Disomic Substitution Lines Research Articles

Identification and DNA Marker Development for a Wheat-Leymus mollis 2Ns (2D) Disomic Chromosome Substitution.

Leymus mollis (2n = 4x = 28, NsNsXmXm), a wild relative of common wheat (Triticum aestivum L.), carries numerous loci which could potentially be used in wheat improvement. In this study, line 17DM48 was isolated from the progeny of a wheat and L. mollis hybrid. This line has 42 chromosomes forming 21 bivalents at meiotic metaphase I. Genomic in situ hybridization (GISH) demonstrated the presence of a pair chromosomes from the Ns genome of L. mollis. This pair substituted for wheat chromosome 2D, as shown by fluorescence in situ hybridization (FISH), DNA marker analysis, and hybridization to wheat 55K SNP array. Therefore, 17DM48 is a wheat-L. mollis 2Ns (2D) disomic substitution line. It shows longer spike and a high level of stripe rust resistance. Using specific-locus amplified fragment sequencing (SLAF-seq), 13 DNA markers were developed to identify and trace chromosome 2Ns of L. mollis in wheat background. This line provides a potential bridge germplasm for genetic improvement of wheat stripe rust resistance.

Genome-wide identification, characteristics and expression of the prolamin genes in Thinopyrum elongatum

BackgroundProlamins, unique to Gramineae (grasses), play a key role in the human diet. Thinopyrum elongatum (syn. Agropyron elongatum or Lophopyrum elongatum), a grass of the Triticeae family with a diploid E genome (2n = 2x = 14), is genetically well-characterized, but little is known about its prolamin genes and the relationships with homologous loci in the Triticeae species.ResultsIn this study, a total of 19 α-gliadin, 9 γ-gliadin, 19 ω-gliadin, 2 high-molecular-weight glutenin subunit (HMW-GS), and 5 low-molecular-weight glutenin subunit (LMW-GS) genes were identified in the Th. elongatum genome. Micro-synteny and phylogenetic analysis revealed dynamic changes of prolamin gene regions and genetic affinities among Th. elongatum, Triticum aestivum, T. urartu and Aegilops tauschii. The Th. elongatum genome, like the B subgenome of T. aestivum, only contained celiac disease epitope DQ8-glia-α1/DQ8.5-glia-α1, which provided a theoretical basis for the low gluten toxicity wheat breeding. The transcriptome data of Th. elongatum exhibited differential expression in quantity and pattern in the same subfamily or different subfamilies. Dough rheological properties of T. aestivum-Th. elongatum disomic substitution (DS) line 1E(1D) showed higher peak height values than that of their parents, and DS6E(6D) exhibited fewer α-gliadins, which indicates the potential usage for wheat quality breeding.ConclusionsOverall, this study provided a comprehensive overview of the prolamin gene family in Th. elongatum, and suggested a promising use of this species in the generation of improved wheat breeds intended for the human diet.

Development of Novel Wheat-Aegilops longissima 3S1 Translocations Conferring Powdery Mildew Resistance and Specific Molecular Markers for Chromosome 3S1.

Powdery mildew of wheat, caused by Blumeria graminis f. sp. tritici, is a destructive disease of common wheat. Cultivation of resistant varieties is the most cost-effective disease management strategy. Previous studies reported that chromosome 3Sl#2 present in Chinese Spring (CS)-Aegilops longissima 3Sl#2(3B) disomic substitution line TA3575 conferred resistance to powdery mildew. In this study, we further located the powdery mildew resistance gene(s) to the short arm of chromosome 3Sl#2 (3Sl#2S) by evaluating for B. graminis f. sp. tritici resistance of newly developed CS-Ae. longissima 3Sl#2 translocation lines. Meanwhile, TA7545, a previously designated CS-Ae. longissima 3Sl#3 disomic addition line, was reidentified as an isochromosome 3Sl#3S addition line and evaluated to confer resistance to powdery mildew, thus locating the resistance gene(s) to the short arm of chromosome 3Sl#3 (3Sl#3S). Based on transcriptome sequences of TA3575, 10 novel chromosome 3SlS-specific markers were developed, of which 5 could be used to distinguish between 3Sl#2S and 3Sl#3S derived from Ae. longissima accessions TL20 and TA1910 (TAM4) and the remaining 5 could identify both 3Sl#2S and 3Sl#3S. Also, CL897, one of five markers specific to both 3Sl#2S and 3Sl#3S, could be used to detect Pm13 located at chromosome 3Sl#1S from Ae. longissima accession TL01 in diverse wheat genetic backgrounds. The powdery mildew resistance genes on chromosomes 3Sl#2S and 3Sl#3S, the CS-Ae. longissima 3Sl#2 translocation lines, and the 3SlS-specific markers developed in this study will facilitate the transfer of B. graminis f. sp. tritici resistance genes into common wheat and provide new germplasm resources for powdery mildew resistance breeding.

Molecular Cytogenetic Identification of a Novel Wheat-Thinopyrum ponticum 1JS (1B) Substitution Line Resistant to Powdery Mildew and Leaf Rust.

Thinopyrum ponticum (2n = 10x = 70) is a wild relative of wheat with high tolerance to both biotic and abiotic stresses; it has been wildly used in wheat genetic improvement. A disomic substitution line named SN19647 was derived from a cross between Triticum aestivum and the wheat–Th. ponticum partial amphiploid SNTE20 (2n = 8x = 56). It was evaluated for disease resistance and characterized via sequential fluorescence in situ hybridization (FISH)-genomic in situ hybridization (GISH) and molecular markers. The results showed that SN19647 carried resistance to both powdery mildew and leaf rust. It contained 42 chromosomes with a pair of wheat chromosome 1B replaced by a pair of JS chromosomes from Th. ponticum. In addition to chromosomal substitution events, structural variation also occurred on wheat chromosomes 2A, 5A, 6B, and 7B. Based on marker analysis, 19 markers specific to the JS chromosome were obtained, of which seventeen markers belonged to homoeologous group one. These results indicated that SN19647 was a 1JS (1B) substitution line. Compared with the known 1JS (1D) substitution line CH10A5, it was found that 17 markers generated different specific bands to Th. ponticum, confirming the novelty of the 1JS chromosome in SN19647. Therefore, SN19647, resistant to powdery mildew and leaf rust, was a novel 1JS (1B) substitution line that can be used in wheat genetic improvement.

Characterization of the Durum Wheat-Aegilops tauschii 4D(4B) Disomic Substitution Line YL-443 With Superior Characteristics of High Yielding and Stripe Rust Resistance.

Durum wheat is one of the important food and cash crops. The main goals in current breeding programs are improving its low yield potential, kernel characteristics, and lack of resistance or tolerance to some biotic and abiotic stresses. In this study, a nascent synthesized hexaploid wheat Lanmai/AT23 is used as the female parent in crosses with its AB genome donor Lanmai. A tetraploid line YL-443 with supernumerary spikelets and high resistance to stripe rust was selected out from the pentaploid F7 progeny. Somatic analysis using multicolor fluorescence in situ hybridization (mc-FISH) revealed that this line is a disomic substitution line with the 4B chromosome pair of Lanmai replaced by the 4D chromosome pair of Aegilops tauschii AT23. Comparing with Lanmai, YL-443 shows an increase in the number of spikelets and florets per spike by 36.3 and 75.9%, respectively. The stripe rust resistance gene Yr28 carried on the 4D chromosome was fully expressed in the tetraploid background. The present 4D(4B) disomic substitution line YL-443 was distinguished from the previously reported 4D(4B) lines with the 4D chromosomes from Chinese Spring (CS). Our study demonstrated that YL-443 can be used as elite germplasm for durum wheat breeding targeting high yield potential and stripe rust resistance. The Yr28-specific PCR marker and the 4D chromosome-specific KASP markers together with its unique features of pubescent leaf sheath and auricles can be utilized for assisting selection in breeding.

Pm67, a new powdery mildew resistance gene transferred from Dasypyrum villosum chromosome 1V to common wheat (Triticum aestivum L.)

Powdery mildew, caused by the biotrophic fungus Blumeria graminis f. sp. tritici (Bgt), is a global disease that poses a serious threat to wheat production. To explore additional resistance gene, a wheat-Dasypyrum villosum 1V#5 (1D) disomic substitution line NAU1813 (2n = 42) with high level of seedling resistance to powdery mildew was used to generate the recombination between chromosomes 1V#5 and 1D. Four introgression lines, including t1VS#5 ditelosomic addition line NAU1815, t1VL#5 ditelosomic addition line NAU1816, homozygous T1DL·1VS#5 translocation line NAU1817, and homozygous T1DS·1VL#5 translocation line NAU1818 were developed from the selfing progenies of 1V#5 and 1D double monosomic line that derived from F1 hybrids of NAU1813/NAU0686. All of them were characterized by fluorescence in situ hybridization, genomic in situ hybridization, 1V-specific markers analysis, and powdery mildew tests at different developmental stages. A new powdery mildew resistance gene named Pm67 was physically located in the terminal bin (FL 0.70–1.00) of 1VS#5. Lines with Pm67 exhibited seedling stage immunity and tissue-differentiated reactions at adult plant stage. The sheaths, stems, and spikes of the Pm67 line were still immune, but the leaves showed a low degree of susceptibility. Microscopic observation showed that most penetration attempts were stopped in association with papillae on the sheath, and colonies cannot form conidia on the susceptible leaf of Pm67 line at adult plant stage, suggesting that the defence layers of the Pm67 line is tissue-differentiated. Thus, the T1DL·1VS#5 translocation line NAU1817 provides a new germplasm in wheat breeding for improvement of powdery mildew resistance.

Random chromosome distribution in the first meiosis of F1 disomic substitution line 2R(2D) x rye hybrids (ABDR, 4× = 28) occurs without bipolar spindle assembly.

The assembly of the microtubule-based spindle structure in plant meiosis remains poorly understood compared with our knowledge of mitotic spindle formation. One of the approaches in our understanding of microtubule dynamics is to study spindle assembly in meiosis of amphyhaploids. Using immunostaining with phH3Ser10, CENH3 and α-tubulin-specific antibodies, we studied the chromosome distribution and spindle organisation in meiosis of F1 2R(2D)xR wheat-rye hybrids (genome structure ABDR, 4× = 28), as well as in wheat and rye mitosis and meiosis. At the prometaphase of mitosis, spindle assembly was asymmetric; one half of the spindle assembled before the other, with simultaneous chromosome alignment in the spindle mid-zone. At diakinesis in wheat and rye, microtubules formed a pro-spindle which was subsequently disassembled followed by a bipolar spindle assembly. In the first meiosis of hybrids 2R(2D)xR, a bipolar spindle was not found and the kinetochore microtubules distributed the chromosomes. Univalent chromosomes are characterised by a monopolar orientation and maintenance of sister chromatid and centromere cohesion. Presence of bivalents did not affect the formation of a bipolar spindle. Since the central spindle was absent, phragmoplast originates from “interpolar” microtubules generated by kinetochores. Cell plate development occurred with a delay. However, meiocytes in meiosis II contained apparently normal bipolar spindles. Thus, we can conclude that: (1) cohesion maintenance in centromeres and between arms of sister chromatids may negatively affect bipolar spindle formation in the first meiosis; (2) 2R/2D rye/wheat chromosome substitution affects the regulation of the random chromosome distribution in the absence of a bipolar spindle.

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 Js 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 1Js. Thus, CH10A5 was a wheat–Th. ponticum 1Js (1D) disomic substitution line. Field disease resistance trials demonstrated that the introduced Th. ponticum chromosome 1Js 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 1Js 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.

Introgression of perennial growth habit from Lophopyrum elongatum into wheat.

A locus for perennial growth was mapped on Lophopyrum elongatum chromosome arm 4ES and introgressed into the wheat genome. Evidence was obtained that in addition to chromosome 4E, other L. elongatum chromosomes control perennial growth. Monocarpy versus polycarpy is one of the fundamental developmental dichotomies in flowering plants. Advances in the understanding of the genetic basis of this dichotomy are important for basic biological reasons and practically for genetic manipulation of growth development in economically important plants. Nine wheat introgression lines (ILs) harboring germplasm of the Lophopyrum elongatum genome present in the octoploid amphiploid Triticum aestivum cv. Chinese Spring (subgenomes AABBDD) × L. elongatum (genomes EE) were selected from a population of ILs developed earlier. These ILs were employed here in genomic analyses of post-sexual cycle regrowth (PSCR), which is a component of polycarpy in caespitose L. elongatum. Analyses of disomic substitution (DS) lines confirmed that L. elongatum chromosome 4E confers PSCR on wheat. The gene was mapped into a short distal region of L. elongatum arm 4ES and was tentatively named Pscr1. ILs harboring recombined chromosomes with 4ES segments, including Pscr1, incorporated into the distal part of the 4DS chromosome arm were identified. Based on the location, Pscr1 is not orthologous with the rice rhizome-development gene Rhz2 located on rice chromosome Os3, which is homoeologous with chromosome 4E, but it may correspond to the Teosinte branched1 (TB1) gene, which is located in the introgressed region in the L. elongatum and Ae. tauschii genomes. A hexaploid IL harboring a large portion of the E-genome but devoid of chromosome 4E also expressed PSCR, which provided evidence that perennial growth is controlled by genes on other L. elongatum chromosomes in addition to 4E.

Development of self-fertile deletion homozygous and ditelosomic lines for the long arm of chromosome 2A in common wheat.

Most deletions for the short arm of chromosome 2A (2AS), and the telocentric chromosome for the long arm of chromosome 2A (2AL), are available only in the heterozygous condition in 'Chinese Spring' hexaploid wheat. This is due to the female sterility, and therefore self-sterility, of their homozygotes, caused by the partial or entire loss of the 2AS chromosome arm on which genes for normal synapsis and female fertility are located. On the other hand, a D-genome disomic substitution line 2D(2A) of 'Langdon' tetraploid wheat, in which chromosome 2D is disomically substituted for chromosome 2A, is available (i.e., self-fertile) despite chromosome 2A being missing in this line. This fact indicates that another gene for female fertility must be present in Langdon 2D(2A). We attempted to develop self-fertile 2AS homozygous deletion and ditelosomic 2AL lines by transferring this female fertility gene, through a series of crosses and cytological screening, from Langdon 2D(2A) to the two aneuploid lines. We finally obtained self-fertile 2AS homozygous deletion and ditelosomic 2AL lines. These lines displayed normal meiotic chromosome pairing and lacked all 12 of the 2AS markers used for PCR analysis.

Characterization of the Wheat-Psathyrostachys huashania Keng 2Ns/2D Substitution Line H139: A Novel Germplasm With Enhanced Resistance to Wheat Take-All.

Take-all is a devastating soil-borne disease that affects wheat production. The continuous generation of disease-resistance germplasm is an important aspect of the management of this pathogen. In this study, we characterized the wheat-Psathyrostachys huashania Keng (P. huashania)-derived progeny H139 that exhibits significantly improved resistance to wheat take-all disease compared with its susceptible parent 7182. Sequential genomic in situ hybridization (GISH) and multicolor fluorescence in situ hybridization (mc-FISH) analyses revealed that H139 is a stable wheat-P. huashania disomic substitution line lacking wheat chromosome 2D. Expressed sequence tag-sequence tagged site (EST-STS) marker and Wheat Axiom 660K Genotyping Array analysis further revealed that H139 was a novel wheat-P. huashania 2Ns/2D substitution line. In addition, the H139 line was shown to be cytologically stable with a dwarf phenotype and increased spikelet number. These results indicate that H139, with its enhanced wheat take-all disease resistance and desirable agronomic traits, provides valuable genetic resources for wheat chromosome engineering breeding.

Characterization and Evaluation of Resistance to Powdery Mildew of Wheat-Aegilops geniculata Roth 7Mg (7A) Alien Disomic Substitution Line W16998.

Aegilops geniculata Roth has been used as a donor of disease-resistance genes, to enrich the gene pool for wheat (Triticum aestivum) improvement through distant hybridization. In this study, the wheat–Ae. geniculata alien disomic substitution line W16998 was obtained from the BC1F8 progeny of a cross between the common wheat ‘Chinese Spring’ (CS) and Ae. geniculata Roth (serial number: SY159//CS). This line was identified using cytogenetic techniques, analysis of genomic in situ hybridization (GISH), functional molecular markers (Expressed sequence tag-sequence-tagged site (EST–STS) and PCR-based landmark unique gene (PLUG), fluorescence in situ hybridization (FISH), sequential fluorescence in situ hybridization–genomic in situ hybridization (sequential FISH–GISH), and assessment of agronomic traits and powdery mildew resistance. During the anaphase of meiosis, these were evenly distributed on both sides of the equatorial plate, and they exhibited high cytological stability during the meiotic metaphase and anaphase. GISH analysis indicated that W16998 contained a pair of Ae. geniculata alien chromosomes and 40 common wheat chromosomes. One EST–STS marker and seven PLUG marker results showed that the introduced chromosomes of Ae. geniculata belonged to homoeologous group 7. Nullisomic–tetrasomic analyses suggested that the common wheat chromosome, 7A, was absent in W16998. FISH and sequential FISH–GISH analyses confirmed that the introduced Ae. geniculata chromosome was 7Mg. Therefore, W16998 was a wheat–Ae. geniculata 7Mg (7A) alien disomic substitution line. Inoculation of isolate E09 (Blumeria graminis f. sp. tritici) in the seedling stage showed that SY159 and W16998 were resistant to powdery mildew, indeed nearly immune, whereas CS was highly susceptible. Compared to CS, W16998 exhibited increased grain weight and more spikelets, and a greater number of superior agronomic traits. Consequently, W16998 was potentially useful. Germplasms transfer new disease-resistance genes and prominent agronomic traits into common wheat, giving the latter some fine properties for breeding.

Development, identification, and characterization of blue-grained wheat-Triticum boeoticum substitution lines.

Diploid wild einkorn wheat, Triticum boeoticum Boiss (AbAb, 2n = 2x = 14), is a wheat-related species with a blue aleurone layer. In this study, six blue-grained wheat lines were developed from F8 progeny of crosses between common wheat and T. boeoticum. The chromosome constitutions of these lines were characterized by fluorescence in situ hybridization (FISH) using the oligonucleotide probes Oligo-pTa535-1, Oligo-pSc119.2-1, Oligo-pTa71-2, and (AAC)7. Multicolor FISH using Oligo-pTa535-1, Oligo-pSc119.2-1, and Oligo-pTa71-2 identified all 42 common wheat chromosomes, while Oligo-pTa535-1 and (AAC)7 discriminated the 14 chromosomes of T. boeoticum. FISH revealed that all six blue-grained lines were wheat-T. boeoticum 4Ab (4B) disomic substitution lines. The substitution lines were validated by genotyping using the wheat 55K single nucleotide polymorphism (SNP) array containing 53,063 markers. These 4Ab (4B) substitution lines represent novel germplasm for blue-grained wheat breeding. The FISH probes and SNP markers used here can be applied in the development of blue-grained wheat-Triticum boeoticum translocation lines.

Identification and characterization of a new stripe rust resistance gene Yr83 on rye chromosome 6R in wheat.

A physical map of Secale cereale chromosome 6R was constructed using deletion mapping, and a new stripe rust resistance gene Yr83 was mapped to the deletion bin of FL 0.73-1.00 of 6RL. Rye (Secale cereale L., RR) possesses valuable genes for wheat improvement. In the current study, we report a resistance gene conferring stripe rust resistance effective from seedling to adult plant stages located on chromosome 6R. This chromosome was derived from triticale line T-701 and also carries highly effective resistance to the cereal cyst nematode species Heterodera avenae Woll. A wheat-rye 6R(6D) disomic substitution line exhibited high levels of seedling resistance to Australian pathotypes of the stripe rust (Puccinia striiformis f. sp. tritici; Pst) pathogen and showed an even greater resistance to the Chinese Pst pathotypes in the field. Ten chromosome 6R deletion lines and five wheat-rye 6R translocation lines were developed earlier in the attempt to transfer the nematode resistance gene to wheat and used herein to map the stripe rust resistance gene. These lines were subsequently characterized by sequential multicolor fluorescence in situ hybridization (mc-FISH), genomic in situ hybridization (GISH), mc-GISH, PCR-based landmark unique gene (PLUG), and chromosome 6R-specific length amplified fragment sequencing (SLAF-Seq) marker analyses to physically map the stripe rust resistance gene. The new stripe rust resistance locus was located in a chromosomal bin with fraction length (FL) 0.73-1.00 on 6RL and was named Yr83. A wheat-rye translocation line T6RL (#5) carrying the stripe rust resistance gene will be useful as a new germplasm in breeding for resistance.

A spontaneous wheat-Aegilops longissima translocation carrying Pm66 confers resistance to powdery mildew.

A spontaneous Robertsonian T4SlS·4BL translocation chromosome carrying Pm66 for powdery mildew resistance was discovered and confirmed by RNA-seq, molecular marker, and in situ hybridization analyses. Powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt) is a severe disease of bread wheat worldwide. Discovery and utilization of resistance genes to powdery mildew from wild relatives of wheat have played important roles in wheat improvement. Aegilops longissima, one of the S-genome diploid wild relatives of wheat, is a valuable source of disease and pest resistance for wheat. Chromosome 4Sl from Ae. longissima confers moderate resistance to powdery mildew. In this study, we conducted RNA-seq on a putative Chinese Spring (CS)-Ae. longissima 4Sl(4B) disomic substitution line (TA3465) to develop 4Sl-specific markers to assist the transfer of a Bgt resistance gene from 4Sl by induced homoeologous recombination. A pairwise comparison of genes between CS and TA3465 demonstrated that a number of genes on chromosome 4BS in CS were not expressed in TA3465. Analysis of 4B- and 4Sl-specific molecular markers showed that 4BS and 4SlL were both missing in TA3465, whereas 4BL and 4SlS were present. Further characterization by genomic and fluorescent in situ hybridization confirmed that TA3465 carried a spontaneous Robertsonian T4SlS·4BL translocation. Powdery mildew tests showed that TA3465 was resistant to 10 of 16 Bgt isolates collected from different regions of China, whereas CS was susceptible to all those Bgt isolates. The powdery mildew resistance gene(s) in TA3465 was further mapped to the short arm of 4Sl and designated as Pm66.

Registration of extra‐hard kernel near‐isogenic hexaploid wheat genetic stocks lacking puroindoline genes

AbstractKernel hardness (texture) is a key end‐use quality trait of wheat (Triticum spp.). Two hexaploid wheat (T. aestivum L.) near‐isogenic lines (NILs), WQL18RE5 (Reg. no. GS‐190, PI 691609) and WQL18CS5 (Reg. no. GS‐191, PI 691610), lack the puroindoline genes at the Hardness locus and thus have kernel texture phenotypes more similar to durum wheat [T. turgidum subsp. durum (Desf.) Husn.]. These two genetic stocks were produced in ‘Alpowa’ soft white spring wheat and comprise additions to an ongoing series of NILs in this soft wheat cultivar. Both NILs are advanced generation BC7F2:5 derivatives (Alpowa/donor/7*Alpowa). WQL18RE5 was derived from a Chinese Spring (CS) disomic substitution line, CS (Red Egyptian 5D), and WQL18CS5 was derived from a CS deletion line (CS5DS del.‐2) that lacks the distal portion of the short arm of chromosome 5D. These lines were developed at the USDA‐ARS Western Wheat Quality Laboratory and will be useful to study kernel texture and end‐use quality in hexaploid wheat; they can also serve as parents in developing cultivars with kernel texture equivalent to that of durum wheat.

Identification of a major dominant gene for race-nonspecific tan spot resistance in wild emmer wheat.

A single dominant gene found in tetraploid and hexaploid wheat controls broad-spectrum race-nonspecific resistance to the foliar disease tan spot caused by Pyrenophora tritici-repentis. Tan spot is an important foliar disease of durum and common wheat caused by the necrotrophic fungal pathogen Pyrenophora tritici-repentis. Genetic studies in common wheat have shown that pathogen-produced necrotrophic effectors interact with host genes in an inverse gene-for-gene manner to cause disease, but quantitative trait loci (QTLs) with broad race-nonspecific resistance also exist. Less work has been done to understand the genetics of tan spot interactions in durum wheat. Here, we evaluated a set of Langdon durum-wild emmer (Triticum turgidum ssp. dicoccoides) disomic chromosome substitution lines for reaction to four P. tritici-repentis isolates representing races 1, 2, 3, and 5 to identify wild emmer chromosomes potentially containing tan spot resistance genes. Chromosome 3B from the wild emmer accession IsraelA rendered the tan spot-susceptible durum cultivar Langdon resistant to all four fungal isolates. Genetic analysis indicated that a single dominant gene, designated Tsr7, governed resistance. Detailed mapping experiments showed that the Tsr7 locus is likely the same as the race-nonspecific QTL previously identified in the hexaploid wheat cultivars BR34 and Penawawa. Four user-friendly SNP-based semi-thermal asymmetric reverse PCR (STARP) markers cosegregated with Tsr7 and should be useful for marker-assisted selection of resistance. In addition to 3B, other wild emmer chromosomes contributed moderate levels of tan spot resistance, and, as has been shown previously for tetraploid wheat, the Tsn1-Ptr ToxA interaction was not associated with susceptibility. This is the first report of a major dominant gene governing resistance to tan spot in tetraploid wheat.

The creation and characterization of the bread wheat line with a centric translocation T2DL.2RL

The development of bread wheat introgressions with alien genetic material from cultural and wild Triticeae species is an effective method for expanding the wheat gene pool necessary for breeding. To date, numerous collections of introgressions as substitutions and chromosome modifications have been obtained; however, the creation and study of wheat with new valuable traits still remain an important line of research. Rye Secale cereale L., whose chromosomes carry genes that control valuable economic and biological characteristics and properties, is widely used to produce new wheat forms. In this study, a wheat-rye translocation obtained by backcrossing the wheat-rye disomic-substitution line 2R(2D)1 with the variety Novosibirskaya 67 was characterized. The chromosomal composition of karyotypes was studied using fluorescent in situ hybridization and C-banding. Two centric translocations, derived from two long arms of chromosomes 2D and 2R, T2DL.2RL, were identified, the remaining 40 wheat chromosomes did not undergo modifications. Meiosis in the lines was stable. Chromosomes T2DL.2RL formed bivalents in all meiocytes, which confirmed their homology. The morphological characteristics of the spike in the T2DL.2RL line and Novosibirskaya 67 did not differ. A comparative analysis of productivity between the T2DL.2RL translocation line and the parental forms, Novosibirskaya 67 and the 2R(2D)1 line, was carried out. The T2DL.2RL line is inferior to Novosibirskaya 67 in all characters with different confidence levels. The productivity characters of the 2R(2D)1 line exceeded or did not differ from those of T2DL.2RL, however, the mass of 1000 grains was significantly lower. The results showed the effect of the T2DL.2RL translocation on the trait “plant height”. This character was significantly lower than that of Novosibirskaya 67 in two vegetation periods. Consequently, the T2DL.2RL translocation reduces plant height and productivity.

Molecular cytogenetic identification of two wheat–Thinopyrum ponticum substitution lines conferring stripe rust resistance

Distant hybridizations are important for developing common wheat germplasm. Thinopyrum ponticum (2n = 10x = 70), which is a wild relative of wheat, has numerous advantages for enhancing the tolerance of plants to biotic and abiotic stresses. ES-11 and ES-12 are two stable lines derived from a cross between the Triticum aestivum–Th. ponticum partial amphiploid line Xiaoyan784 (2n = 8x = 56) and the wheat Abbondanza nullisomic lines (2n = 40) involving consecutive self-crosses and cytological marker-assisted selection. Lines ES-11 and ES-12 were characterized by a cytogenetic analysis, a sequential fluorescence in situ hybridization (FISH)–genomic in situ hybridization (GISH), and a multicolor GISH (mc-GISH) combined with an analysis of functional molecular markers. Moreover, their agronomic traits and disease resistance were evaluated. The cytogenetic results suggested that ES-11 and ES-12 contained 42 chromosomes. In ES-12, wheat chromosome 3D was replaced by a pair of Th. ponticum 3St chromosomes for a genome composition of 14A + 14B + 12D + 2(3St). In ES-11, wheat chromosome 3B and 4D were replaced by chromosomes 3St and 4 J, respectively, for a genome composition of 14A + 12B + 12D + 2(3St) +2(4J). The detected recombination between chromosomes 3St and 4J and the structural variation of chromosome 2A were due to the introduction of two pairs of Th. ponticum chromosomes. Additionally, ES-11 and ES-12 were resistant to stripe rust at the seedling and adult stages. Thus, the highly disease-resistant wheat–Th. ponticum disomic substitution line (ES-12) and double substitution line (ES-11) are potentially useful germplasms for breeding disease-resistant wheat lines.

Development of wheat—Hordeum chilense Chromosome 2Hch Introgression Lines Potentially Useful for Improving Grain Quality Traits

The chromosome 2Hch of Hordeum chilense. has the potential to improve seed carotenoid content in wheat as it carries a set of endosperm carotenoid-related genes. We have obtained structural changes in chromosome 2Hch in a common wheat (Triticum aestivum L. “Chinese Spring”) background by crossing a wheat double disomic substitution 2Hch(2D) and 7Hch(7D) line with a disomic addition line carrying chromosome 2Cc from Aegilops cylindrica Host.. Seven introgressions of chromosome 2Hch into wheat were characterized by fluorescence in situ hybridization (FISH) and DNA markers. Chromosome-specific simple sequence repeats (SSRs) were used for identifying wheat chromosomes. In addition, we tested 82 conserved orthologous set (COS) markers for homoeologous group 2, of which 65 amplified targets in H. chilense and 26 showed polymorphism between H. chilense and wheat. A total of 24 markers were assigned to chromosome 2Hch with eight allocated to 2HchS and 16 to 2HchL. Among the seven introgressions there was a disomic substitution line 2Hch(2D), a ditelosomic addition line for the 2HchL arm, an isochromosome for the 2HchL arm, a homozygous centromeric 2HchS·2DL translocation, a double monosomic 2HchS·2DL plus 7HchS·D translocation, a homozygous centromeric 7HchS·2HchL translocation and, finally, a 2HchL·7HchL translocation. Wheat—H. chilense macrosyntenic comparisons using COS markers revealed that H. chilense chromosome 2Hch exhibits synteny to wheat homoeologous group 2 chromosomes, and the COS markers assigned to this chromosome will facilitate alien gene introgression into wheat. The genetic stocks developed here include new wheat—H. chilense recombinations which are useful for studying the effect of chromosome 2Hch on grain quality traits.