Genetics of avirulence genes in Blumeria graminis f.sp. hordei and physical mapping of AVR(a22) and AVR(a12).

Powdery mildew fungi are parasites that cause disease on a wide range of important crops. Plant resistance (R) genes, which induce host defences against powdery mildews, encode proteins that recognise avirulence (AVR) molecules from the parasite in a gene-for-gene manner. To gain insight into how virulence evolves in Blumeria graminis f.sp. hordei, associations between segregating AVR genes were established. As a prerequisite to the isolation of AVR genes, two loci were selected for further analysis. AVR(a22) is located in a tightly linked cluster comprising AVR(a10) and AVR(k1) as well as up to five other AVR genes. The ratio between physical and genetic distance in the cluster ranged between 0.7 and 35 kB/cM. The AVR(a22) locus was delimited by the previously isolated gene AVR(a10) and two cleaved amplified polymorphic sequence (CAPS) markers, 19H12R and 74E9L. By contrast, AVR(a12) was not linked to other AVR genes in two crosses. Bulk segregant analysis of over 100,000 AFLP fragments yielded two markers, ETAMTG-285 and PAAMACT-473, mapping 10 and 2cM from AVR(a12), respectively, thus delimiting AVR(a12) on one side. All markers obtained for AVR(a12) mapped proximal to it, indicating that the gene is located at the end of a chromosome. Three more AVR(a10) paralogues were identified at the locus interspersed among genes for metabolic enzymes and abundant repetitive elements, especially those homologous to the CgT1 class of retrotransposons. The flanking and close markers obtained will facilitate the isolation of AVR(a22) and AVR(a12) and provide useful tools for studies of the evolution of powdery mildew fungi in agriculture and nature.     

Microsatellite markers linked to 2 powdery mildew resistance genes introgressed from Triticum carthlicum accession PS5 into common wheat.

Two dominant powdery mildew resistance genes introduced from Triticum carthlicum accession PS5 to common wheat were identified and tagged using microsatellite markers. The gene designated PmPS5A was placed on wheat chromosome 2AL and linked to the microsatellite marker Xgwm356 at a genetic distance of 10.2 cM. Based on the information of its origin, chromosome location, and reactions to 5 powdery mildew isolates, this gene could be a member of the complex Pm4 locus. The 2nd gene designated PmPS5B was located on wheat chromosome 2BL with 3 microsatellite markers mapping proximally to the gene: Xwmc317 at 1.1 cM; Xgwm111 at 2.2 cM; and Xgwm382 at 4.0 cM; and 1 marker, Xgwm526, mapping distally to the gene at a distance of 18.1 cM. Since this gene showed no linkage to the other 2 known powdery mildew resistance genes on wheat chromosome 2B, Pm6 and Pm26, we believe it is a novel powdery mildew resistance gene and propose to designate this gene as Pm33.     

Identification and mapping of a new powdery mildew resistance gene on chromosome 6D of common wheat

Powdery mildew, caused by Blumeria graminis f. sp. tritici, is one of the most serious wheat diseases. The rapid evolution of the pathogen's virulence, due to the heavy use of resistance genes, necessitates the expansion of resistance gene diversity. The common wheat line D57 is highly resistant to powdery mildew. A genetic analysis using an F(2) population derived from the cross of D57 with the susceptible cultivar Yangmai 158 and the derived F(2:3) lines indicated that D57 carries two dominant powdery mildew resistance genes. Based on mapping information of polymorphic markers identified by bulk segregant analysis, these two genes were assigned to chromosomes 5DS and 6DS. Using the F(2:3) lines that segregated in a single-gene mode, closely linked PCR-based markers were identified for both genes, and their chromosome assignments were confirmed through linkage mapping. The gene on chromosome 5DS was flanked by Xgwm205 and Xmag6176, with a genetic distance of 8.3 cM and 2.8 cM, respectively. This gene was 3.3 cM from a locus mapped by the STS marker MAG6137, converted from the RFLP marker BCD1871, which was 3.5 cM from Pm2. An evaluation with 15 pathogen isolates indicated that this gene and Pm2 were similar in their resistance spectra. The gene on chromosome 6DS was flanked by co-segregating Xcfd80 and Xmag6139 on one side and Xmag6140 on the other, with a genetic distance of 0.7 cM and 2.7 cM, respectively. This is the first powdery mildew resistance gene identified on chromosome 6DS, and plants that carried this gene were highly resistant to all of the 15 tested pathogen isolates. This gene was designated Pm45. The new resistance gene in D57 could easily be transferred to elite cultivars due to its common wheat origin and the availability of closely linked molecular markers.     

Identification and Mapping of Two New Genes Conferring Resistance to Powdery Mildew from Aegilops tauschii （Coss,） Schmal

Two powdery mildew resistance genes were Identified from Aegilops tauschll accessions Y201 and Y212 and mapped using two different F2 populations derived from the crosses between susceptible accession Y2272 and Y201, and susceptible accession Y2263 and Y212. Genetic analysis of resistance to powdery mildew Indicated that the resistance of Y201 was controlled by a single dominant gene, whereas the resistance of Y212 was controlled by a single recessive gene. We have temporarily designated these genes as PmY201 and PmY212, respectively. By bulk segregation analysis, six mlcrosatelllte markers Including Xgwm174, cfd26, cfd57, cfdl02, Xgwm583 and Xgwm639 were found to be linked to PraY201 with genetic distances of 5.2, 7.7, 9.6, 12.5, 20.2 and 22.1 cM, respectively. Five SSR markers, including cfd57, Xgwm182, cfd7, cfd102, and cfd12, were found to be linked to PmY212 with distances of 5.6, 7.2, 11.5, 14.7, and 18.5 cM, respectively. According to the locations of the linked markers, the two resistance genes were located In the 5DL region. Based on the chromosomal locations and the resistance patterns of the two genes, we propose that PmY201 and PmY212 are two novel powdery mildew resistance genes, and are suitable for marker-assisted selection.     

<Emphasis Type="Italic">Pm37</Emphasis>, a new broadly effective powdery mildew resistance gene from <Emphasis Type="Italic">Triticum </Emphasis><Emphasis Type="Italic">timopheevii</Emphasis>

Powdery mildew is an important foliar disease in wheat, especially in areas with a cool or maritime climate. A dominant powdery mildew resistance gene transferred to the hexaploid germplasm line NC99BGTAG11 from T. timopheevii subsp. armeniacum was mapped distally on the long arm of chromosome 7A. Differential reactions were observed between the resistance gene in NC99BGTAG11 and the alleles of the Pm1 locus that is also located on chromosome arm 7AL. Observed segregation in F_2:3 lines from the cross NC99BGTAG11 × Axminster (Pm1a) demonstrate that germplasm line NC99BGTAG11 carries a novel powdery mildew resistance gene, which is now designated as Pm37. This new gene is highly effective against all powdery mildew isolates tested so far. Analyses of the population with molecular markers indicate that Pm37 is located 16 cM proximal to the Pm1 complex. Simple sequence repeat (SSR) markers Xgwm332 and Xwmc790 were located 0.5 cM proximal and distal, respectively, to Pm37. In order to identify new markers in the region, wheat expressed sequence tags (ESTs) located in the distal 10% of 7AL that were orthologous to sequences from chromosome 6 of rice were targeted. The two new EST-derived STS markers were located distal to Pm37 and one marker was closely linked to the Pm1a region. These new markers can be used in marker-assisted selection schemes to develop wheat cultivars with pyramids of powdery mildew resistance genes, including combinations of Pm37 in coupling linkage with alleles of the Pm1 locus.     

QTLs for tomato powdery mildew resistance (Oidium lycopersici) in Lycopersicon parviflorum G1.1601 co-localize with two qualitative powdery mildew resistance genes

Tomato (Lycopersicon esculentum) is susceptible to the powdery mildew Oidium lycopersici, but several wild relatives such as Lycopersicon parviflorum G1.1601 are completely resistant. An F2 population from a cross of Lycopersicon esculentum cv. Moneymaker x Lycopersicon parviflorum G1.1601 was used to map the O. lycopersici resistance by using amplified fragment length polymorphism markers. The resistance was controlled by three quantitative trait loci (QTLs). Ol-qtl1 is on chromosome 6 in the same region as the Ol-1 locus, which is involved in a hypersensitive resistance response to O. lycopersici. Ol-qtl2 and Ol-qtl3 are located on chromosome 12, separated by 25 cM, in the vicinity of the Lv locus conferring resistance to another powdery mildew species, Leveillula taurica. The three QTLs, jointly explaining 68% of the phenotypic variation, were confirmed by testing F3 progenies. A set of polymerase chain reaction-based cleaved amplified polymorphic sequence and sequence characterized amplified region markers was generated for efficient monitoring of the target QTL genomic regions in marker assisted selection. The possible relationship between genes underlying major and partial resistance for tomato powdery mildew is discussed.     

Mapping of avirulence genes in the rice blast fungus, Magnaporthe grisea, with RFLP and RAPD markers

Three genetically independent avirulence genes, AVR1-Irat7, AVRI-MedNoi; and AVR1-Ku86, were identified in a cross involving isolates Guy11 and 2/0/3 of the rice blast fungus, Magnaporthe grisea. Using 76 random progeny, we constructed a partial genetic map with restriction fragment length polymorphism (RFLP) markers revealed by probes such as the repeated sequences MGL/MGR583 and Pot3/MGR586, cosmids from the M. grisea genetic map, and a telomere sequence oligonucleotide. Avirulence genes AVR1-MedNoi and AVR1-Ku86 were closely linked to telomere RFLPs such as marker TelG (6 cM from AVR1-MedNoi) and TelF (4.5 cM from AVR1-Ku86). Avirulence gene AVR1-Irat7 was linked to a cosmid RFLP located on chromosome 1 and mapped at 20 cM from the avirulence gene AVR1-CO39. Using bulked segregant analysis, we identified 11 random amplified polymorphic DNA (RAPD) markers closely linked (0 to 10 cM) to the avirulence genes segregating in this cross. Most of these RAPD markers corresponded to junction fragments between known or new transposons and a single-copy sequence. Such junctions or the whole sequences of single-copy RAPD markers were frequently absent in one parental isolate. Single-copy sequences from RAPD markers tightly linked to avirulence genes will be used for positional cloning.     

Identification of a major locus conferring resistance to powdery mildew (Erysiphe polygoni DC) in mungbean (Vigna radiata L. Wilczek) by QTL analysis.

A major locus conferring resistance to the causal organism of powdery mildew, Erysiphe polygoni DC, in mungbean (Vigna radiata L. Wilczek) was identified using QTL analysis with a population of 147 recombinant inbred individuals. The population was derived from a cross between 'Berken', a highly susceptible variety, and ATF 3640, a highly resistant line. To test for response to powdery mildew, F7 and F8 lines were inoculated by dispersing decaying mungbean leaves with residual conidia of E. polygoni amongst the young plants to create an artificial epidemic and assayed in a glasshouse facility. To generate a linkage map, 322 RFLP clones were tested against the two parents and 51 of these were selected to screen the mapping population. The 51 probes generated 52 mapped loci, which were used to construct a linkage map spanning 350 cM of the mungbean genome over 10 linkage groups. Using these markers, a single locus was identified that explained up to a maximum of 86% of the total variation in the resistance response to the pathogen.     

Genetic linkage map of melon (<Emphasis Type="Italic">Cucumis melo</Emphasis> L.) and localization of a major QTL for powdery mildew resistance

Powdery mildew caused by Podosphaera xanthii has become a major problem in melon since it occurs all year round irrespective of the growing system. The TGR-1551 melon genotype was found to be resistant to several melon diseases, among them powdery mildew. However, the corresponding resistance genes have been never mapped. We constructed an integrated genetic linkage map using an F2 population derived from a cross between the multi-resistant genotype TGR-1551 and the susceptible Spanish cultivar ‘Bola de Oro’. The map spans 1,284.9 cM, with an average distance of 3.6 cM among markers, and consists of 354 loci (188 AFLP, 39 RAPD, 111 SSR, 14 SCAR/CAPS/dCAPS, and two phenotypic traits) distributed in 14 linkage groups. QTL analysis identified one major QTL (Pm-R) on LG V for resistance to races 1, 2, and 5 of powdery mildew. The PM4-CAPS marker is closely linked to the Pm-R QTL at a genetic distance of 1.9 cM, and the PM3-CAPS marker is located within the support interval of this QTL. These codominant markers, together with the map information reported here, could be used for melon breeding, and particularly for genotyping selection of resistance to powdery mildew in this vegetable crop species.     

抗白粉病基因PmCH1302的遗传分析及染色体定位

CH1302是以来源于中间偃麦草的八倍体小偃麦TAI7047为桥梁亲本选育的高抗白粉病的小麦新品系,对白粉菌多个流行小种均表现出良好抗性。为了解其抗白粉病基因来源及其在染色体上的位置,对绵阳11×CH1302的F_1、F_2及F_(2∶3)家系进行了遗传分析,推断其抗白粉病基因可能来源于中间偃麦草,暂将其命名为PmCH1302。利用i Select 90K SNP芯片对抗、感病池进行扫描,发现位于2AL染色体上的多态性位点最多,为313个,占全部多态性位点的9.79%,且集中于2AL染色体100~105 c M和150~155 cM两个区域附近。在上述位点选取SSR标记,筛选出3对与Pm CH1302连锁的分子标记,Xwmc522、Xgwm356和Xgwm526,其中Xgwm356和Xgwm526位于Pm CH1302两侧,连锁距离分别为3.1 c M和7.8 cM。利用遗传图谱以及中国春缺体、双端体将PmCH1302定位于小麦2AL染色体上。进一步与位于2AL上的Pm4、Pm50比较发现,PmCH1302可能是位于2AL上的一个新基因或等位基因。     

Identification of QTLs for resistance to powdery mildew and SSR markers diagnostic for powdery mildew resistance genes in melon (Cucumis melo L.)

Powdery mildew caused by Podosphaera xanthii is an important foliar disease in melon. To find molecular markers for marker-assisted selection, we constructed a genetic linkage map of melon based on a population of 93 recombinant inbred lines derived from crosses between highly resistant AR 5 and susceptible ‘Earl’s Favourite (Harukei 3)’. The map spans 877 cM and consists of 167 markers, comprising 157 simple sequence repeats (SSRs), 7 sequence characterized amplified region/cleavage amplified polymorphic sequence markers and 3 phenotypic markers segregating into 20 linkage groups. Among them, 37 SSRs and 6 other markers were common to previous maps. Quantitative trait locus (QTL) analysis identified two loci for resistance to powdery mildew. The effects of these QTLs varied depending on strain and plant stage. The percentage of phenotypic variance explained for resistance to the pxA strain was similar between QTLs (R ² = 22–28%). For resistance to pxB strain, the QTL on linkage group (LG) XII was responsible for much more of the variance (41–46%) than that on LG IIA (12–13%). The QTL on LG IIA was located between two SSR markers. Using an independent population, we demonstrated the effectiveness of these markers. This is the first report of universal and effective markers linked to a gene for powdery mildew resistance in melon.     

Microsatellite mapping of the powdery mildew resistance gene <Emphasis Type="Italic">Pm5e</Emphasis> in common wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Powdery mildew, caused by Erysiphe graminis DM f. sp. tritici (Em. Marchal), is one of the most important diseases of common wheat world-wide. Chinese wheat variety 'Fuzhuang 30' carries the powdery mildew resistance gene Pm5e and has proven to be a valuable resistance source of powdery mildew for wheat breeding. Microsatellite markers were employed to identify the gene Pm5e in a F(2) progeny from the cross 'Nongda 15' (susceptible) x 'Fuzhuang 30' (resistant). The gene Pm5e was mapped in the distal region of chromosome 7BL. Seven microsatellite markers were found to be linked to the gene Pm5e, of which two codominant markers Xgwm783 and Xgwm1267 were relatively close to Pm5e with a linkage distance of 11.0 cM and 6.6 cM, respectively. It is possible to use the 136-bp allele of Xgwm1267 in 'Fuzhuang 30' for marker-assisted selection during the wheat resistance breeding process for facilitation of gene pyramiding. The mapping information in the present study provides a starting point for fine mapping of the Pm5 locus and map-based cloning to clarify the molecular structure and function of the different alleles at the Pm5 locus. A microsatellite linkage map of chromosome 7B was constructed with 20 microsatellite loci, nine on the short arm and 11 on the long arm. This information will be very useful for further mapping of agronomically important genes of interest on chromosome 7B.     

Identification of resistance gene analogs linked to a powdery mildew resistance locus in grapevine

Oligonucleotide primers, designed to conserved regions of nucleotide binding site (NBS) motifs within previously cloned pathogen resistance genes, were used to amplify resistance gene analogs (RGAs) from grapevine. Twenty eight unique grapevine RGA sequences were identified and subdivided into 22 groups on the basis of nucleic acid sequence-identity of approximately 70% or greater. Representatives from each group were used in a bulked segregant analysis strategy to screen for restriction fragment length polymorphisms linked to the powdery mildew resistance locus, Run1, introgressed into Vitis vinifera L. from the wild grape species Muscadinia rotundifolia. Three RGA markers were found to be tightly linked to the Run1 locus. Of these markers, two (GLP1–12 and MHD145) cosegregated with the resistance phenotype in 167 progeny tested, whereas the third marker (MHD98) was mapped to a position 2.4 cM from the Run1 locus. The results demonstrate the usefulness of RGA sequences, when used in combination with bulked segregant analysis, to rapidly generate markers tightly linked to resistance loci in crop species. Received: 2 May 2001 / Accepted: 3 August 2001     

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.     

Linkage mapping of powdery mildew and greenbug resistance genes on recombinant 1RS from 'Amigo' and 'Kavkaz' wheat-rye translocations of chromosome 1RS.1AL.

Cultivated rye (Secale cereale L., 2n = 2x = 14, RR) is an important source of genes for insect and disease resistance in wheat (Triticum aestivum L., 2n = 6x = 42). Rye chromosome arm 1RS of S. cereale 'Kavkaz' originally found as a 1BL.1RS translocation, carries genes for disease resistance (e.g., Lr26, Sr31, Yr9, and Pm8), while 1RS of the S. cereale 'Amigo' translocation (1RSA) carries a single resistance gene for greenbug (Schizaphis graminum Rondani) biotypes B and C and also carries additional disease-resistance genes. The purpose of this research was to identify individual plants that were recombinant in the homologous region of.1AL.1RSV and 1AL.1RSA using both molecular and phenotypic markers. Secale cereale 'Nekota' (1AL.1RSA) and S. cereale 'Pavon 76' (1AL.1RSV) were mated and the F1 was backcrossed to 'Nekota' (1AL.1AS) to generate eighty BC1F2:3 families (i.e., ('Nekota' 1AL.1RSA x 'Pavon 76' 1AL.1RSV) x 'Nekota' 1AL.1AS). These families were genotyped using the secalin-gliadin grain storage protein banding pattern generated with polyacrylamide gel electrophoresis to discriminate 1AL.1AS/1AL.1RS heterozygotes from the 1AL.1RSA+V and 1AL.1AS homozygotes. Segregation of the secalin locus and PCR markers based on the R173 family of rye specific repeated DNA sequences demonstrated the presence of recombinant 1AL.1RSA+V families. Powdery mildew (Blumeria graminis) and greenbug resistance genes on the recombinant 1RSA+V arm were mapped in relation to the Sec-1 locus, 2 additional protein bands, 3 SSRs, and 13 RFLP markers. The resultant linkage map of 1RS spanned 82.4 cM with marker order and spacing showing reasonable agreement with previous maps of 1RS. Fifteen markers lie within a region of 29.7 cM next to the centromere, yet corresponded to just 36% of the overall map length. The map position of the RFLP marker probe mwg68 was 10.9 cM distal to the Sec-1 locus and 7.8 cM proximal to the powdery mildew resistance locus. The greenbug resistance gene was located 2.7 cM proximal to the Sec-1 locus.     

Chromosomal Location and Comparative Genomics Analysis of Powdery Mildew Resistance Gene Pm51 in a Putative Wheat-Thinopyrum ponticum Introgression Line

Powdery mildew (PM) is a very destructive disease of wheat (Triticum aestivum L.). Wheat-Thinopyrum ponticum introgression line CH7086 was shown to possess powdery mildew resistance possibly originating from Th. ponticum. Genomic in situ hybridization and molecular characterization of the alien introgression failed to identify alien chromatin. To study the genetics of resistance, CH7086 was crossed with susceptible genotypes. Segregation in F₂ populations and F_2:3 lines tested with Chinese Bgt race E09 under controlled conditions indicated that CH7086 carries a single dominant gene for powdery mildew resistance. Fourteen SSR and EST-PCR markers linked with the locus were identified. The genetic distances between the locus and the two flanking markers were 1.5 and 3.2 cM, respectively. Based on the locations of the markers by nullisomic-tetrasomic and deletion lines of ‘Chinese Spring’, the resistance gene was located in deletion bin 2BL-0.89-1.00. Conserved orthologous marker analysis indicated that the genomic region flanking the resistance gene has a high level of collinearity to that of rice chromosome 4 and Brachypodium chromosome 5. Both resistance specificities and tests of allelism suggested the resistance gene in CH7086 was different from previously reported powdery mildew resistance genes on 2BL, and the gene was provisionally designated PmCH86. Molecular analysis of PmCH86 compared with other genes for resistance to Bgt in the 2BL-0.89-1.00 region suggested that PmCH86 may be a new PM resistance gene, and it was therefore designated as Pm51. The closely linked flanking markers could be useful in exploiting this putative wheat-Thinopyrum translocation line for rapid transfer of Pm51 to wheat breeding programs.     

Cloning of two classes of PR genes and the development of SNAP markers for powdery mildew resistance loci in chestnut rose (<Emphasis Type="Italic">Rosa roxburghii</Emphasis> Tratt)

Pathogenesis-related (PR) genes were isolated from chestnut rose (Rosa roxburghii Tratt) using a PCR approach with degenerate primers designed for the conserved regions of two PR gene families: class 2 (β-1,3-glucanase) and class 5 (osmotin). Thirteen PR2 and ten PR5 genes were obtained, with a nucleotide identity that ranged from 40.1 to 99.7% and from 99.2 to 99.8%, respectively. Sequence comparison revealed the presence of single nucleotide polymorphisms (SNPs) in these sequences with, on an average, one SNP in every 64-bp fragment for the PR2 genes and one in every 68-bp fragment for the PR5 genes. A total of 23 primers were used to genotype these SNPs for use in developing single nucleotide-amplified polymorphisms (SNAP) markers. One marker (Glu7) was found to be linked to powdery mildew resistance loci. Based on genetic mapping of a segregating F₁ population, we determined that 16 of the 23 SNAP markers formed one group and subsequently detected a quantitative trait locus that accounted for 12% of the variation in the powdery mildew resistance phenotype. The results of this study provide a first insight into the genomic structure of PR genes and show that the candidate gene approach in combination with SNAP markers is an attractive strategy to search for powdery mildew resistance loci in chestnut rose.     

RFLP markers linked to powdery mildew resistance genes Pm1, Pm2, Pm3, and Pm4 in wheat.

Near-isogenic lines (NILs) and their recurrent parent Chancellor (Cc) were used to identify restriction fragment length polymorphic markers linked to powdery mildew (Blumeria graminis (DC.) E.O. Speer f.sp. tritici) resistance genes Pm1, Pm2, Pm3, and Pm4 in wheat (Triticum aestivum L. em. Thell). By mapping these polymorphic markers in F2 progenies from crosses of the NILs with Cc, it was found that Pm1 cosegregated with a polymorphic locus detected by DNA probe CDO347; Pm2 was linked to a locus detected by probe BCD1871 with a distance of 3.5 cM; Pm3b was linked to a locus detected by probe BCD1434 with a distance of 1.3 cM; Pm4a cosegregated with Xbcd1231-2A(2) and Xcdo678-2A, and was closely flanked by Xbcd1231-2A(1) and Xbcd292-2A both with a distance of 1.5 cM. Aneuploid mapping of these markers indicated that locus Xcdo347-7A is on 7AL, Xbcd1871-5D on 5DS, Xbcd1434-1A on 1AS, and loci Xbcd292-2A and Xcdo678-2A are on 2AL. The same polymorphic fragments detected in the Pm3b NIL by Xbcd1434-1A were found in Pm3a NIL using several enzyme digestions.     

Genetic and physical mapping of a rice blast resistance locus,Pi-CO39(t), that corresponds to the avirulence gene AVR1-CO39 of Magnaporthe grisea

We have identified, genetically mapped and physically delineated the chromosomal location of a new rice blast resistance locus, designated Pi-CO39(t). This locus confers resistance to Magnaporthe grisea isolates carrying the AVR1-CO39 avirulence locus. The AVR1-CO39 locus is conserved in non-rice (cereals and grasses)-infecting isolates of M. grisea, making Pi-CO39(t) useful for engineering M. grisea resistance in rice and other cereals. The resistance in the rice line CO39 was inherited as a single dominant locus in segregating populations derived from F(2) and F(3) crosses between disease-resistant (CO39) and susceptible (51583) rice genotypes. Microsatellite, RFLP and resistance gene analog (RGA) markers were used to map the Pi-CO39(t) locus to a 1.2-cM interval between the probenazole-responsive ( RPR1) gene (0.2 cM) and RFLP marker S2712 (1.0 cM) on the short arm of rice chromosome 11. RFLP markers G320 and F5003, and resistance gene analogs RGA8, RGA38 and RGACO39 were tightly linked to the Pi-CO39(t) locus (no recombination detected in a sample of ~2400 gametes). A large-insert genomic library of CO39 was constructed in the binary plant transformation vector pCLD04541. A library screen using RGA8, RGA38 and probes derived from the ends of CO39 clones, as well as BAC end probes from the corresponding locus in the rice cv. Nipponbare, resulted in the assembly of three CO39 contigs of 180 kb, 110 kb and 145 kb linked to the Pi-CO39(t) locus. A 650-kb contig was also constructed representing the susceptible locus, pi-CO39(t), in the Nipponbare genome. The two genomes are highly divergent with respect to additions, deletions and translocations at the Pi-CO39(t) locus, as revealed by the presence or absence of mapping markers.     

<Emphasis Type="Italic">Rpp1</Emphasis>, a dominant gene providing race-specific resistance to rose powdery mildew (<Emphasis Type="Italic">Podosphaera pannosa</Emphasis>): molecular mapping,SCAR development and confirmation of disease resistance data

We have previously demonstrated that in the diploid rose population 97/9 resistance to the powdery mildew race 9 is controlled by a major dominant resistance gene, Rpp1. In the study reported here, we isolated several molecular markers closely linked to Rpp1 via bulked segregant analysis, with the gene being tagged in an interval of 5 cM between the two most adjacent markers. It was possible to convert the most closely linked amplified fragment length polymorphic (AFLP) marker into a sequence-characterised amplified region (SCAR) segregating in the same manner. Indirect mapping of Rpp1 in relation to the black spot resistance gene Rdr1 revealed no linkage between the two R genes. Furthermore, the genetic model based on a single dominant resistance gene was supported by the marker data.