Adult Plant Stage Research Articles

Molecular and Agro-physiological Study Associated with Net Blotch Resistance at Seedling and Adult Plant Stages in Some Egyptian Barley Genotypes

Net blotch infection is the most widespread and harmful disease for barley that caused substantial losses grain yield and quality, in this study Greenhouse and field experiments were carried out to recorded the net blotch reaction at seedling and adult stage of twenty barley genotypes during two growing seasons 2020/2021 and 2021/2022 .Start Codon Targeted (SCoT) markers were used to study the genetic variances and relationships among barley genotypes against net blotch reaction. The expression of severity to net blotch infection based on agro- physiological traits and net blotch reaction studied showed that Line 3 and Giza 2000 genotypes appeared the highest net blotch infection response that had lowest phenol content, chlorophyll fluorescence (FV/FM ratio) and total chlorophyll content SPAD were (42.52 mg/100g 0.510, 39. 53 SPAD reading and 43.76 mg/100g, 0.543 and 40.50 SPAD reading) respectively. However Giza 132, Giza 134, Giza 137, Giza 136, Line 4, line 5 and line 7 were proved to be the most resistant genotypes for net blotch that showed high average mean performance values for all studied agro- physiological traits over all the tested barley genotypes and scrod one under greenhouse at seedling stage with lowest net blotch infection that they were related to type R. Genetic changeability and associations among 20 barley genotypes based on using ten SCoT markers showed 77 amplified fragments, out of them 61 (77.92%) were polymorphic. The primer (SCoT -9) was highly informative marker which had higher values of total number of bands, number of polymorphic bands, polymorphism percentage, Polymorphism information content, diversity index, marker index and discriminating power DP were ( 10 ,9, 90.0, 0.389, 0.489, 0.499 and 0.692 ) respectively, so we could consider that useful primer to confirm the genetic differences among barley genotypes for net blotch reaction. The dendrogram based on SCoT showed clear pattern of clustering among the twenty barley genotypes with the resistant and susceptible for net blotch. These results could be useful for barley improvement in terms of biodiversity protection and design of new crosses for disease resistance to net blotch resistance in Egypt.

Development and cytological characterization of wheat-Thinopyrum intermedium translocation lines with novel stripe rust resistance gene.

Wheat stripe rust is a destructive disease in many cool and temperate regions around the world. Exploiting novel sources of resistance can provide wheat cultivars with robust and durable resistance to stripe rust. The wheat-Thinopyrum intermedium addition line TAI-14 was proven to carry a stripe rust resistance gene (named as YrT14) on the alien Th. intermedium chromosome. In order to transfer the resistance gene to wheat, wheat-Th. intermedium translocation lines were created by irradiating the pollen of the line TAI-14. We totally obtained 153 wheat-Th. intermedium translocation lines, among which the long alien segmental translocation line Zhongke 78 and the intercalary translocation line Zhongke 15 not only showed good integrated agronomic traits but also were identified as highly resistant to stripe rust in both seedling and adult plant stages. The alien chromatin in Zhongke 15 was identified as an insertion into the satellite of chromosome 6B, a type of translocation never reported before in chromosome engineering. By screening Simple Sequence Repeat (SSR) and Expressed Sequence Tag (EST) markers as well as the markers developed from RNA-sequencing (RNA-Seq) data, 14 markers were identified specific for the alien chromosome and a physical map was constructed. Both Zhongke 78 and Zhongke 15 could be used as a novel source of stripe rust resistance for wheat breeding, and the linked marker T14K50 can be used for molecular marker-assisted breeding. Finally, based on the karyotype, reaction to stripe rust, and genome resequencing data of different wheat-Th. intermedium translocation lines, the stripe rust resistance gene YrT14 was located to an 88.1 Mb interval from 636.7 to 724.8 Mb on Th. intermedium chromosome 19 corresponding to 7J or 7Js.

Characterization and Molecular Mapping of a Gene Conferring High-Temperature Adult-Plant Resistance to Stripe Rust Originally from Aegilops ventricosa.

Wheat near-isogenic line AvSYr17NIL carrying Yr17, originally from Aegilops ventricosa for all-stage resistance to Puccinia striiformis f. sp. tritici, also shows nonrace-specific, high-temperature adult-plant (HTAP) resistance to the stripe rust pathogen. To separate and identify the HTAP resistance gene, seeds of AvSYr17NIL were treated with ethyl methanesulfonate. Mutant lines with only HTAP resistance were obtained, and one of the lines, M1225, was crossed with the susceptible recurrent parent Avocet S (AvS). Field responses of the F2 plants and F3 lines, together with the parents, were recorded at the adult-plant stage in Pullman and Mount Vernon, WA under natural P. striiformis f. sp. tritici infection. The parents and the F4 population were phenotyped with a Yr17-virulent P. striiformis f. sp. tritici race in the adult-plant stage under the high-temperature profile in the greenhouse. The phenotypic results were confirmed by testing the F5 population in the field under natural P. striiformis f. sp. tritici infection. The F2 data indicated a single recessive gene, temporarily named YrM1225, for HTAP resistance. The F4 lines were genotyped with Kompetitive allele-specific PCR markers converted from single-nucleotide polymorphism markers polymorphic between M1225 and AvS. The HTAP resistance gene was mapped on the short arm of chromosome 2A in an interval of 7.5 centimorgans using both linkage and quantitative trait locus mapping approaches. The separation of the HTAP resistance gene from Yr17 should improve the understanding and utilization of the different types of resistance.

Identification of a Wheat Powdery Mildew Dominant Resistance Gene in the Pm5 Locus for High-Throughput Marker-Assisted Selection.

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), poses a severe threat to wheat yield and quality worldwide. Rapid identification and the accurate transference of effective resistance genes are important to the development of resistant cultivars and the sustainable control of this disease. In the present study, the wheat line AL11 exhibited high levels of resistance to powdery mildew at both the seedling and adult plant stages. Genetic analysis of the AL11 × 'Shixin 733' mapping population revealed that its resistance was controlled by a single dominant gene, tentatively designated PmAL11. Using bulked segregant RNA-Seq and molecular marker analysis, PmAL11 was mapped to the Pm5 locus on chromosome 7B where it cosegregated with the functional marker Pm5e-KASP. Sequence alignment analysis revealed that the Pm5e-homologous sequence in AL11 was identical to the reported recessive gene Pm5e in wheat landrace 'Fuzhuang 30'. It appears that PmAL11 was most probably Pm5e, but it was mediated by a dominant inheritance pattern, so it should provide a valuable resistance resource for both genetic study and wheat breeding. To efficiently use and trace PmAL11 in breeding, a new kompetitive allele-specific PCR marker AL11-K2488 that cosegregated with this gene was developed and confirmed to be applicable in the different wheat backgrounds, thus promoting its use in the marker-assisted selection of PmAL11.

Breeding Wheat for Rust Resistance: Conventional and Modern Approaches

Three rusts are destructive, diminishing produce and nutritious value significantly, affect food availability and consequently food security through reductions in yield. In agricultural research institutes with mandate of wheat improvement, incorporating genes resistant against rust is matter of routine. The dilemma of rusts in wheat has been addressed the most, leading to discovery of principles of plant breeding for resistance e.g. gene disease genes inherit following Mendelian genetics, concept of genetic diversity and concept of gene for gene theory. Two strategies of breeding wheat for disease resistance are being followed. 1- Conventional and 2- Advanced. Among conventional approaches selection and hybridization are well known. However rust resistance has been found short lived and may also be durable in certain cases. Durability of disease resistance is desired and has been explored widely. Durability of resistance is generally attained through incorporation of genes effective at adult plant stage and combination of quantitative genes. Application of biotechnology to improve productivity of rust resistance breeding is the usage of molecular markers in pyramiding genes and substantiates the existence of genes in, and confirming released cultivars are pure. This involves molecular markers that are precise and pertinent across extensive ranges of breeders’ germplasm. This review article encompasses all features of wheat development through application of different techniques of wheat improvement. However, despite development of novel approaches that has accelerated wheat breeding, breeding in pathogen leading to producing more virulent strains. Consequently, wheat breeding is a continuous process.

Association and path analysis for agro-morphological traits among diverse wheat (Triticum aestivum L.) germplasm lines for Northern Hill Zone under rainfed conditions

The present investigation entitled ‘Genetic diversity analysis for agro-morphological traits and disease resistance under rainfed conditions in wheat (Triticum aestivum L.)’ was conducted at Rice and Wheat Research Centre, Malan and the Molecular Cytogenetics & Tissue Culture Laboratory of the Department of Genetics and Plant Breeding, CSK HPKV, Palampur. The objectives were to assess the diversity amongst wheat genotypes using various agro-morphological traits and molecular markers, and screening of genotypes for disease resistance at seedling (yellow rust and brown rust) and adult plant (yellow rust and powdery mildew) stage. The experimental material comprised of 36 wheat genotypes along with four checks viz., HPW 368 (Him Palam Gehun 2), HS 562, Agra Local and LWH (Local Wheat Hango) were evaluated for different agro-morphological traits in α-Randomized Block Design with three replications during rabi 2021-22. Sufficient genetic variability was observed for all the traits viz., days to 50% flowering, flag leaf area, peduncle length, plant height, tillers per plant, grains per spike, 1000-grain weight, biological yield per plant, grain yield per plant and harvest index except days to maturity, suggesting the scope of selection for these traits. Grain yield per plant showed significant and positive correlation with flag leaf area, tillers per plant, grains per spike, 1000-grain weight, biological yield per plant and harvest index. Also, biological yield per plant and harvest index were observed as the best selection indices for increasing grain yield owing to high direct and indirect effects of these traits in path analysis. This study suggests that biological yield per plant and harvest index can be used as selection criteria in breeding study to improve the high yielding wheat genotypes.

Identification of Genetic Resistance to the Crown and Root Rot Caused by Fusarium culmorum and Cereal Cyst Nematode (Heterodera filipjevi) in the Turkish Cereal Varieties

Soilborne pathogens associated with cereals cause significant yield losses throughout the world. Among soilborne pathogens Heterodera filipjevi and Fusarium culmorum are two main destructive causal agents that attack the roots and crowns of cereals and have been reported as the most prevalent species in Türkiye. A total of 245 Turkish cereal varieties consisting of wheat, oat, triticale and rye which were registered between 1931 to 2013; were tested for their resistance to Fusarium culmorum and Heterodera filipjevi. The varieties were screened under controlled and/or field conditions for two successive growing seasons. The bread wheat ‘Murat-1’ was the most resistant variety for both pathogens. The durum wheats ‘Yelken 2000’ and ‘Yılmaz 98’ were found the most promising varieties for resistance to F. culmorum and H. filipjevi, respectively. The triticale ‘Umranhanim’ ranked moderately resistant at adult plant stage while ‘Presto’ and ‘Melez 2001’ were ranked moderately resistant at seedling stage for Fusarium culmorum. The findings of this study are important for the global wheat breeding programs as those genotypes are still being used in crosses for new genotype development.

Effectiveness of Thinopyrum ponticum-derived wheat leaf rust resistance gene, Lr24 in India - a revisit

Leaf or brown rust is one of the most devastating rust diseases in wheat. Development and deployment of resistance wheat cultivars is considered as the most effective, economic and sustainable method of protecting against the yield losses due to leaf rust. Though several alien resistance genes have been reported and utilized, Thinopyron ponticum derived leaf rust resistance gene Lr24/Sr24 has been proved to be effective for nearly three decades in India. The effectiveness of this gene was validated recently at seedling and adult plant stage. In the sixteen (16) backcrossed inbred lines (BILs) along with their corresponding recurrent parents showed resistance reaction to the existing pathotypes. Furthermore the presence of Lr24 gene was confirmed in BILs through molecular markers. The results showed that Lr24 gene conferred all stage resistance to the existing pathotypes of P. triticina f.sp. tritici. This emphasizes the importance of Lr24 gene in Indian wheat breeding program and its prolonged protection of wheat crop from leaf rust in India.

Genome-Wide Association Study of Leaf Rust Resistance at Seedling and Adult Plant Stages in a Global Barley Panel

Barley leaf rust caused by Puccinia hordei (Ph) is one of the major limiting biotic stresses of barley production worldwide and causes yield losses of up to 60%. A diversity panel of 316 barley genotypes (AM2017) composed of released cultivars, advanced breeding lines and landraces was screened for Ph resistance at the seedling stage using two isolates (SRT-SAT and SRT-MRC), while the adult plant stage resistance screening was conducted at the disease hotspot location of Sidi Allal Tazi (SAT) for the cropping seasons of 2017 and 2019. The phenotypic responses were combined with 36,793 single nucleotide polymorphism (SNP) markers in a genome-wide association study (GWAS) using the general linear model (GLM), mixed linear model (MLM), settlement of MLM under progressively exclusive relationship (SUPER), multiple-locus MLM (MLMM), fixed and random model circulating probability unification (FarmCPU), and Bayesian-information and linkage-disequilibrium iteratively nested keyway (BLINK) in GAPIT3, and MLM (K+Q), MLM (K+PCA), and GLM (Q) models in TASSEL to identify genomic regions linked to Ph resistance. Fourteen barley genotypes were resistant (R) at the seedling stage to both Ph isolates, SRT-SAT and SRT-MRC, and twelve genotypes were either resistant (R) or moderately resistant (MR) at the adult plant stage, whereas only one genotype was resistant at the seedling stage, and moderately resistant at the adult plant stage. The genome scan revealed 58 significant marker trait associations (MTA) among which 34 were associated with seedling resistance (SR) and 24 with adult plant resistance (APR). Common genomic regions conferring resistance to Ph were identified at both stages on chromosome 2H (106.53 cM and at 107.37 cM), and on chromosome 7H (126.7 cM). Among the 58 MTA identified, 26 loci had been reported in previous studies, while the remaining 32 loci were regarded as novel. Furthermore, the functional annotation of candidate genes (CGs) adjacent to 36 SNP markers with proteins involved in disease resistance further confirms that some of the SNP markers from our study could be associated with Ph resistance in barley. The resistant barley genotypes and some of the SNP markers from this study with high R2 and additive effects can be converted into high-throughput functional markers for accelerated selection and pyramiding of leaf rust resistance genes in North African barley germplasm.

Evaluation of resistance of Turkish bread wheat (Triticum aestivum) varieties to recently emerged Puccinia striiformis f. sp. tritici races

Using genetic diversity has made significant contribution to stripe rust resistance to improve wheat production. However, rapid evolution of the Puccinia striiformis f. sp. tritici (Pst), and emergence of virulent races can negatively affect the wheat genotypes with race-specific resistance gene(s). In this study, reactions of 130 bread wheat varieties, released from 1931 to 2014, were evaluated to recently emerged Pst races in Turkey, PSTr-6 and PSTr-23, at seedling and adult-plant stages. 65.4% and 67.7% of wheat varieties showed susceptible reaction to PSTr-6 and PSTr-23 at seedling stage, respectively. Moreover, coefficient of infection (CI) values generated by infection type (IT) and disease severity (DS) data demonstrated that PSTr-23 (59.78) was more virulent than PSTr-6 (57.93) at adult-plant stage. In addition to these, the presence of important yellow rust (Yr) genes in these varieties was investigated at molecular level. It was determined that the frequencies of three Yr genes, Yr5, Yr10 and Yr15, among these varieties were 1.5, 6.2 and 3.8%, respectively. However, none of them had Yr36 and only one variety had Yr5+Yr10 combination with frequency of 0.7%. In conclusion, most varieties have not these Yr genes and possess a moderately resistance/susceptible reaction to both races in general.

Identification of high-temperature resistance to stripe rust and molecular detection of Yr genes in Chinese core collections of common wheat

Stripe rust is a serious wheat disease caused by Puccinia striiformis Westend f. sp. tritici Erikss. High-temperature resistance, which can be induced when the diurnal cycle changes to 15–28 °C or warmer temperatures, has been demonstrated to be non-race specific and durable. The objectives of this study were to evaluate a core collection of 305 Chinese wheat cultivars and landraces for responses to stripe rust in both seedling and adult-plant stages in the greenhouse and the field, determine the distribution of previously reported Yr genes, and select accessions with effective resistance, especially high-temperature resistance. Fifty-eight (19.0%) entries were found to carry all-stage resistance, 71 (23.3%) entries showed adult-plant resistance, 13 (4.3%) entries showed high-temperature all-stage (HTAS) resistance, and 8 (2.6%) entries showed high-temperature adult-plant (HTAP) resistance. Molecular marker detection identified Yr9, Yr10, Yr17, Yr18, Yr26, Yr30, Yr41, Yr78, and Yr80 at different frequencies in the collection, but did not detect Yr5, Yr15, and Yr36. The results in this study would be useful for the rational distribution of cultivars in different regions and breeding for new cultivars with effective and durable resistance.

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

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

Multi-stage resistance to Zymoseptoria tritici revealed by GWAS in an Australian bread wheat diversity panel.

Septoria tritici blotch (STB) has been ranked the third most important wheat disease in the world, threatening a large area of wheat production. Although major genes play an important role in the protection against Zymoseptoria tritici infection, the lifespan of their resistance unfortunately is very short in modern wheat production systems. Combinations of quantitative resistance with minor effects, therefore, are believed to have prolonged and more durable resistance to Z. tritici. In this study, new quantitative trait loci (QTLs) were identified that are responsible for seedling-stage resistance and adult-plant stage resistance (APR). More importantly was the characterisation of a previously unidentified QTL that can provide resistance during different stages of plant growth or multi-stage resistance (MSR). At the seedling stage, we discovered a new isolate-specific QTL, QSt.wai.1A.1. At the adult-plant stage, the new QTL QStb.wai.6A.2 provided stable and consistent APR in multiple sites and years, while the QTL QStb.wai.7A.2 was highlighted to have MSR. The stacking of multiple favourable MSR alleles was found to improve resistance to Z. tritici by up to 40%.

Genome-wide association mapping for field and seedling resistance to the emerging Puccinia graminis f. sp. tritici race TTRTF in wheat.

Stem rust of wheat (Triticum spp.), caused by Puccinia graminis f. sp. tritici (Pgt), is one of the most impactful wheat diseases because of its threat to global wheat production. While disease mitigation has primarily been achieved through the deployment of resistant wheat varieties, emerging new virulent races continue to pose risks to the crop. For example, races such as Ug99 (TTKSK), TKTTF, and TTRTF have caused epidemics in different wheat growing regions of the world in recent years. A continual search for new and effective sources of resistance is therefore necessary to safeguard wheat production. This study assessed a breeding panel from the Ethiopian Institute of Agricultural Research (EIAR) wheat breeding program for seedling and field plant resistance to TTRTF and reports genomic regions conferring resistance to TTRTF. Trait correlations (r) were medium to strong (range = .38-.71) and heritabilities were moderate (.32-.56). Association analysis for resistance to TTRTF resulted in detection of 20 markers in 11 chromosomes; the marker S1B_175439851 was associated with resistance at both seedling and adult plant stages. Models with two to four QTL combinations reduced seedling and field disease severity by 12-48 and 9-17%, respectively. Genomic prediction for TTRTF resistance resulted in low to moderately-high predictions (mean correlations of .25-.47). Identification of resistant lines and QTL in the EIAR population is expected to assist in selection toward improved resistance to TTRTF. Specifically, the application of genomic selection (GS) in identifying resistant lines in future related breeding populations will further assist breeding efforts against this new stem rust pathogen race.

Characterization of wheat monogenic lines with known Sr genes and wheat cultivars for resistance to three new races of Puccinia graminis f. sp. tritici in China

Wheat stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is a potentially devastating fungal disease of wheat worldwide. The present study was to evaluate the resistance of 42 wheat monogenic lines with known stem rust resistance (Sr) genes and 69 wheat cultivars to three new Pgt races (34C0MRGQM, 34C3MKGQM, and 34C6MTGSM) identified from aeciospores at the seedling and adult-plant stages. The phenotyping results revealed that monogenic lines harboring resistance genes Sr9e, Sr17, Sr21, Sr22, Sr26, Sr30, Sr31, Sr33, Sr35, Sr36, Sr37, Sr38, Sr47, SrTmp, and SrTt3 were effectively resistant to all three Pgt races at the seedling and adult-plant stages. In contrast, monogenic lines containing Sr5, Sr6, Sr7b, Sr9a, Sr9d, Sr9f, Sr9g, Sr9b, Sr16, Sr24, Sr28, and Sr39 were highly susceptible to these races at both seedling and adult-plant stages. The other lines with Sr8a, Sr10, Sr11, Sr13, Sr14, Sr15, Sr18, Sr20, Sr19, Sr23, Sr25, Sr27, Sr29, Sr32, and Sr34, displayed variable levels of resistance to one or two of the tested races. Seedling infection types (ITs) and adult-plant infection responses (IRs) indicated that 41 (59.4%) of the wheat cultivars showed high resistance to all the three races. Molecular marker analysis showed that four wheat culitvars likely carried Sr2, 20 wheat culitvars likely carried Sr31, 9 wheat culitvars likely carried Sr38, and none of the cultivars carried Sr24, Sr25, and Sr26. Our results provide a scientific basis for rational utilization of the tested Sr genes and wheat cultivars against these novel Pgt races.

Genome-Wide Association Study of Leaf Rust and Stem Rust Seedling and Adult Resistances in Tetraploid Wheat Accessions Harvested in Kazakhstan.

Leaf rust (LR) and stem rust (SR) are diseases increasingly impacting wheat production worldwide. Fungal pathogens producing rust diseases in wheat may cause yield losses of up to 50–60%. One of the most effective methods for preventing such losses is the development of resistant cultivars with high yield potential. This goal can be achieved through complex breeding studies, including the identification of key genetic factors controlling rust disease resistance. The objective of this study was to identify sources of tetraploid wheat resistance to LR and SR races, both at the seedling growth stage in the greenhouse and at the adult plant stage in field experiments, under the conditions of the North Kazakhstan region. A panel consisting of 193 tetraploid wheat accessions was used in a genome-wide association study (GWAS) for the identification of quantitative trait loci (QTLs) associated with LR and SR resistance, using 16,425 polymorphic single-nucleotide polymorphism (SNP) markers in the seedling and adult stages of plant development. The investigated panel consisted of seven tetraploid subspecies (Triticum turgidum ssp. durum, ssp. turanicum, ssp. turgidum, ssp. polonicum, ssp. carthlicum, ssp. dicoccum, and ssp. dicoccoides). The GWAS, based on the phenotypic evaluation of the tetraploid collection’s reaction to the two rust species at the seedling (in the greenhouse) and adult (in the field) stages, revealed 38 QTLs (p < 0.001), comprising 17 for LR resistance and 21 for SR resistance. Ten QTLs were associated with the reaction to LR at the seedling stage, while six QTLs were at the adult plant stage and one QTL was at both the seedling and adult stages. Eleven QTLs were associated with SR response at the seedling stage, while nine QTLs were at the adult plant stage and one QTL was at both the seedling and adult stages. A comparison of these results with previous LR and SR studies indicated that 11 of the 38 QTLs are presumably novel loci. The QTLs identified in this work can potentially be used for marker-assisted selection of tetraploid and hexaploid wheat for the breeding of new LR- and SR-resistant cultivars.

Genetically Dissecting the Novel Powdery Mildew Resistance Gene in Wheat Breeding Line PBDH1607.

Powdery mildew is one of the most destructive diseases in wheat production. Identifying novel resistance genes and deploying them in new cultivars is the most effective approach to minimize wheat losses caused by powdery mildew. In this study, wheat breeding line PBDH1607 showed high resistance to powdery mildew at both the seedling and adult plant stages. Genetic analysis of the seedling data demonstrated that the resistance was controlled by a single dominant gene, tentatively designated PmPBDH. The ΔSNP index based on bulked segregant RNA sequencing indicated that PmPBDH was associated with an interval of about 30.8 Mb (713.5 to 744.3 Mb) on chromosome arm 4AL. Using newly developed markers, we mapped PmPBDH to a 3.2-cM interval covering 7.1 Mb (719,055,516 to 726,215,121 bp). This interval differed from those of Pm61 (717,963,176 to 719,260,469 bp), MlIW30 (732,769,506 to 732,790,522 bp), and MlNSF10 (729,275,816 to 731,365,462 bp) reported on the same chromosome arm. PmPBDH also differed from Pm61, MlIW30, and MlNSF10 by its response spectrum, origin, or inheritance mode, suggesting that PmPBDH should be a new Pm gene. In the candidate interval, five genes were found to be associated with PmPBDH via time course gene expression analysis, and thus they are candidate genes of PmPBDH. Six closely linked markers, including two kompetitive allele-specific PCR markers, were confirmed to be applicable for tracking PmPBDH in marker-assisted breeding.

Molecular Mapping of a Recessive Gene for Stripe Rust Resistance at the YrCf75 Locus Using Bulked Segregant Analysis Combined with Single Nucleotide Polymorphism Genotyping Arrays and Bulked Segregant RNA-Sequencing.

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most important diseases in wheat worldwide. Planting resistant varieties is the most economical, effective, and environment-friendly measure to control wheat stripe rust. Changfeng 75, a Chinese winter wheat variety, shows high stripe rust resistance in both seedling and adult-plant stages. The seedling tests of F1, F2, and F2:3 populations derived from Mingxian 169/Changfeng 75 inoculated with Chinese predominant Pst race CYR34 showed that the stripe rust resistance of Changfeng 75 was controlled by a single recessive gene. The locus was temporarily designated as YrCf75. Bulked segregant analysis (BSA) combined with the wheat 660K single-nucleotide polymorphism (SNP) array and bulked segregant RNA-sequencing indicated that the proportion of polymorphic SNPs on wheat chromosome 2A was the highest, which suggested that YrCf75 was likely located on chromosome 2A. Two hundred and twenty-five Kompetitive allele-specific PCR (KASP) and 75 simple sequence repeat (SSR) markers on chromosome 2A were used to map YrCf75 using the BSA approach. Linkage analysis indicated that 31 KASP markers and one SSR marker were linked to YrCf75, and the genetic distances of the two closest flanking KASP markers, AX-1110060462 and AX-111004763, were 1.2 and 2.7 cM, respectively. YrCf75 was located on wheat chromosome 2AL. The molecular detection, resistance specificity, and chromosome location showed that YrCf75 is likely a new gene that is different from the known stripe rust resistance genes (Yr1 and Yr32) on wheat chromosome 2AL.

Genetic Analysis of Adult Plant Resistance to Stripe Rust in Common Wheat Cultivar "Pascal".

Wheat stripe rust is an important foliar disease that affects the wheat yield globally. Breeding for resistant wheat varieties is one of the most economically and environmentally effective ways to control this disease. The common wheat (Triticum aestivum L.) cultivar “Pascal” exhibited susceptibility to stripe rust at the seedling stage but it showed high resistance to stripe rust at the adult plant stage over 20 years in Gansu, a hotspot of the disease in northwestern China. To understand the genetic mechanism of stripe rust resistance in this cultivar, a 55K SNP array was used to analyze the two parents and the 220 recombinant inbred lines (RILs) derived from the cross of “Huixianhong” × “Pascal.” We detected three new stripe rust adult plant resistance (APR) quantitative trait locus (QTL) contributed by Pascal, viz. QYr.gaas-1AL, QYr.gaas-3DL, and QYr.gaas-5AS, using the inclusive composite interval mapping method. They were flanked by SNP markers AX-111218361—AX-110577861, AX-111460455—AX-108798599, and AX-111523523—AX-110028503, respectively, and explained the phenotypic variation ranging from 11.0 to 23.1%. Bulked segregant exome capture sequencing (BSE-Seq) was used for fine mapping of QYr.gaas-1AL and selection of candidate genes, TraesCS1A02G313700, TraesCS1A02G313800, and TraesCS1A02G314900 for QYr.gaas-1AL. KASP markers BSE-1A-12 and HXPA-3D for QYr.gaas-1AL and QYr.gaas-3DL were developed for breeders to develop durable stripe rust-resistant wheat varieties.

Identification and Characterization of Resistance Loci to Wheat Leaf Rust and Stripe Rust in Afghan Landrace "KU3067".

Leaf rust and stripe rust are important wheat diseases worldwide causing significant losses where susceptible varieties are grown. Resistant cultivars offer long-term control and reduce the use of hazardous chemicals, which can be detrimental to both human health and the environment. Land races have been a valuable resource for mining new genes for various abiotic and biotic stresses including wheat rusts. Afghan wheat landrace “KU3067” displayed high seedling infection type (IT) for leaf rust and low IT for stripe rust; however, it displayed high levels of field resistance for both rusts when tested for multiple seasons against the Mexican rust isolates. This study focused on identifying loci-conferring seedling resistance to stripe rust, and also loci-conferring adult plant resistance (APR) against the Mexican races of leaf rust and stripe rust. A backcrossed inbred line (BIL) population advanced to the BC1F5 generation derived from the cross of KU3067 and Apav (triple rust susceptible line) was used for both, inheritance and QTL mapping studies. The population and parents were genotyped with Diversity Arrays Technology-genotyping-by-sequencing (DArT-Seq) and phenotyped for leaf rust and stripe rust response at both seedling and adult plant stages during multiple seasons in Mexico with relevant pathotypes. Mapping results identified an all-stage resistance gene for stripe rust, temporarily designated as YrKU, on chromosome 7BL. In total, six QTL-conferring APR to leaf rust on 1AS, 2AL, 4DL, 6BL, 7AL, and 7BL, and four QTL for stripe rust resistance on 1BS, 2AL, 4DL, and 7BL were detected in the analyses. Among these, pleiotropic gene Lr67/Yr46 on 4DL with a significantly large effect is the first report in an Afghan landrace-conferring resistance to both leaf and stripe rusts. QLr.cim-7BL/YrKU showed pleiotropic resistance to both rusts and explained 7.5–17.2 and 12.6–19.3% of the phenotypic variance for leaf and stripe rusts, respectively. QYr.cim-1BS and QYr.cim-2AL detected in all stripe environments with phenotypic variance explained (PVE) 12.9–20.5 and 5.4–12.5%, and QLr.cim-6BL are likely to be new. These QTL and their closely linked markers will be useful for fine mapping and marker-assisted selection (MAS) in breeding for durable resistance to multiple rust diseases.