High-temperature wheat leaf rust resistance gene Lr13 exhibits pleiotropic effects on hybrid necrosis

A kinase fusion protein from Aegilops longissima confers resistance to wheat powdery mildew

Many disease resistance genes have been introgressed into wheat from its wild relatives. However, reduced recombination within the introgressed segments hinders the cloning of the introgressed genes. Here, we have cloned the powdery mildew resistance gene Pm13, which is introgressed into wheat from Aegilops longissima, using a method that combines physical mapping with radiation-induced chromosomal aberrations and transcriptome sequencing analysis of ethyl methanesulfonate (EMS)-induced loss-of-function mutants. Pm13 encodes a kinase fusion protein, designated MLKL-K, with an N-terminal domain of mixed lineage kinase domain-like protein (MLKL_NTD domain) and a C-terminal serine/threonine kinase domain bridged by a brace. The resistance function of Pm13 is validated through transient and stable transgenic complementation assays. Transient over-expression analyses in Nicotiana benthamiana leaves and wheat protoplasts reveal that the fragment Brace-Kinase122-476 of MLKL-K is capable of inducing cell death, which is dependent on a functional kinase domain and the three α-helices in the brace region close to the N-terminus of the kinase domain.

Phenotypic characterization and gene mapping of hybrid necrosis in Triticum durum-Haynaldia villosa amphiploids

KEY MESSAGE

Phenotypical, physiological and genetic characterization was carried out on the hybrid necrosis gene from Haynaldia villosa, and the related gene Ne-V was mapped to chromosome arm 2VL. Introducing genetic variation from wild relatives into common wheat through wide crosses is a vital strategy for enriching genetic diversity and promoting wheat breeding. However, hybrid necrosis, a genetic autoimmunity syndrome, often occurs in the offspring of interspecific or intraspecific crosses, restricting both the selection of hybrid parents and the pyramiding of beneficial genes. To utilize the germplasms of Haynaldia villosa (2n = 2x = 14, VV), we conducted wide hybridization between durum wheat (2n = 4x = 28, AABB) and multiple H. villosa accessions to synthesize the amphiploids (2n = 6x = 42, AABBVV). This study revealed that 61.5% of amphiploids derived from the above crosses exhibited hybrid necrosis, with some amphiploids even dying before reaching maturity. However, the initiation time and severity of necrosis varied dramatically among the progenies, suggesting that there were multiple genetic loci or multiple alleles in the same genetic locus conferring to hybrid necrosis in H. villosa accessions. Genetic analysis was performed on the F2 and derived F2:3 populations, which were constructed between amphiploid STH59-1 with normal leaves and amphiploid STH59-2 with necrotic leaves. A semidominant hybrid necrosis-related gene, Ne-V, was mapped to an 11.8-cM genetic interval on the long arm of chromosome 2V, representing a novel genetic locus identified in Triticum-related species. In addition, the hybrid necrosis was correlated with enhanced H2O2 accumulation and cell death, and it was influenced by the temperature and light. Our findings provide a foundation for cloning the Ne-V gene and exploring its molecular mechanism.

Genome-wide atlas of rust resistance loci in wheat

Rust diseases, including leaf rust, stripe/yellow rust, and stem rust, significantly impact wheat (Triticum aestivum L.) yields, causing substantial economic losses every year. Breeding and deployment of cultivars with genetic resistance is the most effective and sustainable approach to control these diseases. The genetic toolkit for wheat breeders to select for rust resistance has rapidly expanded with a multitude of genetic loci identified using the latest advances in genomics, mapping and cloning strategies. The goal of this review was to establish a wheat genome atlas that provides a comprehensive summary of reported loci associated with rust resistance. Our atlas provides a summary of mapped quantitative trait loci (QTL) and characterised genes for the three rusts from 170 publications over the past two decades. A total of 920 QTL or resistance genes were positioned across the 21 chromosomes of wheat based on the latest wheat reference genome (IWGSC RefSeq v2.1). Interestingly, 26 genomic regions contained multiple rust loci suggesting they could have pleiotropic effects on two or more rust diseases. We discuss a range of strategies to exploit this wealth of genetic information to efficiently utilise sources of resistance, including genomic information to stack desirable and multiple QTL to develop wheat cultivars with enhanced resistance to rust disease.

Dissection of a rapidly evolving wheat resistance gene cluster by long-read genome sequencing accelerated the cloning of Pm69

Gene cloning in repeat-rich polyploid genomes remains challenging. Here, we describe a strategy for overcoming major bottlenecks in cloning of the powdery mildew resistance gene (R-gene) Pm69 derived from tetraploid wild emmer wheat. A conventional positional cloning approach was not effective owing to suppressed recombination. Chromosome sorting was compromised by insufficient purity. A Pm69 physical map, constructed by assembling Oxford Nanopore Technology (ONT) long-read genome sequences, revealed a rapidly evolving nucleotide-binding leucine-rich repeat (NLR) R-gene cluster with structural variations. A single candidate NLR was identified by anchoring RNA sequencing reads from susceptible mutants to ONT contigs and was validated by virus-induced gene silencing. Pm69 is likely a newly evolved NLR and was discovered in only one location across the wild emmer wheat distribution range in Israel. Pm69 was successfully introgressed into cultivated wheat, and a diagnostic molecular marker was used to accelerate its deployment and pyramiding with other R-genes.

Identification and introgression of a novel leaf rust resistance gene from Thinopyrum intermedium chromosome 7Js into wheat

KEY MESSAGE

A novel leaf rust resistance locus located on a terminal segment (0-69.29 Mb) of Thinopyrum intermedium chromosome arm 7JsS has been introduced into wheat genome for disease resistance breeding. Xiaoyan 78829, a wheat-Thinopyrum intermedium partial amphiploid, exhibits excellent resistance to fungal diseases in wheat. To transfer its disease resistance to common wheat (Triticum aestivum), we previously developed a translocation line WTT26 using chromosome engineering. Disease evaluation showed that WTT26 was nearly immune to 14 common races of leaf rust pathogen (Puccinia triticina) and highly resistant to Ug99 race PTKST of stem rust pathogen (P. graminis f. sp. tritici) at the seedling stage. It also displayed high adult plant resistance to powdery mildew (caused by Blumeria graminis f. sp. tritici). Cytogenetic and molecular marker analysis revealed that WTT26 carried a T4BS·7JsS chromosome translocation. Once transferred into the susceptible wheat genetic background, chromosome 7JsS exhibited its resistance to leaf rust, indicating that the resistance locus was located on this alien chromosome. To enhance the usefulness of this locus in wheat breeding, we further developed several new translocation lines with small Th. intermedium segments using irradiation and developed 124 specific markers using specific-locus amplified fragment sequencing, which increased the marker density of chromosome 7JsS. Furthermore, a refined physical map of chromosome 7JsS was constructed with 74 specific markers, and six bins were thus arranged according to the co-occurrence of markers and alien chromosome segments. Combining data from specific marker amplification and resistance evaluation, we mapped a new leaf rust resistance locus in the 0-69.29 Mb region on chromosome 7JsS. The translocation lines carrying the new leaf rust resistance locus and its linked markers will contribute to wheat disease-resistance breeding.

TaRBP1 stabilizes TaGLTP and negatively regulates stripe rust resistance in wheat

The dynamic balance and distribution of sphingolipid metabolites modulate the level of programmed cell death and plant defence. However, current knowledge is still limited regarding the molecular mechanism underlying the relationship between sphingolipid metabolism and plant defence. In this study, we identified a wheat RNA-binding protein 1 (TaRBP1) and TaRBP1 mRNA accumulation significantly decreased in wheat after infection by Puccinia striiformis f. sp. tritici (Pst). Knockdown of TaRBP1 via virus-induced gene silencing conferred strong resistance to Pst by enhancing host plant reactive oxygen species (ROS) accumulation and cell death, indicating that TaRBP1 may act as a negative regulator in response to Pst. TaRBP1 formed a homopolymer and interacted with TaRBP1 C-terminus in plants. Additionally, TaRBP1 physically interacted with TaGLTP, a sphingosine transfer protein. Knockdown of TaGLTP enhanced wheat resistance to the virulent Pst CYR31. Sphingolipid metabolites showed a significant accumulation in TaGLTP-silenced wheat and TaRBP1-silenced wheat, respectively. In the presence of the TaRBP1 protein, TaGLTP failed to be degraded in a 26S proteasome-dependent manner in plants. Our results reveal a novel susceptible mechanism by which a plant fine-tunes its defence responses by stabilizing TaGLTP accumulation to suppress ROS and sphingolipid accumulation during Pst infection.

Cloning of the wheat leaf rust resistance gene Lr47 introgressed from Aegilops speltoides

Leaf rust, caused by Puccinia triticina Eriksson (Pt), is one of the most severe foliar diseases of wheat. Breeding for leaf rust resistance is a practical and sustainable method to control this devastating disease. Here, we report the identification of Lr47, a broadly effective leaf rust resistance gene introgressed into wheat from Aegilops speltoides. Lr47 encodes a coiled-coil nucleotide-binding leucine-rich repeat protein that is both necessary and sufficient to confer Pt resistance, as demonstrated by loss-of-function mutations and transgenic complementation. Lr47 introgression lines with no or reduced linkage drag are generated using the Pairing homoeologous1 mutation, and a diagnostic molecular marker for Lr47 is developed. The coiled-coil domain of the Lr47 protein is unable to induce cell death, nor does it have self-protein interaction. The cloning of Lr47 expands the number of leaf rust resistance genes that can be incorporated into multigene transgenic cassettes to control this devastating disease.

Understanding and overcoming hybrid lethality in seed and seedling stages as barriers to hybridization and gene flow

Hybrid lethality is a type of reproductive isolation barrier observed in two developmental stages, hybrid embryos (hybrid seeds) and hybrid seedlings. Hybrid lethality has been reported in many plant species and limits distant hybridization breeding including interspecific and intergeneric hybridization, which increases genetic diversity and contributes to produce new germplasm for agricultural purposes. Recent studies have provided molecular and genetic evidence suggesting that underlying causes of hybrid lethality involve epistatic interaction of one or more loci, as hypothesized by the Bateson-Dobzhansky-Muller model, and effective ploidy or endosperm balance number. In this review, we focus on the similarities and differences between hybrid seed lethality and hybrid seedling lethality, as well as methods of recovering seed/seedling activity to circumvent hybrid lethality. Current knowledge summarized in our article will provides new insights into the mechanisms of hybrid lethality and effective methods for circumventing hybrid lethality.

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.

Advances in the Mining of Disease Resistance Genes from Aegilops tauschii and the Utilization in Wheat

Aegilops tauschii is one of the malignant weeds that affect wheat production and is also the wild species ancestor of the D genome of hexaploid wheat (Triticum aestivum, AABBDD). It contains many disease resistance genes that have been lost in the long-term evolution of wheat and is an important genetic resource for the mining and utilization of wheat disease resistance genes. In recent years, the genome sequence of Aegilops tauschii has been preliminarily completed, which has laid a good foundation for the further exploration of wheat disease resistance genes in Aegilops tauschii. There are many studies on disease resistance genes in Aegilops tauschii; in order to provide better help for the disease resistance breeding of wheat, this paper analyzes and reviews the relationship between Aegilops tauschii and wheat, the research progress of Aegilops tauschii, the discovery of disease resistance genes from Aegilops tauschii, and the application of disease resistance genes from Aegilops tauschii to modern wheat breeding, providing a reference for the further exploration and utilization of Aegilops tauschii in wheat disease resistance breeding.

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.

Mapping and characterization of a novel adult-plant leaf rust resistance gene LrYang16G216 via bulked segregant analysis and conventional linkage method

A novel adult-plant leaf rust resistance gene LrYang16G216 on wheat chromosome 6BL was identified and mapped to a 0.59 cM genetic interval by BSA and conventional linkage method. Leaf rust (Puccinia triticina) is one of the most devastating fungal diseases of wheat (Triticum aestivum L.). Discovery and identification of new resistance genes is essential to develop disease-resistant cultivars. An advanced breeding line Yang16G216 was previously identified to confer adult-plant resistance (APR) to leaf rust. In this research, a recombinant inbred line (RIL) population was constructed from the cross between Yang16G216 and a highly susceptible line Yang16M6393, and genotyped with exome capture sequencing and 55 K SNP array. Through bulked segregant analysis (BSA) and genetic linkage mapping, a stable APR gene, designated as LrYang16G216, was detected and mapped to the distal region of chromosome arm 6BL with a genetic interval of 2.8 cM. For further verification, another RIL population derived from the cross between Yang16G216 and a susceptible wheat variety Yangmai 29 was analyzed using the enriched markers in the target interval, and LrYang16G216 was further narrowed to a 0.59 cM genetic interval flanked by the KASP markers Ax109403980 and Ax95083494, corresponding to the physical position 712.34-713.94 Mb in the Chinese Spring reference genome, in which twenty-six disease resistance-related genes were annotated. Based on leaf rust resistance spectrum, mapping data and physical location, LrYang16G216 was identified to be a novel and effective APR gene. The LrYang16G216 with linked markers will be useful for marker-assisted selection in wheat resistance breeding.

Harnessing genetic resistance to rusts in wheat and integrated rust management methods to develop more durable resistant cultivars

Wheat is one of the most important staple foods on earth. Leaf rust, stem rust and stripe rust, caused by Puccini triticina, Puccinia f. sp. graminis and Puccinia f. sp. striiformis, respectively, continue to threaten wheat production worldwide. Utilization of resistant cultivars is the most effective and chemical-free strategy to control rust diseases. Convectional and molecular biology techniques identified more than 200 resistance genes and their associated markers from common wheat and wheat wild relatives, which can be used by breeders in resistance breeding programmes. However, there is continuous emergence of new races of rust pathogens with novel degrees of virulence, thus rendering wheat resistance genes ineffective. An integration of genomic selection, genome editing, molecular breeding and marker-assisted selection, and phenotypic evaluations is required in developing high quality wheat varieties with resistance to multiple pathogens. Although host genotype resistance and application of fungicides are the most generally utilized approaches for controlling wheat rusts, effective agronomic methods are required to reduce disease management costs and increase wheat production sustainability. This review gives a critical overview of the current knowledge of rust resistance, particularly race-specific and non-race specific resistance, the role of pathogenesis-related proteins, non-coding RNAs, and transcription factors in rust resistance, and the molecular basis of interactions between wheat and rust pathogens. It will also discuss the new advances on how integrated rust management methods can assist in developing more durable resistant cultivars in these pathosystems.

Fine mapping of a recessive leaf rust resistance locus on chromosome 2BS in wheat accession CH1539

Leaf rust (LR), caused by Puccinia triticina (Pt), is one of the most important fungal diseases of wheat worldwide. The wheat accession CH1539 showed a high level of resistance to leaf rust. A mapping population of 184 recombinant inbred lines (RILs) was developed from a cross between the resistant accession CH1539 and the susceptible cultivar SY95-71. The RILs showed segregating infection responses to Puccinia triticina Eriks. (Pt) race THK at the seedling stage. Genetic analysis showed that leaf rust resistance was controlled by a monogenic gene, and the potential locus was temporarily named LrCH1539. Bulked segregant analysis (BSA) using a 35 K DArTseq array located LrCH1539 on the short arm of chromosome 2B. Subsequently, a genetic linkage map of LrCH1539 was constructed using the developed 2BS chromosome-specific markers, and its flanking markers were sxau-2BS136 and sxau-2BS81. An F2 subpopulation with 3619 lines was constructed by crossing the resistant and susceptible lines selected from the RIL population. The inoculation identification results showed that LrCH1539 was recessively inherited and was fine-mapped to a 779.4-kb region between markers sxau-2BS47 and sxau-2BS255 at the end of 2BS. The linkage marker analysis showed that the positions of LrCH1539 and Lr16 were the same, but the identification results of the resistance spectrum indicated that the causal genes of the two might be different. The resistant materials reported in this study and the cosegregation marker can be used for marker-assisted selection breeding of leaf rust-resistant wheat cultivars.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-022-01318-4.

Wheat genomic study for genetic improvement of traits in China

Bread wheat (Triticum aestivum L.) is a major crop that feeds 40% of the world's population. Over the past several decades, advances in genomics have led to tremendous achievements in understanding the origin and domestication of wheat, and the genetic basis of agronomically important traits, which promote the breeding of elite varieties. In this review, we focus on progress that has been made in genomic research and genetic improvement of traits such as grain yield, end-use traits, flowering regulation, nutrient use efficiency, and biotic and abiotic stress responses, and various breeding strategies that contributed mainly by Chinese scientists. Functional genomic research in wheat is entering a new era with the availability of multiple reference wheat genome assemblies and the development of cutting-edge technologies such as precise genome editing tools, high-throughput phenotyping platforms, sequencing-based cloning strategies, high-efficiency genetic transformation systems, and speed-breeding facilities. These insights will further extend our understanding of the molecular mechanisms and regulatory networks underlying agronomic traits and facilitate the breeding process, ultimately contributing to more sustainable agriculture in China and throughout the world.

Comparative Transcriptome Analysis Reveals the Gene Expression and Regulatory Characteristics of Broad-Spectrum Immunity to Leaf Rust in a Wheat–Agropyron cristatum 2P Addition Line

Wheat leaf rust (caused by Puccinia triticina Erikss.) is among the major diseases of common wheat. The lack of resistance genes to leaf rust has limited the development of wheat cultivars. Wheat–Agropyron cristatum (A. cristatum) 2P addition line II-9-3 has been shown to provide broad-spectrum immunity to leaf rust. To identify the specific A. cristatum resistance genes and related regulatory pathways in II-9-3, we conducted a comparative transcriptome analysis of inoculated and uninoculated leaves of the resistant addition line II-9-3 and the susceptible cultivar Fukuhokomugi (Fukuho). The results showed that there were 66 A. cristatum differentially expressed genes (DEGs) and 1389 wheat DEGs in II-9-3 during P. triticina infection. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment and gene set enrichment analysis (GSEA) revealed that the DEGs of II-9-3 were associated with plant–pathogen interaction, MAPK signaling pathway–plant, plant hormone signal transduction, glutathione metabolism, and phenylpropanoid biosynthesis. Furthermore, many defense-related A. cristatum genes, such as two NLR genes, seven receptor kinase-encoding genes, and four transcription factor-encoding genes, were identified. Our results indicated that the key step of resistance to leaf rust involves, firstly, the gene expression of chromosome 2P upstream of the immune pathway and, secondly, the effect of chromosome 2P on the co-expression of wheat genes in II-9-3. The disease resistance regulatory pathways and related genes in the addition line II-9-3 thus could play a critical role in the effective utilization of innovative resources for leaf rust resistance in wheat breeding.

Fine mapping and distribution analysis of hybrid necrosis genes Ne1 and Ne2 in wheat in China

Flanking markers useful for identifying hybrid necrosis alleles were identified by fine mapping Ne1 and Ne2 and the distribution of the two necrosis genes was investigated in Chinese elite wheat varieties. Hybrid necrosis of wheat is caused by the interaction of two dominant complementary genes Ne1 and Ne2 present separately in normal parents and is regarded as a barrier to gene transfer in wheat breeding. However, the necrosis alleles still occur at a high frequency in modern wheat varieties. In this study, we constructed two high-density genetic maps of Ne1 and Ne2 in winter wheat. In these cultivars, Ne1 was found to be located in a span interval of 0.50 centimorgan (cM) on chromosome 5BL delimited by markers Nwu_5B_4137 and Nwu_5B_5114, while Ne2 co-segregated with markers Lseq102 and TC67744 on 2BS. Statistical analysis confirmed that the dosage effect of Ne1 and Ne2 also existed in moderate and severe hybrid necrosis systems, and the symptoms of necrosis can also be affected by the genetic background. Furthermore, we clarified the discrete distribution and proportion of the Ne1 and Ne2 in the 10 China's agro-ecological production zones. We concluded that 26.2% and 33.2% of the 1364 cultivars (lines) were genotyped with Ne1Ne1ne2ne2 and ne1ne1Ne2Ne2, respectively and introduced modern cultivars should directly affect the frequencies of necrosis genes in modern Chinese cultivars (lines), especially that of Ne2. Taking investigations in spring wheat together, we proposed that hybrid necrosis alleles could positively affect breeding owing to their linked excellent genes such as Lr13. Additionally, based on the pedigrees and hybridization tests, we speculated that the Ne1 and Ne2 in winter wheat may directly originate from wild emmer and introduced cultivars or hexaploid triticale, respectively.

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 identity^2,3. 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.

Chromosome-scale genome assembly of the South African bread wheat (Triticum aestivum) cultivar Kariega facilitates the cloning of the stripe rust resistance gene Yr27.

Fine mapping of QPm.caas-3BS, a stable QTL for adult-plant resistance to powdery mildew in wheat (Triticum aestivum L.)

A stable QTL QPm.caas-3BS for adult-plant resistance to powdery mildew was mapped in an interval of 431 kb, and candidate genes were predicted based on gene sequences and expression profiles. Powdery mildew is a devastating foliar disease occurring in most wheat-growing areas. Characterization and fine mapping of genes for powdery mildew resistance can benefit marker-assisted breeding. We previously identified a stable quantitative trait locus (QTL) QPm.caas-3BS for adult-plant resistance to powdery mildew in a recombinant inbred line population of Zhou8425B/Chinese Spring by phenotyping across four environments. Using 11 heterozygous recombinants and high-density molecular markers, QPm.caas-3BS was delimited in a physical interval of approximately 3.91 Mb. Based on re-sequenced data and expression profiles, three genes TraesCS3B02G014800, TraesCS3B02G016800 and TraesCS3B02G019900 were associated with the powdery mildew resistance locus. Three gene-specific kompetitive allele-specific PCR (KASP) markers were developed from these genes and validated in the Zhou8425B derivatives and Zhou8425B/Chinese Spring population in which the resistance gene was mapped to a 0.3 cM interval flanked by KASP14800 and snp_50465, corresponding to a 431 kb region at the distal end of chromosome 3BS. Within the interval, TraesCS3B02G014800 was the most likely candidate gene for QPm.caas-3BS, but TraesCS3B02G016300 and TraesCS3B02G016400 were less likely candidates based on gene annotations and sequence variation between the parents. These results not only offer high-throughput KASP markers for improvement of powdery mildew resistance but also pave the way to map-based cloning of the resistance gene.