Molecular cytogenetic identification of a novel dwarf wheat line with introgressed Thinopyrum ponticum chromatin

The Genomic Variation and Differentially Expressed Genes on the 6P Chromosomes in Wheat-Agropyron cristatum Addition Lines 5113 and II-30-5 Confer Different Desirable Traits

Wild relatives of wheat are essential gene pools for broadening the genetic basis of wheat. Chromosome rearrangements and genomic variation in alien chromosomes are widespread. Knowledge of the genetic variation between alien homologous chromosomes is valuable for discovering and utilizing alien genes. In this study, we found that 5113 and II-30-5, two wheat-A. cristatum 6P addition lines, exhibited considerable differences in heading date, grain number per spike, and grain weight. Genome resequencing and transcriptome analysis revealed significant differences in the 6P chromosomes of the two addition lines, including 143,511 single-nucleotide polymorphisms, 62,103 insertion/deletion polymorphisms, and 757 differentially expressed genes. Intriguingly, genomic variations were mainly distributed in the middle of the chromosome arms and the proximal centromere region. GO and KEGG analyses of the variant genes and differentially expressed genes showed the enrichment of genes involved in the circadian rhythm, carbon metabolism, carbon fixation, and lipid metabolism, suggesting that the differential genes on the 6P chromosome are closely related to the phenotypic differences. For example, the photosynthesis-related genes PsbA, PsbT, and YCF48 were upregulated in II-30-5 compared with 5113. ACS and FabG are related to carbon fixation and fatty acid biosynthesis, respectively, and both carried modification variations and were upregulated in 5113 relative to II-30-5. Therefore, this study provides important guidance for cloning desirable genes from alien homologous chromosomes and for their effective utilization in wheat improvement.

The launch of satellite: DNA repeats as a cytogenetic tool in discovering the chromosomal universe of wild Triticeae

Fluorescence in situ hybridization is a powerful tool that enables plant researchers to perform systematic, evolutionary, and population studies of wheat wild relatives as well as to characterize alien introgression into the wheat genome. This retrospective review reflects on progress made in the development of methods for creating new chromosomal markers since the launch of this cytogenetic satellite instrument to the present day. DNA probes based on satellite repeats have been widely used for chromosome analysis, especially for "classical" wheat probes (pSc119.2 and Afa family) and "universal" repeats (45S rDNA, 5S rDNA, and microsatellites). The rapid development of new-generation sequencing and bioinformatical tools, and the application of oligo- and multioligonucleotides has resulted in an explosion in the discovery of new genome- and chromosome-specific chromosome markers. Owing to modern technologies, new chromosomal markers are appearing at an unprecedented velocity. The present review describes the specifics of localization when employing commonly used vs. newly developed probes for chromosomes in J, E, V, St, Y, and P genomes and their diploid and polyploid carriers Agropyron, Dasypyrum, Thinopyrum, Pseudoroegneria, Elymus, Roegneria, and Kengyilia. Particular attention is paid to the specificity of probes, which determines their applicability for the detection of alien introgression to enhance the genetic diversity of wheat through wide hybridization. The information from the reviewed articles is summarized into the TRepeT database, which may be useful for studying the cytogenetics of Triticeae. The review describes the trends in the development of technology used in establishing chromosomal markers that can be used for prediction and foresight in the field of molecular biology and in methods of cytogenetic analysis.

Anchoring alien chromosome segment substitutions bearing gene(s) for resistance to mustard aphid in Brassica juncea-B. fruticulosa introgression lines and their possible disruption through gamma irradiation

KEY MESSAGE

Heavy doses of gamma irradiation can reduce linkage drag by disrupting large sized alien translocations and promoting exchanges between crop and wild genomes. Resistance to mustard aphid (Lipaphis erysimi) infestation was significantly improved in Brassica juncea through B. juncea-B. fruticulosa introgression. However, linkage drag caused by introgressed chromatin fragments has so far prevented the deployment of this resistance source in commercial cultivars. We investigated the patterns of donor chromatin segment substitutions in the introgression lines (ILs) through genomic in situ hybridization (GISH) coupled with B. juncea chromosome-specific oligonucleotide probes. These allowed identification of large chromosome translocations from B. fruticulosa in the terminal regions of chromosomes A05, B02, B03 and B04 in three founder ILs (AD-64, 101 and 104). Only AD-101 carried an additional translocation at the sub-terminal to intercalary position in both homologues of chromosome A01. We validated these translocations with a reciprocal blast hit analysis using shotgun sequencing of three ILs and species-specific contigs/scaffolds (kb sized) from a de novo assembly of B. fruticulosa. Alien segment substitution on chromosome A05 could not be validated. Current studies also endeavoured to break linkage drag by exposing seeds to a heavy dose (200kR) of gamma radiation. Reduction in the size of introgressed chromatin fragments was observed in many M3 plants. There was a complete loss of the alien chromosome fragment in one instance. A few M3 plants with novel patterns of chromosome segment substitutions displayed improved agronomic performance coupled with resistance to mustard aphid. SNPs in such genomic spaces should aid the development of markers to track introgressed DNA and allow application in plant breeding.

Interpreting Diachronic Size Variation in Prehistoric Central Asian Cereal Grains

The morphology of ancient cereal grains in Central Asia has been heavily discussed as an indicator of specific genetic variants, which are often linked to cultural factors or distinct routes of dispersal. In this paper, we present the largest currently existing database of barley (n= 631) and wheat (n= 349) measurements from Central Asia, obtained from two different periods at the Chap site (ca. 3,500 to 1,000 BC), located in the Tien Shan Mountains of Kyrgyzstan at 2,000 masl. The site is situated at the highest elevation ecocline for successful cereal cultivation and is, therefore, highly susceptible to minor climatic fluctuations that could force gradients up or down in the foothills. We contrast the Chap data with measurements from other second and first millennia BC sites in the region. An evident increase in average size over time is likely due to the evolution of larger grains or the introduction of larger variants from elsewhere. Additionally, site- or region-specific variation is noted, and we discuss potential influences for the formation of genetic varieties, including possible pleiotropic linkages and/or developmental responses to external factors, such as environmental fluctuations, climate, irrigation inputs, soil nutrients, pathologies, and seasonality. External factors acting on developmental or acclamatory responses in plants can be either natural or cultural. We argue that the study of long-term changes in grain morphology on the edges of crop-growing ranges can be informative regarding cultural and environmental constraints in the past.

Wheat, Rye, and Barley Genomes Can Associate during Meiosis in Newly Synthesized Trigeneric Hybrids

Polyploidization, or whole genome duplication (WGD), has an important role in evolution and speciation. One of the biggest challenges faced by a new polyploid is meiosis, in particular, discriminating between multiple related chromosomes so that only homologs recombine to ensure regular chromosome segregation and fertility. Here, we report the production of two new hybrids formed by the genomes of species from three different genera: a hybrid between Aegilops tauschii (DD), Hordeum chilense (H^chH^ch), and Secale cereale (RR) with the haploid genomic constitution H^chDR (n = 7× = 21); and a hybrid between Triticum turgidum spp. durum (AABB), H. chilense, and S. cereale with the constitution ABH^chR (n = 7× = 28). We used genomic in situ hybridization and immunolocalization of key meiotic proteins to establish the chromosome composition of the new hybrids and to study their meiotic behavior. Interestingly, there were multiple chromosome associations at metaphase I in both hybrids. A high level of crossover (CO) formation was observed in H^chDR, which shows the possibility of meiotic recombination between the different genomes. We succeeded in the duplication of the ABH^chR genome, and several amphiploids, AABBH^chH^chRR, were obtained and characterized. These results indicate that recombination between the genera of three economically important crops is possible.

Variation in key leaf photosynthetic traits across wheat wild relatives is accession dependent not species dependent

The wild relatives of modern wheat represent an underutilized source of genetic and phenotypic diversity and are of interest in breeding owing to their wide adaptation to diverse environments. Leaf photosynthetic traits underpin the rate of production of biomass and yield and have not been systematically explored in the wheat relatives. This paper identifies and quantifies the phenotypic variation in photosynthetic, stomatal, and morphological traits in up to 88 wheat wild relative accessions across five genera. Both steady-state measurements and dynamic responses to step changes in light intensity are assessed. A 2.3-fold variation for flag leaf light and CO₂ -saturated rates of photosynthesis A_max was observed. Many accessions showing higher and more variable A_max , maximum rates of carboxylation, electron transport, and Rubisco activity when compared with modern genotypes. Variation in dynamic traits was also significant; with distinct genus-specific trends in rates of induction of nonphotochemical quenching and rate of stomatal opening. We conclude that utilization of wild relatives for improvement of photosynthesis is supported by the existence of a high degree of natural variation in key traits and should consider not only genus-level properties but variation between individual accessions.

Allele mining of TaGRF-2D gene 5'-UTR in Triticum aestivum and Aegilops tauschii genotypes

The low diversity of the D-subgenome of bread wheat requires the involvement of new alleles for breeding. In grasses, the allelic state of Growth Regulating Factor (GRF) gene is correlated with nitrogen uptake. In this study, we characterized the sequence of TaGRF-2D and assessed its diversity in bread wheat and goatgrass Aegilops tauschii (genome DD). In silico analysis was performed for reference sequence searching, primer pairs design and sequence assembly. The gene sequence was obtained using Illumina and Sanger sequencing. The complete sequences of TaGRF-2D were obtained for 18 varieties of wheat. The polymorphism in the presence/absence of two GCAGCC repeats in 5' UTR was revealed and the GRF-2D-SSR marker was developed. Our results showed that the alleles 5' UTR-250 and 5' UTR-238 were present in wheat varieties, 5' UTR-250 was presented in the majority of wheat varieties. In Ae. tauschii ssp. strangulata (likely donor of the D-subgenome of polyploid wheat), most accessions carried the 5' UTR-250 allele, whilst most Ae. tauschii ssp. tauschii have 5' UTR-244. The developed GRF-2D-SSR marker can be used to study the genetic diversity of wheat and Ae. tauschii.

Cytogenetic Analysis and Molecular Marker Development for a New Wheat-Thinopyrum ponticum 1Js (1D) Disomic Substitution Line With Resistance to Stripe Rust and Powdery Mildew

Thinopyrum ponticum (2n = 10x = 70), a member of the tertiary gene pool of wheat (Triticum aestivum L.), harbors many biotic and abiotic stress resistance genes. CH10A5, a novel disomic substitution line from a cross of T. aestivum cv. 7182 and Th. ponticum, was characterized by cytogenetic identification, in situ hybridization, molecular marker analysis, and morphological investigation of agronomic traits and disease resistance. Cytological observations showed that CH10A5 contained 42 chromosomes and formed 21 bivalents at meiotic metaphase I. Genome in situ hybridization (GISH) analysis indicated that two of its chromosomes came from the J^s genome of Th. ponticum, and wheat 15K array mapping and fluorescence in situ hybridization (FISH) revealed that chromosome 1D was absent from CH10A5. Polymorphic analysis of molecular markers indicated that the pair of alien chromosomes belonged to homoeologous group one, designated as 1J^s. Thus, CH10A5 was a wheat-Th. ponticum 1J^s (1D) disomic substitution line. Field disease resistance trials demonstrated that the introduced Th. ponticum chromosome 1J^s was probably responsible for resistance to both stripe rust and powdery mildew at the adult stage. Based on specific-locus amplified fragment sequencing (SLAF-seq), 507 STS molecular markers were developed to distinguish chromosome 1J^s genetic material from that of wheat. Of these, 49 STS markers could be used to specifically identify the genetic material of Th. ponticum. CH10A5 will increase the resistance gene diversity of wheat breeding materials, and the markers developed here will permit further tracing of heterosomal chromosome fragments in the future.

Characterization, identification and evaluation of a set of wheat-Aegilops comosa chromosome lines

This study characterized and evaluated a set of wheat-Aegilops comosa introgression lines, including six additions and one substitution. A total of 47 PLUG markers and a set of cytogenetic markers specific for Ae. comosa chromosomes were established after screening 526 PLUG primer pairs and performing FISH using oligonucleotides as probes. Marker analysis confirmed that these lines were wheat-Ae. comosa 2M–7M addition lines and a 6M(6A) substitution line. The molecular and cytogenetic markers developed herein could be used to trace Ae. comosa chromatin in wheat background. In order to evaluate the breeding value of the material, disease resistance tests and agronomical trait investigations were carried out on these alien chromosome introgression lines. Disease resistance tests showed that chromosomes 2M and 7M of Ae. comosa might harbor new stripe rust and powdery mildew resistance genes, respectively, therefore, they could be used as resistance sources for wheat breeding. Investigations into agronomical traits showed that all chromosomes 2M to 7M had detrimental effects on the agronomic performance of wheat, therefore, the selection of plants with relatively negative effects should be avoided when inducing wheat-A. comosa chromosome translocations using chromosome engineering procedures.

Development of new cytogenetic markers for Thinopyrum ponticum (Podp.) Z.-W. Liu & R.-C. Wang

Thinopyrum ponticum (Podpěra, 1902) Z.-W. Liu & R.-C.Wang, 1993 is an important polyploid wild perennial Triticeae species that is widely used as a source of valuable genes for wheat but its genomic constitution has long been debated. For its chromosome identification, only a limited set of FISH probes has been used. The development of new cytogenetic markers for Th. ponticum chromosomes is of great importance both for cytogenetic characterization of wheat-wheatgrass hybrids and for fundamental comparative studies of phylogenetic relationships between species. Here, we report on the development of five cytogenetic markers for Th. ponticum based on repetitive satellite DNA of which sequences were selected from the whole genome sequence of Aegilops tauschii Cosson, 1849. Using real-time quantitative PCR we estimated the abundance of the found repeats: P720 and P427 had the highest abundance and P132, P332 and P170 had lower quantity in Th. ponticum genome. Using fluorescence in situ hybridization (FISH) we localized five repeats to different regions of the chromosomes of Th. ponticum. Using reprobing multicolor FISH we colocalized the probes between each other. The distribution of these found repeats in the Triticeae genomes and its usability as cytogenetic markers for chromosomes of Th. ponticum are discussed.

Construction of Agropyron Gaertn. genetic linkage maps using a wheat 660K SNP array reveals a homoeologous relationship with the wheat genome

Agropyron Gaertn. (P genome) is a wild relative of wheat that harbours many genetic variations that could be used to increase the genetic diversity of wheat. To agronomically transfer important genes from the P genome to a wheat chromosome by induced homoeologous pairing and recombination, it is necessary to determine the chromosomal relationships between Agropyron and wheat. Here, we report using the wheat 660K single nucleotide polymorphism (SNP) array to genotype a segregating Agropyron F1 population derived from an interspecific cross between two cross-pollinated diploid collections 'Z1842' [A. cristatum (L.) Beauv.] (male parent) and 'Z2098' [A. mongolicum Keng] (female parent) and 35 wheat-A. cristatum addition/substitution lines. Genetic linkage maps were constructed using 913 SNP markers distributed among seven linkage groups spanning 839.7 cM. The average distance between adjacent markers was 1.8 cM. The maps identified the homoeologous relationship between the P genome and wheat and revealed that the P and wheat genomes are collinear and relatively conserved. In addition, obvious rearrangements and introgression spread were observed throughout the P genome compared with the wheat genome. Combined with genotyping data, the complete set of wheat-A. cristatum addition/substitution lines was characterized according to their homoeologous relationships. In this study, the homoeologous relationship between the P genome and wheat was identified using genetic linkage maps, and the detection mean for wheat-A. cristatum introgressions might significantly accelerate the introgression of genetic variation from Agropyron into wheat for exploitation in wheat improvement programmes.

Molecular cytogenetic identification of a novel wheat-Agropyron elongatum chromosome translocation line with powdery mildew resistance

Agropyron elongatum (Host.) Neviski (synonym, Thinopyrum ponticum Podp., 2n = 70) has been used extensively as a valuable source for wheat breeding. Numerous chromosome fragments containing valuable genes have been successfully translocated into wheat from A. elongatum. However, reports on the transfer of powdery mildew resistance from A. elongatum to wheat are rare. In this study, a novel wheat-A. elongatum translocation line, 11-20-1, developed and selected from the progenies of a sequential cross between wheat varieties (Lankaoaizaoba, Keyu 818 and BainongAK 58) and A. elongatum, was evaluated for disease resistance and characterized using molecular cytogenetic methods. Cytological observations indicated that 11-20-1 had 42 chromosomes and formed 21 bivalents at meiotic metaphase I. Genomic in situ hybridization analysis using whole genomic DNA from A. elongatum as a probe showed that the short arms of a pair of wheat chromosomes were replaced by a pair of A. elongatum chromosome arms. Fluorescence in situ hybridization, using wheat D chromosome specific sequence pAs1 as a probe, suggested that the replaced chromosome arms of 11-20-1 were 5DS. This was further confirmed by wheat SSR markers specific for 5DS. EST-SSR and EST-STS multiple loci markers confirmed that the introduced A. elongatum chromosome arms belonged to homoeologous group 5. Therefore, it was deduced that 11-20-1 was a wheat-A. elongatum T5DL∙5AgS translocation line. Both resistance observation and molecular marker analyses using two specific markers (BE443538 and CD452608) of A. elongatum in a F₂ population from a cross between line 11-20-1 and a susceptible cultivar Yannong 19 verified that the A. elongatum chromosomes were responsible for the powdery mildew resistance. This work suggests that 11-20-1 likely contains a novel resistance gene against powdery mildew. We expect this line to be useful for the genetic improvement of wheat.

High-density SNP genotyping array for hexaploid wheat and its secondary and tertiary gene pool

In wheat, a lack of genetic diversity between breeding lines has been recognized as a significant block to future yield increases. Species belonging to bread wheat's secondary and tertiary gene pools harbour a much greater level of genetic variability, and are an important source of genes to broaden its genetic base. Introgression of novel genes from progenitors and related species has been widely employed to improve the agronomic characteristics of hexaploid wheat, but this approach has been hampered by a lack of markers that can be used to track introduced chromosome segments. Here, we describe the identification of a large number of single nucleotide polymorphisms that can be used to genotype hexaploid wheat and to identify and track introgressions from a variety of sources. We have validated these markers using an ultra-high-density Axiom(®) genotyping array to characterize a range of diploid, tetraploid and hexaploid wheat accessions and wheat relatives. To facilitate the use of these, both the markers and the associated sequence and genotype information have been made available through an interactive web site.

Development and Molecular Cytogenetic Identification of a Novel Wheat-Leymus mollis Lm#7Ns (7D) Disomic Substitution Line with Stripe Rust Resistance

Leymus mollis (2n = 4x = 28, NsNsXmXm) possesses novel and important genes for resistance against multi-fungal diseases. The development of new wheat—L. mollis introgression lines is of great significance for wheat disease resistance breeding. M11003-3-1-15-8, a novel disomic substitution line of common wheat cv. 7182 –L. mollis, developed and selected from the BC₁F₅ progeny between wheat cv. 7182 and octoploid Tritileymus M47 (2n = 8x = 56, AABBDDNsNs), was characterized by morphological and cytogenetic identification, analysis of functional molecular markers, genomic in situ hybridization (GISH), sequential fluorescence in situ hybridization (FISH)—genomic in situ hybridization (GISH) and disease resistance evaluation. Cytological observations suggested that M11003-3-1-15-8 contained 42 chromosomes and formed 21 bivalents at meiotic metaphase I. The GISH investigations showed that line contained 40 wheat chromosomes and a pair of L. mollis chromosomes. EST-STS multiple loci markers and PLUG (PCR-based Landmark Unique Gene) markers confirmed that the introduced L. mollis chromosomes belonged to homoeologous group 7, it was designated as Lm#7Ns. While nulli-tetrasomic and sequential FISH-GISH analysis using the oligonucleotide Oligo-pSc119.2 and Oligo-pTa535 as probes revealed that the wheat 7D chromosomes were absent in M11003-3-1-15-8. Therefore, it was deduced that M11003-3-1-15-8 was a wheat–L. mollis Lm#7Ns (7D) disomic substitution line. Field disease resistance demonstrated that the introduced L. mollis chromosomes Lm#7Ns were responsible for the stripe rust resistance at the adult stage. Moreover, M11003-3-1-15-8 had a superior numbers of florets. The novel disomic substitution line M11003-3-1-15-8, could be exploited as an important genetic material in wheat resistance breeding programs and genetic resources.

Chromosomal location and comparative genomics analysis of powdery mildew resistance gene Pm51 in a putative wheat-Thinopyrum ponticum introgression line

Powdery mildew (PM) is a very destructive disease of wheat (Triticum aestivum L.). Wheat-Thinopyrum ponticum introgression line CH7086 was shown to possess powdery mildew resistance possibly originating from Th. ponticum. Genomic in situ hybridization and molecular characterization of the alien introgression failed to identify alien chromatin. To study the genetics of resistance, CH7086 was crossed with susceptible genotypes. Segregation in F2 populations and F2:3 lines tested with Chinese Bgt race E09 under controlled conditions indicated that CH7086 carries a single dominant gene for powdery mildew resistance. Fourteen SSR and EST-PCR markers linked with the locus were identified. The genetic distances between the locus and the two flanking markers were 1.5 and 3.2 cM, respectively. Based on the locations of the markers by nullisomic-tetrasomic and deletion lines of 'Chinese Spring', the resistance gene was located in deletion bin 2BL-0.89-1.00. Conserved orthologous marker analysis indicated that the genomic region flanking the resistance gene has a high level of collinearity to that of rice chromosome 4 and Brachypodium chromosome 5. Both resistance specificities and tests of allelism suggested the resistance gene in CH7086 was different from previously reported powdery mildew resistance genes on 2BL, and the gene was provisionally designated PmCH86. Molecular analysis of PmCH86 compared with other genes for resistance to Bgt in the 2BL-0.89-1.00 region suggested that PmCH86 may be a new PM resistance gene, and it was therefore designated as Pm51. The closely linked flanking markers could be useful in exploiting this putative wheat-Thinopyrum translocation line for rapid transfer of Pm51 to wheat breeding programs.

Strategies for transferring resistance into wheat: from wide crosses to GM cassettes

The domestication of wheat in the Fertile Crescent 10,000 years ago led to a genetic bottleneck. Modern agriculture has further narrowed the genetic base by introducing extreme levels of uniformity on a vast spatial and temporal scale. This reduction in genetic complexity renders the crop vulnerable to new and emerging pests and pathogens. The wild relatives of wheat represent an important source of genetic variation for disease resistance. For nearly a century farmers, breeders, and cytogeneticists have sought to access this variation for crop improvement. Several barriers restricting interspecies hybridization and introgression have been overcome, providing the opportunity to tap an extensive reservoir of genetic diversity. Resistance has been introgressed into wheat from at least 52 species from 13 genera, demonstrating the remarkable plasticity of the wheat genome and the importance of such natural variation in wheat breeding. Two main problems hinder the effective deployment of introgressed resistance genes for crop improvement: (1) the simultaneous introduction of genetically linked deleterious traits and (2) the rapid breakdown of resistance when deployed individually. In this review, we discuss how recent advances in molecular genomics are providing new opportunities to overcome these problems.

Molecular cytogenetic characterization of a wheat - Leymus mollis 3D(3Ns) substitution line with resistance to leaf rust

Leymus mollis (Trin.) Pilger (NsNsXmXm, 2n = 28), a wild relative of common wheat, possesses many potentially valuable traits that could be transferred to common wheat during breeding programs. In this study, the karyotypic constitution of a wheat - L. mollis 3D(3Ns#1) disomic substitution line isolated from the F5 progeny of octoploid Tritileymus M842-16 × Triticum durum cv. D4286, which was designated as 10DM57, was determined using genomic in situ hybridization (GISH), fluorescent in situ hybridization (FISH), SSR markers, and EST-STS markers. Screening of mitosis and meiosis showed that 10DM57 had a chromosome karyotype of 2n = 42 = 21II. GISH indicated that 10DM57 was a line with 40 chromosomes from wheat and two of the Ns chromosomes from L. mollis, which formed a ring bivalent in pollen mother cells at metaphase I. FISH analysis showed that the chromosome 3D may be replaced by 3Ns#1 in 10DM57. DNA markers, including SSR and EST-STS primers, showed that the pair of wheat chromosome 3D in 10DM57 was substituted by the pair of chromosome 3Ns#1 from L. mollis. Evaluation of the agronomic traits showed that, compared with its common wheat relative 7182, 10DM57 was resistant to leaf rust while the spike length and number of spikes per plant were improved significantly, which correlated with a higher wheat yield. The new germplasm, 10DM57, could be exploited as an intermediate material in wheat genetic and breeding programs.

Development and characterization of a Psathyrostachys huashanica Keng 7Ns chromosome addition line with leaf rust resistance

The aim of this study was to characterize a Triticum aestivum-Psathyrostachys huashanica Keng (2n = 2x = 14, NsNs) disomic addition line 2-1-6-3. Individual line 2-1-6-3 plants were analyzed using cytological, genomic in situ hybridization (GISH), EST-SSR, and EST-STS techniques. The alien addition line 2-1-6-3 was shown to have two P. huashanica chromosomes, with a meiotic configuration of 2n = 44 = 22 II. We tested 55 EST-SSR and 336 EST-STS primer pairs that mapped onto seven different wheat chromosomes using DNA from parents and the P. huashanica addition line. One EST-SSR and nine EST-STS primer pairs indicated that the additional chromosome of P. huashanica belonged to homoeologous group 7, the diagnostic fragments of five EST-STS markers (BE404955, BE591127, BE637663, BF482781 and CD452422) were cloned, sequenced and compared. The results showed that the amplified polymorphic bands of P. huashanica and disomic addition line 2-1-6-3 shared 100% sequence identity, which was designated as the 7Ns disomic addition line. Disomic addition line 2-1-6-3 was evaluated to test the leaf rust resistance of adult stages in the field. We found that one pair of the 7Ns genome chromosomes carried new leaf rust resistance gene(s). Moreover, wheat line 2-1-6-3 had a superior numbers of florets and grains per spike, which were associated with the introgression of the paired P. huashanica chromosomes. These high levels of disease resistance and stable, excellent agronomic traits suggest that this line could be utilized as a novel donor in wheat breeding programs.

Isolation and characterization of a Psathyrostachys huashanica Keng 6Ns chromosome addition in common wheat

The development of alien addition lines is important for transferring useful genes from exotic species into common wheat. A hybrid of common wheat cv. 7182 (2n = 6x = 42, AABBDD) and Psathyrostachys huashanica Keng (2n = 2x = 14, NsNs) via embryo culture produced the novel intergeneric disomic addition line 59-11. The seed morphology of 59-11 resembled the parent 7182 and it exhibited extreme agronomic characteristics, i.e., twin stable spikelets, fertile florets, and multi-kernel clusters. Furthermore, 59-11 produced plump kernels with a high seed-setting percentage during the advanced maturation stage. The line was screened based on genomic in situ hybridization, EST-SSR, EST-STS, and gliadin to identify P. huashanica chromatin in the wheat background. The chromosome number and configuration of 59-11 was 2n = 44 = 22 II and we confirmed the 6Ns disomic chromosome additions based on A-PAGE analysis and molecular markers. The results suggested that the production of twin spikelets and multiple kernels per spike in the wheat-P. huashanica addition line was related to homologous group 6 in the wheat chromosome. This is the first report of the introduction of improved spike traits into common wheat from the alien species P. huashanica and it opens up the possibility of increasing the wheat yield based on this enlarged gene pool.