Cloning and mapping of genes involved in wheat-leaf rust interaction through gene-expression analysis using chromosome-deleted near-isogenic wheat lines

Molecular markers on wheat chromosome 6BL were isolated using mRNA differential display. Two wheat isolines inoculated with Puccinia recondita were analysed: Sinvalocho MA line carrying the Lr3 gene for leaf rust resistance on distal chromosome 6BL, and a rust-susceptible derivative of the Sinvalocho MA line with a deletion at the distal end of chromosome 6BL. Comparison of mRNA fingerprinting profiles, obtained from control and rust-inoculated plants, let to the isolation of 34 differentially displayed cDNAs. All these genes, except TaRr16, were up-regulated in the rust-inoculated resistant line. TaRr16 has constitutive expression in the rust-resistant line while no expression was detected in the rust-susceptible line. A number of those cDNAs revealed homology to genes previously identified in other plant-pathogen interactions. Two out of the 34 cDNAs, mapped in the distal part of chromosome 6BL and TaRr16, was genetically linked to the Lr3 gene. DNA sequence differences and differential expression between non-allelic copies of TaRr16, are also reported.     

Genetic analysis of leaf rust resistance genes and associated markers in the durable resistant wheat cultivar Sinvalocho MA

In the cross of the durable leaf rust resistant wheat Sinvalocho MA and the susceptible line Gama6, four specific genes were identified: the seedling resistance gene Lr3, the adult plant resistance (APR) genes LrSV1 and LrSV2 coming from Sinvalocho MA, and the seedling resistance gene LrG6 coming from Gama6. Lr3 was previously mapped on 6BL in the same cross. LrSV1 was mapped on chromosome 2DS where resistance genes Lr22a and Lr22b have been reported. Results from rust reaction have shown that LrSV1 from Sinvalocho is not the same allele as Lr22b and an allelism test with Lr22a showed that they could be alleles or closely linked genes. LrSV1 was mapped in an 8.5-cM interval delimited by markers gwm296 distal and gwm261 proximal. Adult gene LrSV2 was mapped on chromosome 3BS, cosegregating with gwm533 in a 7.2-cM interval encompassed by markers gwm389 and gwm493, where other disease resistance genes are located, such as seedling gene Lr27 for leaf rust, Sr2 for stem rust, QTL Qfhs.ndsu-3BS for resistance to Fusarium gramineum and wheat powdery mildew resistance. The gene LrG6 was mapped on chromosome 2BL, with the closest marker gwm382 at 0.6 cM. Lines carrying LrSV1, LrSV2 and LrG6 tested under field natural infection conditions, showed low disease infection type and severity, suggesting that this kind of resistance can be explained by additive effects of APR and seedling resistance genes. The identification of new sources of resistance from South American land races and old varieties, supported by modern DNA technology, contributes to sustainability of agriculture through plant breeding.     

Physical and genetic mapping of amplified fragment length polymorphisms and the leaf rust resistance Lr3 gene on chromosome 6BL of wheat

The Argentinian wheat cultivar Sinvalocho MA carries the Lr3 gene for leaf rust resistance on distal chromosome 6BL. In this cultivar, 33 spontaneous susceptible lines were isolated and cytogenetically characterized by C-banding. The analysis revealed deletions on chromosome 6BL in most lines. One line was nulli-6B, two lines were ditelo 6BS, two, three, and ten lines had long terminal deletions of 40, 30, and 20%, respectively, three lines showed very small terminal deletions, and one line had an intercalary deletion of 11%. Physical mapping of 55 amplified fragment length polymorphism (AFLP) markers detected differences between deletions and led to the division of 6BL into seven bins delimited by deletion breakpoints. The most distal bin, with a length smaller than 5% of 6BL, contained 22 AFLP markers and the Lr3 gene. Polymorphism for nine AFLPs between Sinvalocho MA and the rust leaf susceptible cultivar Gamma 6 was used to construct a linkage map of Lr3. This gene is at a genetic distance of 0.9 cM from a group of seven closely linked AFLPs. The location of the gene in a high recombinogenic region indicated a physical distance of approximately 1 Mb to the markers.     

Mapping a gene on wheat chromosome 4BL involved in a complementary interaction with adult plant leaf rust resistance gene <Emphasis Type="Italic">LrSV2</Emphasis>

Key message

A complementary gene to LrSV2 for specific adult plant leaf rust resistance in wheat was mapped on chromosome 4BL, tightly linked to Lr12 / 31.

Abstract

LrSV2 is a race-specific adult plant leaf rust (Puccinia triticina) resistance gene on subdistal chromosome 3BS detected in the cross of the traditional Argentinean wheat (Triticum aestivum) variety Sinvalocho MA and the experimental line Gama6. The analysis of the cross of R46 [recombinant inbred line (RIL) derived from Sinvalocho MA carrying LrSV2 gene and the complementary gene Lrc-SV2 identified in the current paper] and the commercial variety Relmo Siriri (not carrying neither of these two genes) allowed the detection of the unlinked complementary gene Lrc-SV2 because the presence of one dominant allele of both is necessary to express the LrSV2-specific adult plant resistance. Lrc-SV2 was mapped within a 1-cM interval on chromosome 4BL using 100 RILs from the cross Sinvalocho MA?×?Purple Straw. This genetic system resembles the Lr27+31 seedling resistance reported in the Australian varieties Gatcher and Timgalen where interacting genes map at similar chromosomal positions. However, in high-resolution maps, Lr27 and LrSV2 were already mapped to adjacent intervals on 3BS and Lrc-SV2 map position on 4BL is distal to the reported Lr12/31-flanking microsatellites.

     

Fine mapping of LrSV2, a race-specific adult plant leaf rust resistance gene on wheat chromosome 3BS

Key message

Fine mapping permits the precise positioning of genes within chromosomes, prerequisite for positional cloning that will allow its rational use and the study of the underlying molecular action mechanism.

Abstract

Three leaf rust resistance genes were identified in the durable leaf rust resistant Argentinean wheat variety Sinvalocho MA: the seedling resistance gene Lr3 on distal 6BL and two adult plant resistance genes, LrSV1 and LrSV2, on chromosomes 2DS and 3BS, respectively. To develop a high-resolution genetic map for LrSV2, 10 markers were genotyped on 343 F2 individuals from a cross between Sinvalocho MA and Gama6. The closest co-dominant markers on both sides of the gene (3 microsatellites and 2 STMs) were analyzed on 965 additional F2s from the same cross. Microsatellite marker cfb5010 cosegregated with LrSV2 whereas flanking markers were found at 1 cM distal and at 0.3 cM proximal to the gene. SSR markers designed from the sequences of cv Chinese Spring BAC clones spanning the LrSV2 genetic interval were tested on the recombinants, allowing the identification of microsatellite swm13 at 0.15 cM distal to LrSV2. This delimited an interval of 0.45 cM around the gene flanked by the SSR markers swm13 and gwm533 at the subtelomeric end of chromosome 3BS.     

小麦遗传背景对黑麦抗叶锈基因Lr26的抗性表达的影响

利用1套从小麦纯系和黑麦自交系培育出的1R附加系、代换系和易位系,研究了1RS上的抗叶锈基因Lr26在小麦中的表达。结果发现,1R二体附加系和纯合1RS/1BL易位系高抗小麦叶锈病;而其小麦亲本、1R(1B)代换系和1BS/1RL易位系重感叶锈病。这一结果指出了黑麦染色体臂1RS上的抗小麦叶锈病基因Lr26在小麦中的表达受小麦染色体臂1BL上的基因的强烈影响,指出了外源基因在小麦中的表达可受染色体臂或基因水平上的相互作用的制约。文中讨论了外源基因与小麦遗传背景相互作用在小麦育种中的意义。     

Identification of microsatellite markers linked to leaf rust resistance gene <Emphasis Type="Italic">Lr25</Emphasis> in wheat

The leaf rust resistance gene Lr25, transferred from Secale cereale L. into wheat and located on chromosome 4B, imparts resistance to all pathotypes of leaf rust in South-East Asia. In an F₂-derived F₃ population, created by crossing TcLr25 that carries the gene Lr25 for leaf rust resistance with leaf rust-susceptible parent Agra Local, three microsatellite markers located on the long arm of chromosome 4B were found to be linked to the Lr25 locus. The donor parent TcLr25 is a near-isogenic line derived from the variety Thatcher. The most virulent pathotype of leaf rust in the South-East Asian region, designated 77–5 (121R63-1), was used for challenging the population under artificially controlled conditions. The marker Xgwm251 behaved as a co-dominant marker placed 3.8 cM away from the Lr25 locus on 4BL. Two null allele markers, Xgwm538 and Xgwm6, in the same linkage group were located at a distance of 3.8 cM and 16.2 cM from the Lr25 locus, respectively. The genetic sequence of Xgwm251, Lr25, Xgwm538, and Xgwm6 covered a total length of 20 cM on 4BL. The markers were validated for their specificity to Lr25 resistance in a set of 43 wheat genetic stocks representing 43 other Lr genes.     

Development and validation of molecular markers linked to an Aegilops umbellulata-derived leaf-rust-resistance gene, Lr9, for marker-assisted selection in bread wheat.

An Aegilops umbellulata-derived leaf-rust-resistance gene, Lr9, was tagged with 3 random amplified polymorphic DNA (RAPD) markers, which mapped within 1.8 cM of gene Lr9 located on chromosome 6BL of wheat. The markers were identified in an F2 population segregating for leaf-rust resistance, which was generated from a cross between 2 near-isogenic lines that differed in the alien gene Lr9 in a widely adopted agronomic background of cultivar 'HD 2329'. Disease phenotyping was done in controlled environmental conditions by inoculating the population with the most virulent pathotype, 121 R63-1 of Puccinia triticina. One RAPD marker, S5550, located at a distance of 0.8+/-0.008 cM from the Lr9 locus, was converted to sequence-characterized amplified region (SCAR) marker SCS5550. The SCAR marker was validated for its specificity to gene Lr9 against 44 of the 50 known Lr genes and 10 wheat cultivars possessing the gene Lr9. Marker SCS5550 was used with another SCAR marker, SCS73719, previously identified as being linked to gene Lr24 on a segregating F2 population to select for genes Lr9 and Lr24, respectively, demonstrating the utility of the 2 markers in marker-assisted gene pyramiding for leaf-rust resistance in wheat.     

Spontaneous Genetic Variation for Leaf Rust Reaction in Sinvalocho MA Wheat

Spontaneous off-type plants for leaf rust reaction to Argentine races 66 and 77 of Puccinia recondita tritici were found at rates of 3.4 per 1000 and 0.44 per 1000, respectively, in the progeny of self-pollinated (bagged) spikes of Sinvalocho, MA wheat. Leaf rust reaction changes were associated to aneuploidy in most cases. The variation to race 66 was associated to monosomy of chromosome 6B or probably deletions on chromosome arm 6BL. Some off-type plants however showed, in subsequent generations. changes for reaction to race 77 or simultaneous changes to races 66 and 77 as well as changes in leucine aminopeptidase isozyme expression, which cannot be explained on grounds of allelic dosage. The origin of these genetic and chromosomal changesis not clear in some cases, however, a common origin could be suggested by the presence of transposonlike elements.     

Localization of Structural and Regulatory Genes for Phosphodiesterase in Wheat (TRITICUM AESTIVUM)

Genes (Pde-A3; Pde-B3; Pde-D3) for phosphodiesterase (PDE; E.C. 3.1.4.1.) isoenzymes in hexaploid wheat were located on the three homoeologous chromosomes of group 3 by testing the electrophoretic banding pattern of monosomic, nullisomic and nullisomic/tetrasomic compensation lines of "Chinese Spring" variety. In plants nullisomic for chromosome 5B, the 3D structural gene is not expressed and this lack of expression can be overcome by four doses of either homoeologous chromosome 5A or 5D. Our data conclusively indicate that there are genes on group 5 chromosomes which positively control the expression of the 3D structural gene. In addition, the expression of the "regulatory genes" is dosage dependent. Thus, our study reveals a complex interaction of the three genomes of wheat for regulation of PDE gene expression.     

Targeted mapping of ESTs linked to the adult plant resistance gene Lr46 in wheat using synteny with rice

The gene Lr46 has provided slow-rusting resistance to leaf rust caused by Puccinia triticina in wheat (Triticum aestivum), which has remained durable for almost 30 years. Using linked markers and wheat deletion stocks, we located Lr46 in the deletion bin 1BL (0.84–0.89) comprising 5% of the 1BL arm. The distal part of chromosome 1BL of wheat is syntenic to chromosome 5L of rice. Wheat expressed sequence tags (ESTs) mapping in the terminal 15% of chromosome 1BL with significant homology to sequences from the terminal region of chromosome 5L of rice were chosen for sequence-tagged site (STS) primer design and were mapped physically and genetically. In addition, sequences from two rice bacterial artificial chromosome clones covering the targeted syntenic region were used to identify additional linked wheat ESTs. Fourteen new markers potentially linked to Lr46 were developed; eight were mapped in a segregating population. Markers flanking (2.2 cM proximal and 2.2 cM distal) and cosegregating with Lr46 were identified. The physical location of Lr46 was narrowed to a submicroscopic region between the breakpoints of deletion lines 1BL-13 [fraction length (FL)=0.89–1] and 1BL-10 (FL=0.89–3). We are now developing a high-resolution mapping population for the positional cloning of Lr46.     

Mapping and characterization of the new adult plant leaf rust resistance gene <Emphasis Type="Italic">Lr77</Emphasis> derived from Santa Fe winter wheat

Key message

A new gene for adult plant leaf rust resistance in wheat was mapped to chromosome 3BL. This gene was designated as Lr77.

Abstract

‘Santa Fe’ is a hard red winter cultivar that has had long-lasting resistance to the leaf rust fungus, Puccinia triticina. The objective of this study was to determine the chromosome location of the adult plant leaf rust resistance in Santa Fe wheat. A partial backcross line of ‘Thatcher’ (Tc) wheat with adult plant leaf rust resistance derived from Santa Fe was crossed with Thatcher to develop a Thatcher//Tc*2/Santa Fe F₆ recombinant inbred line (RIL) population. The RIL population and parental lines were evaluated for segregation of leaf rust resistance in three field plot tests and in an adult plant greenhouse test. A genetic map of the RIL population was constructed using 90,000 single-nucleotide polymorphism (SNP) markers with the Illumina Infinium iSelect 90K wheat bead array. A significant quantitative trait locus for reduction of leaf rust severity in all four tests was found on chromosome 3BL that segregated as a single adult plant resistance gene. The RILs with the allele from the resistant parent for SNP marker IWB10344 had lower leaf rust severity and a moderately resistant to moderately susceptible response compared to the susceptible RILs and Thatcher. The gene derived from Santa Fe on chromosome 3BL was designated as Lr77. Kompetitive allele-specific polymerase chain reaction assay markers linked to Lr77 on 3BL should be useful for selection of wheat germplasm with this gene.

     

NBS-LRR sequence family is associated with leaf and stripe rust resistance on the end of homoeologous chromosome group 1S of wheat

A detailed RFLP map was constructed of the distal end of the short arm of chromosome 1D of Aegilops tauschii and wheat. At least two unrelated resistance-gene analogs (RGAs) mapped close to known leaf rust resistance genes (Lr21 and Lr40) located distal to seed storage protein genes on chromosome 1DS. One of the two RGA clones, which was previously shown to be part of a candidate gene for stripe rust resistance (Yr10) located within the homoeologous region on 1BS, identified at least three gene family members on chromosome 1DS of Ae. tauschii. One of the gene members co-segregated with the leaf rust resistance genes, Lr21 and Lr40, in Ae. tauschii and wheat segregating families. Hence, a RGA clone derived from a candidate gene for stripe rust resistance located on chromosome 1BS detected candidate genes for leaf rust resistance located in the corresponding region on 1DS of wheat. Received: 10 January 2000 / Accepted: 25 March 2000     

Identification of chromosome arms influencing expression of the HMW glutenins in wheat

The high-molecular-weight (HMW) glutenin genes, located on the group 1L chromosome arms, are a major determinant for baking quality in wheat ( Triticum aestivum L.). In addition, the HMW glutenin genes provide a valuable model system for studying the evolution and regulation of orthologous and paralogous genes in polyploid species. The goal of this study was to identify loci that modify the expression of the HMW glutenins, and to map them to specific chromosome arms. Comparisons were made between endosperms with zero versus three (or three versus six) doses for each of the 42 chromosome arms of wheat. SDS-PAGE and scanning densitometry were used to quantify the protein expression levels of the four HMW glutenin genes in cv. Chinese Spring, for each of the dosage comparisons. Fifteen chromosome arms were found to have significant effects on Glu-B1-1, excluding the structural gene dosage effect: eight positive effects on 1AL, 2AS, 2BL, 2DS, 5DS, 6AL, 6DL, and 7AL and seven negative effects on 1BS, 1DS, 1DL, 4DL, 6BS, 6DS, and 7AS. Nineteen chromosome arms had significant effects on Glu-B1-2, excluding the structural gene dosage effect: eight positive effects on 1AL, 2AS, 2BS, 3AL, 4BL, 6DS, 7BL and 7DS and 11 negative effects on 1AS, 1BS, 1DS, 1DL, 2AL, 2BL, 3DS, 4BS, 4DL, 5BL, and 6BS. Twenty chromosome arms had significant effects on Glu-D1-1, excluding the structural gene dosage effect: 11 positive effects on 1AL, 1BL, 2BS, 2DS, 5BS, 5DS, 6AL, 6DS, 6DL, 7AL, and 7BL and nine negative effects on 1AS, 1BS, 1DS, 2BL, 4DL, 5BL, 5DL, 6BL, and 7DS. Twenty-five chromosome arms had significant effects on Glu-D1-2, excluding the structural gene dosage effect: 17 positive effects on 1BL, 2AS, 2BS, 2DS, 2DL, 3AS, 3AL, 3BS, 5AS, 5BS, 5DL, 6AL, 6DL, 7AL, 7BS, 7BL, and 7DL and eight negative effects on 1DS, 4DL, 5AL, 5BL, 6BS, 6BL, 6DS and 7DS. Of the 164 gene-chromosome arm tests performed, about 52% (85/164) showed no significant effects, and 48% (79/164) showed significant effects, excluding the structural gene dosage effects. Of the significant effects, 56% (44/79) were positive effects, and 44% (35/79) were negative effects. Comparisons of dosage effects on orthologous loci (both x-type or both y-type HMW glutenins) showed that orthologous HMW glutenin genes are largely influenced by the same regulatory systems. Less correlation was found for comparisons between paralogous genes, although considerable conservation was observed at this level as well. These observations suggest that after polyploidization, many of the duplicated orthologous regulatory loci were inactivated by mutation, thus consolidating control over the HMW glutenin genes. Possible candidates for orthologous regulatory genes were identified in maize and barley. This study represents the first comprehensive search of the wheat genome for regulators of the HMW glutenins.     

Lr70, a new gene for leaf rust resistance mapped in common wheat accession KU3198

Key message

KU3198 is a common wheat accession that carries one novel leaf rust resistance (Lr) gene, Lr70 , and another Lr gene which is either novel, Lr52 or an allele of Lr52.

Abstract

Leaf rust, caused by Puccinia triticina Eriks. (Pt), is a broadly distributed and economically important disease of wheat. Deploying cultivars carrying effective leaf rust resistance (Lr) genes is a desirable method of disease control. KU3198 is a common wheat (Triticum aestivum L.) accession from the Kyoto collection that was highly resistant to Pt in Canada. An F₂ population from the cross HY644/KU3198 showed segregation for two dominant Lr genes when tested with Pt race MBDS which was virulent on HY644. Multiple bulk segregant analysis (MBSA) was employed to find putative chromosome locations of these Lr genes using SSR markers that provided coverage of the genome. MBSA predicted that the Lr genes were located on chromosomes 5B and 5D. A doubled haploid population was generated from the cross of JBT05-714 (HY644*3/KU3198), a line carrying one of the Lr genes from KU3198, to Thatcher. This population segregated for a single Lr gene conferring resistance to Pt race MBDS, which was mapped to the terminal region of the short arm of chromosome 5B with SSR markers and given the temporary designation LrK1. One F₃ family derived from the HY644/KU3198 F₂ population that segregated only for the second Lr gene from KU3198 was identified. This family was treated as an F₂-equivalent population and used for mapping the Lr gene, which was located to the terminal region of chromosome 5DS. As no other Lr gene has been mapped to 5DS, this gene is novel and has been designated as Lr70.     

Lr34 multi-pathogen resistance ABC transporter: molecular analysis of homoeologous and orthologous genes in hexaploid wheat and other grass species

The Triticum aestivum (bread wheat) disease resistance gene Lr34 confers durable, race non-specific protection against three fungal pathogens, and has been a highly relevant gene for wheat breeding since the green revolution. Lr34, located on chromosome 7D, encodes an ATP-binding cassette (ABC) transporter. Both wheat cultivars with and without Lr34-based resistance encode a putatively functional protein that differ by only two amino acid polymorphisms. In this study, we focused on the identification and characterization of homoeologous and orthologous Lr34 genes in hexaploid wheat and other grasses. In hexaploid wheat we found an expressed and putatively functional Lr34 homoeolog located on chromosome 4A, designated Lr34-B. Another homoeologous Lr34 copy, located on chromosome 7A, was disrupted by the insertion of repetitive elements. Protein sequences of LR34-B and LR34 were 97% identical. Orthologous Lr34 genes were detected in the genomes of Oryza sativa (rice) and Sorghum bicolor (sorghum). Zea mays (maize), Brachypodium distachyon and Hordeum vulgare (barley) lacked Lr34 orthologs, indicating independent deletion of this particular ABC transporter. Lr34 was part of a gene-rich island on the wheat D genome. We found gene colinearity on the homoeologous A and B genomes of hexaploid wheat, but little microcolinearity in other grasses. The homoeologous LR34-B protein and the orthologs from rice and sorghum have the susceptible haplotype for the two critical polymorphisms distinguishing the LR34 proteins from susceptible and resistant wheat cultivars. We conclude that the particular Lr34-haplotype found in resistant wheat cultivars is unique. It probably resulted from functional gene diversification that occurred after the polyploidization event that was at the origin of cultivated bread wheat.     

An N-band marker for gene Lr18 for resistance to leaf rust in wheat

The leaf rust resistance gene, Lr18, of common wheat cultivars has been derived from Triticum timopheevi and is located on chromosome arm 5BL. Chromosome banding (N-banding) analyses revealed that in the wheat cultivars carrying Lr18 that were examined, which had been bred in 6 different countries, chromosome arm 5BL possessed a specific terminal band not carried by their susceptible parental cultivars. It was suggested that this terminal N-band was introduced from T. timopheevi together with Lr18. N-banding analysis of a T. timopheevi strain showed that one of two timopheevi chromosomes had provided Japanese wheat lines containing Lr18 with the terminal band.     

Application of STS markers for leaf rust resistance genes in near-isogenic lines of spring wheat cv. Thatcher

Sequence tagged site (STS) markers for eight resistance genes against Puccinia recondita f. sp. tritici were used to screen a set of near-isogenic lines of wheat cv. Thatcher containing in total 40 different Lr genes and their alleles. Polymerase chain reaction (PCR) analysis was carried out by using STS, SCAR and CAPS primers specific for the leaf rust resistance genes Lr1, Lr9, Lr10, Lr19, Lr24, Lr28, Lr37 and Lr47. The STS, CAPS and SCAR markers linked to resistance genes Lr9, Lr10, Lr19, Lr24, Lr37 and Lr47 were found to be reliable in diverse genetic backgrounds. The amplification product of the Lr1 gene marker was detected in the susceptible cv. Thatcher and in all of the near-isogenic lines examined except Lr2a, Lr2b, Lr2c and Lr19. The sequence analysis of PCR products amplified in lines Lr1, Lr10, Lr28 and in cv. Thatcher indicated that the near-isogenic lines and cv. Thatcher contained in the targeted chromosome region an allele that differed from the original alleles corresponding to Lr1/6*Thatcher (TLR621) and susceptible Thatcher (TH621). The amplification product specific to the STS marker of the Lr1 gene was amplified in almost all Thatcher near-isogenic lines and in cv. Thatcher because their alleles possessed primer sequences identical to the original allele TLR621. The marker for the Lr28 resistance gene was identified in line Lr28, carrying gene Lr28, and in 21 other near-isogenic lines. The sequencing of PCR products specific to Lr28 and generated in lines Lr1, Lr10 and Lr28 indicated that the lines Lr1, Lr10 and Lr28 are heterozygous in this region.     

Homoeologous set of NBS-LRR genes located at leaf and stripe rust resistance loci on short arms of chromosome 1 of wheat

Homoeologous group 1 chromosomes of wheat contain important genes that confer resistance to leaf, stem and stripe rusts, powdery mildew and Russian wheat aphid. A disease resistance gene analog encoding nucleotide binding site-leucine rich repeat (NBS-LRR), designated RgaYr10, was previously identified at the stripe rust resistant locus, Yr10, located on chromosome 1BS distal to the storage protein, Gli-B1 locus. RgaYr10 identified gene members in the homoeologous region of chromosome 1DS cosegregating with the leaf rust resistance gene, Lr21, which originally was transferred from a diploid D genome progenitor. Four RgaYr10 gene members were isolated from chromosome 1DS and compared to two gene members previously isolated from the chromosome 1BS homeologue. NBS-LRR genes tightly linked to stripe rust resistance gene Yr10 on chromosome 1BS were closely related in sequence and structure to NBS-LRR genes tightly linked to leaf rust resistance gene Lr21 located within the homoeologous region on chromosome 1DS. The level of sequence homology was similar between NBS-LRR genes that were isolated from different genomes as compared to genes from the same genome. Electronic Publication     

Molecular mapping of leaf rust resistance gene LrFun in Romanian wheat line Fundulea 900

Leaf rust, caused by Puccinia triticina, is one of the major wheat diseases worldwide and poses a constant threat to common wheat (Triticum aestivum L.) production and food security. Results from the F₂ and F_2:3 populations derived from a cross between resistant line Fundulea 900 and susceptible cultivar Thatcher indicated that a single dominant gene, tentatively designated LrFun, conferred resistance to leaf rust. In order to identify other possible genes in Fundulea 900, nine P. triticina pathotypes avirulent on Fundulea 900 were used to inoculate F_2:3 families. The results showed that at least two leaf rust resistance genes were present in Fundulea 900. A total of 1,706 pairs of simple sequence repeat (SSR) primers were used to test the parents and resistant and susceptible bulks. Eight polymorphic markers from chromosome 7BL were used for genotyping the F₂ and F_2:3 populations. LrFun was linked to eight SSR loci on chromosome 7BL. The two closest flanking SSR loci were Xgwm344 and Xwmc70, with genetic distances of 4.4 and 5.7 cM, respectively. At present four leaf rust resistance genes, Lr14a, Lr14b, Lr68 and LrBi16, are located on chromosome 7BL. In a seedling test with 12 P. triticina isolates, the reaction patterns of LrFun were different from those of lines carrying Lr14a, Lr14b and LrBi16. Lr68 is an adult plant resistance gene, and it is different from the seedling resistance gene LrFun. Therefore, we concluded that LrFun is a new leaf rust resistance gene.