested that both D. breviaristatum chromosomes in Y93-1-6-6 and Y93-1-A6-4 were rearranged. Stem rust resistance screening indicated that both additions were highly resistant to race RKQQC, whereas only Y93-1-6-6 was resistant to race TTKSK (Ug99). Powdery mildew resistance screening showed that only Y93-1-6-6 was resistant. Pedigree analysis suggested that the stem rust and powdery mildew resistance of Y93-1-6-6 was derived from D. breviaristatum, indicating that the D. breviaristatum chromosomes in Y93-1-6-6 possess a new powdery mildew resistance gene(s), and new stem rust resistance gene(s). These two additions could be used as stem rust or powdery mildew resistance sources in wheat breeding programs.