Lr Genes Research Articles

Mapping of quantitative trait loci for leaf rust resistance in the wheat population 'Xinmai 26/Zhoumai 22'.

Leaf rust, caused by the fungal pathogen Puccinia triticina (Pt), is one of the major and dangerous diseases of wheat, and has caused serious yield loss of wheat worldwide. Here, we investigated adult-plant resistance (APR) to leaf rust in a recombinant inbred line (RIL) population derived from 'Xinmai 26' and 'Zhoumai 22' over 3 years. Linkage mapping for APR to leaf rust revealed four quantitative trait loci (QTL) in this RIL population. Two QTL, QLr.hnau-2BS and QLr.hnau-3BS were contributed by 'Zhoumai22', whereas QLr.hnau-2DS and QLr.hnau-5AL were contributed by 'Xinmai 26'. The QLr.hnau-2BS covering a race-specific resistance gene Lr13 showed the most stable APR to leaf rust. Overexpression of Lr13 significantly increased APR to leaf rust. Interestingly, we found that a CNL(coiled coil-nucleotide-binding site-leucine-rich repeat)-like gene, TaCN, in QLr.hnau-2BS completely co-segregated with leaf rust resistance. The resistant haplotype TaCN-R possessed half the sequence of the coiled-coil domain of TaCN protein. Lr13 strongly interacted with TaCN-R, but did not interact with the full-length TaCN (TaCN-S). In addition, TaCN-R was significantly induced after Pt inoculation and changed the sub-cellular localization of Lr13 after interaction. Therefore, we hypothesized that TaCN-R mediated leaf rust resistance possibly by interacting with Lr13. This study provides important QTL for APR to leaf rust, and new insights into understanding how a CNL gene modulates disease resistance in common wheat.

High Resolution Melting (HRM) based marker development for wheat leaf rust resistance gene Lr34.

Deploying adult plant resistance (APR) against rust diseases is an important breeding objective of most wheat breeding programs. The gene Lr34 is an effective and widely deployed broad spectrum APR gene in wheat against leaf rust fungus Puccinia triticina. Various molecular markers have been developed for Lr34 but, either they require post-PCR handling processes or are not economical. Herein, we developed a high resolution melting (HRM) based diagnostic assay for Lr34 based on a three bp 'TTC' deletion in exon 11 of the resistant allele. The susceptible cv. Thatcher (Tc) and the near-isogenic Thatcher line (RL6058) with Lr34, yielded distinct melting profiles and were differentiated with high reproducibility. For further validation, all three copies of Lr34 were cloned in plasmid vectors and HRM analysis using individual and combination (equimolar mixture of three copies) of homoeologs yielded distinguishing melting profiles. An additional layer of genotyping was provided by a LunaProbe assay. The allele-specific probes successfully distinguished the homoeologs but not Tc and RL6058. Further, the practical deployment of the HRM assay was tested by running the marker on a set of breeding lines. When compared with a kompetitive allele-specific PCR (KASP) Lr34 assay, the HRM assay had similar genotyping results and was able to accurately differentiate the resistant and susceptible breeding lines. However, our HRM assay was unable to detect the heterozygote. To our knowledge, this is the first report of an HRM assay for genotyping a wheat rust resistance gene.

Variations in exons 11 and 12 of the multi-pest resistance wheat gene Lr34 are independently additive for leaf rust resistance.

Characterization of germplasm collections for the wheat leaf rust gene Lr34 previously defined five haplotypes in spring wheat. All resistant lines had a 3-bp TTC deletion (null) in exon 11, resulting in the absence of a phenylalanine residue in the ABC transporter, as well as a single nucleotide C (Tyrosine in Lr34+) to T (Histidine in Lr34-) transition in exon 12. A rare haplotype present in Odesskaja 13 and Koktunkulskaja 332, both of intermediate rust resistance, had the 3-bp deletion typical of Lr34+ in exon 11 but the T nucleotide of Lr34- in exon 12. To quantify the role of each mutation in leaf rust resistance, Odesskaja 13 and Koktunkulskaja 332 were crossed to Thatcher and its near-isogenic line Thatcher-Lr34 (RL6058). Single seed descent populations were generated and evaluated for rust resistance in six different rust nurseries. The Odesskaja 13 progeny with the TTC/T haplotype were susceptible with an average severity rating of 62.3%, the null/T haplotype progeny averaged 39.7% and the null/C haplotype was highly resistant, averaging 13.3% severity. The numbers for the Koktunkulskaja 332 crosses were similar with 63.5%, 43.5% and 23.7% severity ratings, respectively. Differences between all classes in all crosses were statistically significant, indicating that both mutations are independently additive for leaf rust resistance. The three-dimensional structural models of LR34 were used to analyze the locations and putative interference of both amino acids with the transport channel. Koktunkulskaja 332 also segregated for marker csLV46 which is linked to Lr46. Rust severity in lines with Lr34+ and csLV46+ had significantly lower rust severity ratings than those without, indicating the additivity of the two loci. This has implications for the deployment of Lr34 in wheat cultivars and for the basic understanding of this important wheat multi-pest durable resistance gene.

Genetics of Resistance to Leaf Rust in Wheat: An Overview in a Genome-Wide Level

Due to the global warming and dynamic changes in pathogenic virulence, leaf rust caused by Puccinia triticina has greatly expanded its epidermic region and become a severe threat to global wheat production. Genetic bases of wheat resistance to leaf rust mainly rely on the leaf rust resistance (Lr) gene or quantitative trait locus (QLr). Although these genetic loci have been insensitively studied during the last two decades, an updated overview of Lr/QLr in a genome-wide level is urgently needed. This review summarized recent progresses of genetic studies of wheat resistance to leaf rust. Wheat germplasms with great potentials for genetic improvement in resistance to leaf rust were highlighted. Key information about the genetic loci carrying Lr/QLr was summarized. A genome-wide chromosome distribution map for all of the Lr/QLr was generated based on the released wheat reference genome. In conclusion, this review has provided valuable sources for both wheat breeders and researchers to understand the genetics of resistance to leaf rust in wheat.

Identification of leaf rust resistance loci in a geographically diverse panel of wheat using genome-wide association analysis.

Leaf rust, caused by Puccinia triticina (Pt) is among the most devastating diseases posing a significant threat to global wheat production. The continuously evolving virulent Pt races in North America calls for exploring new sources of leaf rust resistance. A diversity panel of 365 bread wheat accessions selected from a worldwide population of landraces and cultivars was evaluated at the seedling stage against four Pt races (TDBJQ, TBBGS, MNPSD and, TNBJS). A wide distribution of seedling responses against the four Pt races was observed. Majority of the genotypes displayed a susceptible response with only 28 (9.8%), 59 (13.5%), 45 (12.5%), and 29 (8.1%) wheat accessions exhibiting a highly resistant response to TDBJQ, TBBGS, MNPSD and, TNBJS, respectively. Further, we conducted a high-resolution multi-locus genome-wide association study (GWAS) using a set of 302,524 high-quality single nucleotide polymorphisms (SNPs). The GWAS analysis identified 27 marker-trait associations (MTAs) for leaf rust resistance on different wheat chromosomes of which 20 MTAs were found in the vicinity of known Lr genes, MTAs, or quantitative traits loci (QTLs) identified in previous studies. The remaining seven significant MTAs identified represent genomic regions that harbor potentially novel genes for leaf rust resistance. Furthermore, the candidate gene analysis for the significant MTAs identified various genes of interest that may be involved in disease resistance. The identified resistant lines and SNPs linked to the QTLs in this study will serve as valuable resources in wheat rust resistance breeding programs.

Long-Term Studies of Wheat Leaf Rust in the North-Western Region of Russia

Leaf rust, caused by Puccinia triticina (Pt), is a widely occurring disease of wheat in the North-Western Region of Russia. Annual Pt surveys of wheat in this region have been conducted between 2001 and 2021. In total, 740 single urediniospore isolates were analyzed over 20 years. Virulence to Lr9, Lr19 and Lr24 were rare in 2001–2010 and was not detected after 2010. Temporal variation in virulence was determined on Thatcher lines with Lr1, Lr2a, Lr2b and Lr2c genes and was found to be relatively high. Virulence to Lr1 increased to 100% from 2001 to 2014. Until 2010, most northwestern Pt isolates were avirulent to Lr2a and virulent to Lr2b and Lr2c. In the middle of 2010, avirulence to Lr2a, Lr2b, Lr2c and Lr15 began to increase. Strong variability between years was revealed for virulence to Lr20 and Lr26. Based on a set of 20 differential lines, 122 virulence pathotypes were detected. More than half of those were observed only once across all years. Pathotypes were divided into groups of B-, C-, D- and F-, virulent to Lr1 and Lr2a, dominating until 2009. From 2010 pathotype groups M- and P-, virulent to Lr1 and avirulent to Lr2a, began to dominate. Temporal differentiation of northwestern Pt population for virulence was determined. High similarity was observed for Pt accessions in 2001–2009 and 2010–2015 and these two groups differed moderately from each other. Pt accessions from 2016–2019 and 2020–2021 differed from each other and from accessions from the previous collection period. Field response of Lr differential lines was studied in the North-Western Region during 1998–2022. Wheat genotypes with genes Lr9, Lr19, Lr23, Lr24, Lr25, Lr28, Lr29, Lr35, Lr39, Lr42, Lr43, Lr45, Lr47, Lr48, Lr49, Lr50, Lr51, Lr53 and Lr57 remained resistant throughout the period of the study. Leaf rust severity in lines TcLr12, TcLr21, TcLr22a, Gatcher (Lr27+31), TcLr44 and Pavon (Lr46) varied from 1% to 30% before 2014 and significantly decreased after 2014. A general trend of decreasing virulence of the Pt pathogen has been observed in the North-Western Region over the recent years.

Lipoprotein receptors in ovary of eel, Anguilla australis: molecular characterisation of putative vitellogenin receptors

Lipoprotein receptors, including low-density lipoprotein receptor (LDLr) relatives (Lrs) and LDLr-related proteins (Lrps), belong to the LDLr supergene family and participate in diverse physiological functions. In this study, novel sequences of lr and lrp genes expressed in the ovary of the short-finned eel, Anguilla australis, during early gonadal development are presented. The genes encoding the LDLr-like, Lrp1-like, Lrp1b-like, Lrp3, Lrp4-like, Lrp5-like, Lrp6, Lrp10, Lrp11, Lrp12-like, and Lr11-like proteins were found and identified by sequence and structure analysis, in addition to phylogenetic analysis. Genes encoding proteins previously implicated in follicle development and vitellogenin (Vtg) uptake in oviparous vertebrates were also identified, i.e. lr8 (including lr8 + and lr8- variants) and lrp13; their identification was reinforced by conserved synteny with orthologues in other teleost fish. Compared to other lr/lrp genes, the genes encoding Lr8 + , Lr8-, and Lrp13 were highly expressed in ovary during early development, decreasing as oocyte development advanced when induced by hypophysation. Furthermore, lr8 + , lr8-, and lrp13 were dominantly expressed in the ovary when compared with 17 other tissues. Finally, this study successfully detected the expression of both lr8 variants, which showed different expression patterns to those reported in other oviparous vertebrates and provided the first characterisation of Lrp13 in Anguilla sp. We propose that lr8 + , lr8-, and lrp13 encode putative Vtg receptors in anguillid eels.

Genome-wide association analyses of leaf rust resistance in cultivated emmer wheat.

Fifteen and eleven loci, with most loci being novel, were identified to associate with seedling and adult resistances, respectively, to the durum-specific races of leaf rust pathogen in cultivated emmer. Leaf rust, caused by Puccinia triticina (Pt), constantly threatens durum (Triticum turgidum ssp. durum) and bread wheat (Triticum aestivum) production worldwide. A Pt race BBBQD detected in California in 2009 poses a potential threat to durum production in North America because resistance source to this race is rare in durum germplasm. To find new resistance sources, we assessed a panel of 180 cultivated emmer wheat (Triticum turgidum ssp. dicoccum) accessions for seedling resistance to BBBQD and for adult resistance to a mixture of durum-specific races BBBQJ, CCMSS, and MCDSS in the field, and genotyped the panel using genotype-by-sequencing (GBS) and the 9K SNP (Single Nucleotide Polymorphism) Infinium array. The results showed 24 and nine accessions consistently exhibited seedling and adult resistance, respectively, with two accessions providing resistance at both stages. We performed genome-wide association studies using 46,383 GBS and 4,331 9K SNP markers and identified 15 quantitative trait loci (QTL) for seedling resistance located mostly on chromosomes 2B and 6B, and 11 QTL for adult resistance on 2B, 3B and 6A. Of these QTL, one might be associated with leaf rust resistance (Lr) gene Lr53, and two with the QTL previously reported in durum or hexaploid wheat. The remaining QTL are potentially associated with new Lr genes. Further linkage analysis and gene cloning are necessary to identify the causal genes underlying these QTL. The emmer accessions with high levels of resistance will be useful for developing mapping populations and adapted durum germplasm and varieties with resistance to the durum-specific races.

Multiplex PCR assay for the simultaneous identification of race specific and non-specific leaf resistance genes in wheat (Triticum aestivum L.)

Race-nonspecific resistance is a key to sustainable management of pathogens in bread wheat (Triticum aestivum L.) breeding. It is more durable compared to race-specific immunity, conferred by the major genes (R), which are often overcome by pathogens. The accumulation of the genes, which provide the resistance to a specific race of a pathogen, together with the introduction of race-non-specific resistance genes is the most effective strategy aimed at preventing the breakdown of genetically conditioned immunity. PCR markers improved the productivity and accuracy of classical plant breeding by means of marker-assisted selection (MAS). Multiplexing assays provide increased throughput, reduced reaction cost, and conservation of limited sample material, which are beneficial for breeding purposes. Here, we described the process of customizing multiplex PCR assay for the simultaneous identification of the major leaf rust resistance genes Lr19, Lr24, Lr26, and Lr38, as well as the slow rusting, race-nonspecific resistance genes: Lr34 and Lr68, in thirteen combinations. The adaptation of PCR markers for multiplex assays relied on: (1) selection of primers with an appropriate length; (2) selection of common annealing/extension temperature for given primers; and (3) PCR mixture modifications consisting of increased concentration of primers for the scanty band signals or decreased concentration of primers for the strong bands. These multiplex PCR protocols can be integrated into a marker-assisted selection of the leaf rust-resistant wheat genotypes.

Leaf rust responsive miRNA and their target genes in wheat.

Small RNA sequencing (sRNA-seq) and degradome analysis were used for the identification of miRNAs and their target host genes in a pair of near-isogenic lines (NILs), which differed for the presence of leaf rust resistance gene Lr28. The study led to identification of (i) 506 known and 346 novel miRNAs; and (ii) 5054 target genes including 4557 in silico predicted and 497 degradome-based genes using 105 differentially expressed (DE) miRNAs. A subset of 128 targets (67 in silico + 61 degradome-based) was differentially expressed in RNA-seq data that was generated by us earlier using the same pair of NILs; among these 128 targets, 58 target genes exhibited an inverse relationship with the DE miRNAs (expression of miRNAs and activation/suppression of target genes). Eight miRNAs which belonged to the conserved miRNA families and were known to be induced in response to fungal diseases in plants included the following: miR156, miR158, miR159, miR168, miR169, miR172, miR319, miR396. The target genes belonged to the following classes of genes known to be involved in downstream disease resistance pathways; peroxidases, sugar transporters, auxin response signaling, oxidation-reduction, etc. It was also noticed that although a majority of miRNAs and target genes followed the above classical inverse relationship, there were also examples, where no such relationship was observed. Among the target genes, there were also 51 genes that were not only regulated by miRNAs, but were also differentially methylated at sequences including the following segments: promotors, introns, TSS, exons. The results of the present study suggest a complex interplay among miRNA genes, target genes, and various epigenetic controls, which regulate the expression of genes involved in downstream pathways for disease resistance.

Diversity of new Russian bread wheat cultivars according to leaf rust resistance genes

Background. Cultivation of resistant cultivars is an effective method of wheat protection against leaf rust. The purpose of this work was to characterize the juvenile leaf rust resistance of bread wheat cultivars listed in the State Register for Selection Achievements in 2021 and identify their Lr genes using molecular markers.Materials and methods. The material included 18 cultivars of winter bread wheat and nine spring ones. Juvenile resistance in the seedling phase was assessed with two test clones (kLr9 и kLr19) and the Krasnodar population of Puccinia triticina Erikss. Molecular markers were used to identify 18 Lr genes.Results and discussion. A high level of resistance (score 0 or 0;) was shown by cvs. ‘Khamdan’, ‘Sharm’ and ‘Omskaya 44’; moderate resistance (score 2, 2+) by ‘Albidum 2030’. Reactions of ‘Polina’, ‘Rossyp’, ‘Status’, ‘Balkysh’ and ‘Bogema’ were variable. The studied cultivars did not contain juvenile genes Lr9, Lr24, Lr25, Lr28, Lr29, Lr39, Lr47 or Lr66 and adult plant resistance genes Lr21 and Lr35. Markers of identifiable genes were not detected in cv. ‘Sharm’, highly resistant to leaf rust. ‘Khamdan’ had an ineffective Lr10 gene and a partial resistance gene Lr34, which offered no protection in the seedling stage. These cultivars seem to contain additional resistance genes. A high level of resistance to leaf rust in ‘Omskaya 44’ is provided by a combination of the Lr19, Lr26, Lr1 and Lr3 genes. In ‘Nemchinovskaya 85’, the partially effective adult plant resistance gene Lr37 was identified. In other tested cultivars, Lr1, Lr3, Lr10, Lr26 and Lr34 were widely represented.

Screening of leaf rust resistance genes (Lr) in the breeding lines of winter bread wheat

In the Rostov region, among cereal crops, winter wheat occupies a leading position in terms of the sown area. Breeders have developed wheat varieties, a productivity potential of which is 1.5–2 times higher than their actual yield in production. One of the most important factors that can destabilize gross grain harvests and reduce productivity are parasitic organisms, the most dangerous of which are rust pathogens (Puccinia triticina, P.striiformis, P.graminis). Brown rust (pathogen Puccinia triticina Erikss.) is one of the dangerous wheat diseases. The genetic diversity of cultivated varieties according to resistance types and genes that control it, provides reliable wheat protection against this pathogen. The purpose of the current study was to identify leaf rust resistance genes (Lr-genes) using marker selection for the winter bread wheat lines. The study was carried out in 2020–2021. The objects of research were 311 winter bread wheat lines of the FSBSI Agricultural Research Center «Donskoy». In the study of winter bread wheat lines, there were used such methods as DNA isolation using CTAB, PCR, and electrophoresis on agarose gels. Using molecular markers, there have been identified 24 samples with a functional allele of the Lr10 gene (1672, 518/21 (1), 595/21 (1) 595 (4), 625/21, 626/21, etc.), 49 samples with the dominant allele Lr26 (1105, 502/21, 526/21 (1), 526/21 (2), 529/21 (12), 557/21, etc.), 13 lines with the resistance allele of the Lr37 gene (1105, 1609, 1610, 1611, 1612, 1613, 1615, etc.). There was also found that the Lr17a gene was not detected in the studied lines.

Identification and characterization of leaf rust (Puccinia triticina) and Fusarium head blight (Fusarium graminearum) related genes in domesticated wheat varieties in Mongolia

Wheat is recognized as the major crop among all cereals. For better quality and disease-free production, the current study was designed to evaluate the prevalence of genetic leaf rust resistance and fusarium head blight in nineteen genotypes of wheat, which are commonly grown in Mongolia. For example Khalkhgol-1, Darkhan-131, Darkhan-160, Darkhan-144, Orkhon, Darkhan-34, Darkhan-74, Darkhan-193, Altaiskaya-100, Darkhan-181, Darkhan-141, Buryatskaya osistiya, Darkhan-166, Buryatskaya-79, Buryatskaya-34, Selenge, Altaiskaya-530, Altaiskaya-325 and Altaiskaya jinitsa genotypes. The presence of Lr34 and Fhbt1 genes were evaluated for leaf rust and fusarium head blight respectively. Lr34 gene was reported in the Darkhan-160 and Darkhan-181 genotypes, while fusarium head blight was not reported in any of the genotype.

Broad-Spectrum Resistance to Leaf Rust in the Argentinean Wheat Cultivar “Klein Proteo” Is Controlled by LrKP Located on Chromosome 2BS

Wheat leaf rust, caused by Puccinia triticina, is a severe fungal disease threatening global wheat production. The rational application of genetic loci controlling wheat resistance to leaf rust in breeding practice is still the best choice for disease control. A previous study indicated that the Argentinean wheat cultivar “Klein Proteo” might carry leaf rust resistance (Lr) genes Lr3a and Lr10, as well as an unknown Lr gene. In this study, seedlings of “Klein Proteo” showed high resistance to all the 20 Pt pathotypes isolated in China. Using bulked segregant RNA sequencing (BSR-seq) and developed CAPS markers, the single-dominant gene LrKP was initially mapped to a 114–168 Mb region on chromosome 2BS. Using gene-specific primers of a previously cloned chromosome 2BS-located Lr13 gene, we found that “Klein Proteo” also carried the Lr13 gene. Moreover, the expression of Lr13 in the resistant bulk was significantly higher than that in the susceptible bulk. Nevertheless, “Klein Proteo” showed a much broader and higher resistance compared with the near isogenic line and “ZhouMai 22” carrying Lr13. In conclusion, the wheat cultivar “Klein Proteo” showed great potential in the genetic improvement of wheat resistance to leaf rust in China and the genetic bases controlling the broad-spectrum resistance were initially revealed.

Evaluation of the resistance to Chinese predominant races of Puccinia triticina and analysis of effective leaf rust resistance genes in wheat accessions from the U.S. National Plant Germplasm System.

Puccinia triticina, which is the causative agent of wheat leaf rust, is widely spread in China and most other wheat-planting countries around the globe. Cultivating resistant wheat cultivars is the most economical, effective, and environmentally friendly method for controlling leaf rust-caused yield damage. Exploring the source of resistance is very important in wheat resistance breeding programs. In order to explore more effective resistance sources for wheat leaf rust, the resistance of 112 wheat accessions introduced from the U.S. National Plant Germplasm System were identified using a mixture of pathogenic isolates of THTT, THTS, PHTT, THJT and THJS which are the most predominant races in China. As a result, all of these accessions showed high resistance at seedling stage, of which, ninety-nine accessions exhibited resistance at adult plant stage. Eleven molecular markers of eight effective leaf rust resistance genes in China were used to screen the 112 accessions. Seven effective leaf rust resistance genes Lr9, Lr19, Lr24, Lr28, Lr29, Lr38 and Lr45 were detected, except Lr47. Twenty-three accessions had only one of those seven effective leaf rust resistance gene. Eleven accessions carried Lr24+Lr38, and 7 accessions carried Lr9+Lr24+Lr38, Lr24+Lr38+Lr45, Lr24+Lr29+Lr38 and Lr19+Lr38+Lr45 respectively. The remaining seventy-one accessions had none of those eight effective leaf rust resistance genes. This study will provide theoretical guidance for rational utilization of these introduted wheat accessions directly or for breeding the resistant wheat cultivars.

Marker assisted improvement for leaf rust and moisture deficit stress tolerance in wheat variety HD3086.

There is a significant yield reduction in the wheat crop as a result of different biotic and abiotic stresses, and changing climate, among them moisture deficit stress and leaf rust are the major ones affecting wheat worldwide. HD3086 is a high-yielding wheat variety that has been released for commercial cultivation under timely sown irrigated conditions in the Indo-Gangetic plains of India. Variety HD3086 provides a good, stable yield, and it is the choice of millions of farmers in India. It becomes susceptible to the most prevalent pathotypes 77-5 and 77-9 of Puccinia triticina (causing leaf rust) in the production environment and its potential yield cannot be realized under moisture deficit stress. The present study demonstrates the use of a marker-assisted back cross breeding approach to the successful transfer of leaf rust resistance gene Lr24 and QTLs linked to moisture deficit stress tolerance in the background of HD3086. The genotype HI1500 was used as a donor parent that possesses leaf rust-resistant gene Lr24, which confers resistance against the major pathotypes found in the production environment. It possesses inbuilt tolerance under abiotic stresses with superior quality traits. Foreground selection for gene Lr24 and moisture deficit stress tolerance QTLs linked to Canopy temperature (CT), Normal Differential Vegetation Index (NDVI) and Thousand Kernel Weight (TKW) in different generations of the backcrossing and selection. In BC2F2, foreground selection was carried out to identify homozygous lines based on the linked markers and were advanced following pedigree based phenotypic selection. The selected lines were evaluated against P. triticina pathotypes 77-5 and 77-9 under controlled conditions. Recurrent parent recovery of the selected lines ranged from 78-94%. The identified lines were evaluated for their tolerance to moisture stress under field conditions and their resistance to rust under artificial epiphytotic conditions for two years. In BC2F5 generation, eight positive lines for marker alleles were selected which showed resistance to leaf rust and recorded an improvement in component traits of moisture deficit stress tolerance such as CT, NDVI, TKW and yield compared to the recurrent parent HD3086. The derived line is named HD3471 and is nominated for national trials for testing and further release for commercial cultivation.

Fine mapping and marker development for the wheat leaf rust resistance gene Lr32.

Wheat leaf rust is caused by the fungal pathogen Puccinia triticina and is one of the wheat diseases of concern globally. Among the known leaf rust resistance genes (Lr) genes, Lr32 is a broadly effective gene derived from the diploid species Aegilops tauschii coss. accession RL5497-1 and has been genetically mapped to chromosome arm 3DS. However, Lr32 resistance has not been utilized in current cultivars in part due to the lack of modern, predictive DNA markers. The goals of this study were to fine map the Lr32 region and develop SNP-based kompetitive allele-specific polymerase chain reaction markers. The genomic analysis was conducted by using doubled haploid and F2-derived mapping populations. For marker development, a 90K wheat chip array, 35K and 820K Axiom R SNPs, A. tauschii pseudomolecules v4.0 and International Wheat Genome Sequencing Consortium ReqSeq v2.1 reference genomes were used. Total 28 kompetitive allele-specific polymerase chain reaction and 2 simple sequence repeat markers were developed. The Lr32 region was fine mapped between kompetitive allele-specific polymerase chain reaction markers Kwh142 and Kwh355 that flanked 34-35 Mb of the diploid and hexaploid reference genomes. Leaf rust resistance mapped as a Mendelian trait that cosegregated with 20 markers, recombination restriction limited the further resolution of the Lr32 region. A total of 10-11 candidate genes associated with disease resistance were identified between the flanking regions on both reference genomes, with the majority belonging to the nucleotide-binding domain and leucine-rich repeat gene family. The validation analysis selected 2 kompetitive allele-specific polymerase chain reaction markers, Kwh147 and Kwh722, for marker-assisted selection. The presence of Lr32 along with other Lr genes such as Lr67 and Lr34 would increase the resistance in future wheat breeding lines and have a high impact on controlling wheat leaf rust.

Mutations in Puccinia triticina pathotypes in wheat rust repository in India

AbstractTwo new variants of Puccinia triticina were identified in the repository cultures of pathotypes 20 (5R27 = SGQPL) and 107‐1 (45R35 = JCGPL) being maintained as live cultures in the national repository at Shimla, Himachal Pradesh, India, for 87 and 24 years, respectively. Mixtures of infection types were observed on Lr15 in one pathotype 20 whereas on Lr3 in 107‐1. The single pustule isolations and further purification in both the cases yielded two new pathotypes designated as 20‐2 (57R27 = SHKPL) and 57 (45R39 = KGTPL). The pathotype 20‐2 was one‐step gain in virulence to Lr15 in mother culture of pathotype 20. Contrarily, the second new pathotype though close to 107‐1 (with additional virulence to Lr3), however, resembled standard race 57 of the classical differentials. The difference in virulence on one gene as compared to the respective mother culture and their non‐detection from the field samples reflects mutation for virulence in situ. To confirm the novelty of new pathotypes, detailed studies were conducted on differentials, avirulence/virulence on Lr genes, DNA polymorphism using SSR markers, and the results are presented in this publication. The new variants have been added to the live culture collection of the centre and designated as PrtI 57 and PrtI 20‐2.

Phenotypic and molecular dissection of all-stage and adult-plant leaf rust resistance in Iranian Aegilops tauschii

Leaf rust caused by Puccinia triticina (Pt) is the most prevalent disease of wheat, which threatens its production worldwide. The most viable strategy to control this disease is genetic resistance, which can be achieved through deploying new resistance genes. Hence, we studied a collection of 117 Iranian Ae. tauschii along with 31 near isogenic lines lines of the wheat cultivar Thatcher at the seedling stage using 12 Pt pathotypes to postulate leaf rust resistance (Lr) gene(s). Nine specific markers for the genes Lr1, Lr19, Lr21, Lr22a, Lr24, Lr32, Lr37, Lr39, and Lr42 were also utilized to investigate the presence of corresponding Lr genes in the germplasm and validate the phenotyping results. Fifty-two accessions produced high infection types (ITs) of ‘3-’ to ‘3+’ to at least one pathotype, while the remaining 65 showed low ITs (0;= to 2+) against all pathotypes. Resistant accessions often belonged to the southeastern shores of the Caspian Sea and the strangulata subspecies. Based on phenotyping results and molecular markers the genes Lr1, Lr15, Lr19, Lr22a, Lr32, Lr37, Lr39, and Lr42 in addition to unknown Lr gene(s) were present either individually or in combinations in 112 accessions of Ae. tauschii, while the remaining five accessions probably did not carry any detectable Lr gene. The presence of the all-stage resistance genes Lr1 and Lr32 was confirmed in all accessions postulated to carry them. Adult plant resistance (APR) was also evaluated where 19 accessions were found to possess potentially novel APR gene(s). Overall, this study identified genotypes with possibly new genes, which could be used in wheat breeding programs, and are valuable for genetic analysis of their resistance gene(s). Moreover, the environment and subspecies in which higher resistance levels are more common, were identified.

AN OVERVIEW OF LEAF RUST RESISTANCE GENES IN TRITICUM AESTIVUM

Wheat is the world's third big crop producing 600 million tonnes yearly. For example, wheat harvest in 2007 was 607 million tonnes compared to rice and maize production of rice was 652 million tonnes and production of maize was 785 million tonnes. Although, due to fungus diseases, we lose 10% of our crops yearly. Leaf rust (Lr), Stripe rust (Sr), and yellow rust (Yr) are the three types of rust that are present in wheat. In this article, we discussed leaf rust and its resistance genes. Leaf rust is also known as “Brown Rust”. This disease is caused by the fungus Puccinia recondita f. sp tritici, which is the most serious in common wheat (Triticum aestivum). These fungal pathogen-caused resistance genes degrade the amount and quality of wheat fields. Leaf rust is primarily found on leaves, but it can also infect glumes. Scientists studying the illness have discovered that there are many types of resistance genes present in Leaf rust, which is also known as Lr. Until today there are 80 resistance genes have been discovered in leaf rust (Lr). So, the resistance genes Lr1 to Lr3ka, Lr10 to Lr13, Lr14b to Lr17b, Lr20, Lr22b, Lr27, Lr30, Lr31, Lr33, Lr34, Lr46, Lr48, Lr49, Lr52, Lr60, Lr67 to Lr70, Lr73 to Lr75, Lr78 and Lr80 theses all resistance genes of leaf rust (Lr) present in wheat (Triticum aestivum). These genes, Lr9 and Lr76 were discovered in (Aegilops umbellulate). Lr14a is a subset of Lr14 (Triticum dicoccum). Lr18 and Lr50 (Triticum timopheevii). Lr19, Lr24, Lr29 (Thinopyrum ponticum). Lr21, Lr22a, Lr32, Lr39, Lr42 (Aegilops tauschii). Lr23, Lr61 and Lr72 are different LRs (Triticum turgidum ssp. Durum). Lr25, Lr26, and Lr45 (Secale cereale). Lr28, Lr35, Lr36, Lr47, Lr51, Lr66 (Aegilops speltoides). Lr37 is an abbreviated form of the word (Triticum ventricosum). Lr38 is a slang name for a (Thinopyrum intermedium). Lr44, Lr65 and Lr71 (Triticum aestivum spelta). Lr53 and Lr64 (Triticum dicoccides). Lr54 is the resistance gene assigned to (Aegilops kotschyi). Lr55 is slang (Elymus trachycaulis). Lr56(Aegilops sharonensis). Lr57(Aegilops geniculate). Lr58(Aegilops triuncialis). Lr59(Aegilops peregrina). Lr62 (Aegilops neglecta). Lr63 (Triticum monococcum). Lr77 (Santa Fe). Lr79 (Triticum durum). Different varieties of wheat include these resistance genes. These resistance genes were identified because farmers don’t use spares or toxic chemicals on wheat. After all, these chemicals affect human health, so these resistance genes were identified to save human health.