Lr Genes Research Articles

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.

Selection of winter soft wheat for resistance to brown rust

The article presents the results of the phytopathological test and marker analysis of the selection material of winter wheat for resistance to the pathogen of brown rust (Puccinia recondita Rob. ex Desm f. sp. tritici.). The object of research was 10 cultivars of various ecological and geographical origin. Using molecular markers, the studied wheat varieties did not reveal the highly and partially effective genes Lr9, Lr19/Sr25, Lr24/Sr24, Lr41 and Lr47 in Russia, and the ineffective gene Lr20/Sr1. The combination of the Lr34 gene with ineffective genes can provide an increase in the level of field resistance of wheat varieties. In the variety type Leaf 25, the age-related resistance gene Lr37 is assumed to be partially effective in Russia. This type of stability is characterized by a longer latent period, a decrease in the number of pustules per unit leaf surface, their size and the number of spores in the pustule. According to the results of a comprehensive assessment of winter wheat cultivars to brown rust, the following cultivars showed a stable reaction type (R): Zhiva (Lr1, Lr3, Lr10, Lr26, Lr34) and Leaf 25 (Lr1, Lr3, Lr37;); a susceptible reaction type (S) in Malvina cultivars -(Lr1, Lr26;), Solara (Lr1, Lr34), Etude - Lr3. Genes in various combinations can provide field resistance of winter wheat to brown rust. Most cultivars were moderately susceptible to the disease.

Validation of CAPS marker WR003 for the leaf rust resistance gene Lr1 and the molecular evolution of Lr1 in wheat

The wheat leaf rust resistance gene Lr1 encodes a typical coiled-coil nucleotide-binding site leucine-rich repeat (CC-NBS-LRR) of resistance protein containing 1 344 amino acids. WR003, a cleaved amplified polymorphic sequence (CAPS) marker is derived from the LRR regions of Lr1. In this study, a worldwide collection of 120 Aegilops tauschii accessions and 282 hexaploid wheat varieties was screened for Lr1 alleles using WR003, and the specificity of WR003 for Lr1 was confirmed by pathogenicity tests and genotype analysis. The sequence alignment and phylogenetic tree analysis of 38 Lr1 haplotypes provided a further view of the molecular evolution of Lr1. The results showed that there were very few polymorphisms between the Lr1 alleles from Ae. tauschii and hexaploid wheat with the same resistance phenotype. The polymorphisms of the Lr1 haplotypes were mainly between the different resistance lines, rather than between the different ploidy levels. These results indicate that Lr1 originated from Ae. tauschii and differentiated into resistant and susceptible genotypes before its introgression into hexaploid wheat. Therefore, it is likely that wheat Lr1 has at least two major variants for disease resistance and susceptibility, and except for certain point mutations, few gene conversions and genetic re-combinations occurred during the hexaploid wheat domestication.

DETECTION OF CARRIERS OF RESISTANCE GENES TO LEAF RUST USING MOLECULAR GENETIC ANALYSIS IN VARIETIES OF SOFT AND DURUM WHEAT

Brown or leaf rust is one of the devastating wheat diseases, caused by the fungus Puccinia triticina, which can lead to crop losses and also to deterioration of grain quality. The brown rust resistance of soft and durum wheat is a prerequisite for consistently high yields. Eleven samples (of local and Russian selection) were used as a research material. In order to study wheat resistance to leaf rust, seven genes were selected – Lr9, Lr10, Lr14, Lr22a, Lr28, Lr34, and Lr67. Based on the results of the molecular screening, it was found that both soft and durum wheat varieties have Lr10, Lr22a, Lr34 and Lr67 genes in their genomes and are carriers of both effective and ineffective resistance genes. The marker linked to the Lr9 gene was identified only in the control sample Novosibirskaya 29, which indicates the absence of this gene in durum wheat materials. Even so durum wheat samples are protected by genes Lr10, Lr14 and highly efficient gene Lr28. Wheat varieties in which resistance genes have been amplified can be pyramidized with other resistance genes and successfully used in appropriate breeding programs.

Evaluation of Seedling Resistance and Marker Assisted Selection for Leaf Rust (Puccinia triticina) Resistance in Pakistani Wheat Landraces, Cultivars and Advanced Lines

Leaf rust is amongst major biotic constraints of wheat (Triticum aestivum L.) having ability to cause substantial yield reductions worldwide. A continuous exploration for novel sources of resistance is pre-requisite for its management. Objectives of study were to conduct resistance evaluation of 112 Pakistani landraces and 48 advanced lines/ cultivars at seedling stage with total 10 virulent pathotypes of leaf rust, 3 from Pakistan and 7 from U.S.A and to detect closely linked markers for Lr10, 16, 34 and 67 genes through marker-assisted selection (MAS). Findings revealed most of Pakistani landraces showed lack of resistance at seedling stage. Only 7 accessions of landraces and 11 advanced lines were found highly resistant against all pathotypes of Pakistan. Similarly, 10 advanced lines exhibited high resistance while variability in resistance was recorded for landraces against all pathotypes tested from USA. Marker-assisted selection revealed Lr genes i.e. Lr10, Lr16, Lr34 and Lr67 were present at various frequencies. Highest frequency was observed for Lr34 followed by Lr16 Lr67 while lowest was recorded for Lr10. These genetic resources and lines identified effective against Pakistan and USA pathotypes are potential sources for improvement of leaf rust (LR) resistance and can be utilized as valuable material for breeding resistant wheat cultivars.

Molecular screening of the landraces from Turkey and modern bread wheat (Triticum aestivum L.) cultivars for HMW-GS, wbm, waxy genes and Lr34 gene

Molecular screening of the landraces from Turkey and modern bread wheat (Triticum aestivum L.) cultivars for HMW-GS, wbm, waxy genes and Lr34 gene

Is virulence phenotype evolution driven exclusively by Lr gene deployment in French Puccinia triticina populations?

AbstractPuccinia triticina is a highly damaging wheat pathogen. The efficacy of leaf rust control by genetic resistance is mitigated by the adaptive capacity of the pathogen, expressed as changes in its virulence combinations (pathotypes). An extensive P. triticina population survey has been carried out in France over the last 30 years, describing the evolutionary dynamics of this pathogen in response to cultivar deployment. We analysed the data set for the 2006–2016 period to determine the relationship between the Lr genes in the cultivars and virulence in the pathotypes. Rust populations were dominated by a small number of pathotypes, with variations in most of the virulence frequencies related to the corresponding Lr gene frequencies in the cultivated landscape. Furthermore, the emergence and spread of a new virulence matched the introduction and use of the corresponding Lr gene (Lr28), confirming that the deployment of qualitative resistance genes is an essential driver of evolution in P. triticina populations. However, principal component analysis (PCA) revealed that certain pathotype–cultivar associations cannot be explained solely by the distribution of Lr genes in the landscape. This conclusion is supported by the predominance of a few pathotypes on some cultivars, with the persistence of several other compatible pathotypes at low frequencies. Specific interactions are not, therefore, sufficient to explain the distribution of virulence in rust populations. The hypothesis that quantitative interactions between P. triticina populations and bread wheat cultivars—based on differences in aggressiveness—is also a driver of changes in pathotype frequencies deserves further investigation.

Analysis of miRNA expression associated with gene Lr34 responsible for resistance mechanisms to wheat leaf rust

Analysis of miRNA expression associated with gene Lr34 responsible for resistance mechanisms to wheat leaf rust

A Review on Origin and Genetic Analysis of Wheat Genes Conferring Resistance to Wheat Rust in Common Bread Wheat (Triticum aestivum L.)

Wheat rusts, produced by three species of Puccinia, are severe diseases and important biotic impediments in efforts to keep wheat production going around the world.The most commercially significant and prevalent diseases among global wheat varieties includes leaf rust also known as brown rust, caused by Puccinia graminis triticina Eriks, stem or black rust caused by Puccinia graminis f. sp. tritici, and stripe or yellow rust caused by Puccinia striiformis f. Tritici.Currently,more than 200 rust resistance genes (100 leaf rust, 60 stem rust, and 51 stripe rust) have been identified by using various molecular approaches from several wheat crop species and related wild species. This review highlights various aspects of Lr (Leaf rust), Sr (Stem rust) and Yr(yellow rust) resistance genes, their primitive origins, and their prevalence in globally wheat cultivars.

Interactions Between Lr67 or Lr34 and Other Leaf Rust Resistance Genes in Wheat (Triticum aestivum).

The wheat multi-pest resistance genes Lr67 and Lr34 are similar in that they both condition resistance to many diseases, in a non-race-specific manner, and code for cellular transporters. Lr34 plays a critical role in breeding wheat for disease resistance in large part because it interacts with other resistance genes to result in effective and durable resistance. To determine if Lr67 interacts with other resistance genes in a similar manner as Lr34 six different doubled haploid populations were developed which segregated for either Lr67 or Lr34 along with a second resistance gene, either Lr13, Lr16, or Lr32. The presence or absence of each of these genes in the progeny lines was determined by molecular marker analysis. These six populations were tested for leaf rust field resistance in the same environments to compare the effects of Lr34 and Lr67 alone, and in combination with Lr13, Lr16 or Lr32. Lr67 and Lr34 significantly reduced the levels of rust severity, Lr34 showed a significant interaction with Lr13 but Lr67 did not. Both genes interacted with Lr16, and Lr67 had a significant interaction with Lr32. This analysis demonstrates the similar effect of Lr67, as seen with Lr34, on the interaction with other resistance genes to give a better level of resistance than with single resistance genes. While Lr67 is not widely deployed in agriculture, it could play an important role in disease resistance in future wheat cultivars.

Virulence Phenotypes of the Wheat Leaf Rust Pathogen, Puccinia triticina, in the United States from 2018 to 2020.

Collections of wheat leaves infected with the leaf rust fungus, Puccinia triticina, were obtained from the southeastern states, the Ohio Valley, the Great Plains, and Washington in 2018, 2019, and 2020 to determine the prevalent virulence phenotypes in the wheat-growing regions of the United States. In the hard red winter wheat region of the southern and mid Great Plains, MNPSD and MPPSD were the two most common phenotypes in 2018 and 2019. In 2020, BBBQD with high virulence to durum wheat was the most common phenotype in the southern Great Plains. In the hard red spring wheat region of the northern Great Plains, MNPSD, MPPSD, MBDSD, and TBBGS were the predominant phenotypes. In the soft red winter wheat region of the southeastern states and Ohio Valley region, MBTNB, MCTNB, and MNPSD were the three most common phenotypes. Collections in Washington had phenotypes LBDSG, LCDSG, LCDJG, and MBDSB that were not found in any other region. Isolates with virulence to the leaf rust resistance (Lr) gene Lr11 were most frequent in the southeastern states and Ohio Valley regions. The frequency of isolates with virulence to the Lr39 gene was highest in the Great Plains region and frequency of isolates with virulence to the Lr21 gene was highest in the northern Great Plains region. Selection of virulence phenotypes by Lr genes in the different market classes of wheat, combined with the effects of clonal reproduction, overwintering in southern regions, and low migration between the Great Plains region and eastern wheat-producing regions, has maintained the different P. triticina populations in the United States.

Evaluation of Pakistani wheat germplasm for leaf rust resistance at various locations.

341 entries comprising of 250 genotypes/lines and 91 gene differentials were tested for leaf rust (Puccinia triticina Erik) in different ecological zones of Punjab during 2016–17 and 2017–18. Each entry was planted in a single 1 m long row and Morocco was used as a spreader. Data on leaf rust severity was recorded once in 3rd week of March during both study years at all locations by following Modified Cobb Scale while the data was recorded three times on 2nd, 22nd and 29th March during 2018 at Faisalabad location to study rust development pattern. The disease severity ranged from 0-100S during 2016–17 and from 0-80S during 2017–18. The genotype HYT 60–5 and the genes Lr-19, Lr-26 and Lr 27+31 showed no disease symptoms at any location during both the study years. These genes can be used for future breeding material development. Area under disease progressive curve (AUDPC), calculated on the basis of periodical readings from Faisalabad, ranged from 0–550 and the susceptible check Morocco has AUDPC value of 600. 120 entries including HYT 60–5 have disease progression 0, which showed that there may be a major gene based resistance in these entries. Area under disease progressive curve/Day (AUDPC/DAY) was calculated for the rest of 130 genotypes to have an understanding of the disease progression pattern and out of which 43 entries have AUDPC/Day value ranging from 1–2 and 28 entries have AUDPC/Day value ranging from 2–3 which revealed that these entries are very useful for use in breeding for durable rust resistance and can be utilized as a parent in back cross and top cross breeding schemes. Material with AUDPC value less than 10 is the best source of resistance against the leaf rust. Varieties/advanced lines, Ujala-16, V-14154, and V-14124 have shown slow rust development and are very good sources of resistance. Similarly, HYT 60–5 has proven an excellent source of resistance. The advance line V-14154 has been approved as a commercial cultivar by the name “Akbar-19”.

Diversity of leaf rust resistance in Indonesian sorghum genetic resources

Abstract. Dinanty F, Wirnas D, Trikoesoemaningtyas, Nawangsih AA. 2022. Diversity of leaf rust resistance in Indonesian sorghum genetic resources. Biodiversitas 23: 2570-2579. Sorghum is an alternative source as a substitute for rice. Leaf rust (Puccinia purpurea) is a constraint in sorghum cultivation and resistance to rust disease is a condition for releasing sorghum varieties. This study aimed to screen sorghum accessions for resistance to leaf rust disease. The screening was carried out on 48 sorghum accessions and seven check varieties, namely Numbu, Kawali, Bioguma 1, Pahat, Soraya 1, Soraya 2, and Soraya 3. Evaluation of leaf rust resistance under field conditions was carried out in IPB University experimental field Cikarawang-Bogor (275 asl) from February 2021 to June 2021. The experiment was conducted in an augmented design with four replications for check varieties. Identification of leaf rust resistance was also carried out using molecular markers designed from the Lr34 and Rp1D genes. The results revealed that 5 genotypes, namely genotypes 31 (Demak 2), 24 (IS 18551), 43 (Lokal bima 3), 17 (ICSV 93036), and 33 (Demak 5) were resistant to leaf rust with high yield potential. The results of identification using molecular markers showed that all accessions had Lr34 and Rp1D gene fragments.

An Update on Resistance Genes and Their Use in the Development of Leaf Rust Resistant Cultivars in Wheat.

Wheat is one of the most important cereal crops in the world. The production and productivity of wheat is adversely affected by several diseases including leaf rust, which can cause yield losses, sometimes approaching >50%. In the present mini-review, we provide updated information on (i) all Lr genes including those derived from alien sources and 14 other novel resistance genes; (ii) a list of QTLs identified using interval mapping and MTAs identified using GWAS (particular those reported recently i.e., after 2018) and their association with known Lr genes; (iii) introgression/pyramiding of individual Lr genes in commercial/prominent cultivars from 18 different countries including India. Challenges and future perspectives of breeding for leaf rust resistance are also provided at the end of this mini-review. We believe that the information in this review will prove useful for wheat geneticists/breeders, not only in the development of leaf rust-resistant wheat cultivars, but also in the study of molecular mechanism of leaf rust resistance in wheat.

BS-Seq reveals major role of differential CHH methylation during leaf rust resistance in wheat (Triticum aestivum L.).

Epigenetic regulation of the activity of defense genes during onset of diseases or resistance against diseases in plants is an active area of research. In the present study, a pair of wheat NILs for leaf rust resistance gene Lr28(R) in the background of an Indian cultivar HD2329(S) was used for a study of DNA methylation mediated regulation of gene expression. Leaf samples were collected at 0h before (S0 and R0) and 96h after inoculation (S96 and R96). The DNA samples were subjected to BS-Seq and sequencing data were used for identification of differentially methylated/demethylated regions/genes (DMRs and DMGs). Following four pairs of comparisons were used for this purpose: S0 vs S96; S0 vs R0; R0 vs R96; S96 vs R96. Major role of CHH methylation relative to that of CG and CHG methylation was observed. Some important observations include the following: (i) abundance of CHH methylation among DMRs; (ii) predominance of DMRs in intergenic region, relative to other genomic regions (promoters, exons, introns, TSS and TTS); (iii) abundance of transposable elements (TEs) in DMRs with CHH context; (iv) demethylation mediated high expression of genes during susceptible reaction (S0 vs S96) and methylation mediated low expression of genes during resistant reaction (R0 vs R96 and S96 vs R96); (v) major genes under regulation encode proteins, which differ from those encoded by genes regulated during susceptible reaction and (vi) ~ 500 DMGs carried differential binding sites for H3K4/K27me3 marks suggesting joint involvement of DNA and H3 methylation. Thus, CHH methylation either alone or in combination with histone methylation plays a major role in regulating the expression of genes involved in wheat-leaf rust interaction.

Effectiveness of Leaf Rust Resistance Genes in the Adult and Juvenile Stages in Southern Russia in 2011-2020.

Puccinia triticina Erikss. is a causative agent of wheat leaf rust spread worldwide. Wheat rust is a major disease on wheat in southern regions of Russia, which are leaders in grain production and have favorable conditions for pathogen development. In this paper we studied the effectiveness of 52 NILs of cv. Thatcher with Lr genes in field trials and 41 NILs—in the juvenile phase in a greenhouse during 2011–2020. We conclude that the lines with Lr9, Lr42 and Lr43+24 genes remained immune in the adult phase during ten years of research. Lines with Lr genes: 19, 24, 29, 36, 37, 38, 43, 45, 47, 50 showed efficiency in field tests (1–5 R on the CIMMYT scale). No immune lines to Puccinia triticina were registered in the juvenile phase during 2011–2020. The line with the Lr9 gene remained immune up to 2020; Lr19 and Lr41—up to 2015; Lr42—up to 2018, and Lr50—up to 2019. In 2020, there was an increase of P. triticina isolates with virulence to Thatcher lines with Lr: 9, 14a, 16, 19, 21, 28, 30, 33, 40, 45, W, 50. Additionally, we registered a change in infection types towards more susceptible in isogenic Lr gene lines: 1, 2a, 12, 14b, 15, 18, 20, 23, 25, 28, 29, 32, 35, 36, 37, 38, 40, 44, 45 in the field. A sharp increase in the frequencies of virulent isolates was recorded in 2018–2020 due to unfavorable weather in the growing seasons. This indicates the ability of a dangerous pathogen to rapidly evolve in response to biotic and abiotic stresses. Therefore, annual monitoring of the reaction of isogenic lines, selected released varieties and the study of the virulence of the phytopathogen are important measures necessary to prevent and control leaf rust in grain-producing regions of the world.

Characterization of leaf rust resistance in a set of wheat-Thinopyrum amphiploid-derived hexaploid breeding lines

In order to identify new sources of resistance to leaf rust, a globally important disease of wheat, caused by the fungal pathogen Puccinia triticina Eriks. (Pt), a total of 170 hexaploid breeding lines, which have similar morphology with wheat and were derived from crosses of wheat-Thinopyrum ponticum or wheat-Th. intermedium partial amphiploids with susceptible wheat cultivars, were inoculated with the selected Chinese Pt races for evaluating seedling leaf rust response in the greenhouse. The response of adult plants to leaf rust was assessed on seedling susceptible lines over three cropping seasons from 2017 to 2020. In addition, 24 specific markers for 20 known Lr genes were used. Based on the results from gene postulation and molecular marker detection, two adult plant resistance (APR) genes (Lr34 and Lr37) and nine seedling resistance genes (Lr1, Lr2a, Lr2b, Lr3ka, Lr10, Lr15, Lr17, Lr18, and Lr26) were identified in 118 lines either singly or in combination. Most commonly identified Lr genes were Lr37 in 81 (47.6%) lines and Lr26 in 40 (23.5%) lines. Less frequently detected genes were Lr1 in nine lines; Lr2b and Lr3ka each in eight lines; Lr17 in seven lines; Lr2a and Lr34 each in four lines; Lr10 in three lines; Lr18 in two lines; and Lr15 was found in only one line. Twenty-eight lines were resistant to almost all the races used, but no known resistance gene was identified except Lr26, a gene with widespread ineffectiveness, suggesting that these derivatives could possess uncharacterized seedling Lr gene(s). Eleven seedling-susceptible lines were found to have APR over three cropping seasons, with an average maximum disease severity (MDS) below 15%, and hence could be potential sources of new APR genes. This study showed that these hexaploid breeding lines derived from wheat-Thinopyrum amphiploids could serve as new sources for wheat leaf rust resistance.

Long-read genome sequencing of bread wheat facilitates disease resistance gene cloning

The cloning of agronomically important genes from large, complex crop genomes remains challenging. Here we generate a 14.7 gigabase chromosome-scale assembly of the South African bread wheat (Triticum aestivum) cultivar Kariega by combining high-fidelity long reads, optical mapping and chromosome conformation capture. The resulting assembly is an order of magnitude more contiguous than previous wheat assemblies. Kariega shows durable resistance to the devastating fungal stripe rust disease1. We identified the race-specific disease resistance gene Yr27, which encodes an intracellular immune receptor, to be a major contributor to this resistance. Yr27 is allelic to the leaf rust resistance gene Lr13; the Yr27 and Lr13 proteins show 97% sequence identity2,3. Our results demonstrate the feasibility of generating chromosome-scale wheat assemblies to clone genes, and exemplify that highly similar alleles of a single-copy gene can confer resistance to different pathogens, which might provide a basis for engineering Yr27 alleles with multiple recognition specificities in the future.

Molecular analyses in wheat and Aegilops tauschii reveal a new orthologue of the leaf rust resistance gene Lr19 on chromosome 7DL of Ae. tauschii

AbstractLeaf rust is one of the most devastating wheat diseases worldwide, to which many resistance genes have been successfully introgressed from wheat wild relatives. Though the Thinopyrum ponticum‐derived leaf rust resistance gene Lr19 is widely effective, and previous studies have shown its likely presence in Aegilops tauschii, no thorough investigation has been conducted to confirm this. The current study examined the presence of Lr19 in Ae. tauschii using molecular and bioinformatic analyses. Accordingly, the wheat cultivar Thatcher was used as a susceptible control, and the Lr19‐carrying genotypes; Thatcher + Lr19 (TcLr19) and Agatha were used as resistant controls. Phenotyping using pathotype CDHLQ accompanied with genotyping using two DNA markers verified previous results of the likely presence of an orthologue for Lr19 on chromosome 7DL of Ae. tauschii (AtLr19). Sequencing of the STS GB marker products from Ae. tauschii and TcLr19 showed 99% homology between the corresponding fragments, confirming the phenotyping and genotyping results. Both sequenced fragments matched to the melatonin biosynthesis gene, O‐methyltransferase‐2 (OMT2). A hierarchical gene network was reconstructed using all identified putative genes within a genomic region containing 2.5 cM upstream and downstream of OMT2. Results indicated that numerous important biotic stress‐responsive genes such as RPM1, RGA2, TRIUR3, BURP12 and myosin‐11, were located downstream of melatonin as a master regulator molecule through the OMT2 node. To our knowledge, this is the first report of the identification of an orthologue for Lr19 in Ae. tauschii, which provides insights into the possible regulatory route of this gene.

Long-Term Multilocal Monitoring of Leaf Rust Resistance in the Spring Bread Wheat Genetic Resources from Institute of Plant Genetic Resources (VIR)

Triticum aestivum L. (bread wheat) is the most important cereal crop in world grain production, including in the territory of the Russian Federation. One of the most important factors influencing the yield and quality of wheat grain is the affection of plants with leaf rust (Puccinia triticina Erikss.). To broaden the set of sources for effective rust resistance, spring bread wheat samples from N.I. Vavilov All-Russian Institute of Plant Genetic Resources (VIR) were monitored for adult resistance to the disease under natural infections for many decades at three distant locations of the Russian Federation: the Dagestan Experimental Station (DES) of VIR (10,549 accessions), Yekaterinino Experimental Station (YES) (4384 accessions), and Pushkin Experimental Field (PEF) (7704 accessions). Information on the disease development at these three stations is presented at least for 51 last years. As a result of disease development evaluation under natural epiphytotic conditions for not less than 3 years, 293 (15 landraces, 127 breeding lines, and 151 commercial varieties), 118 (1 landrace, 38 breeding lines, and 79 commercial varieties), and 127 (10 landraces, 48 breeding lines, and 69 commercial varieties) samples were classified as resistant to leaf rust at DES, YES, and PEF, respectively. Among samples from the State Register of Breeding Achievements in Russia, 15, 13, and 8 spring wheat varieties were resistant to leaf rust at DES, YES, and PEF, respectively. Juvenile resistance was estimated under laboratory conditions after seedling inoculation with a complex population of P. triticina: 73 highly resistant varieties and breeding lines were identified; all landraces, including those classified as resistant in the fields, were susceptible to disease at the seedling stage. A total of 26 wheat accessions were identified to be resistant to leaf rust at two to three locations; 14 of them possess adult resistance, and 12 samples have seedling resistance. According to results of PCR amplification with primers specific to markers of effective genes for leaf rust resistance, 6 accessions have gene Lr9, 1 sample is protected by Lr19, and 1 sample possesses gene Lr24. Wheat samples identified as possessing effective seedling or adult resistance could be of interest for breeding in some regions of the Russian Federation and other countries.