Conversion of AFLP markers associated with FHB resistance in wheat into STS markers with an extension-AFLP method.

Amplified fragment length polymorphism (AFLP) has proven a powerful tool for tagging genes or quantitative trait loci (QTLs) of interest in plants. However, conversion of AFLP markers into sequence-tagged site (STS) markers is technically challenging in wheat owing to the complicated nature of its genome. In this study, we developed an "extension-AFLP" method to convert AFLP markers associated with Fusarium head blight (FHB) resistance into STS markers. When an AFLP marker of interest was detected with an EcoRI+3-MseI+4-selective primer combination, the PCR product was used as a template for an additional selective amplification with four primer pairs, in which one additional selective base (either A, C, G, or T) was added to the 3' end of one of the two primers. The extended primer pair that produced the targeted band was further extended by adding each of the four selective nucleotide bases for the next round of selective amplification. Extension selective amplification was performed until the target bands became clear enough for subsequent cloning and sequencing. By using the extension-AFLP method, we successfully converted two AFLP markers located on chromosome 3BS and associated with FHB resistance into STS markers. Our results indicated that the extension-AFLP method is an efficient approach for converting AFLP markers into STS markers in wheat. The developed STS markers might be used for marker-assisted selection (MAS) for FHB resistance in wheat breeding programs.     

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     

Development of STS markers linked to Hessian fly resistance gene H6 in wheat

Hessian fly is one of the world's most destructive insect pests of wheat Triticum aestivum L. We have used the combination of near-isogenic lines (NIL) and random amplified polymorphic DNA (RAPD) analysis to screen up to 2,000 primers to identify DNA markers that are linked to gene H6 that confers resistance to biotype B of the insect. This screen produced six primers that show polymorphic fragments associated with resistance by H6. We have screened 440 F₂ individuals from a cross of the susceptible cultivar Newton and a NIL that contains H6 to verify the linkage between these markers and the resistance gene. A high-resolution genetic map was constructed based on recombination frequency. Two of the markers were tightly linked to the gene with no recombination observed, three were within 2.0 cM, and one was 11 cM from the gene. Three of the six markers were successfully converted to sequence tagged site (STS) markers. Both RAPD and STS primers were used to screen for the presence or absence of the resistance gene in wheat varieties. The identification of markers and construction of the genetic high resolution map provide the first steps toward localization of this resistance gene.     

Identification and molecular tagging of a gene from PI 289824 conferring resistance to leaf rust (Puccinia triticina) in wheat

Host-plant resistance is the most economically viable and environmentally responsible method of control for Puccinia triticina, the causal agent of leaf rust in wheat (Triticum aestivum L.). The identification and utilization of new resistance sources is critical to the continued development of improved cultivars as shifts in pathogen races cause the effectiveness of widely deployed genes to be short lived. The objectives of this research were to identify and tag new leaf rust resistance genes. Forty landraces from Afghanistan and Iran were obtained from the National Plant Germplasm System and evaluated under field conditions at two locations in Texas. PI 289824, a landrace from Iran, was highly resistant under field infection. Further evaluation revealed that PI 289824 is highly resistant to a broad spectrum of leaf rust races, including the currently prevalent races of leaf rust in the Great Plains area of the USA. Eight F₁ plants, 176 F₂ individuals and 139 F_2:3 families of a cross between PI 289824 and T112 (susceptible) were evaluated for resistance to leaf rust at the seedling stage. Genetic analysis indicated resistance in PI 289824 is controlled by a single dominant gene. The AFLP analyses resulted in the identification of a marker (P39 M48-367) linked to resistance. The diagnostic AFLP band was sequenced and that sequence information was used to develop an STS marker (TXW₂₀₀) linked to the gene at a distance of 2.3 cM. The addition of microsatellite markers allowed the gene to be mapped to the short arm of Chromosome 5B. The only resistance gene to be assigned to Chr 5BS is Lr52. The Lr52 gene was reported to be 16.5 cM distal to Xgwm443 while the gene in PI 289824 mapped 16.7 cM proximal to Xgwm443. Allelism tests are needed to determine the relationship between the gene in PI 289824 and Lr52. If the reported map positions are correct, the gene in PI 289824 is unique.     

An EST-SSR marker linked with yellow rust resistance in wheat

Expressed sequenced tags containing simple sequence repeats (EST-SSRs) were used to identify molecular markers associated with yellow rust resistance in wheat (Triticum aestivum L.). A cross between yellow rust resistant (PI178383) and susceptible (Harmankaya99) wheat genotypes was performed and respective DNA pools from the resistant and susceptible F₂ seedlings were constructed. 78 EST-SSR primers were used for bulked segregant analysis and one EST-SSR marker (Pk54), identified as 200 bp fragment, was present in the resistant parent and resistant F₂ hybrids but not in the susceptible ones. 108 wheat genotypes differing in yellow rust resistance were screened with Pk54 and 68 % of the wheat genotypes, known to be yellow rust resistant, had the Pk54 marker, further suggesting that the presence of this marker correlates with yellow rust resistance.     

Development of a molecular marker for the adult plant leaf rust resistance gene Lr35 in wheat

The objective of this work was to develop a marker for the adult plant leaf rust resistance gene Lr35. The Lr35 gene was originally introgressed into chromosome 2B from Triticum speltoides, a diploid relative of wheat. A segregating population of 96 F ₂ plants derived from a cross between the resistant line ThatcherLr35 and the susceptible variety Frisal was analysed. Out of 80 RFLP probes previously mapped on wheat chromosome 2B, 51 detected a polymorphism between the parents of the cross. Three of them were completely linked with the resistance gene Lr35. The co-segregating probe BCD260 was converted into a PCR-based sequence-tagged-site (STS) marker. A set of 48 different breeding lines derived from several European breeding programs was tested with the STS marker. None of these lines has a donor for Lr35 in its pedigree and all of them reacted negatively with the STS marker. As no leaf rust races virulent on Lr35 have been found in different areas of the world, the STS marker for the Lr35 resistance gene is of great value to support the introgression of this gene in combination with other leaf rust (Lr) genes into breeding material by marker-assisted selection. Received: 14 December 1998 / Accepted: 30 January 1999     

AFLP and STS tagging of Lr19, a gene conferring resistance to leaf rust in wheat

Amplified fragment length polymorphism (AFLP) markers were used to enrich the map of the wheat chromosomal region containing the Thinopyrum-derived Lr19 leaf rust resistance gene. The region closest to Lr19 was targeted through the use of deletion and recombinant lines of the translocated segment. One of the AFLP bands thus identified was converted into a sequence-tagged-site (STS) marker. This assay generated a 130-bp PCR fragment in all Lr19-carrying lines tested, except for one deletion mutant, while non-carrier template failed to amplify any product. This sequence represents the first marker to map on the distal side of Lr19 on chromosome 7el₁. The conversion process of AFLP fragments to STS markers was technically difficult, mainly because of the presence of contaminating fragments. Various approaches were taken to reduce the frequency of false positives and to identify the correct clone. We were able to formulate a general verification strategy prior to clone sequencing. Various other factors causing problems with converting AFLP bands to an STS assays are also discussed. Received: 15 September 2000 / Accepted: 5 January 2001     

Identification and mapping of molecular markers linked to rust resistance genes located on chromosome 1RS of rye using wheat-rye translocation lines

The short arm of rye (Secale cereale) chromosome 1 has been widely used in breeding programs to incorporate new disease resistance genes into wheat. Using wheat-rye translocation and recombinant lines, molecular markers were isolated and mapped within chromosomal regions of 1RS carrying rust resistance genes Lr26, Sr31, Yr9 from 'Petkus' and SrR from 'Imperial' rye. RFLP markers previously mapped to chromosome 1HS of barley - flanking the complex Mla powdery mildew resistance gene locus - and chromosome 1DS of Aegilops tauschii - flanking the Sr33 stem rust resistance gene - were shown to map on either side of rust resistance genes on 1RS. Three non cross-hybridising Resistance Gene Analog markers, one of them being derived from the Mla gene family, were mapped within same region of 1RS. PCR-based markers were developed which were tightly linked to the rust resistance genes in 'Imperial' and 'Petkus' rye and which have potential for use in marker-assisted breeding.     

Leaf tip necrosis, molecular markers and β1-proteasome subunits associated with the slow rusting resistance genes Lr46/Yr29

Resistance based on slow-rusting genes has proven to be a useful strategy to develop wheat cultivars with durable resistance to rust diseases in wheat. However this type of resistance is often difficult to incorporate into a single genetic background due to the polygenic and additive nature of the genes involved. Therefore, markers, both molecular and phenotypic, are useful tools to facilitate the use of this type of resistance in wheat breeding programs. We have used field assays to score for both leaf and yellow rust in an Avocet-YrA × Attila population that segregates for several slow-rusting leaf and yellow rust resistance genes. This population was analyzed with the AFLP technique and the slow-rusting resistance locus Lr46/Yr29 was identified. A common set of AFLP and SSR markers linked to the Lr46/Yr29 locus was identified and validated in other recombinant inbred families developed from single chromosome recombinant populations that segregated for Lr46. These populations segregated for leaf tip necrosis (LTN) in the field, a trait that had previously been associated with Lr34/Yr18. We show that LTN is also pleiotropic or closely linked to the Lr46/Yr29 locus and suggest that a new Ltn gene designation should be given to this locus, in addition to the one that already exists for Lr34/Yr18. Coincidentally, members of a small gene family encoding β-1 proteasome subunits located on group 1L and 7S chromosomes implicated in plant defense were linked to the Lr34/Yr18 and Lr46/Yr29 loci.     

Evaluation of Pakistan wheat germplasms for stripe rust resistance using molecular markers

Wheat production in Pakistan is seriously constrained due to rust diseases and stripe rust (yellow) caused by Puccinia striiformis f. sp. tritici, which could limit yields. Thus development and cultivation of genetically diverse and resistant varieties is the most sustainable solution to overcome these diseases. The first objective of the present study was to evaluate 100 Pakistan wheat cultivars that have been grown over the past 60 years. These cultivars were inoculated at the seedling stage with two virulent stripe rust isolates from the United States and two from Pakistan. None of the wheat cultivars were resistant to all tested stripe rust isolates, and 16% of cultivars were susceptible to the four isolates at the seedling stage. The data indicated that none of the Pakistan wheat cultivars contained either Yr5 or Yr15 genes that were considered to be effective against most P. striiformis f. sp. tritici isolates from around the world. Several Pakistan wheat cultivars may have gene Yr10, which is effective against isolate PST-127 but ineffective against PST-116. It is also possible that these cultivars may have other previously unidentified genes or gene combinations. The second objective was to evaluate the 100 Pakistan wheat cultivars for stripe rust resistance during natural epidemics in Pakistan and Washington State, USA. It was found that a higher frequency of resistance was present under field conditions compared with greenhouse conditions. Thirty genotypes (30% of germplasms) were found to have a potentially high temperature adult plant (HTAP) resistance. The third objective was to determine the genetic diversity in Pakistan wheat germplasms using molecular markers. This study was based on DNA fingerprinting using resistance gene analog polymorphism (RGAP) marker analysis. The highest polymorphism detected with RGAP primer pairs was 40%, 50% and 57% with a mean polymorphism of 36%. A total of 22 RGAP markers were obtained in this study. RGAP, simple sequence repeat (SSR) and sequence tagged site (STS) markers were used to determine the presence and absence of some important stripe rust resistance genes, such as Yr5, Yr8, Yr9, Yr15 and Yr18. Of the 60 cultivars analyzed, 17% of cultivars showed a RGAP marker band for Yr9 and 12% of cultivars exhibited the Yr18 marker band. No marker band was detected for Yr5, Yr8 and Yr15, indicating a likely absence of these genes in the tested Pakistan wheat cultivars. Cluster analysis based on molecular and stripe rust reaction data is useful in identifying considerable genetic diversity among Pakistan wheat cultivars. The resistant germplasms identified with 22 RGAP markers and from the resistance evaluations should be useful in developing new wheat cultivars with stripe rust resistance.     

Molecular mapping of a stripe rust resistance gene in wheat line C51

Stripe rust, a major disease in areas where cool temperatures prevail, can strongly influence grain yield. To control this disease, breeders have incorporated seedling resistance genes from a variety of sources outside the primary wheat gene pool. The wheat line C51, introduced from the International Center for Agricultural Research in the Dry Areas (ICARDA), Syria, confers resistance to all races of Puccinia striiformis f. sp. tritici (PST) in China. To map the resistant gene(s) against stripe rust in wheat line C51, 212 F ₈ recombinant inbred lines (RILs) derived from the cross X440 × C51 were inoculated with Chinese PST race CYR33 (Chinese yellow rust, CYR) in the greenhouse. The result showed that C51 carried a single dominant gene for resistance (designated YrC51) to CYR33. Simple sequence repeat (SSR) and resistance gene-analogue polymorphism (RGAP) markers that were polymorphic between the parents were used for genotyping the 212 F ₈ RILs. YrC51was closely linked to two SSR loci on chromosome 2BS with genetic distances of 5.1 cM (Xgwm429) and 7.2 cM (Xwmc770), and to three RGAP markers C51R1 (XLRR For / NLRR For), C51R2 (CLRR Rev / Cre3LR-F) and C51R3 (Pto kin4/ NLRR-INV2) with genetic distances of 5.6, 1.6 and 9.2 cM, respectively. These RGAP-linked markers were then converted into STS markers. Among them, one STS marker, C51STS-4, was located at a genetic distance of 1.4 cM to YrC51 and was closely associated with resistance when validated in several populations derived from crosses between C51 and Sichuan cultivars. The results indicated that C51STS-4 can be used for marker assisted selection (MAS) and would facilitate the pyramiding of YrC51 with other genes for stripe rust resistance.     

Mapping a stripe rust resistance gene YrC591 in wheat variety C591 with SSR and AFLP markers

Stripe rust, caused by Puccinia striiformis Westend. f. sp. tritici (PST), is one of the most destructive diseases of common wheat (Triticum aestivum L.). To determine inheritance of stripe rust resistance and map the resistance gene(s) in wheat variety C591, F₁, F_2, and F₃ progenies derived from the Taichung 29 × C591 cross were inoculated with Chinese PST race CY32 in the greenhouse. Genetic analysis identified a single dominant gene, temporarily designated YrC591. A total of 178 SSR and 130 AFLP markers were used to test the parents and resistant and susceptible bulks. From the bulk segregant analysis, seven polymorphic SSR and two AFLP markers were selected for genotyping the F₂ population. SSR marker Xcfa2040-7B, and SCAR marker SC-P35M48 derived from AFLP marker P35M48 ₃₇₃ were identified to be closely linked to the resistance gene with genetic distances of 8.0 and 11.7 cM, respectively. The SSR markers mapped the resistance gene on chromosome arm 7BL. In the seedling test with five PST races, the reaction patterns of C591 were different from wheat cultivars or lines carrying Yr2 or Yr6 that also are found on chromosome 7B. The results indicate that YrC591 is probably a novel stripe rust resistance gene.     

Genetic mapping of a putative Thinopyrum intermedium-derived stripe rust resistance gene on wheat chromosome 1B

Key message

Stripe rust resistance transferred from Thinopyrum intermedium into common wheat was controlled by a single dominant gene, which mapped to chromosome 1B near Yr26 and was designated YrL693.

Abstract

Stripe rust caused by Puccinia striiformis f. sp. tritici (Pst) is a highly destructive disease of wheat (Triticum aestivum). Stripe rust resistance was transferred from Thinopyrum intermedium to common wheat, and the resulting introgression line (L693) exhibited all-stage resistance to the widely virulent and predominant Chinese pathotypes CYR32 and CYR33 and to the new virulent pathotype V26. There was no cytological evidence that L693 had alien chromosomal segments from Th. intermedium. Genetic analysis of stripe rust resistance was performed by crossing L693 with the susceptible line L661. F₁, F₂, and F_2:3 populations from reciprocal crosses showed that resistance was controlled by a single dominant gene. A total 479 F_2:3 lines and 781 pairs of genomic simple sequence repeat (SSR) primers were employed to determine the chromosomal location of the resistance gene. The gene was linked to six publicly available and three recently developed wheat genomic SSR markers. The linked markers were localized to wheat chromosome 1B using Chinese Spring nulli-tetrasomic lines, and the resistance gene was localized to chromosome 1B based on SSR and wheat genomic information. A high-density genetic map was also produced. The pedigree, molecular marker data, and resistance response indicated that the stripe rust resistance gene in L693 is a novel gene, which was temporarily designated YrL693. The SSR markers that co-segregate with this gene (Xbarc187-1B, Xbarc187-1B-1, Xgwm18-1B, and Xgwm11-1B) have potential application in marker-assisted breeding of wheat, and YrL693 will be useful for broadening the genetic basis of stripe rust resistance in wheat.     

Genetic analysis and location of gene for resistance to stripe rust in wheat international differential host Strubes Dickkopf

Strubes Dickkopf is the sixth differential in the world set for wheat stripe (yellow) rust. It is very important to clarify its genetic character of resistance to stripe rust and to develop the molecular markers linked to resistance genes. The NIL Taichung 29*6/Strubes Dickkopf, which was obtained by Strubes Dickkopf as the gene donor and Taichung 29 as the genetic background through backcross breeding, was crossed with the recurrent parent Taichung 29, inbred, and backcrossed to obtain the F₁, F₂ and BC₁ population. The genetic analysis of the cross Taichung 29/(Taichung 29*6/Strubes Dickkopf) was assessed by inoculating the rust race CYR26 at seedling stage. Bulked segregant analysis (BSA) and F₂ segregation analysis were used for detecting polymorphic primers to locate the gene. The resistance of the NIL Taichung 29*6/Strubes Dickkopf to CYR26 was controlled by a single dominant gene, named YrSD. The primer pair Xbarc59 on 5B was linked to YrSD and the genetic distance between Xbarc59 and YrSD was 2.4 cM. The molecular marker Xbarc59 closely linked to the gene YrSD could be used in marker-assisted selection for resistance to stripe rust in wheat breeding programmes.     

Molecular Mapping of Rice Blast Resistance Gene Pi-k h in the Rice Variety Tetep

We have used rice line Tetep as a resistant donor with the aim of mapping a durable blast resistance gene Pi-k ^h using RAPD and AFLP techniques in conjunction with bulk segregant analysis. An F₂ mapping population consisting of 205 plants was generated by crossing Tetep with HP2216, a highly susceptible cultivar. Inoculation with specific isolate (PLP-1) of Magnaporthe grisea at seeding stage showed that the Pi-k ^h gene inherited as a single dominant gene in F2 population. RAPD analysis was performed with 240 primers to detect polymorphism between resistant and susceptible parents. Of these, 48 primers produced polymorphic banding pattern between resistant and susceptible parents. Bulk segregant analysis was performed with 48 primers of which 5 showed polymorphism between resistant and susceptible bulks. A 700 bp DNA band was obtained in resistant F2 plants with primer 5-129 indicating its linkage to the resistance gene. Out of 64 AFLP primer combinations used for polymorphism survey between HP 2216 and Tetep, 11 AFLP primer combinations were able to distinguish the resistant and susceptible bulks. An AFLP band of 75 bp obtained with primer combination, E-TAlM-CTC co-segregated with the resistance gene. The RAPD marker 5-129₇₀₀ and AFLP₇₅ were placed on the linkage map at a distance of 2.1 eM and 15.1 eM flanking to Pi-k ^hgene, respectively. The RAPD band closely linked to Pi-k ^h gene was sequenced and used for the development of CAPs markers which also co-segregated with resistant phenotype in the mapping population. On sequence analysis and homology search of RAPD fragment with whole rice genome sequence database and the information available on physical, genetic and sequence maps of rice, the co-segregating CAPs marker was placed at long arm of rice chromosome 11. CAPs marker developed in this study showed polymorphism in different rice cultivars grown in North-Western Himalayan region and is being used for the pyramiding of Pi-k ^h gene along with other blast resistance genes using marker-assisted selection.     

Identification of a rice gene (Bph 1) conferring resistance to brown planthopper (Nilaparvata lugens Stal) using STS markers

This study was carried out to identify a high-resolution marker for a gene conferring resistance to brown planthopper (BPH) biotype 1, using japonica type resistant lines. Bulked segregant analyses were conducted using 520 RAPD primers to identify RAPD fragments linked to the BPH resistance gene. Eleven RAPDs were shown to be polymorphic amplicons between resistant and susceptible progeny. One of these primers, OPE 18, which amplified a 923 bp band tightly linked to resistance, was converted into a sequence-tagged-site (STS) marker. The STS marker, BpE18-3, was easily detectable as a dominant band with tight linkage (3.9cM) to Bph1. It promises to be useful as a marker for assisted selection of resistant progeny in backcross breeding programs to introgress the resistance gene into elite japonica cultivars.     

An RGA – like marker detects all known Lr21 leaf rust resistance gene family members in Aegilops tauschii and wheat

Leaf rust is one of the most important diseases of wheat worldwide, particularly in the Great Plains region of the USA. One long-term strategy for the control of this disease may be through durable genetic resistance by gene pyramiding. An important step in this strategy is identifying molecular markers linked to different leaf rust-resistance genes. Here we report the molecular tagging of a leaf rust-resistance gene that may have the potential for durable resistance through further genetic manipulation and gene pyramiding. Lr39 was previously designated for a leaf rust-resistance gene introgressed from Aegilops tauschii accession TA1675 into the common wheat germplasm WGRC2. Lr40 was designated for a gene derived from Ae. tauschii accession TA1649 and is present in germplasm WGRC7. These genes are now believed to be allelic to Lr21, which was transferred to wheat from a different accession of Ae. tauschii. Molecular mapping of Lr39 and Lr40 indicates that both genes come from TA1649. WGRC2 and WRGC7 also have a similar infection type against rust culture PRTUS6. We suggest the designation of the gene in WGRC2 should be changed to Lr40. RFLP marker KSUD14 (locus Xksud14) was found 0.2-cM proximal to Lr40 in a WGRC2/Wichita F₂ population (218 individuals), and co-segregated with the gene in a WGRC7/ Wichita F₂ population (165 individuals). A PCR-based molecular marker developed from the sequence-tagged-site (STS) of Xksud14 was mapped to the same locus as the RFLP marker KSUD14 in both populations. KSUD14 has the structure of a resistance gene analog (RGA) including kinase2a and kinase3 domains similar to the Cre3 gene of wheat and the rust resistance gene Rp1-D of maize. When the PCR products amplified from KSU14 STS were cleaved with restriction enzyme MspI, an 885-bp fragment was found in WGRC2, WGRC7, the Lr21 near-isogenic line, and eight accessions of Ae. tauschii shown to have resistance gene alleles at the Lr21 locus. The KSUD14 PCR-based assay provides an excellent marker for Lr40 and Lr21 in diverse wheat breeding and wild Ae. tauschii populations. Received: 22 December 2000 / Accepted: 12 February 2001     

Identification of molecular markers for the detection of the yellow rust resistance gene Yr17 in wheat

The Yr17 gene, which is present in many European wheat cultivars, displays yellow rust resistance at the seedling stage. The gene introduced into chromosome 2A from Aegilops ventricosa was previously found to be closely linked (0.5 cM) to leaf and stem rust resistance genes Lr37 and Sr38, respectively. The objective of this study was to identify molecular markers linked to the Yr17 gene. We screened with RAPD primers, for polymorphism, the DNAs of cv. Thatcher and the leaf rust-resistant near-isogenic line (NIL) RL 6081 of cv. Thatcher carrying the Lr37 gene. Using a F2 progeny of the cross between VPM1 (resistant) and Thésée (susceptible), the RAPD marker OP-Y15580 was found to be closely linked to the Yr17 gene. We converted the OP- Y15580 RAPD marker into a sequence characterized amplified region (SCAR). This SCAR marker (SC-Y15) was linked at 0.8 ± 0.7 cM to the Yr17 resistance gene. We tested the SC-Y15 marker over a survey of 37 wheat cultivars in order to verify its consistency in different genetic backgrounds and to explain the resistance of some cultivars against yellow rust. Moreover, we showed that the Xpsr150-2Mv locus marker of Lr gene described by Bonhomme et al. [6] which possesses A. ventricosa introgression on the 2A chromosome was also closely linked to the Yr17 gene. Both the SCAR SC-Y15 and Xpsr150-2Mv markers should be used in breeding programmes in order to detect the cluster of the three genes Yr17, Lr37 and Sr38 in cross progenies. This revised version was published online in June 2006 with corrections to the Cover Date.     

Mapping of stripe rust resistance gene in an <Emphasis Type="Italic">Aegilops caudata</Emphasis> introgression line in wheat and its genetic association with leaf rust resistance

A pair of stripe rust and leaf rust resistance genes was introgressed from Aegilops caudata, a nonprogenitor diploid species with the CC genome, to cultivated wheat. Inheritance and genetic mapping of stripe rust resistance gene in backcross-recombinant inbred line (BC-RIL) population derived from the cross of a wheat–Ae. caudata introgression line (IL) T291-2(pau16060) with wheat cv. PBW343 is reported here. Segregation of BC-RILs for stripe rust resistance depicted a single major gene conditioning adult plant resistance (APR) with stripe rust reaction varying from TR-20MS in resistant RILs signifying the presence of some minor genes as well. Genetic association with leaf rust resistance revealed that two genes are located at a recombination distance of 13%. IL T291-2 had earlier been reported to carry introgressions on wheat chromosomes 2D, 3D, 4D, 5D, 6D and 7D. Genetic mapping indicated the introgression of stripe rust resistance gene on wheat chromosome 5DS in the region carrying leaf rust resistance gene LrAc, but as an independent introgression. Simple sequence repeat (SSR) and sequence-tagged site (STS) markers designed from the survey sequence data of 5DS enriched the target region harbouring stripe and leaf rust resistance genes. Stripe rust resistance locus, temporarily designated as YrAc, mapped at the distal most end of 5DS linked with a group of four colocated SSRs and two resistance gene analogue (RGA)-STS markers at a distance of 5.3 cM. LrAc mapped at a distance of 9.0 cM from the YrAc and at 2.8 cM from RGA-STS marker Ta5DS_2737450, YrAc and LrAc appear to be the candidate genes for marker-assisted enrichment of the wheat gene pool for rust resistance.