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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 (BSR-Seq) and molecular marker analysis, PmAL11 was mapped to the Pm5 locus on chromosome 7B where it co-segregated 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 (KASP) marker AL11-K2488 that co-segregated with this gene was developed and was confirmed to be applicable in the different wheat backgrounds, thus promoting its use in the marker-assisted selection (MAS) of PmAL11.

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a devastating disease that seriously threatens the wheat yield and quality. To control this disease, host resistance is the preferred measure. However, wheat breeding is a complex process with elusive exchange and recombination of the traits from their parents. Increased resistance often leads to a decline in other key traits, such as yield and quality. Developing breakthrough germplasms with harmonious powdery mildew resistance and other key breeding traits is attractive in wheat breeding. In this study, we developed an ideal wheat breeding line AL46 that pyramided its hexaploid triticale parent-derived desirable yield traits and its wheat parent-derived powdery mildew resistance gene Pm2. Sequential genomic in situ hybridization (GISH), multicolor GISH (mc-GISH), multicolor fluorescence in situ hybridization (mc-FISH), and molecular marker analyses revealed that AL46 was a wheat-rye T1RS·1BL translocation line. Genetic analysis combined with function marker detection and sequence alignment were used to confirm that AL46 carried the Pm2 gene. Then, we evaluated the powdery mildew resistance and comprehensive traits of AL46, and just as we designed, AL46 showed harmonious powdery mildew resistance and some key breeding traits. This study not only developed an ideal wheat germplasm resource, but also provided a successful example for pyramiding breeding, which could be a promising direction for wheat improvement in the future.

Powdery mildew and leaf rust, caused by Blumeria graminis f. sp. tritici and Puccinia triticina, respectively, are widespread diseases of wheat worldwide. The use of resistant cultivars is considered the most economical, environment-friendly, and effective method to control these diseases. In the present study, a collection of 2,978 wheat accessions consisting of 1,394 advanced breeding lines, 1,078 Chinese cultivars, 291 introduced cultivars, 132 lines containing alien chromosomes, and 83 landraces was tested for reactions to powdery mildew and leaf rust. The results indicated that 659 wheat accessions (22.1%) were highly resistant to a widely prevalent B. graminis f. sp. tritici isolate, E09, at the seedling stage, and 390 were consistently resistant to the mixture of B. graminis f. sp. tritici isolates at the adult plant stage. Meanwhile, 63 accessions (2.1%) were highly resistant to leaf rust at the adult plant stage, of which 54 were resistant to a predominant and highly virulent P. triticina race, THTT, at the seedling stage. Notably, 17 accessions were resistant to both powdery mildew and leaf rust. To detect known genes for resistance to powdery mildew and leaf rust, these accessions were tested with gene-specific or tightly linked markers for seven powdery mildew genes (Pm genes; Pm2, Pm4, Pm5, Pm6, Pm8, Pm21, and Pm24) and 10 Lr genes (Lr1, Lr9, Lr10, Lr19, Lr20, Lr24, Lr26, Lr34, Lr37, and Lr46). Of the 659 powdery mildew-resistant accessions, 328 might carry single Pm genes and 191 carry combined Pm genes. Pm2 was detected at the highest frequency of 59.6%, followed by Pm8, Pm6, Pm21, Pm4, and Pm5, whereas Pm24 was not detected. In addition, 139 accessions might contain unknown Pm genes different from those tested in this study. In the 63 accessions resistant to leaf rust, four leaf rust genes (Lr genes; Lr1, Lr10, Lr26, and Lr34) were detected in 41 accessions singly or in combination, whereas six genes (Lr9, Lr19, Lr20, Lr24, Lr37, and Lr46) were not detected. Twenty-two accessions might contain unknown Lr genes different from those tested in this study. This study not only provided important information for rationally distributing resistance genes in wheat breeding programs, but also identified resistant germplasm that might have novel genes to enrich the diversity of resistance sources.

Wheat-rye T1RS·1BL translocations have been widely used worldwide in wheat production for multiple disease resistance and superior yield traits. However, many T1RS·1BL translocations have successively lost their resistance to pathogens due to the coevolution of pathogen virulence with host resistance. Because of the extensive variation in rye (Secale cereale L.) as a naturally cross-pollinating relative of wheat, it still has promise to widen the variation of 1RS and to fully realize its application value in wheat improvement. In the present study, the wheat-rye breeding line R2207 was characterized by comprehensive analyses using genomic in situ hybridization (GISH), multicolor fluorescence in situ hybridization with multiple probes, multicolor GISH, and molecular marker analysis, and then was proven to be a cytogenetically stable wheat-rye T1RS·1BL translocation line. Based on the disease responses to different isolates of powdery mildew and genetic analysis, R2207 appears to possess a novel variation for resistance, which was confirmed to be located on the rye chromosome arm 1RS. Line R2207 also exhibited high levels of resistance to stripe rust at both seedling and adult stages, as well as enhanced agronomic performance, so it has been transferred into a large number of commercial cultivars using an efficient 1RS-specific kompetitive allele specific PCR marker for marker-assisted selection.

Powdery mildew, caused by Blumeria graminis f. sp. tritici, is a devastating disease of wheat that seriously affects yield and quality worldwide. Because of the extensive growth of wheat cultivars with homogeneous genetic background, exploring novel resistant resources from wheat relatives has become important for increasing the genetic diversity of wheat. Rye (Secale cereale) is a wheat relative possessing abundant resistance genes because of its high variation. Wheat line AL69, resistant to powdery mildew, was developed by crossing, backcrossing, and self-pollination for multiple generations between hexaploid triticale Zhongsi 237 and common wheat cultivar Zimai 17. Through genomic in situ hybridization (GISH) and multicolor fluorescence in situ hybridization (FISH), nondenaturing FISH, multicolor GISH, and selection with specific molecular markers, AL69 was determined to be a wheat-rye 2R (2D) disomic substitution line. Testing with different B. graminis f. sp. tritici isolates and genetic analysis showed that the all-stage resistance (also called seedling resistance) of AL69 was conferred by the cataloged powdery mildew resistance gene Pm4b derived from Zimai 17, and its adult-plant resistance was derived from the alien chromosome 2R of Zhongsi 237, which was found to be different from the previously reported rye-derived Pm genes, including Pm7 on 2RL. In addition, AL69 showed improved spike number per plant, spike length, fertile spikelet number per spike, kernel number per spike, and grain yield per plant compared with its wheat parent Zimai 17. An elite line S251 combining powdery mildew resistance with excellent agronomic performance was selected from the progenies of AL69 and wheat cultivar Jimai 22. Therefore, AL69 has two types of resistance genes to powdery mildew and improved agronomic traits through pyramiding and thus can be used as a promising genetic stock for wheat breeding.

Chinese wheat landrace Dahongtou was resistant to 35 of 38 tested Chinese isolates of Blumeria graminis f. sp. tritici at the seedling stage. Genetic analysis of the F2 populations and their derived F2:3 families of crosses of Dahongtou with the susceptible varieties Mingxian 169 and Huixianhong indicated that the resistance of Dahongtou to B. graminis f. sp. tritici isolate E09 was conferred by a single recessive gene, tentatively designated as pmDHT. The gene was mapped to chromosome arm 7BL and flanked by markers Xwmc526/XBE443877 and Xgwm611/Xwmc511 at genetic distances of 0.8 and 0.3 cM, respectively. The chromosomal position of pmDHT was similar to the multi-allelic Pm5 locus on 7BL. Allelism tests with crosses of Dahongtou with Fuzhuang 30 (Pm5e) and Xiaobaidong (mlxbd) indicated that pmDHT was allelic to both Pm5e and mlxbd. However, pmDHT showed a different pattern of resistance to the 38 B. graminis f. sp. tritici isolates compared with wheat lines with Pm5a, Pm5b, Pm5e, mlxbd, and PmHYM and also differed from PmSGA. Thus, pmDHT was identified most likely as a new allele or at least a closely linked gene of the Pm5 locus. This gene can be transferred into susceptible wheat cultivars/lines and pyramided with other resistance genes through marker-assisted selection to improve powdery mildew resistance.

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most destructive diseases of wheat worldwide. The disease is most preferably managed by developing and growing cultivars with high-level, durable resistance. To achieve high-level and long-lasting resistance, we developed a wheat line, RIL-Yr64/Yr15, by pyramiding Yr64 and Yr15, both on the chromosome 1BS and providing high resistance to all tested Pst races. To validate RIL-Yr64/Yr15 possessing both genes, we crossed it to Avocet S (AvS). The F4 RILs from this cross were phenotyped with Pst races under controlled greenhouse conditions and also under natural Pst infection in the field. The population was genotyped with SSR markers previously reported to be linked to the resistance gene loci and with additional SSR and SNP-KASP markers along chromosome 1B. Both phenotype and genotype data confirmed the copresence of Yr64 and Yr15 in RIL-Yr64/Yr15, and the high-resolution linkage map dissected the chromosomal regions and traced their origins. New lines possessing these genes were selected from the F5 population of cross AvS × RIL-Yr64/Yr15 by marker-assisted selection. These lines with the two highly effective genes should be more useful than individual gene lines for developing high-level, durable resistant wheat cultivars.

Rye (Secale cereale L.) is an important gene donor for wheat improvement because of its many valuable traits, especially disease resistance. Development of novel wheat-rye translocations with disease resistance can contribute to transferring resistance into common wheat. In a previous study, a wheat-rye T4BL·4RL and T7AS·4RS translocation line (WR41-1) was developed by distant hybridization, and it was speculated that its resistance to powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), was derived from rye based on pedigree analysis. To make accurate use of chromosome 4R in wheat improvement, a set of new 4R translocations involving different arm translocations (e.g., 4RS monosomic, 4RL monosomic, 4RL disomic, 4RS monosomic plus 4RL monosomic, 4RS monosomic plus 4RL disomic, and 4RS disomic plus 4RL disomic translocations) was developed from crosses with common wheat. Those translocations were characterized by genomic in situ hybridization and expressed sequence tag simple sequence repeat marker analysis. To confirm the source of powdery mildew resistance, the translocation plants were tested against Bgt isolate E09. The results indicated that all translocations with 4RL were resistant at all tested growth stages, whereas those with only 4RS translocation or no alien translocation were susceptible. This further indicated that the powdery mildew resistance of WR41-1 was derived from the alien chromosome arm 4RL. To effectively use 4RL resistance in wheat improvement, two competitive allele-specific PCR markers specific for chromosome arm 4RL were developed to detect the alien chromosome in the wheat genome. These new translocation lines with diagnostic markers can efficiently serve as important bridges for wheat improvement.

Wheat (Triticum aestivum) genotypes with rye (Secale cereale) 1RS chromosomal translocations are widely used in wheat breeding programs because 1RS carries genes for resistance to several diseases. However, some of the pathogens have evolved into new races that overcome the resistance due to extensive use of cultivars with the resistance genes from rye. Therefore, identification and deployment of new resistance sources with desirable agronomic characteristics are important and urgent. We have used winter rye cultivar German White as a source of genes for desirable traits in wheat improvement. A new genotype named WR04-32 was produced through hybridization and chromosome manipulation between common winter wheat cultivar Xiaoyan 6 and German White. This genotype was highly resistant to a wide spectrum of the wheat stripe rust (Puccinia striiformis f. sp. tritici) and powdery mildew (Blumeria graminis f. sp. tritici) pathotypes prevalent in China. The polymerase chain reaction (PCR) result using EST-STS (expressed sequence tag-site tagged sequence) marker STSWE126 specific to 1RS confirmed 1RS in WR04-32, and it was further proved to be a wheat-rye T2BL·1RS translocation line using sequential genomic in situ hybridization (GISH) and multicolor fluorescence in situ hybridization (FISH) with probes pAs1 and pSc119.2 (or pHvG38). In addition to its resistance to stripe rust and powdery mildew, WR04-32 was genetically stable and had desirable agronomic traits, making it a desirable germplasm for wheat breeding.

Exploitation of host resistance is important for controlling powdery mildew of wheat (Triticum aestivum L.). In this study, a wheat-Thinopyrum intermedium introgression line, designated WE99, conferred seedling resistance to 47 of 49 Blumeria graminis f. sp. tritici isolates. Genetic analysis demonstrated that the resistance segregation deviated significantly from a single gene Mendelian ratio. However, marker analysis indicated that only a single recessive resistance gene, temporarily designated PmWE99, conferred powdery mildew resistance (Pm). PmWE99 was mapped to chromosome arm 2BS and linked to the three simple-sequence repeat markers Gwm148, Gwm271, and Barc55. Using race spectrum analysis, PmWE99 was shown to be significantly different from the documented genes Pm42 and MlIW170 located on chromosome arm 2BS and, thus, appeared to be a new Pm gene. Examination of the genotype frequencies in the F2:3 families showed that a genetic variation in the PmWE99 interval that favored the transmission of the WE99 allele could be the cause of the deviated segregation. Further investigation revealed that the abnormal segregation only occurred at the PmWE99 interval and was not common at other loci in this population. Identification of PmWE99 will increase the diversity of the Pm genes for wheat improvement.

Powdery mildew, caused by Blumeria graminis f. sp. tritici, is a serious disease of wheat (Triticum aestivum L.) throughout the world. Host resistance is the most effective and preferred means for managing this disease. Line 10V-2, a wheat breeding line with superior agronomic performance, shows broad-spectrum seedling resistance to powdery mildew. Genetic analysis demonstrated that its resistance was controlled by a single dominant gene, tentatively designated Pm10V-2. This gene was localized near the documented Pm2 locus on chromosome 5DS using the simple sequence repeat (SSR) marker Cfd81. To saturate the marker map of Pm10V-2, more markers were developed using bulked segregant RNA-Seq. Two single-nucleotide polymorphism (SNP) markers (Swgi047 and Swgi064), three expressed sequence tag markers (Swgi007, Swgi029, and Swgi038), and one SSR marker (Swgi066) were polymorphic between the resistant and susceptible bulks and showed tightly linked to the Pm10V-2 gene. Pm10V-2 was flanked by the new developed markers Swgi064 and Swgi066 at genetic distances of 0.4 and 1.2 centimorgans (cM), respectively, and cosegregated with Swgi007 and Swgi038. The homologous sequence of Pm2a was cloned from 10V-2 based on a recent study. Although the sequence cloned from 10V-2 was completely identical to that of the reported Pm2a-related gene, they did not cosegregate but were separated at a genetic distance of 1.6 cM, indicating that Pm10V-2 was different from the reported of Pm2a-related gene. When inoculated with multiple B. graminis f. sp. tritici isolates, Pm10V-2 had a significantly different resistance spectrum from Pm2a and other powdery mildew (Pm) resistance genes at or near the Pm2 locus. Therefore, Pm10V-2 may be a new Pm2 allele or Pm2-linked gene. To use Pm10V-2 in marker-assisted selection (MAS) breeding, seven markers applicable for MAS were confirmed, including three newly developed markers (Swgi029, Swgi038, and Swgi064) in the present work. Using these markers, a great number of resistant lines with desirable agronomic performance were selected from crosses involving 10V-2, including the breeding line KM5016, which has been entered in the Regional trials in Hebei Province, China.