Dosage Effect of Lr3 Gene in the Triticum aestivum–Puccinia recondita Specific Interaction

Gene dosage effects of Lr3 gene were studied in the Triticum aestivum–Puccinia recondita tritici specific interaction. Deletion-duplication lines carrying different doses of Lr3 gene in chromosome 6B were obtained from a cross between standard Sinvalocho MA wheat and an isogenic translocated Sinvalocho MA 1BS/6BS-1BL/6BL line. Cytogenetic analysis and assessment of pathogen development revealed evidence for Lr3 gene dosage dependence in the expression of both resistance and avirulence. Increasing doses of chromosome 6B, from nullisomic to tetrasomic condition, increased the resistance, reaching the maximum at the tetrasomic level. The role of reciprocal translocations in the evolution of disease resistance genes in hexaploid wheat, the duplication of genes for resistance as a strategy to be used in plant breeding and the implications of gene-dosage dependence in host–parasite associations are discussed.     

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.     

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.     

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.

     

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.     

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.     

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.     

QTL for spot blotch resistance in bread wheat line Saar co-locate to the biotrophic disease resistance loci Lr34 and Lr46

Spot blotch caused by Bipolaris sorokiniana is a major disease of wheat in warm and humid wheat growing regions of the world including south Asian countries such as India, Nepal and Bangladesh. The CIMMYT bread wheat line Saar which carries the leaf tip necrosis (LTN)-associated rust resistance genes Lr34 and Lr46 has exhibited a low level of spot blotch disease in field trials conducted in Asia and South America. One hundred and fourteen recombinant inbred lines (RILs) of Avocet (Susceptible) × Saar, were evaluated along with parents in two dates of sowing in India for 3 years (2007–2008 to 2009–2010) to identify quantitative trait loci (QTL) associated with spot blotch resistance, and to determine the potential association of Lr34 and Lr46 with resistance to this disease. Lr34 was found to constitute the main locus for spot blotch resistance, and explained as much as 55 % of the phenotypic variation in the mean disease data across the six environments. Based on the large effect, the spot blotch resistance at this locus has been given the gene designation Sb1. Two further, minor QTL were detected in the sub-population of RILs not containing Lr34. The first of these was located about 40 cM distal to Lr34 on 7DS, and the other corresponded to Lr46 on 1BL. A major implication for wheat breeding is that Lr34 and Lr46, which are widely used in wheat breeding to improve resistance to rust diseases and powdery mildew, also have a beneficial effect on spot blotch.     

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.     

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。     

Characterization of genetic loci conferring adult plant resistance to leaf rust and stripe rust in spring wheat.

Leaf (brown) and stripe (yellow) rusts, caused by Puccinia triticina and Puccinia striiformis, respectively, are fungal diseases of wheat (Triticum aestivum) that cause significant yield losses annually in many wheat-growing regions of the world. The objectives of our study were to characterize genetic loci associated with resistance to leaf and stripe rusts using molecular markers in a population derived from a cross between the rust-susceptible cultivar 'Avocet S' and the resistant cultivar 'Pavon76'. Using bulked segregant analysis and partial linkage mapping with AFLPs, SSRs and RFLPs, we identified 6 independent loci that contributed to slow rusting or adult plant resistance (APR) to the 2 rust diseases. Using marker information available from existing linkage maps, we have identified additional markers associated with resistance to these 2 diseases and established several linkage groups in the 'Avocet S' x 'Pavon76' population. The putative loci identified on chromosomes 1BL, 4BL, and 6AL influenced resistance to both stripe and leaf rust. The loci on chromosomes 3BS and 6BL had significant effects only on stripe rust, whereas another locus, characterized by AFLP markers, had minor effects on leaf rust only. Data derived from Interval mapping indicated that the loci identified explained 53% of the total phenotypic variation (R2) for stripe rust and 57% for leaf rust averaged across 3 sets of field data. A single chromosome recombinant line population segregating for chromosome 1B was used to map Lr46/Yr29 as a single Mendelian locus. Characterization of slow-rusting genes for leaf and stripe rust in improved wheat germplasm would enable wheat breeders to combine these additional loci with known slow-rusting loci to generate wheat cultivars with higher levels of slow-rusting resistance.     

15个小麦农家品种抗叶锈基因分析

本研究旨在明确小麦农家品种中可能含有的抗叶锈病基因,为抗源的选择和利用提供理论依据。以15个小麦农家品种、感病对照品种郑州5389和36个含有已知抗叶锈病基因的载体品种为材料,苗期接种19个具有鉴别力的叶锈菌生理小种进行基因推导,同时利用12个与抗叶锈病基因紧密连锁的分子标记进行分析。为明确其成株期抗性,分别于2016-2017年和2017-2018年在河北保定对小麦农家品种、感病对照品种郑州5389与慢锈品种SAAR进行田间接种,调查并记录田间严重度及普遍率。基因推导和分子标记检测结果显示,在15个小麦农家品种中共检测到7个抗叶锈病基因,其中部分品种还有多个抗性基因,如红狗豆含有Lr1和Lr46;黄花麦含有Lr13和Lr34;大白麦含有Lr14b和Lr26;洋麦含有Lr37和Lr46;成都光头含有Lr34和Lr46;墨脱麦和西山扁穗含有Lr26和Lr46。部分品种含有1个成株期慢叶锈病抗性基因,如同家坝小麦、武都白茧儿、边巴春麦-6、白花麦含有Lr34;红抢麦、白扁穗和白火麦含有Lr46。这些携带有效抗叶锈病基因的农家品种,可为小麦抗叶锈病育种提供抗源。     

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.     

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     

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.     

Genetic analysis of Aegilops tauschii -derived seedling resistance to leaf rust in synthetic hexaploid wheat

Seedling resistance to leaf rust available in the synthetic hexaploid wheat line Syn137 was characterised by means of cytogenetic and linkage mapping. Monosomic analysis located a single dominant gene for leaf rust resistance on chromosome 5D. Molecular mapping not only confirmed this location but also positioned the gene to the distal part of the long arm of chromosome 5D. A test of allelism showed that the gene, tentatively named LrSyn137, is independent but closely linked to Lr1. It appears that Syn137 is occasionally heterogeneous for Lr1 since the analysis of the Lr1-specific marker RGA567-5 in the genetic mapping population indicated the presence of Lr1. Syn137 represents another source of genetic variation that can be useful for the diversification of leaf rust resistance in wheat cultivars.     

Mapping genes affecting flowering time and frost resistance on chromosome 5B of wheat

Two populations of single chromosome recombinant lines were used to map genes controlling flowering time on chromosome 5B of wheat, and one of the populations was also used to map a new frost resistance gene. Genetic maps were developed, mainly using microsatellite markers, and QTL analysis was applied to phenotypic data on the performance of each population collected from growth-room tests of flowering time and frost tolerance. Using a recombinant substitution-line mapping population derived from a cross between the substitution-line 'Chinese Spring' ('Cheyenne' 5B) and 'Chinese Spring' (CS), the gene Vrn-B1, affecting vernalization response, an earliness per se locus, Eps-5BL1, and a gene, Fr-B1, affecting frost resistance, were mapped. Using a 'Hobbit Sib' ('Chinese Spring' 5BL) x 'Hobbit Sib' recombinant substitution line mapping population, an earliness per se locus, Eps-5BL2 was mapped. The Vrn-B1 locus was mapped on the distal portion of the long arm of chromosome 5B, to a region syntenous with the segments of chromosomes 5A and 5D containing Vrn-A1 and Vrn-D1 loci, respectively. The two Eps-5BL loci were mapped close to the centromere with a 16-cM distance from each other, one in agreement with the position of a homoeologous locus previously mapped on chromosome 5H of barley, and suggested by the response of 'Chinese Spring' deletion lines. The Fr-B1 gene was mapped on the long arm of chromosome 5B, 40 cM from the centromeric marker. Previous comparative mapping data with rice chromosome 9 would suggest that this gene could be orthologous to the other Fr genes mapped previously by us on chromosomes 5A or 5D of wheat, although in a more proximal position. This study completes the mapping of these homoeoallelic series of vernalization requirement genes and frost resistance genes on the chromosomes of the homoeologous group 5 in wheat.     

Genetic mapping of adult plant leaf rust resistance genes Lr48 and Lr49 in common wheat

Hypersensitive adult plant resistance genes Lr48 and Lr49 were named based on their genetic independence of the known adult plant resistance genes. This study was planned to determine genomic locations of these genes. Recombinant inbred line populations derived from crosses involving CSP44 and VL404, sources of Lr48 and Lr49, respectively, and the susceptible parent WL711, were used to determine the genomic locations of these genes. Bulked segregant analyses were performed using multiplex-ready PCR technology. Lr48 in genotype CSP44 was mapped on chromosome arm 2BS flanked by marker loci Xgwm429b (6.1 cM) and Xbarc7 (7.3 cM) distally and proximally, respectively. Leaf rust resistance gene Lr13, carried by the alternate parent WL711, was proximal to Lr48 and was flanked by Xksm58 (5.1 cM) and Xstm773-2 (8.7 cM). Lr49 was flanked by Xbarc163 (8.1 cM) and Xwmc349 (10.1 cM) on chromosome arm 4BL. The likely presence of the durable leaf rust resistance gene Lr34 in both CSP44 and VL404 was confirmed using the tightly linked marker csLV34. Near-isogenic lines for Lr48 and Lr49 were developed in cultivar Lal Bahadur. Genotypes combining Lr13 and/or Lr34 with Lr48 or Lr49 were identified as potential donor sources for cultivar development programs.     

Molecular characterization of durum and common wheat recombinant lines carrying leaf rust resistance (Lr19) and yellow pigment (Y) genes from Lophopyrum ponticum

Chromosome 7E from Lophopyrum ponticum carries a valuable leaf rust resistant gene designated Lr19. This gene has not been widely used in common wheat breeding because of linkage with the yellow pigment gene Y. This gene tints flour yellow, reducing its appeal in bread making. However, a high level of yellow pigment is desirable in durum wheat breeding. We produced 97 recombinant chromosomes between L. ponticum transfer 7D.7E#1 and its wheat homoeologues, using the ph1b mutation that promotes homoeologous pairing. We characterized a subset of 37 of these lines with 11 molecular markers and evaluated their resistance to leaf rust and the abundance of yellow pigment. The Lr19 gene was mapped between loci Xwg420 and Xmwg2062, whereas Y was mapped distal to Xpsr687, the most distal marker on the long arm of chromosome 7. A short terminal 7EL segment translocated to 7A, including Lr19 and Y (line 1-23), has been transferred to durum wheat by backcrossing. The presence of this alien segment significantly increased the abundance of yellow pigment. The Lr19 also conferred resistance to a new durum leaf rust race from California and Mexico that is virulent on most durum wheat cultivars. The new durum lines with the recombinant 7E segment will be useful parents to increase yellow pigment and leaf rust resistance in durum wheat breeding programs. For the common wheat breeding programs, we selected the recombinant line 1-96, which has an interstitial 7E segment carrying Lr19 but not Y. This recombinant line can be used to improve leaf rust resistance without affecting flour color. The 7EL/7DL 1-96 recombinant chromosome did not show the meiotic self-elimination previously reported for a 7EL/7BL translocation.