Levels Of Adult Plant Resistance Research Articles

Introgression of an adult-plant powdery mildew resistance gene Pm4VL from Dasypyrum villosum chromosome 4V into bread wheat.

Powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt) seriously threatens wheat production worldwide. It is imperative to identify novel resistance genes from wheat and its wild relatives to control this disease by host resistance. Dasypyrum villosum (2n = 2x = 14, VV) is a relative of wheat and harbors novel genes for resistance against multi-fungal diseases. In the present study, we developed a complete set of new wheat-D. villosum disomic introgression lines through genomic in situ hybridization (GISH), fluorescence in situ hybridization (FISH) and molecular markers analysis, including four disomic substitution lines (2n=42) containing respectively chromosomes 1V#6, 2V#6, 3V#6, and 6V#6, and four disomic addition lines (2n=44) containing respectively chromosomes 4V#6, 5V#6, 6V#6 and 7V#6. These lines were subsequently evaluated for their responses to a mixture Bgt isolates at both seedling and adult-plant stages. Results showed that introgression lines containing chromosomes 3V#6, 5V#6, and 6V#6 exhibited resistance at both seedling and adult-plant stages, whereas the chromosome 4V#6 disomic addition line NAU4V#6-1 exhibited a high level of adult plant resistance to powdery mildew. Moreover, two translocation lines were further developed from the progenies of NAU4V#6-1 and the Ph1b mutation line NAU0686-ph1b. They were T4DL·4V#6S whole-arm translocation line NAU4V#6-2 and T7DL·7DS-4V#6L small-fragment translocation line NAU4V#6-3. Powdery mildew tests of the two lines confirmed the presence of an adult-plant powdery mildew resistance gene, Pm4VL, located on the terminal segment of chromosome arm 4V#6L (FL 0.6-1.00). In comparison with the recurrent parent NAU0686 plants, the T7DL·7DS-4V#6L translocation line NAU4V#6-3 showed no obvious negative effect on yield-related traits, providing a new germplasm in breeding for resistance.

Comparisons of stripe rust response, grain yield and quality between fungicide sprayed and non-sprayed treatments for newly developed wheat lines carrying different genes for adult-plant resistance to stripe rust

Wheat genes Yr39, Yr48, Yr52, Yr59, and Yr62 conferring different levels of adult-plant resistance (APR) to stripe rust have been introgressed into Chinese wheat cultivars. To determine the effects of five newly developed wheat lines carrying these APR genes on reduction of stripe rust severity, grain yield, and quality, field experiments including non-sprayed and fungicide sprayed plots were conducted in the 2021 and 2022 growth seasons. Compared to the 100% relative area under the disease progress curve (rAUDPC) of a susceptible check cultivar, the resistant lines had relatively low rAUDPC values, ranging from 0.38% in SWUST-445 (Yr62) to 42.04% in SWUST-006 (Yr39 + Yr26) on average of the two years in the non-sprayed plots. The two-time fungicide applications almost completely controlled stripe rust on the susceptible check and the resistant lines in both years. Stripe rust significantly reduced yield by 29.96% in 2021 and by 84.40% in 2022, whereas the yield differences of the resistant lines were not significant in both years, except SWUST-006 and SWUST-445 in 2022. Stripe rust significantly reduced the thousand kernel weight (TKW) of the susceptible check by 30.36% on the average of both years but did not cause significant TKW reduction in the resistant lines. Except few cases, the various measurements for grain quality did not show significant differences for the susceptible check and resistant lines. The results showed that the resistant lines are useful for further development of wheat cultivars with adequate and durable resistance to stripe rust.

Identification and molecular mapping of YrBm for adult plan resistance to stripe rust in Chinese wheat landrace Baimangmai.

A new adult plan resistance gene YrBm for potentially durable resistance to stripe rust was mapped on wheat chromosome arm 4BL in landrace Baimangmai. SSR markers closely flanking YrBm were developed and validated for use in marker-assisted selection. The wheat stripe rust pathogen Puccinia striiformis f. sp. tritici (Pst) frequently acquires new virulences and rapidly adapts to environmental stress. New virulences in Pst populations can cause previously resistant varieties to become susceptible. If those varieties were widely grown, consequent epidemics can lead to yield losses. Identification and deployment of genes for durable resistance are preferred method for disease control. The Chinese winter wheat landrace Baimangmai showed a high level of adult plant resistance (APR) to stripe rust in a germplasm evaluation trial at Langfang in Hebei province in 2006 and has continued to confer high resistance over the following 15years in field nurseries in Hebei, Sichuan and Gansu. A recombinant inbred line population of 200 F10 lines developed from a cross of Baimangmai and a susceptible genotype segregated for APR at a single locus on chromosome 4BL; the resistance allele was designated YrBm. Allelism tests of known Yr genes on chromosome 4B and unique closely flanking marker alleles Xgpw7272189 and Xwmc652164 among a panel of Chinese wheat varieties indicated that YrBm was located at a new locus. Moreover, those markers can be used for marker-assisted selection in breeding for stripe rust resistance.

QTL Mapping of Adult Plant Resistance to Stripe Rust in a Doubled Haploid Wheat Population.

Stripe rust caused by Puccinia striiformis Westend. f. sp. tritici. is a major bread wheat disease worldwide with yield losses of up to 100% under severe disease pressure. The deployment of resistant cultivars with adult plant resistance to the disease provides a long-term solution to stripe rust of wheat. An advanced line from the International Winter Wheat Improvement Program (IWWIP) 130675 (Avd/Vee#1//1-27-6275/Cf 1770/3/MV171-C-17466) showed a high level of adult plant resistance to stripe rust in the field. To identify the adult plant resistance genes in this elite line, a mapping population of 190 doubled haploid (DH) lines was developed from a cross between line 130675 and the universal stripe rust-susceptible variety Avocet S. The DH population was evaluated at precision wheat stripe rust phenotyping platform, in Izmir during 2019, 2020, and 2021 cropping seasons under artificial inoculations. Composite interval mapping (CIM) identified two stable QTLs QYr.rcrrc-3B.1, and QYr.rcrrc-3B.2, which were detected in multiple years. In addition to these two QTLs, five more QTLs, QYr.rcrrc-1B, QYr.rcrrc-2A, QYr.rcrrc-3A, QYr.rcrrc-5A, and QYr.rcrrc-7D, were identified, which were specific to the cropping year (environment). All QTLs were derived from the resistant parent, except QYr.rcrrc-3A. The significant QTLs explained 3.4–20.6% of the phenotypic variance. SNP markers flanking the QTL regions can be amenable to marker-assisted selection. The best DH lines with high yield, end-use quality, and stripe rust resistance can be used for further selection for improved germplasm. SNP markers flanking the QTL regions can aid in identifying such lines.

Pathogenicity and microsatellite characterization of Puccinia hordei in South Africa

Cultivated barley (Hordeum vulgare) is an important winter cereal in South Africa (SA), ranked second after wheat. Leaf rust, caused by Puccinia hordei Otth. (Ph), is one of the most common diseases affecting grain yield and quality of barley. In this study, isolates of Ph were pathotyped using differential cultivars and lines with designated Rph-resistance genes, as well as a set of Bowman introgression lines (BW) containing resistance genes Rph1 to Rph15. Single pustule isolates derived from recently collected field isolates, typed as Ph race UVPh7235, showed increased virulence to Rph3 when compared with previously described races from SA. Discrepancies in phenotypic responses were recorded between standard differential lines carrying Rph2, Rph6 and Rph9 and the corresponding BW lines. Results for barley cultivars with designated sources of adult plant resistance revealed low seedling infection types (ITs) for Baronesse (Rph20 + Rph24) to all Ph isolates and for Lenka (Rph20 + Rph23 + Rph24) to isolates of Ph races UVPh3231 and UVPh7231. The barley cultivars Agulhas and Cristalia showed low seedling ITs and moderate to high levels of adult plant resistance under field and greenhouse conditions, respectively. Genotyping of 48 Ph isolates with 20 microsatellite markers revealed five closely related genetic lineages with low gene diversity and allelic richness levels. While STRUCTURE analysis revealed three clusters, no clear division of the isolates into the clusters was evident, as the isolates were admixed for all three. Linkage disequilibrium analysis, as well as higher HO versus HE values, supported the hypothesis that the South African Ph population is clonal, consisting of a single genetic lineage.

Quantitative trait loci mapping reveals the complexity of adult plant resistance to leaf rust in spring wheat ‘Copio’

AbstractThe spring wheat (Triticum aestivum L.) line ‘Copio’ has exhibited high level of adult plant resistance (APR) to the leaf rust (Puccinia triticina) pathogen in Mexico during field evaluations. To elucidate the genetic basis of leaf rust resistance in Copio, 176 F4‐derived F6‐recombinant inbred lines (RILs) from a cross of wheat lines ‘Apav’ and Copio were phenotyped in the field for two seasons in the United States and Mexico. A total of 762 genotyping‐by‐sequencing (GBS) single nucleotide polymorphic (SNP) markers were used to develop linkage maps. Composite interval mapping identified seven quantitative trait loci (QTL), all contributed by Copio. Three QTL on chromosome arms 1BL (QLr.umn‐1B), 2AS (QLr.umn‐2A), and 3BS (QLr.umn‐3B) were consistently expressed across all four environments. The QTL on 1BL represents Lr46, which is a pleiotropic APR gene, while the QTL on 2AS is colocated to the Lr37 gene in the 2NS/2AS translocation fragment. The QTL on 3BS, mapped to the Sr2/Yr30/Lr27 genomic region, is more likely to be a unique locus conferring APR to leaf rust races because all phenotyping environments had Lr27 virulent pathotypes. Moreover, the functionality of Lr27 is complimented by Lr31 on chromosome 4BS, which is lacking in both parents. Marker haplotypes identified seven RILs carrying a combination of resistance alleles at all three loci. This combination reduced leaf rust coefficient of infection up to 52 and 36% in the Mexican and U.S. environments, respectively. This study reports the complex genetic mechanism of APR to leaf rust in Copio and its importance as a potential resistance source for gene pyramiding through recombination breeding.

Cytological and genetic analyses of a wheat-rye 2RL ditelosomic addition line with adult plant resistance to powdery mildew

Rye (Secale cereale genome RR), a close relative of common wheat, possesses valuable resistance genes for wheat improvement. Due to the co-evolution of pathogen virulence and host resistance, some resistance genes derived from rye have lost effectiveness. Development and identification of new, effective resistance genes from rye is thus required. In the current study, wheat-rye line WR56 was produced through distant hybridization, embryo rescue culture, chromosome doubling and backcrossing. WR56 was then proved to be a wheat-rye 2RL ditelosomic addition line using GISH (genomic in situ hybridization), mc-FISH (multicolor fluorescence in situ hybridization), ND-FISH (non-denaturing FISH), mc-GISH (multicolor GISH) and rye chromosome arm-specific marker analysis. WR56 exhibited a high level of adult plant resistance to powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt). This resistance was carried by the added 2RL telosomes and presumed to be different from Pm7 which is also located on chromosome arm 2RL but confers resistance at the seedling and adult stages. WR56 will be a promising bridging parent for transfer of the resistance to a more stable wheat breeding line. A newly developed 2RL-specific KASP (kompetitive allele specific PCR) marker should expedite that work.

Identification of Stripe Rust Resistance Genes in Common Wheat Cultivars and Breeding Lines from Kazakhstan.

Stripe (yellow) rust, caused by Puccinia striiformis f.sp. tritici (Pst), is a fungal disease that presents one of the most serious threats to the wheat crops, causing severe yield losses worldwide, including Kazakhstan. The objectives of this study were to: (1) evaluate a winter wheat collection for stripe rust resistance during an adult plant growth stage, (2) identify the presence of selected Yr genes using linked molecular markers in wheat germplasm, (3) identify potentially useful resistant wheat genotypes among leading cultivars and advanced breeding lines. This study evaluated 70 winter wheat genotypes for stripe rust resistance. According to the field reactions, 42 entries (60%) had R or MR reactions including 27 breeding lines (38.6%) and 15 (21.4%) cultivars. Twenty-eight breeding lines/cultivars (40.0%) were susceptible in both years. According to the average coefficient of infection value (ACI) six genotypes were regarded as possessing high level of adult plant resistance. Cultivars/lines carrying Yr10 alone or in combination with other Yr resistance genes provided resistance to stripe rust. Eleven breeding lines showed <5% disease severity in both years. Linked marker analysis revealed the presence of several gene and gene complexes (Yr5, Yr10, Yr15, Yr17/Lr37/Sr38 and Yr18/Lr34). Among a collection of 70 winter wheat breeding lines and cultivars produced in Kazakhstan three stripe rust resistance genes (Yr10, Yr5 and Yr15) demonstrated high frequency occurrence (31.4%, 14.0% and 7.0%, respectively). The most abundant was gene Yr10 identified in 22 genotypes. It was followed by the Yr5 gene, which conferred resistance in 14 lines (20%) and Yr18 gene-11 lines (15.7%). Yr15 was identified in 7 genotypes. Yr17/Lr37/Sr38 gene complex was found in 2 entries. Among 70 evaluated germplasm sources, 42 disease resistant entries are potentially useful resistant wheat genotypes. These carriers of different Yr genes can be used directly in breeding programs to improve stripe rust resistance of winter wheat. Marker-assisted selection can be efficiently applied to develop wheat cultivars with effective gene combinations that would directly assist in developing durable resistance in Kazakhstan.

Evaluation of Ethiopian Bread Wheat Cultivars for Slow Rusting Resistance to Yellow Rust (&amp;lt;i&amp;gt;Puccinia striiformis&amp;lt;/i&amp;gt; f.s Tritici)

Wheat stripe rust (<i>Puccinia striiformis</i> f.s. <i>tritici</i>) is the greatest vicious rust disease in wheat-growing areas of Ethiopia. The cultivating of cultivars with polygenic gene resistance is the most efficient way of monitoring the disease. Field experiments were carried out at Kulumsa Agricultural Research Center main station and, Meraro and Bekoji substations of Ethiopia during 2019 to 2020 main cropping seasons to disclose variability for field based adult plant resistance to yellow rust among 25 newly developed bread wheat cultivars advanced in Ethiopia. Features used as criteria to identify adult plant resistance comprised response of wheat cultivars to yellow rust, Coefficient of infection (CI), relative final rust severity (FRS) and area under disease progress curve (rAUDPC) were found to be reliable to evaluate slow rusting in the cultivars. The outcomes shown that wheat cultivar only Balcha had low disease severity (< 30%) with MRMS reaction, lower rAUDPC values (>30%) and CI (< 20) and were recognized to have good level of adult plant resistance while eighty eight percent of the tested cultivars exhibited susceptible and grouped under low slow rusting resistance with high disease pressure over all three locations. Cultivars Dashen, Daka, Wane and Sanate had moderate values for slow rusting parameters and were recognized as having moderate level of slow rusting. The slow rusting cultivars identified from the present work can be used for extra management in wheat development programs.

GENETIC ASSESSMENT OF LEAF RUST RESISTANCE IN SOME WHEAT VARIETIES

The experiments of this study were carried out through four growing seasons i.e., 2015/16 to 2018/19 at the farm of the faculty of Agriculture, Shibin El-Kom, Menoufia University.Using10 Egyptian wheat varieties,16 wheat promising lines from (CIMMYT) and 20 adult plant leaf rust resistance genes (Lr). lines Lr were used as (male) for crosses with the wheat cultivars (female) to obtain the F1 grains to produce F2 grains and perform genetic analysis. Recording final rust severity (FRS), rate of disease increase (r-value) and the area under disease progress curve (AUDPC) from varieties and lines to responses leaf rust resistance. While STS marker specific for Lr19 and Lr28 genes were performed on the ten wheat varieties and the sixteen promising lines. The responses of rust severity and infection type of the 20 Lr strains were divided into three groups; I resistant genes i.e., Lr17, Lr18, Lr28, Lr 38 and Lr42, II susceptible genes i.e., Lr2c, Lr9, Lr14b, Lr24, Lr34, Lr35, Lr36, Lr37, Lr44 and Lr45, and III genes with variable reactions i.e. Lr2a, Lr19, Lr29, Lr30 and Lr39. Results suggested that genes of group I are important for breeding for leaf rust resistance under Egyptian field conditions. The ten wheat cultivars exhibited low values of FRS and AUDPC except Sids1, and no variety has high rate of (r-value). These cultivars except Sids1 have a good level of adult plant resistance to leaf rust and can be used as resistance sources, 16 wheat promising lines gave lowest values of (FRS), (r-value) and (AUDPC), and consequently they can be used in breeding programs. Genetic analysis showed that Sids1 did not have any of genes under study. However, Gemmeiza 7, Gemmeiza 9, Gemmeiza 10, Gemmeiza 11, Gemmeiza 12, Misr 1, Misr 2, Giza168 and Giza 171 have several Lr genes. Using STS marker specific for Lr19 and Lr28 genes, Lr19 was identified in Gemmeiza 7 and Gemmeiza 11 and Lr28 detected in Gemmeiza 9 and Gemmeiza 10, while Lr19 detected in 13 promising lines, Lr28 found only in five of them. These results showed that molecular markers for Lr genes might be a useful tool in marker-assisted breeding (MAS) for developing Egyptian wheat cultivars.

Genome-Wide Mapping of Adult Plant Resistance to Leaf Rust and Stripe Rust in CIMMYT Wheat Line Arableu#1.

Leaf (brown) rust (LR) and stripe (yellow) rust (YR), caused by Puccinia triticina and P. striiformis f. sp. tritici, respectively, significantly reduce wheat production worldwide. Disease-resistant wheat varieties offer farmers one of the most effective ways to manage these diseases. The common wheat (Triticum aestivum L.) Arableu#1, developed by the International Maize and Wheat Improvement Center and released as Deka in Ethiopia, shows susceptibility to both LR and YR at the seedling stage but a high level of adult plant resistance (APR) to the diseases in the field. We used 142 F5 recombinant inbred lines (RILs) derived from Apav#1 × Arableu#1 to identify quantitative trait loci (QTLs) for APR to LR and YR. A total of 4,298 genotyping-by-sequencing markers were used to construct a genetic linkage map. The study identified four LR resistance QTLs and six YR resistance QTLs in the population. Among these, QLr.cim-1BL.1/QYr.cim-1BL.1 was located in the same location as Lr46/Yr29, a known pleiotropic resistance gene. QLr.cim-1BL.2 and QYr.cim-1BL.2 were also located on wheat chromosome 1BL at 37 cM from Lr46/Yr29 and may represent a new segment for pleiotropic resistance to both rusts. QLr.cim-7BL is likely Lr68 given its association with the tightly linked molecular marker cs7BLNLRR. In addition, QLr.cim-3DS, QYr.cim-2AL, QYr.cim-4BL, QYr.cim-5AL, and QYr.cim-7DS are probably new resistance loci based on comparisons with published QTLs for resistance to LR and YR. Our results showed the diversity of minor resistance QTLs in Arableu#1 and their role in conferring near-immune levels of APR to both LR and YR, when combined with the pleiotropic APR gene Lr46/Yr29.

Occurrence and pathogenicity of Puccinia coronata var avenae f. sp. avenae on oat in South Africa

Crown rust, caused by Puccinia coronata Corda var. avenae f. sp. avenae (Urban & Marková) (Pca), can negatively impact oat (Avena sativa L.) production in South Africa and little is known about pathogenic variability and cultivar response. Pca infected leaves were obtained from oat trial plots, commercial fields and wild oat (Avena spp.) during the 2016 and 2017 growing seasons for race analysis. Uncharacterised collections from 1998 to 2005 were also included. Single pustule isolates were derived from field collections and used for race typing on 16 international differential lines. Six races were identified from 88 isolates pathotyped with race JBLL originating from wild oat samples, SGLL, SQPL and SSTL from commercial oat samples and SBLL+ from both wild and commercial oat samples. Isolates collected in 1998 typed as races SBLL and SBLL+ and the 2005 isolates as race SQPL. Race SBLL was not detected in the 2016 and 2017 samples with SBLL+ being dominant during 2016–17. This is the first report of South African races with virulence for the resistance genes Pc38, Pc58 and Pc59. Seedling infection types of 70 additional oat lines and cultivars to the described races showed incompatible phenotypes for 27 entries. Field data revealed moderate to high levels of adult plant resistance for a few cultivars to races SBLL+ and SSTL. Genetic analysis of 31 isolates, including two USA control isolates, revealed three genetic lineages. No apparent correlation was observed among year of collection, geographic origin, phenotype and genotype of isolates except for race JBLL that originated from wild oat collections in the Western Cape.

Diversity in Puccinia graminis f. sp. avenae and its impact on oat cultivar response in South Africa

Puccinia graminis f. sp. avenae (Pga) samples were collected from cultivated oat (Avena sativa L.) in trial plots and commercial fields and from wild oat (Avena spp.) during the 2016 and 2017 seasons. Field samples were purified through selection of single pustule isolates and subsequent urediniospore increases using the susceptible cultivar Swan. For race phenotyping, a set of 12 international differential lines was used that resulted in the identification of races RSJ, RJS and RJJ. Race RSJ was the most prevalent (60% of isolates) followed by races RJS (34%) and RJJ (6%). These races varied in virulence for Pg6 and Pg12, with no avirulence recorded for Pg1, 2, 4, 8, 9, 13 and Pg15 and no virulence for Pg3, 10 and Pg16. Seedling infection types of 32 oat cultivars to the three described races showed compatible phenotypes for all cultivars towards at least one of the races. Moderate levels of adult plant resistance against races RJS and RSJ were recorded for seven cultivars during field tests in 2017 and 2018. Thirteen microsatellite markers used to assess genetic variability amongst twenty four field isolates revealed three sub-populations of which only one correlated with the race phenotype. The results contributed to our understanding of the diversity of the Pga population in South Africa, including useful resistance sources and cultivar responses.

Characterization of molecular diversity and genome-wide association study of stripe rust resistance at the adult plant stage in Northern Chinese wheat landraces

BackgroundStripe rust is a serious fungal disease of wheat (Triticum aestivum L.) caused by Puccinia striiformis f. sp. tritici (Pst), which results in yield reduction and decreased grain quality. Breeding for genetic resistance to stripe rust is the most cost-effective method to control the disease. In the present study, a genome-wide association study (GWAS) was conducted to identify markers linked to stripe rust resistance genes (or loci) in 93 Northern Chinese wheat landraces, using Diversity Arrays Technology (DArT) and simple sequence repeat (SSR) molecular marker technology based on phenotypic data from two field locations over two growing seasons in China.ResultsSeventeen accessions were verified to display stable and high levels of adult plant resistance (APR) to stripe rust via multi-environment field assessments. Significant correlations among environments and high heritability were observed for stripe rust infection type (IT) and disease severity (DS). Using mixed linear models (MLM) for the GWAS, a total of 32 significantly associated loci (P < 0.001) were detected. In combination with the linkage disequilibrium (LD) decay distance (6.4 cM), 25 quantitative trait loci (QTL) were identified. Based on the integrated map of previously reported genes and QTL, six QTL located on chromosomes 4A, 6A and 7D were mapped far from resistance regions identified previously, and represent potentially novel stripe rust resistance loci at the adult plant stage.ConclusionsThe present findings demonstrated that identification of genes or loci linked to significant markers in wheat by GWAS is feasible. Seventeen elite accessions conferred with stable and high resistance to stripe rust, and six putative newly detected APR loci were identified among the 93 Northern Chinese wheat landraces. The results illustrate the potential for acceleration of molecular breeding of wheat, and also provide novel sources of stripe rust resistance with potential utility in the breeding of improved wheat cultivars.

Adult Plant Resistance to Stem Rust and Molecular Marker Analysis of some Egyptian and Exotic Bread Wheat Genotypes

Stem rust caused by Puccinia graminis f. sp. tritici is the most dangerous and common disease among global wheat cultivars. Twelve local Egyptian and four exotic genotypes of bread wheat (Triticum aestivum L.) obtained from the International Maize and Wheat Improvement Center (CIMMYT) were evaluated under Egyptian field conditions for adult plant resistance (APR) levels to stem rust at Sakha location during the two successive growing seasons (2015/16 and 2016/17). Also, DNA characterization for genotypes by specific markers were tested to determine the presence of the effective resistance genes (Sr's); Sr22, Sr24, Sr25 and Sr26. Out of the tested genotypes, four Egyptian bread wheat cultivars; (Misr3, Sakha94, Gemmeiza9 and Gemmeiza11), and four of CIMMYT lines (Line6043, Line6091, Line6107 and Line6197) show high levels of adult plant resistance to stem rust. Among the tested genotypes, Sr22 found to be the most frequent gene, present in most of them. While, Sr24 was present only in one local wheat cultivar and two exotic lines. Sr25 was present in five local wheat cultivars and two exotic lines. In addition, a resistance gene Sr26 was present in three exotic lines. The obtained results in this study evince that a combination of two or more resistance genes in one cultivar confer high adult plant resistance level in this cultivar, under field condition.

Mapping adult plant stem rust resistance in barley accessions Hietpas-5 and GAW-79.

Key message Major stem rust resistance QTLs proposed to be Rpg2 from Hietpas-5 and Rpg3 from GAW-79 were identified in chromosomes 2H and 5H, respectively, and will enhance the diversity of stem rust resistance in barley improvement programs. Stem rust is a devastating disease of cereal crops worldwide. In barley (Hordeum vulgaressp. vulgare), the disease is caused by two pathogens: Puccinia graminis f. sp. secalis (Pgs) and Puccinia graminis f. sp. tritici (Pgt). In North America, the stem rust resistance gene Rpg1 has protected barley from serious losses for more than 60years; however, widely virulent Pgt races from Africa in the Ug99 group threaten the crop. The accessions Hietpas-5 (CIho 7124) and GAW-79 (PI 382313) both possess moderate-to-high levels of adult plant resistance to stem rust and are the sources of the resistance genes Rpg2 and Rpg3, respectively. To identify quantitative trait loci (QTL) for stem rust resistance in Hietpas-5 and GAW-79, two biparental populations were developed with Hiproly (PI 60693), a stem rust-susceptible accession. Both populations were phenotyped to the North American Pgt races of MCCFC, QCCJB, and HKHJC in St. Paul, Minnesota, and to African Pgt races (predominately TTKSKin the Ug99 group) in Njoro, Kenya. In the Hietpas-5/Hiproly population, a major effect QTL was identified in chromosome 2H, which is proposed as the location for Rpg2. In the GAW-79/Hiproly population, a major effect QTL was identified in chromosome 5H and is the proposed location for Rpg3. These QTLs will enhance the diversity of stem rust resistance in barley improvement programs.

Evaluation of Advanced Bread Wheat Lines for Field and Seedling Resistance to Stem Rust (&amp;lt;i&amp;gt;Puccinia graminis&amp;lt;/i&amp;gt; f. sp. &amp;lt;i&amp;gt;tritici&amp;lt;/i&amp;gt;)

Field-based adult plant resistance assessment at multi-location rust hot spot sites is a crucial job for those plant pathologists screening several wheat lines at a time against the rusts. Rust resistant bread wheat genotypes that have been extracted from previous studies have sustained wheat production in Ethiopia. The objective of this study was to evaluate advanced bread wheat lines extracted from wheat breeding trials against stem rust at adult plat stage under stem rust hot spot sites and at seedling stages in the greenhouse. Eighty three lines were further re-evaluated in consecutive two years. Check varieties were included for comparison. High disease pressure was developed on adult plant in the trial as it has been revealed by high severity on susceptible check varieties. Over years average final rust severity, co-efficient of infection and field reaction have used for differentiating Adult plant resistances. Based on ACI, the 843 genotypes evaluated in initial trial in 2013 were categorized into 10 resistance levels, of which 188 genotypes were in high level resistance category, revealing that various level of adult plant resistance is operating in these test materials. Most of 83 genotypes r-evaluated in consecutive two years after initial stage have sustained low final stem rust severity and coefficient of infection as compared with check varieties. Genotypes were varied by adult plant reaction to stem rust, however, lines ETBW7818, ETBW7819, ETBW7258, ETBW 8008, ETBW 8009, ETBW 8017, ETBW 8027, ETBW 8052, ETBW 8054 and ETBW 8055 concisely showed a reaction of R to R-MR invariably with environments. Of the 83 lines tested at seedling stages against four races, 21 lines exhibited resistance to three races JRCQC, TKTTF, TTKSK and TRTTF whereas 24 lines showed susceptibility to the latter three races. Based on adult reaction, final disease severity and coefficient of infection data, Sixty six bread wheat lines and two cultivars Shorima and Huluka sustained final rust severity <30% and low ACI are acceptable for rust resistance breeding in wheat, However, 52 lines showed comparable resistance to Shorima or Hulluka are the priority materials to be used for developing resistant cultivars potentially combining non-race specific and race specific genes which is more durable than cultivars with major resistance gene effect and more efficient than sole adult plant resistance. Inherent resistance genes of these lines are unknown and warrant further description.

Rapid identification of an adult plant stripe rust resistance gene in hexaploid wheat by high-throughput SNP array genotyping of pooled extremes.

High-throughput SNP array analysis of pooled extreme phenotypes in a segregating population by KASP marker genotyping permitted rapid, cost-effective location of a stripe rust resistance QTL in wheat. German wheat cultivar "Friedrichswerther" has exhibited high levels of adult plant resistance (APR) to stripe rust in field environments for many years. F2:3 lines and F6 recombinant inbred line (RILs) populations derived from a cross between Friedrichswerther and susceptible landrace Mingxian 169 were evaluated in the field in 2013, 2016 and 2017. Illumina 90K iSelect SNP arrays were used to genotype bulked extreme pools and parents; 286 of 1135 polymorphic SNPs were identified on chromosome 6B. Kompetitive Allele-Specific PCR (KASP) markers were used to verify the chromosome region associated with the resistance locus. A linkage map was constructed with 18 KASP-SNP markers, and a major effect QTL was identified within a 1.4cM interval flanked by KASP markers IWB71602 and IWB55937 in the region 6BL3-0-0.36. The QTL, named QYr.nwafu-6BL, was stable across environments, and explained average 54.4 and 47.8% of the total phenotypic variation in F2:3 lines and F6 RILs, respectively. On the basis of marker genotypes, pedigree analysis and relative genetic distance QYr.nwafu-6BL is likely to be a new APR QTL. Combined high-throughput SNP array genotyping of pooled extremes and validation by KASP assays lowers sequencing costs compared to genome-wide association studies with SNP arrays, and more importantly, permits rapid isolation of major effect QTL in hexaploid wheat as well as improving accuracy of mapping in the QTL region. QYr.nwafu-6BL with flanking KASP markers developed and verified in a subset of 236 diverse lines can be used in marker-assisted selection to improve stripe rust resistance in breeding programs.

Genetic analysis and mapping of adult plant resistance loci to leaf rust in durum wheat cultivar Bairds.

New leaf rust adult plant resistance (APR) QTL QLr.cim - 6BL was mapped and confirmed the known pleotropic APR gene Lr46 effect on leaf rust in durum wheat line Bairds. CIMMYT-derived durum wheat line Bairds displays an adequate level of adult plant resistance (APR) to leaf rust in Mexican field environments. A recombinant inbred line (RIL) population developed from a cross of Bairds with susceptible parent Atred#1 was phenotyped for leaf rust response at Ciudad Obregon, Mexico, during 2013, 2014, 2015 and 2016 under artificially created epidemics of Puccinia triticina (Pt) race BBG/BP. The RIL population and its parents were genotyped with the 50K diversity arrays technology (DArT) sequence system and simple sequence repeat (SSR) markers. A genetic map comprising 1150 markers was used to map the resistance loci. Four significant quantitative trait loci (QTLs) were detected on chromosomes 1BL, 2BC (centromere region), 5BL and 6BL. These QTLs, named Lr46, QLr.cim-2BC, QLr.cim-5BL and QLr.cim-6BL, respectively, explained 13.5-60.8%, 9.0-14.3%, 2.8-13.9%, and 11.6-29.4%, respectively, of leaf rust severity variation by the inclusive composite interval mapping method. All of these resistance loci were contributed by the resistant parent Bairds, except for QLr.cim-2BC, which came from susceptible parent Atred#1. Among these, the QTL on chromosome 1BL was the known pleiotropic APR gene Lr46, whereas QLr.cim-6BL, a consistently detected locus, should be a new leaf rust resistance locus in durum wheat. The mean leaf rust severity of RILs carrying all four QTLs ranged from 8.0 to 17.5%, whereas it ranged from 10.9 to 38.5% for three QTLs (Lr46+5BL+6BL) derived from the resistant parent Bairds. Two RILs with four QTLs combinations can be used as sources of complex APR in durum wheat breeding.

Genetic mapping of resistance to Puccinia hordei in three barley doubled-haploid populations

The success of breeding for barley leaf rust (BLR) resistance relies on regular discovery, characterization and mapping of new resistance sources. Greenhouse and field studies revealed that the barley cultivars Baronesse, Patty and RAH1995 carry good levels of adult plant resistance (APR) to BLR. Doubled haploid populations [(Baronesse/Stirling (B/S), Patty/Tallon (P/T) and RAH1995/Baudin (R/B)] were investigated in this study to understand inheritance and map resistance to BLR. The seedlings of two populations (B/S and R/B) segregated for leaf rust response that conformed to a single gene ratio ( $${\text{X}}_{1:1}^{2}$$ = 0.12, P > 0.7 for B/S and $${\text{X}}_{1:1}^{2}$$ = 0.34, P > 0.5 for R/B) whereas seedlings of third population (P/T) segregated for two-gene ratio ( $${\text{X}}_{1:1}^{2}$$ = 0.17, P > 0.6) when tested in greenhouse. It was concluded that the single gene in Baudin and one of the two genes in Tallon is likely Rph12, whereas gene responsible for seedling resistance in Stirling is Rph9.am (allele of Rph12). The second seedling gene in Tallon is uncharacterized. In the field, APR was noted in lines that were susceptible as seedlings. A range of disease responses (CI 5–90) was observed in all three populations. Marker trait association analysis detected three QTLs each in populations B/S (QRph.sun-2H.1, QRph.sun-5H.1 and QRph.sun-6H.1) and R/B (QRph.sun-1H, QRph.sun-2H.2, QRph.sun-3H and QRph.sun-6H.2), and four QTLs in population P/T (QRph.sun-6H.2, QRph.sun-1H.2, QRph.sun-5H.2 and QRph.sun-7H) that significantly contributed to low leaf rust disease coefficients. High frequency of QRph. sun-5H.1, QRph. sun-6H.1, QRph. sun-1H.1, QRph. sun-2H.2, QRph. sun-6H.2, QRph. sun-7H (based on presence of the marker, closely associated to the respective QTLs) was observed in international commercial barley germplasm and hence providing an opportunity for rapid integration into breeding programmes. The identified candidate markers closely linked to these QTLs will assist in selecting and assembling new APR gene combinations; expectantly this will help in achieving good levels of durable resistance for controlling BLR.