Stem Rust Resistance Genes Research Articles

Characterization of some local and commercial bread wheat (Triticum aestivum L.) genotypes with allele-specific DNA markers

Landraces play a significant role as genetic reservoirs in wheat breeding endeavors. Advances in functional marker technology have facilitated early and more precise selection processes. This study involved the characterization of a total of 96 bread wheat genotypes, comprising 76 landraces and 20 registered cultivars, utilizing allele-specific DNA markers targeting various genes including those for gluten strength, yellow rust resistance, stem rust resistance, dwarfism, rye translocation, hardness, and softness. Molecular analysis revealed the presence of 148 alleles, with an average of 21.14 alleles per marker, and an average polymorphic information content (PIC) value of 0.5625. Specific genes such as the rye translocation gene were identified in genotypes 161 and 884, while the hardness gene was found in genotypes 672, 3088, 3384, 3414, and 3541. Stem rust resistance gene was detected in the cultivar Adana-99, yellow rust resistance gene in genotypes 1635 and 2115, and the softness gene in 31 genotypes including the cultivar Masaccio. Based on the dendrogram analysis, genotype 3652 exhibited around 93% genetic similarity with the cultivar Masaccio, while genotypes 2190, 2715, and 2897 showed similarity to genotype 2946. Genotypes 2959 and 2960 and genotypes 3334 and 3359 shared approximately 91% genetic similarity.

Mapping rust resistance in European winter wheat: many QTLs for yellow rust resistance, but only a few well characterized genes for stem rust resistance

Key messageStem rust resistance was mainly based on a few, already known resistance genes; for yellow rust resistance there was a combination of designated genes and minor QTLs.Yellow rust (YR) caused by Puccinia striiformis f. sp. tritici (Pst) and stem rust (SR) caused by Puccinia graminis f. sp. tritici (Pgt) are among the most damaging wheat diseases. Although, yellow rust has occurred regularly in Europe since the advent of the Warrior race in 2011, damaging stem rust epidemics are still unusual. We analyzed the resistance of seven segregating populations at the adult growth stage with the parents being selected for YR and SR resistances across three to six environments (location–year combinations) following inoculation with defined Pst and Pgt races. In total, 600 progenies were phenotyped and 563 were genotyped with a 25k SNP array. For SR resistance, three major resistance genes (Sr24, Sr31, Sr38/Yr17) were detected in different combinations. Additional QTLs provided much smaller effects except for a gene on chromosome 4B that explained much of the genetic variance. For YR resistance, ten loci with highly varying percentages of explained genetic variance (pG, 6–99%) were mapped. Our results imply that introgression of new SR resistances will be necessary for breeding future rust resistant cultivars, whereas YR resistance can be achieved by genomic selection of many of the detected QTLs.

Effectiveness of Stem Rust Resistance Genes in Southern Russia

ABSTRACTWheat stem rust (caused by Puccinia graminis f.sp. tritici) is a damaging disease widespread in all grain‐producing regions of the world. In this work, the effectiveness of Sr genes was analysed under field conditions in the southern region of Russia (Krasnodar Krai, Stavropol Krai and Rostov Oblast) during 2016‐2021. The data were obtained using a set of 46 isogenic lines and varieties with artificial inoculation. The Sr31 gene proved absolute effectiveness in the field. Effective (1R–10R) Sr genes were the following: 5, 12, 35 and 37; moderately effective (10MR–30MR) Sr genes: 1, 6, 9g, 10, 11, 13, 14, 15, 20, 22, 23, 24, 25, 32, 33, 38 and WLD. Lines with Sr genes 7a, 7b, 8a, 8b, 9a, 9b, 9d, 9e, 9f, 16, 17, 19, 21, 26, 27, 29, 30, 36, 39, 40, 44, Dp2, Gt and Tmp were ineffective in the adult plant phase (30MS–70S). Polymorphism of infection types and disease severity was noted for most of these lines in different years. Ongoing analysis of the efficiency of Sr genes in the region is important to prevent the risk of epidemics, and lines with stem rust resistance genes that have shown efficiency can be used as donors in breeding programmes.

Identification of Candidate Avirulence and Virulence Genes Corresponding to Stem Rust (Puccinia graminis f. sp. tritici) Resistance Genes in Wheat.

Stem rust, caused by the biotrophic fungal pathogen Puccinia graminis f. sp. tritici (Pgt), is an important disease of wheat. However, the majority of Pgt virulence/avirulence loci and underlying genes remain uncharacterized due to the constraints of developing bi-parental populations with this obligate biotroph. Genome-wide association studies (GWAS) using a sexual Pgt population mainly collected from the Pacific Northwestern United States were used to identify candidate virulence/avirulence effector genes corresponding to the six wheat Sr genes: Sr5, Sr21, Sr8a, Sr17, Sr9a, and Sr9d. The Pgt isolates were genotyped using whole-genome shotgun sequencing that identified approximately 1.2 million single nucleotide polymorphisms (SNPs) and were phenotyped at the seedling stage on six Sr gene differential lines. Association mapping analyses identified 17 Pgt loci associated with virulence or avirulence phenotypes on six Pgt resistance genes. Among these loci, 16 interacted with a specific Sr gene, indicating Sr-gene specific interactions. However, one avirulence locus interacted with two separate Sr genes (Sr9a and Sr17), suggesting two distinct Sr genes identifying a single avirulence effector. A total of 24 unique effector gene candidates were identified, and haplotype analysis suggests that within this population, AvrSr5, AvrSr21, AvrSr8a, AvrSr17, and AvrSr9a are dominant avirulence genes, while avrSr9d is a dominant virulence gene. The putative effector genes will be fundamental for future effector gene cloning efforts, allowing for further understanding of rust effector biology and the mechanisms underlying virulence evolution in Pgt with respect to race-specific R-genes. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Stem Rust Resistance and Resistance-Associated Genes in 64 Wheat Cultivars from Southern Huanghuai, China.

Wheat stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is a devastating fungal disease that affects wheat globally. The planting of resistant cultivars is the most cost-effective strategy for controlling this disease. The Huanghuai region, as a major wheat-growing area, plays a crucial role in the spread and prevalence of wheat stem rust in China. In this study, 64 wheat accessions from this region were tested at the adult stage against two major Pgt races, 34MKGQM and 21C3CTHQM. DNA markers associated with the known resistance genes Sr31, Sr24, Sr25, Sr26, and Sr38 were measured to determine their presence in the tested accessions. In the 2023 field tests, 5 (7.8%) accessions were immune to 21C3CTHQM and 34MKGQM, while 35 (54.7%) and 39 (60.9%) were moderately resistant and resistant, respectively. The remaining 20 (30.7%) accessions were moderately susceptible and susceptible. In the 2024 tests, 12 (18.8%) and 14 (21.9%) entries were immune to both races; 29 (45.3%) and 30 (46.9%) were moderately resistant and resistant, respectively. Only two cultivars, Xinong 816 and Yimai 211, were immune in both years, and three entries showed some degrees of resistance in both years. Seven cultivars, including Zhongzhimai 23, Longxing 1, Yunong 937, Huaguan 301, Wanke 800, Shaanhe 285, and Yunong 612, showed increased susceptibility. DNA markers showed that 30 entries carried Sr31, while 6 entries carried Sr38. Genes Sr24, Sr25, and Sr26, which confer good resistance to the globally prevalent cultivars TKTTF and TTTRF, were absent from the set of tested entries. While this study surveyed the resistance levels of a cross-section of wheat from the southern part of the Huanghuai region and confirmed the presence of two known resistance genes, the basis of immunity or high levels of resistance in several lines remains obscure.

Mapping and Candidate Gene Analysis of an All-Stage Stem Rust Resistance Gene in Durum Wheat Landrace PI 94701.

Puccinia graminis f. sp. tritici (Pgt), the causal agent of wheat stem rust, poses a significant threat to global wheat production. Genetic resistance offers a cost-effective and sustainable solution. The durum wheat landrace PI 94701 was previously hypothesized to carry two stem rust resistance (Sr) genes, but their chromosomal locations were unknown. In this study, we mapped and characterized an all-stage Sr gene in PI 94701, temporarily designated as SrPI94701. In seedling tests, SrPI94701 was effective against all six Pgt races tested. Using a large segregating population, we mapped SrPI94701 on chromosome arm 5BL within a 0.17-cM region flanked by markers pku69124 and pku69228, corresponding to 1.04 and 2.15 Mb genomic regions in the Svevo and Chinese Spring reference genomes. Within the candidate region, eight genes exhibited differential expression between the Pgt-inoculated resistant and susceptible plants. Among them, two nucleotide-binding leucine-rich repeat (NLR) genes, TraesCS5B03G1334700 and TraesCS5B03G1335100, showed high polymorphism between the parental lines and were upregulated in Pgt-inoculated resistant plants. However, the flanking and completely linked markers developed in this study could not accurately predict the presence of SrPI94701 in a survey of 104 wheat accessions. SrPI94701 is a promising resource for enhancing stem rust resistance in wheat breeding programs.

Association mapping with a diverse population of Puccinia graminis f. sp. tritici identified avirulence loci interacting with the barley Rpg1 stem rust resistance gene

BackgroundWheat stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is an important disease of barley and wheat. A diverse sexual Pgt population from the Pacific Northwest (PNW) region of the US contains a high proportion of individuals with virulence on the barley stem rust resistance (R) gene, Rpg1. However, the evolutionary mechanisms of this virulence on Rpg1 are mysterious considering that Rpg1 had not been deployed in the region and the gene had remained remarkably durable in the Midwestern US and prairie provinces of Canada.Methods and resultsTo identify AvrRpg1 effectors, genome wide association studies (GWAS) were performed using 113 Pgt isolates collected from the PNW (n = 89 isolates) and Midwest (n = 24 isolates) regions of the US. Disease phenotype data were generated on two barley lines Morex and the Golden Promise transgenic (H228.2c) that carry the Rpg1 gene. Genotype data was generated by whole genome sequencing (WGS) of 96 isolates (PNW = 89 isolates and Midwest = 7 isolates) and RNA sequencing (RNAseq) data from 17 Midwestern isolates. Utilizing ~1.2 million SNPs generated from WGS and phenotype data (n = 96 isolates) on the transgenic line H228.2c, 53 marker trait associations (MTAs) were identified. Utilizing ~140 K common SNPs generated from combined analysis of WGS and RNAseq data, two significant MTAs were identified using the cv Morex phenotyping data. The 55 MTAs defined two distinct avirulence loci, on supercontig 2.30 and supercontig 2.11 of the Pgt reference genome of Pgt isolate CRL 75-36-700-3. The major avirulence locus designated AvrRpg1A was identified with the GWAS using both barley lines and was delimited to a 35 kb interval on supercontig 2.30 containing four candidate genes (PGTG_10878, PGTG_10884, PGTG_10885, and PGTG_10886). The minor avirulence locus designated AvrRpg1B identified with cv Morex contained a single candidate gene (PGTG_05433). AvrRpg1A haplotype analysis provided strong evidence that a dominant avirulence gene underlies the locus.ConclusionsThe association analysis identified strong candidate AvrRpg1 genes. Further analysis to validate the AvrRpg1 genes will fill knowledge gaps in our understanding of rust effector biology and the evolution and mechanism/s of Pgt virulence on Rpg1.

Prospects for tritordeum (×Tritordeum martinii A. Pujadas, Nothosp. Nov.) cereal breeding: Key points for future challenges

AbstractTritordeum is the new cereal derived from crosses between the wild barley Hordeum chilense Roem. et Schultz. and either durum or bread wheat, resulting in hexaploid and octoploid tritordeums, respectively. The success of tritordeum as a crop depends on the effectiveness of its breeding programme. In this work, new advanced tritordeum lines are screened for grain carotenoid content and disease susceptibility to analyse the impact of the current breeding strategies and to identify their strengths and putative limitations for future challenges. We conclude that selection for grain carotenoid content, the main strength for the tritordeum commercialization, should be reinforced not only by using the diversity of H. chilense but also incorporating beneficial alleles from durum wheat. Furthermore, genes for stem rust resistance from the A and B wheat genomes must be incorporated into tritordeum breeding programme. Finally, when selecting for threshability, tritordeums without chromosome substitutions should be preferentially selected using a marker‐assisted selection approach.

Evaluation of genetic variation and host resistance to wheat stem rust pathogen (Puccinia graminis f. sp. tritici) in bread wheat (Triticum aestivum L.) varieties grown in Türkiye.

Wheat stem rust, which is caused by Puccinia graminis f. sp. tritici (Pgt), is a highly destructive disease that affects wheat crops on a global scale. In this study, the reactions of 150 bread wheat varieties were evaluated for natural Pgt infection at the adult-plant stage in the 2019-2020 and 2020-2021 growing seasons, and they were analyzed using specific molecular markers to detect stem rust resistance genes (Sr22, Sr24, Sr25, Sr26, Sr31, Sr38, Sr50, and Sr57). Based on phenotypic data, the majority of the varieties (62%) were resistant or moderately resistant to natural Pgt infection. According to molecular results, it was identified that Sr57 was present in 103 varieties, Sr50 in nine varieties, Sr25 in six varieties, and Sr22, Sr31, and Sr38 in one variety each. Additionally, their combinations Sr25 + Sr50, Sr31 + Sr57, Sr38 + Sr50, and Sr38 + Sr57 were detected in these varieties. On the other hand, Sr24 and Sr26 were not identified. In addition, many varieties had low stem rust scores, including a large minority that lacked Sr57. These varieties must have useful resistance to stem rust and could be the basis for selecting greater, possibly durable resistance.

Cytological and molecular characterization of wheat lines carrying leaf rust and stem rust resistance genes Lr24 and Sr24

Previous studies showed that Australian wheat cultivars Janz and Sunco carry leaf rust and stem rust resistance genes Lr24 and Sr24 derived from Thinopyrum ponticum chromosome arm 3AgL. However, the size of the alien segments carrying Lr24 and Sr24 in the lines were not determined. In this study, we used non-denaturing fluorescence in situ hybridization (ND-FISH), genomic in situ hybridization (GISH), and PCR-based landmark unique gene (PLUG) markers to visualize the alien segments in Janz and Sunco, and further compared them with the segments in US cultivars Agent and Amigo. The fraction length (FL) of the alien translocation in Agent was 0.70–1.00, whereas those in Janz, Sunco, and Amigo were smaller, at FL 0.85–1.00. It was deduced that the alien gene RAg encoding for red grain color and rust resistance genes Lr24 and Sr24 on chromosome arm 3AgL were in bins of FL 0.70–0.85 and 0.85–1.00, respectively. We retrieved and extracted nucleotide-binding site-leucine-rich repeat (NBS-LRR) receptor genes corresponding to the region of Lr24 and Sr24 on chromosomes 3E, and 3J, 3Js and 3St from the reference genome sequences of Th. elongatum and Th. intermedium, respectively. A set of molecular markers developed for Lr24 and Sr24 from those extracted NBS-LRR genes will provide valuable information for fine mapping and cloning of these genes.

Physio-Biochemical, Anatomical, and Molecular Analysis of Resistant and Susceptible Wheat Cultivars Infected with TTKSK, TTKST, and TTTSK Novel Puccinia graminis Races.

Stem rust, caused by Puccinia graminis f.sp. tritici, is one of the most dangerous rust diseases on wheat. Through physiological, biochemical, and molecular analysis, the relationship between the change in resistance of 15 wheat cultivars to stem rust disease and the response of 41 stem rust resistance genes (Sr,s) as well as TTKSK, TTKST, and TTTSK races was explained. Some cultivars and Sr genes, such as Gemmeiza-9, Gemmeiza-11, Sids-13, Sakha-94, Misr-1, Misr-2, Sr31, and Sr38, became susceptible to infection. Other new cultivars include Mir-3 and Sakha-95, and Sr genes 13, 37, 40, GT, and FR*2/SRTT3-SRTT3-SR10 remain resistant. Some resistance genes have been identified in these resistant cultivars: Sr2, Sr13, Sr24, Sr36, and Sr40. Sr31 was not detected in any cultivars. Reactive oxygen species such as hydrogen peroxide and superoxide, enzymes activities (catalase, peroxidase, and polyphenoloxidase), and electrolyte leakage were increased in the highly susceptible cultivars, while they decreased in the resistant ones. Anatomical characteristics such as the thickness of the epidermis, ground tissue, phloem tissue and vascular bundle diameter in the midrib were decreased in susceptible cultivars compared with resistant cultivars. Our results indicated that some races (TTKSK, TTKST, and TTTSK) appeared for the first time in Egypt and many other countries, which broke the resistant cultivars. The wheat rust breeding program must rely on land races and pyramiding genes in order to develop new resistance genes that will survive for a very long time.

Phylogenesis of virulent races of Puccinia graminis f. sp. tritici based on phenotyping and genotyping using newly developed SNP markers for genetic groups in clades

Ug99 (TTKSK) and Digalu (TKTTF) race groups of Puccinia graminis f. sp. tritici (Pgt), are thought to be the most virulent, rendering many wheat stem rust resistance genes (Sr) ineffective. A total of 600 single pustule Pgt isolates were collected from eight Egyptian provinces during 2016–2022, undergoing both phenotyping and genotyping assays. Among these, 129 viable samples (v-samples) underwent phenotyping using the North American differentials delineated to Pgt races in the TTKS (Ug99) and TKTTF race groups, identifying 24 distinct physiologic races of Pgt. Notably, seven virulent races, TKTTF (Digalu), TKKTF, TKPTF, TKKTP, TTRTF, TTTTF, and TKFTF, were discovered in Egypt. The host reaction of wheat germplasm to these seven races indicated a high level of susceptibility. A set of 437 dead samples (d-samples) of Pgt isolates from Egypt were genotyped using newly created 17 core SNP markers. Genotypic analysis revealed that these seven races could be classified into two major clades: III and IV. Within these clades, six subclades were identified, namely III-B, IV-A.2, IV-B, IV-E.1, IV-E.2, and IV-F. These SNP genotypes exhibited a broad geographic distribution, highlighting the global movement of Pgt populations across Europe, Asia, and Africa. Notably, none of these genetic groups were present in Egypt before 2016. The most prevalent genotypes were subclades IV-A.2 (TKTTF; Digalu), IV-E.2 (TKKTF, TKPTF, TKFTF), and III-B (TTRTF). The prevalence of these unique genotypes/races suggests clonal reproduction and evolution within them. Race TKKTP (subclade IV-E.1) is particularly concerning because of its ability to overcome the resistance conferred by gene Sr24 against race TTKSK (Ug99). Phylogenetic analysis of Pgt genetic groups revealed that the majority of identified races belong to TKTTF (Digalu) race group (subclade IV-A.2). Notably, no races were found to belong to the TTKS (Ug99) race group (clade I). This information should help breeders select a broader range of resistance genes that are both diverse and effective to enhance the durability of stem rust resistance.

High-resolution mapping of Ryd4Hb, a major resistance gene to Barley yellow dwarf virus from Hordeum bulbosum

Key messageWe mapped Ryd4Hb in a 66.5 kbp interval in barley and dissociated it from a sublethality factor. These results will enable a targeted selection of the resistance in barley breeding.Virus diseases are causing high yield losses in crops worldwide. The Barley yellow dwarf virus (BYDV) complex is responsible for one of the most widespread and economically important viral diseases of cereals. While no gene conferring complete resistance (immunity) has been uncovered in the primary gene pool of barley, sources of resistance were searched and identified in the wild relative Hordeum bulbosum, representing the secondary gene pool of barley. One such locus, Ryd4Hb, has been previously introgressed into barley, and was allocated to chromosome 3H, but is tightly linked to a sublethality factor that prevents the incorporation and utilization of Ryd4Hb in barley varieties. To solve this problem, we fine-mapped Ryd4Hb and separated it from this negative factor. We narrowed the Ryd4Hb locus to a corresponding 66.5 kbp physical interval in the barley ‘Morex’ reference genome. The region comprises a gene from the nucleotide-binding and leucine-rich repeat immune receptor family, typical of dominant virus resistance genes. The closest homolog to this Ryd4Hb candidate gene is the wheat Sr35 stem rust resistance gene. In addition to the fine mapping, we reduced the interval bearing the sublethality factor to 600 kbp in barley. Aphid feeding experiments demonstrated that Ryd4Hb provides a resistance to BYDV rather than to its vector. The presented results, including the high-throughput molecular markers, will permit a more targeted selection of the resistance in breeding, enabling the use of Ryd4Hb in barley varieties.

Identification of Stem Rust Resistance Genes in Triticum Wheat Cultivars and Evaluation of Their Resistance to Puccinia graminis f. sp. tritici

Wheat stem rust, caused by the fungus Puccinia graminis f. sp. tritici (Pgt), poses a substantial threat to global wheat production. Utilizing stem rust resistance (Sr) genes represents an economically viable, effective, and environmentally friendly approach to disease control. In this study, gene postulation, molecular testing, and pedigree analysis were used to identify the presence of Sr genes in 45 wheat cultivars. In addition, the resistance of these cultivars was evaluated against two predominant Pgt races, 34MRGQM and 21C3CTHTM, at the adult-plant stage during 2021–2022. The results identify seven Sr genes (Sr31, Sr38, Sr30, SrTmp, Sr22, Sr19, and Sr5) within 35 wheat cultivars. Among these, 23 cultivars contained Sr31, whereas Sr5 and SrTmp were present in four cultivars each. Han 5316, Shimai 15, Shiyou 20, and Kenong 1006 exhibited the presence of Sr19, Sr22, Sr30, and Sr38, respectively. Molecular studies confirmed the absence of Sr25 and Sr26 in any of the wheat cultivars. During field evaluation, 37 (82.2%) and 39 (86.7%) wheat cultivars demonstrated resistance to races 34MRGQM and 21C3CTHTM, respectively. Moreover, 33 wheat cultivars (73.3%) exhibited resistance to all the tested races. These study findings will significantly contribute to future research in wheat pre-breeding and abiotic stress tolerance.

Identification of Sr67, a new gene for stem rust resistance in KU168-2 located close to the Sr13 locus in wheat

Key messageSr67 is a new stem rust resistance gene that represents a new resource for breeding stem rust resistant wheat cultivarsRe-appearance of stem rust disease, caused by the fungal pathogen Puccinia graminis f. sp. tritici (Pgt), in different parts of Europe emphasized the need to develop wheat varieties with effective resistance to local Pgt populations and exotic threats. A Kyoto University wheat (Triticum aestivum L.) accession KU168-2 was reported to carry good resistance to leaf and stem rust. To identify the genomic region associated with the KU168-2 stem rust resistance, a genetic study was conducted using a doubled haploid (DH) population from the cross RL6071 × KU168-2. The DH population was phenotyped with three Pgt races (TTKSK, TPMKC, and QTHSF) and genotyped using the Illumina 90 K wheat SNP array. Linkage mapping showed the resistance to all three Pgt races was conferred by a single stem rust resistance (Sr) gene on chromosome arm 6AL, associated with Sr13. Presently, four Sr13 resistance alleles have been reported. Sr13 allele-specific KASP and STARP markers, and sequencing markers all showed null alleles in KU168-2. KU168-2 showed a unique combination of seedling infection types for five Pgt races (TTKSK, QTHSF, RCRSF, TMRTF, and TPMKC) compared to Sr13 alleles. The phenotypic uniqueness of the stem rust resistance gene in KU168-2 and null alleles for Sr13 allele-specific markers showed the resistance was conferred by a new gene, designated Sr67. Since Sr13 is less effective in hexaploid background, Sr67 will be a good source of stem rust resistance in bread wheat breeding programs.

Comparative transcriptomics of stem rust resistance in wheat NILs mediated by Sr24 rust resistance gene

Stem rust of wheat is a deleterious fungal disease across the globe causing severe yield losses. Although, many stem rust resistance genes (Sr) are being used in wheat breeding programs, new emerging stem rust pathotypes are a challenge to important Sr genes. In recent years, multiple studies on leaf and yellow rust molecular mechanism have been done, however, for stem rust such studies are lacking. Current study investigated stem rust induced response in the susceptible wheat genotype C306 and its Near Isogenic Line (NIL) for Sr24 gene, HW2004, using microarray analysis to understand the transcriptomic differences at different stages of infection. Results showed that HW2004 has higher basal levels of several important genes involved in pathogen detection, defence, and display early activation of multiple defence mechanisms. Further Gene Ontology (GO) and pathway analysis identified important genes responsible for pathogen detection, downstream signalling cascades and transcription factors (TFs) involved in activation and mediation of defence responses. Results suggest that generation of Reactive Oxygen Species (ROS), cytoskeletal rearrangement, activation of multiple hydrolases, and lipid metabolism mediated biosynthesis of certain secondary metabolites are collectively involved in Sr24-mediated defence in HW2004, in response to stem rust infection. Novel and unannotated, but highly responsive genes were also identified, which may also contribute towards resistance phenotype. Furthermore, certain DEGs also mapped close to the Sr24-linked marker on Thinopyrum elongatum translocated fragment on wheat 3E chromosome, which advocate further investigations for better insights of the Sr24-mediated stem rust resistance.

Development of Winter Common Wheat Lines with the Stem Rust Resistance Gene Sr33

Development of Winter Common Wheat Lines with the Stem Rust Resistance Gene Sr33

Single amino acid change alters specificity of the multi-allelic wheat stem rust resistance locus SR9

Most rust resistance genes thus far isolated from wheat have a very limited number of functional alleles. Here, we report the isolation of most of the alleles at wheat stem rust resistance gene locus SR9. The seven previously reported resistance alleles (Sr9a, Sr9b, Sr9d, Sr9e, Sr9f, Sr9g, and Sr9h) are characterised using a synergistic strategy. Loss-of-function mutants and/or transgenic complementation are used to confirm Sr9b, two haplotypes of Sr9e (Sr9e_h1 and Sr9e_h2), Sr9g, and Sr9h. Each allele encodes a highly related nucleotide-binding site leucine-rich repeat (NB-LRR) type immune receptor, containing an unusual long LRR domain, that confers resistance to a unique spectrum of isolates of the wheat stem rust pathogen. The only SR9 protein effective against stem rust pathogen race TTKSK (Ug99), SR9H, differs from SR9B by a single amino acid. SR9B and SR9G resistance proteins are also distinguished by only a single amino acid. The SR9 allelic series found in the B subgenome are orthologs of wheat stem rust resistance gene Sr21 located in the A subgenome with around 85% identity in protein sequences. Together, our results show that functional diversification of allelic variants at the SR9 locus involves single and multiple amino acid changes that recognize isolates of wheat stem rust.

High-resolution genetic mapping and identification of candidate genes for the wheat stem rust resistance gene Sr8155B1

Stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), threatens global wheat production. Development of cultivars with increased resistance to stem rust by identification, mapping, and deployment of resistance genes is the best strategy for controlling the disease. In this study, we performed fine mapping and characterization of the all-stage stem rust resistance (Sr) gene Sr8155B1 from the durum wheat line 8155-B1. In seedling tests of biparental populations, Sr8155B1 was effective against six Chinese Pgt races tested. In a segregating population of 5060 gametes, Sr8155B1 was mapped to a 0.06-cM region flanked by markers Pku2772 and Pku43365, corresponding to 1.5- and 2.7-Mb regions in the Svevo and Chinese Spring reference genomes. Both regions include several typical nucleotide-binding leucine-rich repeat (NLR) and protein kinase genes that represent candidate genes. Among them, three NLR genes and three receptor-like protein kinases were highly polymorphic between the parental lines and their transcripts were upregulated in the homozygous resistant line TdR2 relative to its susceptible sister line TdS4. Four markers (Pku2772, Pku43365, Pku2950, and Pku3721) developed in this study, together with seedling resistance responses, correctly predicted Sr8155B1 absence or presence in 78 tetraploid wheat genotypes tested. The presence of Sr8155B1 in tetraploid wheat accessions CItr 14916, PI 197492, and PI 197493 was confirmed by mapping in three F2 populations. The genetic map and linked markers developed in this study may accelerate the deployment of Sr8155B1-mediated resistance in wheat breeding programs.

Screening of new wheat cultivars originating from Kazakhstan for stem and leaf rust resistance genes using PCR markers

Leaf and stem rust that infect wheat lines are the most prevalent and damaging fungal diseases affecting the wheat production rates globally. One of the efficient and economically wise ways of controlling the disease progression is the breeding resistant wheat varieties. Use of molecular markers associated with resistance genes, might be useful for identifying the varieties, that carry the specific resistant genes. Sixty-four wheat cultivars and lines provided by domestic agricultural experimental stations were examined using DNA-markers for the presence of leaf (Lr) and stem (Sr) rust resistance genes. The reactions were carried out using eight pairs of different primers. Six Lr genes (Lr10, Lr13, Lr16, Lr19 and Lr39) responsible for wheat resistance were detected using PCR. The molecular marker detection demonstrated the presence of a combination of several Lr genes, particularly Lr16, Lr34 and Lr39 in the fifteen spring wheat accessions. Six varieties in the nursery of spring soft wheat from KarabAES, two varieties from AktAES (Ekada 113, Lin. 225/21g.) and seven varieties from NorthKazAES (435/Lut 2, 659/12, 486/Lut 22, 23/07, Erith 42/12, 453 SP-2/19) carried the combination these three genes.