Susceptible Wheat Research Articles

The E3 ubiquitin ligase TaGW2 facilitates TaSnRK1γ and TaVPS24 degradation to enhance stripe rust susceptibility in wheat.

Wheat stripe rust, caused by the fungal pathogen Puccinia striiformis f. sp. tritici (Pst), threatens global wheat production, and therefore discovering genes involved in stripe rust susceptibility is essential for balancing yield with disease resistance in sustainable breeding strategies. Although TaGW2 is well known to negatively regulate wheat kernel size and weight, its role in stress response remains unclear. Here, we found that TaGW2 transcription levels increased following inoculation with Pst or treatment with flg22 or chitin. TaGW2 knockdown lines showed enhanced resistance to multiple Pst races, while TaGW2 overexpression reduced host defence response, promoted Pst growth and development and increased wheat susceptibility to Pst. Additionally, TaGW2 could mediate the ubiquitination and degradation of both TaSnRK1γ and TaVPS24 via the 26S proteasome pathway. Silencing TaSnRK1γ or TaVPS24 in wheat increased sensitivity to Pst, whereas overexpressing either gene enhanced wheat defence response, indicating that TaSnRK1γ and TaVPS24 act as positive regulators of Pst resistance. This study reveals a previously unrecognized mechanism inhibiting plant immunity to Pst through TaGW2-mediated ubiquitination and degradation of TaSnRK1γ and TaVPS24. This work also provides crucial genetic resources for breeding high-yield, stripe rust-resistant wheat varieties.

Genome-wide mapping of quantitative trait loci conferring resistance to stripe rust in spring wheat line PI 660072.

Two major QTL for resistance to stripe rust were mapped on chromosome 2BL and 4BL in spring wheat PI 660072, and their KASP markers were developed. Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most devastating diseases of wheat worldwide. Identifying resistance genes is crucial for developing resistant cultivars to control the disease. Spring wheat PI 660072 (Triticum aestivum) has been identified to possess both adult-plant resistance (APR) and all-stage resistance (ASR) to stripe rust. To elucidate the genetic basis of the resistance in PI 660072, a mapping population consisting of 211 F5-F7 recombinant-inbred lines (RILs) was developed from a cross of PI 660072 with susceptible spring wheat Avocet S. The mapping population was phenotyped for stripe rust responses across five field environments from 2020 to 2022 and genotyped using the 15K SNP (single nucleotide polymorphism) array to map stripe rust resistance loci. The mapping population was also tested at the seedling stage with predominant Chinese Pst races CYR31, CYR32, CYR34 and PST-YX1-3-1 in the greenhouse. Stripe rust resistance genes were identified using the quantitative trait locus (QTL) mapping approach. Two QTL were identified with QYrPI660072.swust-2BL mapped on the long arm of chromosome 2B for ASR and QYrPI660072.swust-4BL on the long arm of chromosome 4B for APR. To facilitate marker-assisted selection breeding, Kompetitive allele specific PCR (KASP) markers, KASP-1269 for QYrPI660072.swust-2BL and KASP-3209 for QYrPI660072.swust-4BL, were developed. These markers could be used to introgress the effective resistance QTL into new wheat cultivars.

Effect of Sowing Dates and Wheat Cultivars on Agro Meteorological Indices of Wheat under Conditions of North-western Himalayas, India

Climate change in recent times have presented a scenario of elevated susceptibility of wheat to rising temperatures. Agro-meteorological indices can present a scenario of variable response of wheat to diverse conditions. A field investigation was conducted in rabi season of 2016-17 at Research farm, Department of Agronomy, CSK Himachal Pradesh Krishi Vishvavidyalaya, Palampur to evaluate the influence of sowing dates and wheat cultivars on agro-meteorological indices such as growing degree days, photothermal units, Helio thermal units and phenothermal index of wheat crop. The field investigation involved five sowing dates (15th October, 30th October, 15th November, 30th November and 15th December) and wheat cultivars (HPW-349 and HPW-155) which were studied in a factorial randomized block design with three replications. The results of the investigation revealed that timely sown crop i.e., on 15th October recorded the highest values for agro-meteorological indices for both the wheat cultivars such as growing degree days, Helio thermal units, photothermal units and phenothermal index across various wheat development stages such as complete emergence, crown root initiation, tillering, ear emergence and physiological maturity. Therefore, timely sowing of wheat by 15th October was concluded to be the best for optimized agro-meteorological indices such as growing degree days, photothermal units, Helio thermal units and phenothermal index under conditions of North-Western Himalayas.

A critical review of the factors influencing pre‐harvest sprouting of wheat

AbstractPre‐harvest sprouting (PHS) is a global issue affecting a multitude of crops, including wheat (Triticum aestivum L.). The combination of conducive conditions and a lack of genetic seed dormancy results in the sprouting of intact grain at or prior to harvesting. The initiation of germination synthesizes gibberellic acid resulting in the activation of the alpha‐amylase synthesis via a calcium‐dependent signal transduction pathway. Alpha‐amylase synthesized via this pathway degrades the endosperm, decreasing bread‐making quality. A commonly used indicator for bread‐making quality is the Hagberg Falling Number. Environmental, phenotypic, genetic, and management factors influence the susceptibility of wheat to PHS. Rainfall, temperature, and relative humidity are commonly associated with PHS. The combination of these conditions results in the greatest severity of PHS. Morphological features such as awns and epicuticular waxes may increase the quantity of rainfall retained against the grain, increasing the risk of PHS. Similarly, management factors such as fertilization and fungicide application also may increase the risk of PHS occurring. Further research is necessary to understand the mechanisms and impact of management factors on PHS. Additionally, further investigations are needed to explore how environmental and genotypic interactions affect PHS susceptibility.

Characterization of novel wheat-Thinopyrum ponticum introgression lines derived from partial amphiploid AUS6770 for resistance to stripe rust

The wild decaploid species Thinopyrum ponticum (Podp.) Barkworth & D.R. Dewey is an important source of genes against biotic and abiotic stresses affecting wheat. The wheat–Th. ponticum partial amphiploid AUS6770 shows resistance to multiple diseases, including stripe rust, stem rust, and powdery mildew. Mitotic chromosomes of AUS6770 were characterized by non-denaturing-fluorescence in situ hybridization (ND-FISH), and the individual Th. ponticum chromosomes 1Ae to 7Ae were karyotypically distinguished by Oligo-FISH painting using bulked oligo pools based on wheat-barley collinear regions. A novel stripe rust resistant line A155, derived from AUS6770, was found to have 44 chromosomes, including a pair of 2Ae chromosomes and a pair of 6B-6Ae translocations. To detect plants with transfer of resistance genes from A155 to wheat chromosomes, 1770 plants were developed from F2–F5 progenies of A155 crossed with the susceptible wheat cultivar MY11 and characterized with ND-FISH using multiple probes. A high frequency of transmission of chromosome 2Ae was observed, and 31 types of 2Ae chromosomal aberrations were identified using ND-FISH. Ten chromosomal bins on the 2Ae chromosome were determined from the deletion and translocation lines based on genome-based PCR markers. In combination with the evaluation of disease resistance, the gene(s) for stripe rust resistance was located on the FL0.79–1.00 of 2AeS and covers the corresponding region of 0–58.26 Mb in the reference genome of Th. elongatum. The newly identified wheat-Th. ponticum 2Ae translocation lines can be exploited as potential germplasm in wheat breeding for stripe rust resistance.

The Puccinia striiformis effector Pst11215 manipulates mitochondria to suppress host immunity by promoting TaVDIP1-mediated ubiquitination of TaVDAC1.

Mitochondria-induced cell death is closely correlated with plant immune responses against pathogens. However, the molecular mechanisms by which pathogens manipulate mitochondria to suppress host resistance remain poorly understood. In this study, a haustorium-specific effector Pst11215 from the wheat stripe rust pathogen Puccinia striiformis f. sp. tritici (Pst) was characterized by host-induced gene silencing. The interaction partners regulated by Pst11215 were screened using the yeast two-hybrid system. In addition, Pst11215-mediated immune regulation modes were further determined. The results showed that Pst11215 was required for Pst virulence. Pst11215 interacted with the wheat voltage-dependent anion channel TaVDAC1, the negative regulator of wheat resistance to stripe rust, in mitochondria. Furthermore, the E3 ubiquitin ligase TaVDIP1 targeted and ubiquitinated TaVDAC1, which can be promoted by Pst11215. TaVDIP1 conferred enhanced wheat susceptibility to Pst by cooperating with TaVDAC1. Overexpression of TaVDIP1 reduced reactive oxygen species (ROS) accumulation and abnormal mitochondria. Our study revealed that Pst11215 functions as an important pathogenicity factor secreted to the host mitochondria to compromise wheat resistance to Pst possibly by facilitating TaVDIP1-mediated ubiquitination of TaVDAC1, thereby protecting mitochondria from ROS-induced impairment. This research unveils a novel regulation mode of effectors hijacking host mitochondria to contribute to pathogen infection.

Novel resistance loci for quantitative resistance to Septoria tritici blotch in Asian wheat (Triticum aestivum) via genome-wide association study

BackgroundSeptoria tritici blotch (STB) disease causes yield losses of up to 50 per cent in susceptible wheat cultivars and can reduce wheat production. In this study, genomic architecture for adult-plant STB resistance in a Septoria Association Mapping Panel (SAMP) having 181 accessions and genomic regions governing STB resistance in a South Asian wheat panel were looked for.ResultsField experiments during the period from 2019 to 2021 revealed those certain accessions, namely BGD52 (CHIR7/ANB//CHIR1), BGD54 (CHIR7/ANB//CHIR1), IND92 (WH 1218), IND8 (DBW 168), and IND75 (PBW 800), exhibited a high level of resistance. Genetic analysis revealed the presence of 21 stable quantitative trait nucleotides (QTNs) associated with resistance to STB (Septoria tritici blotch) on all wheat chromosomes, except for 2D, 3A, 3D, 4A, 4D, 5D, 6B, 6D, and 7A. These QTNs were predominantly located in chromosome regions previously identified as associated with STB resistance. Three Quantitative Trait Loci (QTNs) were found to have significant phenotypic effects in field evaluations. These QTNs are Q.STB.5A.1, Q.STB.5B.1, and Q.STB.5B.3. Furthermore, it is possible that the QTNs located on chromosomes 1A (Q.STB.1A.1), 2A (Q.STB_DH.2A.1, Q.STB.2A.3), 2B (Q.STB.2B.4), 5A (Q.STB.5A.1, Q.STB.5A.2), and 7B (Q.STB.7B.2) could potentially be new genetic regions associated with resistance.ConclusionOur findings demonstrate the importance of Asian bread wheat as a source of STB resistance alleles and novel stable QTNs for wheat breeding programs aiming to develop long-lasting and wide-ranging resistance to Zymoseptoria tritici in wheat cultivars.

Identification and Mapping of QTLs for Adult Plant Resistance in Wheat Line XK502.

Stripe rust is a serious wheat disease occurring worldwide. At present, the most effective way to control it is to grow resistant cultivars. In this study, a population of 221 recombinant inbred lines (RILs) derived via single-seed descent from a hybrid of a susceptible wheat line, SY95-71, and a resistant line, XK502, was tested in three crop seasons from 2022 to 2024 in five environments. A genetic linkage map was constructed using 12,577 single-nucleotide polymorphisms (SNPs). Based on the phenotypic data of infection severity and the linkage map, five quantitative trait loci (QTL) for adult plant resistance (APR) were detected using the inclusive composite interval mapping (ICIM) method. These five loci are QYrxk502.swust-1BL, QYrxk502.swust-2BL, QYrxk502.swust-3AS, QYrxk502.swust-3BS, and QYrxk502.swust-7BS, explaining 5.67-19.64%, 9.63-36.74%, 9.58-11.30%, 9.76-23.98%, and 8.02-12.41% of the phenotypic variation, respectively. All these QTL originated from the resistant parent XK502. By comparison with the locations of known stripe rust resistance genes, three of the detected QTL, QYrxk502.swust-3AS, QYrxk502.swust-3BS, and QYrxk502.swust-7BS, may harbor new, unidentified genes. From among the tested RILs, 16 lines were selected with good field stripe rust resistance and acceptable agronomic traits for inclusion in breeding programs.

Cellular changes and PR-1 gene expression accompanying infection-related morphogenesis and cell progression during invasive growth Pyricularia oryzae pathotype Triticum in resistant and susceptible wheat cultivars

Pyricularia oryzae pathotype Triticum (PoT) causes Wheat Blast, a devastating crop disease present in many wheat-producing countries. With the aim to contribute with the understanding of the mechanisms underlying pathogenesis of the fungus on wheat (Triticum aestivum), cytological and molecular studies were performed here.Susceptible and resistant interactions of wheat-PoT in cultivars of different levels of resistance were investigated by cellular changes and the molecular responses of wheat leaves according PR-1 expression. There was significant difference between susceptible (Apogee-PY15-PY34, Buck, MSINTA-PY15) and resistant (Buck-PY34, MSINTA-PY34) interactions in the responses tested. The two isolates of PoT analysed showed different ability to infect wheat plants at the cellular level during early tissue penetration analysed and documented by epi-fluorescence microscopy, patterns of PR-1 genes, and wheat plant defense reaction.Microscopic time-course analysis (24, 48, 72 and 96 h after inoculation) of individual interaction sites per leaf revealed different leaf invasion strategies of the more and less aggressive PoT isolates during the first stages of the course of pathogenesis.The results and conclusions of the present study provides the first evidence that different PR-1 spatial and temporal expression patterns occur in the early infective process of wheat-PoT, underlying two different defence mechanisms in plants according susceptible or resistant interactions. Thus, the results here laid a theoretical foundation for the future control of wheat blast using the different pattern of PR-1 gene as markers for disease resistance during the first stages of infection providing a significant contribution to a more efficient selection of wheat genotypes in breeding studies.

Genome and transcriptome based comparative analysis of Tilletia indica to decipher the causal genes for pathogenicity of Karnal bunt in wheat

Tilletia indica Mitra causes Karnal bunt (KB) in wheat by pathogenic dikaryophase. The present study is the first to provide the draft genomes of the dikaryon (PSWKBGD-3) and its two monosporidial lines (PSWKBGH-1 and 2) using Illumina and PacBio reads, their annotation and the comparative analyses among the three genomes by extracting polymorphic SSR markers. The trancriptome from infected wheat grains of the susceptible wheat cultivar WL711 at 24 h, 48h, and 7d after inoculation of PSWKBGH-1, 2 and PSWKBGD-3 were also isolated. Further, two transcriptome analyses were performed utilizing T. indica transcriptome to extract dikaryon genes responsible for pathogenesis, and wheat transcriptome to extract wheat genes affected by dikaryon involved in plant-pathogen interaction during progression of KB in wheat. A total of 54, 529, and 87 genes at 24hai, 48hai, and 7dai, respectively were upregulated in dikaryon stage while 21, 35, and 134 genes of T. indica at 24hai, 48hai, and 7dai, respectively, were activated only in dikaryon stage. While, a total of 23, 17, and 52 wheat genes at 24hai, 48hai, and 7dai, respectively were upregulated due to the presence of dikaryon stage only. The results obtained during this study have been compiled in a web resource called TiGeR (http://backlin.cabgrid.res.in/tiger/), which is the first genomic resource for T. indica cataloguing genes, genomic and polymorphic SSRs of the three T. indica lines, wheat and T. indica DEGs as well as wheat genes affected by T. indica dikaryon along with the pathogenecity related proteins of T. indica dikaryon during incidence of KB at different time points. The present study would be helpful to understand the role of dikaryon in plant-pathogen interaction during progression of KB, which would be helpful to manage KB in wheat, and to develop KB-resistant wheat varieties.

The effect of quantitative wheat resistance on the aggressiveness of Fusarium graminearum.

Little is known about the selection pressures acting on plant pathogen populations, especially those applied by quantitative forms of resistance. Fusarium graminearum causes Fusarium Head Blight (FHB) in wheat, producing significant yield losses and mycotoxin contamination. Quantitative host resistance is the best method to control FHB. However, there needs to be more understanding of how disease resistance affects the evolution of plant pathogens. This study aimed to determine if the presence or absence of wheat resistance influenced the fitness components and genomic regions of F. graminearum. Thirty-one isolates from highly susceptible and 25 isolates from moderately resistant wheat lines were used. Isolate aggressiveness was measured by area under the disease progress curve (AUDPC), visually damaged kernels, and deoxynivalenol contamination. In vitro growth rate and spore production were also measured. Two whole-genome scans for selection were conducted with 333,297 SNPs. One scan looked for signatures of selection in the entire sample and the other scan was for divergent selection between the isolates from moderately resistant wheat and highly susceptible wheat. The population of isolates from highly susceptible wheat was primarily aggressive. Several regions of the F. graminearum genome with signatures for selection were identified. The moderately resistant wheat varieties used in this study did not select more aggressive isolates, suggesting that quantitative resistance is a durable method to control FHB.

Genetic Basis Identification of a NLR Gene, TaRGA5-like, That Confers Partial Powdery Mildew Resistance in Wheat SJ106.

Wheat powdery mildew is an important fungal disease that seriously jeopardizes wheat production, which poses a serious threat to food safety. SJ106 is a high-quality, disease-resistant spring wheat variety; this disease resistance is derived from Wheat-wheatgrass 33. In this study, the powdery mildew resistance genes in SJ106 were located at the end of chromosome 6DS, a new disease resistance locus tentatively named PmSJ106 locus. This interval was composed of a nucleotide-binding leucine-rich repeat (NLR) gene cluster containing 19 NLR genes. Five NLRs were tandem duplicated genes, and one of them (a coiled coil domain-nucleotide binding site-leucine-rich repeat (CC-NBS-LRR; CNL) type gene, TaRGA5-like) expressed 69-836-fold in SJ106 compared with the susceptible control. The genome DNA and cDNA sequences of TaRGA5-like were amplified from SJ106, which contain several nucleotide polymorphisms in LRR regions compared with susceptible individuals and Chinese Spring. Overexpression of TaRGA5-like significantly increased resistance to powdery mildew in susceptible receptor wheat Jinqiang5. However, Virus induced gene silence (VIGS) of TaRGA5-like resulted in only a small decrease of SJ106 in disease resistance, presumably compensated by other NLR duplicated genes. The results suggested that TaRGA5-like confers partial powdery mildew resistance in SJ106. As a member of the PmSJ106 locus, TaRGA5-like functioned together with other NLR duplicated genes to improve wheat resistance to powdery mildew. Wheat variety SJ106 would become a novel and potentially valuable germplasm for powdery mildew resistance.

The pivotal role of trichomes in wheat susceptibility to Fusarium head blight

The pivotal role of trichomes in wheat susceptibility to Fusarium head blight

Fusarium pseudograminearum biomass and toxin accumulation in wheat tissues with and without Fusarium crown rot symptoms.

Fusarium crown rot (FCR) is an important and devastating disease of wheat (Triticum aestivum) caused by the fungus Fusarium pseudograminearum and related pathogens. Using two distinct susceptible cultivars, we investigated the isolation frequencies of F. pseudograminearum and quantified its biomass accumulation and the levels of the associated toxins deoxynivalenol (DON) and DON-3-glucoside (D3G) in inoculated field-grown wheat plants. We detected F. pseudograminearum in stem, peduncle, rachis, and husk tissues, but not in grains, whereas DON and D3G accumulated in stem, rachis, husk, and grain tissues. Disease severity was positively correlated with the frequency of pathogen isolation, F. pseudograminearum biomass, and mycotoxin levels. The amount of F. pseudograminearum biomass and mycotoxin contents in asymptomatic tissue of diseased plants were associated with the distance of the tissue from the diseased internode and the disease severity of the plant. Thus, apparently healthy tissue may harbor F. pseudograminearum and contain associated mycotoxins. This research helps clarify the relationship between F. pseudograminearum occurrence, F. pseudograminearum biomass, and mycotoxin accumulation in tissues of susceptible wheat cultivars with or without disease symptoms, providing information that can lead to more effective control measures.

Bulked segregant RNA-seq reveals complex resistance expression profile to powdery mildew in wild emmer wheat W762.

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most destructive fungal diseases threatening global wheat production. Exploring powdery mildew resistance (Pm) gene(s) and dissecting the molecular mechanism of the host resistance are critical to effectively and reasonably control this disease. Durum wheat (Triticum turgidum L. var. durumDesf.) is an important gene donor for wheat improvement against powdery mildew. In this study, a resistant durum wheat accession W762 was used to investigate its potential resistance component(s) and profile its expression pattern in responding to Bgt invasion using bulked segregant RNA-Seq (BSR-Seq) and further qRT-PCR verification. Genetic analysis showed that the powdery mildew resistance in W762 did not meet monogenic inheritance and complex genetic model might exist within the population of W762 × Langdon (susceptible durum wheat). After BSR-Seq, 6,196 consistently different single nucleotide polymorphisms (SNPs) were called between resistant and susceptible parents and bulks, and among them, 763 SNPs were assigned to the chromosome arm 7B. Subsequently, 3,653 differentially expressed genes (DEGs) between resistant and susceptible parents and bulks were annotated and analyzed by Gene Ontology (GO), Cluster of Orthologous Groups (COG), and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment. The potential regulated genes were selected and analyzed their temporal expression patterns following Bgt inoculation. As a result, nine disease-related genes showed distinctive expression profile after Bgt invasion and might serve as potential targets to regulate the resistance against powdery mildew in W762. Our study could lay a foundation for analysis of the molecular mechanism and also provide potential targets for the improvement of durable resistance against powdery mildew.

Volatile Organic Compounds Mediate Host Selection of Wheat Midge, Sitodiplosis Mosellana (Géhin) (Diptera: Cecidomyiidae) between Preanthesis and Postanthesis Stages of Wheat.

The orange wheat blossom midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae), is a significant wheat pest in the Prairie Provinces of Canada and northern regions of the USA. Wheat phenology plays a critical role in wheat midge oviposition. We hypothesized that S. mosellana oviposition behaviour is influenced by volatile organic compounds (VOCs) emitted by wheat at two adjacent wheat growth stages: preanthesis and postanthesis. A higher number of S. mosellana eggs laid on preanthesis than postanthesis spikes in an oviposition choice experiment using the susceptible spring wheat cultivar 'Roblin'. In preanthesis, wheat emitted higher amounts of Z-3-hexenyl acetate (Z3-06:OAc) than at the postanthesis stage. Higher amounts of methyl ketones such as 2-tridecanone, 2-pentadecanone, and 2-undecanone were emitted by wheat in the postanthesis stage and these VOCs were sensitive to S. mosellana antennae used in the Gas Chromatography-Electroantennographic Detection. Females were attracted to synthetic Z3-06:OAc but were deterred by 2-tridecanone relative to the solvent control in the vertical Y-tube olfactometer. 2-Undecanone and 2-pentadecanone did not show any attractiveness or deterrence. In a no-choice oviposition experiment, fewer eggs were laid in preanthesis wheat exposed to a synthetic VOC blend of Z3-06:OAc, 2-undecanone, 2-tridecanone, and 2-pentadecanone at the concentrations released by postanthesis spikes. This study shows that the reduction of Z3-06:OAc, in the VOC mix, and possibly the increase in 2-tridecanone, are likely responsible for the reduction in oviposition on postanthesis wheat. These results elucidate for the first time the role of specific VOCs mediating S. mosellana oviposition in preanthesis and postanthesis wheat.

Impact of susceptible wheat cultivars on epidemiological parameters involved in the introduction and spread of wheat dwarf disease

AbstractDefence mechanisms in plants have been naturally or artificially selected to cope with virus infection and/or insect colonization. This creates a range of host susceptibility to viruses and/or insects that can impact the epidemiology of insect‐borne viral diseases. Wheat dwarf disease (WDD), one of the most important viral diseases on small‐grain cereals, is caused by wheat dwarf virus (WDV), which is transmitted by the leafhopper Psammotettix alienus. In the current context of the unavailability of either WDV‐resistant/tolerant wheat cultivars or effective methods to control WDD in French cereal fields, the accurate characterization of WDV‐susceptible genotypes must be considered to improve management strategies against this viral disease. In this study, the impact of 12 wheat cultivars on epidemiological parameters related to the introduction (host selection and virus infection) and spread (insect performance and virus transmission) of WDD was evaluated. Results showed no differences between the tested cultivars for host selection made by P. alienus, whereas four tested cultivars (Complice, Filon, Hyking and Nemo) reduced survival and/or fecundity of the leafhopper. Characterization of virus–host interactions highlights the lower host and source quality of cv. Filon for WDV. Finally, multivariate analyses allowed the identification of cvs Filon, Boregar, Solindo CS, Complice and Hyking as less suitable hosts for WDV and/or P. alienus, suggesting that these cultivars could present interesting genetic resource(s) that should be considered for future breeding programmes against WDD.

Genome-wide expression analysis of novel heat-responsive microRNAs and their targets in contrasting wheat genotypes at reproductive stage under terminal heat stress.

Heat stress at terminal stage of wheat is critical and leads to huge yield losses worldwide. microRNAs (miRNAs) play significant regulatory roles in gene expression associated with abiotic and biotic stress at the post-transcriptional level. In the present study, we carried out a comparative analysis of miRNAs and their targets in flag leaves as well as developing seeds of heat tolerant (RAJ3765) and heat susceptible (HUW510) wheat genotypes under heat stress and normal conditions using small RNA and degradome sequencing. A total of 84 conserved miRNAs belonging to 35 miRNA families and 93 novel miRNAs were identified in the 8 libraries. Tae-miR9672a-3p, tae-miR9774, tae-miR9669-5p, and tae-miR5048-5p showed the highest expression under heat stress. Tae-miR9775, tae-miR9662b-3p, tae-miR1120a, tae-miR5084, tae-miR1122a, tae-miR5085, tae-miR1118, tae-miR1130a, tae-miR9678-3p, tae-miR7757-5p, tae-miR9668-5p, tae-miR5050, tae-miR9652-5p, and tae-miR9679-5p were expressed only in the tolerant genotype, indicating their role in heat tolerance. Comparison between heat-treated and control groups revealed that 146 known and 57 novel miRNAs were differentially expressed in the various tissues. Eight degradome libraries sequence identified 457 targets of the differentially expressed miRNAs. Functional analysis of the targets indicated their involvement in photosynthesis, spliceosome, biosynthesis of nucleotide sugars and protein processing in the endoplasmic reticulum, arginine and proline metabolism and endocytosis. This study increases the number of identified and novel miRNAs along with their roles involved in heat stress response in contrasting genotypes at two developing stages of wheat.

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.

A Combination of Resistance Genes Confers High and Durable Resistance Against Stripe Rust in Wheat Cultivar Lantian 26.

'Lantian 26', a leading elite winter wheat cultivar in Gansu Province since its release in 2010, exhibits high resistance or immunization to stripe rust in the adult-plant stage under a high disease pressure in Longnan (southeastern Gansu). Identifying the resistance genes in 'Lantian 26' could provide a basis for enhanced durability and high levels of resistance in wheat cultivars. Here, a segregating population was developed from a cross between a highly susceptible wheat cultivar Mingxian 169 and the highly stripe rust-resistant 'Lantian 26'. The F2 and F2:3 progenies of the cross were inoculated with multiple prevalent virulent races of stripe rust for adult-plant-stage-resistance evaluation in two different environments. Exon sequence alignment analysis revealed that a stripe rust resistance gene on the 718.4- to 721.2-Mb region of chromosome 7BL, tentatively named as YrLT26, and a cosegregation sequence-tagged site (STS) marker GY17 was developed and validated using the F2:3 population and 103 wheat cultivars. The other two resistance genes, Yr9 and Yr30, were also identified in 'Lantian 26' using molecular markers. Therefore, the key to high and durable resistance to stripe rust at the adult stage is the combination of Yr9, Yr30, and YrLT26 genes in 'Lantian 26'. This could be a considerable strategy for improving the wheat cultivars with effective and durable resistance in the high-pressure region for stripe rust.