Yr Genes Research Articles

Stripe rust resistance gene Yr15 in Turkish and Kazakhstan wheat germplasms and the potential of Turkish wild emmer for stripe rust breeding

Stripe rust resistance gene Yr15 in Turkish and Kazakhstan wheat germplasms and the potential of Turkish wild emmer for stripe rust breeding

Characterization of the Northwestern Population of <i>Puccinia striiformis</i> f. sp. <i>tritici</i> on the Basis of Virulence and Representation of Invasive <i>PstS1</i> and <i>PstS2</i> Races

The expansion of the area of significance of yellow rust was observed in the last years. Until recently, in the conditions of the North-West, the disease occurred sporadically. However, in recent years, its strong development has been observed on wheat samples studied on the collection fields of scientific research institutes and State variety plots, as well as on some commercial fields in the Leningrad region. The aim of this work is to study the virulence and racial composition of the yellow rust pathogen in the Northwest and to conduct a molecular analysis of population samples for the presence of invasive races PstS1 and PstS2. Leaves of common wheat samples with of Puccinia striiformis urediniopustules were collected on commercial fields, State variety plots and experimental fields of the Research Institutes in 2020–2022. Near isogenic Avocet lines (Av NIL) with genes Yr1, Yr5, Yr6, Yr7, Yr8, Yr9, Yr10, Yr15, Yr17, Yr18, Yr24, Yr26, YrSp, Yr27 and differential varieties from international [Chinese 166 (Yr1), Lee (Yr7, Yr+), Heines Kolben (Yr6, Yr+), Vilmorin 23 (Yr3), Moro (Yr10, YrMor), Strubes Dickkopf (YrSD, Yr25, Yr+), Suwon 92/Omar) (YrSu, Yr+)] and European [Hybrid 46 (Yr4, Yr+), Reichersberg 42 (Yr7, Yr+), Heines Peko (Yr2, Yr6, Yr25, Yr+), Nord Desprez (Yr3, YrND, Yr+), Compair (Yr8, Yr19), Carstens V (Yr32, Yr25, Yr+), Spaldings Prolific (YrSP, Yr+), Heines VII (Yr2, Yr25, Yr+)] sets used for characteristic of pathogen virulence. Set of SCAR markers (SCP19M24a1, SCP19M24a2, SCP19M26a1, SCP19M26a2) used for identification of invasive races. A total 92 isolates were studied. High effectiveness at the seedling stage had genes Yr5, Yr10, Yr15, Yr24, Yr26. Isolates virulent to differential varieties Moro (Yr10, YrMor) and Nord Desprez (Yr3, YrND, Yr+) was not determined. Virulence to wheat genotypes with Yr17 gene was rare. Twenty-four virulence phenotypes identified using 29 virulence testers. The number of virulence alleles varied from 7 to 21. At the same time, differences between the phenotypes of P. striiformis on the studied common wheat varieties were insignificant. Most of them have united in a common group. Two groups of isolates slightly differentiated from them. The first included isolates from varieties characterized by a smaller number of virulence alleles, the second – with the maximum number of virulence alleles. Molecular analysis of the northwestern po-pulation revealed isolates belonging to the invasive PstS2 group in 2020 and 2022. Their virulence did not differ significantly from other northwestern phenotypes. The high evolutionary potential predetermines the need for annual monitoring of pathogen populations based on virulence and representation of invasive races.

Resistance of Modern Russian Winter Wheat Cultivars to Yellow Rust.

Over the last decade, the significance of yellow rust caused by Puccinia striiformis (Pst) has substantially increased worldwide, including in Russia. The development and cultivation of resistant genotypes is the most efficient control method. The present study was conducted to explore the yellow rust resistance potential of modern common winter wheat cultivars included in the Russian Register of Breeding Achievements in 2019-2022 using the seedling tests with an array of Pst races and molecular markers linked with Yr resistance genes. Seventy-two winter wheat cultivars were inoculated with five Pst isolates differing in virulence and origin. Molecular markers were used to identify genes Yr2, Yr5, Yr7, Yr9, Yr10, Yr15, Yr17, Yr18, Yr24, Yr25 and Yr60. Thirteen cultivars were resistant to all Pst isolates. The genes Yr5, Yr10, Yr15 and Yr24 that are effective against all Russian Pst races in resistant cultivars were not found. Using molecular methods, gene Yr9 located in translocation 1BL.1RS was detected in 12 cultivars, gene Yr18 in 24, gene Yr17 in 3 and 1AL.1RS translocation with unknown Yr gene in 2. While these genes have lost effectiveness individually, they can still enhance genetic diversity and overall yellow rust resistance, whether used in combination with each other or alongside other Yr genes.

Characterization of Pre-Breeding Wheat (Triticum aestivum L.) Germplasm for Stripe Rust Resistance Using Field Phenotyping and Genotyping.

Wheat is highly affected by stripe rust disease, particularly under cooler environments, and the losses can reach up to 100 percent depending on the intensity of infection and the susceptibility of the genotype. The most effective method to manage this disease is the use of resistant varieties. In the present study, 192 wheat genotypes were evaluated for stripe rust resistance under field conditions and also in a laboratory using molecular markers. These lines included pre-breeding germplasm developed for rust resistance and some high-yielding commercially grown wheat varieties. Out of 192 genotypes, 53 were found to be resistant, and 29 showed moderate resistance reaction under field conditions, whereas the remaining genotypes were all either moderately susceptible or susceptible. Under controlled conditions, out of 109 genotypes, only 12 were found to be resistant to all the six virulent/pathogenic pathotypes. Additionally, a selection of 97 genotypes were found resistant in field screening and were subjected to molecular validation using the markers linked to major R-genes, viz., Yr5, Yr10, Yr15 and Yr17. Nine genotypes possessed the Yr5 gene, twelve had the Yr10 gene, fourteen had the Yr15 gene and thirty-two had the Yr17 gene. The resistance genes studied in the current study are effective in conferring resistance against stripe rust disease. The genotypes identified as resistant under both field and controlled conditions can be used as sources in stripe rust resistance breeding programs.

The Detection of Yr Genes in Xinjiang Wheat Cultivars Using Different Molecular Markers.

Wheat stripe rust is a fungal disease caused by Puccinia striiformis f. sp. Tritici (Pst). It significantly impacts wheat yields in Xinjiang, China. Breeding and promoting disease-resistant cultivars carrying disease-resistance genes remains the most cost-effective strategy with which to control the disease. In this study, 17 molecular markers were used to identify Yr5, Yr9, Yr10, Yr15, Yr17, Yr18, Yr26, Yr41, Yr44, and Yr50 in 82 wheat cultivars from Xinjiang. According to the differences in SNP loci, the KASP markers for Yr30, Yr52, Yr78, Yr80, and Yr81 were designed and detected in the same set of 82 wheat cultivars. The results showed that there was a diverse distribution of Yr genes across all wheat cultivars in Xinjiang, and the detection rates of Yr5, Yr15, Yr17, Yr26, Yr41, and Yr50 were the highest, ranging from 74.39% to 98.78%. In addition, Yr5 and Yr15 were prevalent in spring wheat cultivars, with detection rates of 100% and 97.56%, respectively. A substantial 85.37% of wheat cultivars carried at least six or more different combinations of Yr genes. The cultivar Xindong No.15 exhibited the remarkable presence of 11 targeted Yr genes. The pedigree analysis results showed that 33.33% of Xinjiang wheat cultivars shared similar parentage, potentially leading to a loss of resistance against Pst. The results clarified the Yr gene distribution of the Xinjiang wheat cultivars and screened out varieties with a high resistance against Pst.

Genetic analysis of stripe rust resistance in the common wheat line Kfa/2*Kachu under a Chinese rust environment.

We mapped a new race-specific seedling stripe rust resistance gene on wheat chromosome 5BL and a new APR locus QYr.hazu-2BS from CIMMYT wheat line Kfa/2*Kachu. Breeding resistant wheat (Triticum aestivum) varieties is the most economical and efficient way to manage wheat stripe rust, but requires the prior identification of new resistance genes and development of associated molecular markers for marker-assisted selection. To map stripe rust resistance loci in wheat, we used a recombinant inbred line population generated by crossing the stripe rust-resistant parent 'Kfa/2*Kachu' and the susceptible parent 'Apav#1'. We employed genotyping-by-sequencing and bulked segregant RNA sequencing to map a new race-specific seedling stripe rust resistance gene, which we designated YrK, to wheat chromosome arm 5BL. TraesCS5B02G330700 encodes a receptor-like kinase and is a high-confidence candidate gene for YrK based on virus-induced gene silencing results and the significant induction of its expression 24h after inoculation with wheat stripe rust. To assist breeding, we developed functional molecular markers based on the polymorphic single nucleotide polymorphisms in the coding sequence region of YrK. We also mapped four adult plant resistance (APR) loci to wheat chromosome arms 1BL, 2AS, 2BS and 4AL. Among these APR loci, we determined that QYr.hazu-1BL and QYr.hazu-2AS are allelic to the known pleiotropic resistance gene Lr46/Yr29/Pm39 and the race-specific gene Yr17, respectively. However, QYr.hazu-2BS is likely a new APR locus, for which we converted closely linked SNP polymorphisms into breeder-friendly Kompetitive allele-specific PCR (KASP) markers. In the present study, we provided new stripe rust resistance locus/gene and molecular markers for wheat breeder to develop rust-resistant wheat variety.

Highly Aggressive Invasive Race Group PstS2 in Russian Populations of the Wheat Yellow Rust Pathogen

The expansion of the area of harmfulness of the wheat yellow rust pathogen (Puccinia striiformis) (Pst) has be observed all over the world in the 2000s. This is due to the emergence of new highly aggressive invasive groups of races PstS1 and PstS2, adopted to the high temperatures, and also as a result of virulence mutations of regional pathogen populations. SCAR-markers were developed for identification of invasive races, and pathogen collections from many countries were studied. In these studies in first in Russia, the analysis of regional populations of P. striiformis for the presence of invasive races PstS1 and PstS2 was carried out. Single pustule isolates were obtained from urediosamples collected from common and durum wheat, triticale and wild grasses in seven regions of the Russian Federation (North Caucasian, Northwestern, Central Black Earth, Lower Volga, Middle Volga, Volga–Vyatka, West Siberian) in 2019–2020. In total 82 isolates were studied. Using SCAR markers, three genotypes were identified in the studied collection of P. striiformis, and one of which belongs to the invasive group PstS2. The other two genotypes had a different origin (other). Isolates of PstS2 group were received from pathogen population samples collected in the Russian Northwest in 2020. Virulence analysis revealed two phenotypes among them: PstS2_R1 (3 isolates) and PstS2_R2 (1 isolate). According to information from the Global Rust Reference Center (http://www.wheatrust.org/), the main characteristic of isolates from invasive PstS2 group is virulence to wheat lines with resistance genes Yr2, Yr6, Yr7, Yr8, Yr9, and Yr25. The Russian R1 phenotype PstS2 was also characterized by virulence to these genes, as well as to Yr1, Yr32, and YrSp. The PstS2_R2 phenotype differed from PstS2_R1 for avirulence to Yr25 and virulence to Yr3 and Yr4. The main difference of Russian PstS2 isolates with detected in other countries is virulence to wheat lines with genes Yr4, Yr32, and YrSp. The first detection of invasive races in the Northwest of Russia indicates the relevance of annual monitoring of regional populations of P. striiformis.

Stripe rust resistance gene(s) postulation in wheat germplasm with the help of differentials and tagged molecular markers

Thirteen known Yr gene-associated markers pertaining to genes (Yr5,Yr10,Yr15,Yr24/Yr26) were used to identify the genes in selected wheat germplasm which were found resistant under field conditions at two locations in Punjab, India against stripe rust. In field evaluation, 38 genotypes exhibited highly resistant response, with a final rust severity (FRS) ranging from 0 to TR. Seven genotypes expressed a resistant to moderately resistant response with FRS ranging from 5MR–10S. In race-specific phenotying against most prevalent pathotypes of Pucciniastriiformistritici (46S119,110S119 &238S119) by seedling reaction test (SRT) 14 genotypes (29.2%) were found to be immune (IT = 0), 28 genotypes (58.3%) were resistant (IT = 1), and 3 genotypes (6.3%) were moderately resistant (IT = 2). Yr5 was detected in sixteen lines with the help of two markers Xwmc175 and Xgwm120 linked with Yr5. Yr10 was detected in ten lines with the marker Xpsp3000 and Yr15 was detected in fourteen lines with two linked markers; Xgwm413 and Xgwm273. Likewise, Yr24/26 was detected in 15 lines with two linked markers, namely Xbarc181 and Xbarc187. Based on the race specific phenotyping data and marker data, fourteen lines were found to carry a single gene, 16 showed the presence of two gene combinations, and seven genotypes were found to have a combination of three genes. Frequencies of Yr5, Yr15 and Yr26/Yr24 was high among test wheat germplasm in comparison to Yr10.

Pyramiding of Adult-Plant Resistance Genes Enhances All-Stage Resistance to Wheat Stripe Rust.

Stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most destructive diseases in wheat production. Pyramiding of adult-plant resistance (APR) genes is a promising strategy to increase durability of resistance. The stripe rust resistance (R) genes Yr18, Yr28, and Yr36 encode different protein families which confer partial resistance to a broad array of P. striiformis f. sp. tritici races. Here, we developed BC3F5 wheat lines representing all possible combinations of Yr18, Yr28, and Yr36 in a genetic background of the highly P. striiformis f. sp. tritici-susceptible wheat line SY95-71 that is widely used in stripe rust analysis. These lines enabled us to accurately evaluate these genes singly and in combination in a common genetic background. The adult plant resistance experiments were analyzed in the field, where stripe rust epidemics occurred frequently. The field results indicated that these partial R genes act additively in enhancing the levels of resistance, and a minimum of two-gene combinations can generate adequate stripe rust resistance. The Yr28 + Yr36 and Yr18 + Yr28 + Yr36 combinations also showed adequate resistance at the seedling stage, implying that APR gene pyramiding can achieve all-stage resistance. Meanwhile, the three genes were simultaneously introduced into elite wheat lines through gene-based marker selection. Elite lines exhibited strong all-stage resistance to stripe rust. This work provides valuable insights and resources for developing durable P. striiformis f. sp. tritici-resistant varieties and for elucidating the regulation mechanism of partial R gene pyramiding.

Direct Evidence Demonstrates that Puccinia striiformis f. sp. tritici Infects Susceptible Barberry to Complete Sexual Cycle in Autumn.

Wheat stripe rust is an airborne and destructive disease caused by a heteroecious rust fungus Puccinia striiformis f. sp. tritici (Pst). Studies have demonstrated that the rust pathogen accomplishes sexual reproduction on susceptible barberry under natural conditions in spring, whereas Pst infection on barberry is still in blank in other seasons. In late October 2016, aecial production on barberry shrubs were observed in Linzhi, Tibet, China. Therefore, experimental tests were conducted to verify the existence of sexual cycles of Pst in this season. By inoculating 52 aecial clusters from 30 rusted barberry leaves, four Pst samples, T1 to T4, were successfully recovered from the rusted barberry shrubs. Sixty-five single uredinium (SU) isolates were derived from the four Pst samples. Based on virulence tests on the Chinese differential hosts, T1 to T4 samples were unknown races and showed mixed reactions on some differentials. Twenty-one known races and 44 unknown races belonging to five race groups were identified among the 65 SU isolates. Meanwhile, the 65 SU isolates produced 26 various virulence patterns (VPs; called VP1-VP26) on 25 single Yr gene lines and 15 multilocus genotypes (MLGs) at nine simple sequence repeat marker loci. Clustering analysis showed similar lineage among subpopulations and different lineage between subpopulations. Linkage disequilibrium analysis indicated that the SU population was produced sexually. This study first reported that Pst infects susceptible barberry to complete sexual reproduction in autumn. The results update the knowledge of disease cycle and management of wheat stripe rust and contribute to the understanding of rust genetic diversity in Tibet.

Virulence characterization of the wheat stripe rust pathogen, Puccinia striiformis f. sp. tritici, in Turkey from 2018 to 2020

Stripe (yellow) rust caused by Puccinia striiformis f. sp. tritici (Pst) is the most devastating disease of wheat in Turkey. Virulence characterization of the Pst population is critical to prevent large-scale epidemics, by developing wheat cultivars with durable resistance against the disease. In this study, 38 Pst races, including 25 races that were not previously reported, were identified from 140 isolates obtained from most regions of Turkey from 2018 to 2020 using a differential set containing 18 single Yr gene wheat lines (NILs) of ‘Avocet’. Virulence to Yr15 was not observed among any of the isolates. Virulence to the remaining 17-Yr genes was detected at various frequencies. The frequencies of virulence to Yr6, Yr9, Yr7, Yr8, Yr43, YrExp2, Yr44, YrTr1, and Yr27 were high (57.1 to 100.0%), to Yr1, Yr17, Yr32, and YrTye were moderate (24.3 to 42.9%), and to YrSP, Yr24, and Yr10 were low (9.3 to 17.1%). Only one race was virulent to Yr5 (0.7%). Many of the races identified were common among regions, indicating that Pst races migrate throughout Turkey. However, the Black Sea (BS) and the Mediterranean (ME) regions were differentiated from other regions by unique races absent in other regions, and the Yr5-virulent race, respectively. To sum up, the virulences of the races identified and their distributions among regions provided an understanding of pathogen migration and may contribute to the development of resistant wheat cultivars against stripe rust.

A Highly Aggressive Invasive Race Group <i>Pst</i>S2 in Russian Populations of the Wheat Yellow Rust Pathogen

The expansion of the area of harmfulness of the wheat yellow rust pathogen (Puccinia striiformis) (Pst) has be observed all over the world in the 2000s. This is due to the emergence of new highly aggressive invasive groups of races PstS1 and PstS2, adopted to the high temperatures, and also as a result of virulence mutations of regional pathogen populations. SCAR-markers were developed for identification of invasive races, and pathogen collections from many countries were studied. In these studies in first in Russia, the analysis of regional populations of P. striiformis for the presence of invasive races PstS1 and PstS2 was carried out. Single pustule isolates were obtained from urediosamples collected from common and durum wheat, triticale and wild grasses in seven regions of the Russian Federation (North Caucasian, Northwestern, Central Black Earth, Lower Volga, Middle Volga, Volga-Vyatka, West Siberian) in 2019–2020. In total 82 isolates were studied. Using SCAR markers, three genotypes were identified in the studied collection of P. striiformis, and one of which belongs to the invasive group PstS2. The other two genotypes had a different origin (other). Isolates of PstS2 group were received from pathogen population samples collected in the Russian Northwest in 2020. Virulence analysis revealed two phenotypes among them: PstS2_R1 (3 isolates) and PstS2_R2 (1 isolate). According to information from the Global Rust Reference Center (http://www.wheatrust.org/), the main characteristic of isolates from invasive PstS2 group is virulence to wheat lines with resistance genes Yr2, Yr6, Yr7, Yr8, Yr9 and Yr25. The Russian R1 phenotype PstS2 was also characterized by virulence to these genes, as well as to Yr1, Yr32, and YrSp. The PstS2_R2 phenotype differed from PstS2_R1 for avirulence to Yr25 and virulence to Yr3 and Yr4. The main difference of Russian PstS2 isolates with detected in other countries is virulence to wheat lines with genes Yr4, Yr32, and YrSp. The first detection of invasive races in the Northwest of Russia indicates the relevance of annual monitoring of regional populations of P. striiformis.

The Efficacity Investigation for Some Markers Detecting Yellow Rust Resistance Genes in Bread Wheat Varieties

Yellow rust is (Puccinia striiformis Westend. f. sp. tritici) is among the supreme diseases causing serious losses in wheat production. The chemical fungicides are commonly used in this disease-fighting. However, chemical control is not economical and also causes environmental pollution. Therefore, the use of resistant wheat varieties in production has critical importance. The resistance against yellow rust disease is expressed with Yr genes. In the breeding studies, knowing which parents include resistance genes provides a great advantage in the development of new resistant varieties. This study aims to determine the efficiency of markers used to detect resistance genes against yellow rust disease. The efficiency of molecular markers (Xgwm582, RgaYr10a, Xgwm413, Xgwm11, Wmc44, Barc101, Cfa2149, Sun104, Xgwm273) that are identified for nine genes (Yr9, Yr10, Yr15, Yr26, Yr29, Yr36, Yr48, Yr51, and YrCH52) providing resistance against yellow rust disease was investigated using PCR method. Twenty bread wheat varieties were used as material. Resistance gene profiles determined using PCR-based molecular markers and data obtained from registration information and field resistance data in the literature were analysed comparatively. As a result of the analysis, the efficiency/productivity of the markers defined for different resistance genes in detecting the resistance gene profile of wheat varieties was determined. Moreover, resistance gene profiles of varieties that are known resistance states in the field and sensitive varieties were compared. Genes that are prominent in providing resistance and detected with markers were determined and the efficiency of these genes was evaluated according to their homozygous/heterozygous states. It was concluded that the efficacy of markers such as RgaYr10a, Xgwm413, Barc101, and Cfa2149, which gave positive results in all wheat varieties, was low.

Race composition and genetic diversity of a Puccinia striiformis f. sp. tritici population from Yunnan and Guizhou epidemiological regions in China in 2018

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is an extremely destructive wheat disease worldwide. Yunnan and Guizhou provinces are the main overwintering regions for Pst and inoculum sources for the disease in China. Surveillance of race dynamics of the Pst population is essential for managing the disease in local and other wheat-growing regions of China. However, Pst population dynamics in this region is not monitored yearly. In this study, a Pst population of 113 isolates from Yunnan and Guizhou in 2018 were phenotyped on the two wheat differential sets and analyzed by 12 simple sequence repeat (SSR) markers. As a result, 25 races were identified from the Pst population on Chinese differentials and predominant races was CYR32 with a frequency of 17.70%. None of the isolates was virulent to Yr5 and Yr15. Only a few isolates showed virulence to YrTr1 and differentials Zhong 4. The Kosman index (K) of the Pst population was 0.292 on the Chinese differentials, and 0.274 on single Yr gene lines and additional differentials, respectively. In total, 64 MLGs were detected among 113 isolates and the expected heterozygosity (He) was 0.424. A close genetic relationship was detected between Lufeng (Yunnan) / Nayong (Guizhou), Fuyuan (Yunnan) / Bijie (Guizhou), and Shizong (Yunnan) / Xingyi (Guizhou). This study provided useful information on population structure and virulence to Yr genes in the Yunnan and Guizhou epidemiological regions, and will be used to guide the control of wheat stripe rust and targeted wheat breeding in this region.

Molecular Characterization of Diverse Wheat Genetic Resources for Resistance to Yellow Rust Pathogen (Puccinia striiformis)

Yellow rust (YR) epidemics have affected wheat productivity worldwide. YR resistance (Yr) is eminent in wheat; however, it is continuously invaded by evolving YR pathogen Puccinia striiformis (Pst.). Understanding the Yr genes’ diversity among the available germplasm is paramount to developing YR-resistant cultivars. In this study, 14 wheat genotypes were screened for their relative resistance index (RRI) and Yr genes/QTL via linked microsatellite markers. RRI screening categorized the studied genotypes into susceptible (<5; 4.44 ± 0.75), moderate (5–7; 6.11 ± 0.64), and resistant (>7; 8.45 ± 0.25) bulks (p < 0.001). Genetic analysis using 19 polymorphic microsatellite markers revealed 256 alleles, which were divergent among the three resistance bulks. Markers Xbarc7 and Xgwm429 showed the highest allelic diversity in comparison to Xbarc181, Xwmc419, SCAR1400, and Xgwm130. Resistant bulk showed associated alleles at Yr18 gene-linked markers Xgwm295, cssfr6, and csLV34. Other RRI-associated alleles at markers Xbarc7 and Xbarc101 showed weak and moderate linkages, respectively, with the Yr5 gene; whereas, a moderate association was noted for the Yr15 gene-linked marker Xgwm11. Marker Xwe173 linked with the Yr26 gene showed associated alleles among the susceptible bulk. Cross combinations of the parental lines forming recombinant inbred lines (RILs) demonstrated net higher RRI implying favorable allelic recombination. These results support reports and field observations on novel Pst. races that triggered Yr26, Yr5, and Yr15 busts in recent past. This study further implies that pyramiding all stage resistance genes (Yr5, Yr10, Yr15, and Yr26) with adult plant resistance genes (Yr18 and Yr62) should provide sustained YR resistance. The associated alleles at Yr genes-linked markers provide a basis for marker-assisted YR resistance breeding in wheat.

Virulence Diversity of Puccinia striiformis f. sp. Tritici in Common Wheat in Russian Regions in 2019–2021

Yellow (stripe) rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a major disease of common wheat worldwide. Disease epidemics in Russia have been frequent and destructive, mostly in the North Caucasus. However, over the last 5 years, the significance of Pst has markedly increased in other Russian regions. Therefore, the Pst virulence diversity was investigated in Triticum aestivum in six geographically distant regions of the European (North Caucasus, North-West, Low Volga, Central Black Earth region, and Volga-Vyatka) and Asian (West Siberia) parts of Russia, with strongly different climates, environmental conditions, and growing wheat genotypes. Seventy-nine virulence pathotypes among 117 isolates were identified using the 12 Avocet Yr gene lines (Yr1, Yr5, Yr6, Yr7, Yr8, Yr9, Yr10, Yr15, Yr17, Yr24, Yr27, and YrSp) and eight supplemental wheat differentials (Heines VII, Vilmorin 23, Hybrid 46, Strubes Dickkopf, Carstens V, Suwon 92/Omar, Nord Desprez, and Heines Peko). Only four pathotypes occurred in two or more regions. High variability was detected within Pst populations from Dagestan, Central, North-West, and West Siberia that postulated to form an intrapopulation subdivision of each of them into several subgroups. Most regional virulence groups of pathotypes were closely related, except for several small subgroups of pathotypes from West Siberia, Dagestan, North-West, and Central European regions. All Pst isolates were avirulent in lines with Yr5, Yr10, Yr15, and Yr24 genes. Virulence to Yr17 was detected for several isolates of two pathotypes, one each from the North-West and Low Volga regions. Variation in virulence frequency was observed in other differential lines.

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.

Genetic basis analysis of key Loci in 23 Yannong series wheat cultivars/lines.

Fungal diseases, drought, pre-harvest sprouting (PHS) and other biotic and abiotic stresses have seriously affected the quality and yield in wheat production. Identifying related genes/loci in released cultivars/lines can provide reference information and theoretical basis for wheat improvement. Yannong series wheat cultivars/lines have distinctive characteristics in wheat cultivars and play an important role in genetic improvement and production of Chinese wheat production system. To dissect their genetic basis of the stress-resistant traits, in this study, 23 representative Yannong series wheat cultivars/lines were tested by 58 molecular markers for 40 genes related to adaptability, disease resistance and stress tolerance to clarify the genetic composition of the key loci. The results showed that most of the tested wheat accessions carried dwarfing genes RhtB1b/RhtD1b/Rht8 and recessive vernalization genes vrn-A1/vrn-B1/vrn-D1/vrn-B3. It was also consistent with the phenotypic traits of tested Yannong series wheat which were dwarf and winter or semi winter wheat. In addition, the overall level of seedling powdery mildew resistance in 23 Yannong wheat cultivars/lines was moderate or inadequate. Eleven accessions carried none of the tested Pm genes and twelve accessions carried Pm2, Pm6, Pm42 and Pm52 singly or in combination. Then, 23 wheat cultivars/lines were also tested by 17 diagnostic markers for 14 Yr genes. The results showed that 16 wheat cultivars/lines were likely to carry one or more of tested Yr genes, whereas Yannong 15, Yannong 17, Yannong 23, Yannong 24, Yannong 377, Yannong 572 and Yannong 999 carried none of the tested Yr genes. Moreover, in our study, nine markers for four genes related to drought tolerance and PHS were used to evaluate the stress tolerance of the 23 wheat cultivars/lines. The results indicated that all 23 wheat cultivars/lines carried drought resistance genes Ta-Dreb1/TaCRT-D, indicating that they had the drought resistance to the extent. Except for Yannong 30, Yannong 377, Yannong 390, Yannong 745 and Yannong 1766, other wheat cultivars/lines carried one to three elite PHS-resistant alleles Vp-1Bc/Vp-1Bf/TaAFP-1Bb.

Fine mapping of a stripe rust resistance gene YrZM175 in bread wheat.

A stripe rust resistance gene YrZM175 in Chinese wheat cultivar Zhongmai 175 was mapped to a genomic interval of 636.4 kb on chromosome arm 2AL, and a candidate gene was predicted. Stripe rust, caused by Puccinia striiformis f. sp. tritici (PST), is a worldwide wheat disease that causes large losses in production. Fine mapping and cloning of resistance genes are important for accurate marker-assisted breeding. Here, we report the fine mapping and candidate gene analysis of stripe rust resistance gene YrZM175 in a Chinese wheat cultivar Zhongmai 175. Fifteen F1, 7,325 F2 plants and 117 F2:3 lines derived from cross Avocet S/Zhongmai 175 were inoculated with PST race CYR32 at the seedling stage in a greenhouse, and F2:3 lines were also evaluated for stripe rust reaction in the field using mixed PST races. Bulked segregant RNA-seq (BSR-seq) analyses revealed 13 SNPs in the region 762.50-768.52Mb on chromosome arm 2AL. By genome mining, we identified SNPs and InDels between the parents and contrasting bulks and mapped YrZM175 to a 0.72-cM, 636.4-kb interval spanned by YrZM175-InD1 and YrZM175-InD2 (763,452,916-764,089,317bp) including two putative disease resistance genes based on IWGSC RefSeq v1.0. Collinearity analysis indicated similar target genomic intervals in Chinese Spring, Aegilops tauschii (2D: 647.7-650.5Mb), Triticum urartu (2A: 750.7-752.3Mb), Triticum dicoccoides (2A: 771.0-774.5Mb), Triticum turgidum (2B: 784.7-788.2Mb), and Triticum aestivum cv. Aikang 58 (2A: 776.3-778.9Mb) and Jagger (2A: 789.3-791.7Mb). Through collinearity analysis, sequence alignments of resistant and susceptible parents and gene expression level analysis, we predicted TRITD2Bv1G264480 from Triticum turgidum to be a candidate gene for map-based cloning of YrZM175. A gene-specific marker for TRITD2Bv1G264480 co-segregated with the resistance gene. Molecular marker analysis and stripe rust response data revealed that YrZM175 was different from genes Yr1, Yr17, Yr32, and YrJ22 located on chromosome 2A. Fine mapping of YrZM175 lays a solid foundation for functional gene analysis and marker-assisted selection for improved stripe rust resistance in wheat.