Trigenomic chromosomes by recombination of <Emphasis Type="Italic">Thinopyrum intermedium </Emphasis>and <Emphasis Type="Italic">Th. ponticum </Emphasis>translocations in wheat

Rusts and barley yellow dwarf virus (BYDV) are among the main diseases affecting wheat production world wide for which wild relatives have been the source of a number of translocations carrying resistance genes. Nevertheless, along with desirable traits, alien translocations often carry deleterious genes. We have generated recombinants in a bread wheat background between two alien translocations: TC5, ex-Thinopyrum (Th) intermedium, carrying BYDV resistance gene Bdv2; and T4m, ex-Th. ponticum, carrying rust resistance genes Lr19 and Sr25. Because both these translocations are on the wheat chromosome arm 7DL, homoeologous recombination was attempted in the double hemizygote (TC5/T4m) in a background homozygous for the ph1b mutation. The identification of recombinants was facilitated by the use of newly developed molecular markers for each of the alien genomes represented in the two translocations and by studying derived F₂, F₃ and doubled haploid populations. The occurrence of recombination was confirmed with molecular markers and bioassays on families of testcrosses between putative recombinants and bread wheat, and in F₂ populations derived from the testcrosses. As a consequence it has been possible to derive a genetic map of markers and resistance genes on these previously fixed alien linkage blocks. We have obtained fertile progeny carrying new tri-genomic recombinant chromosomes. Furthermore we have demonstrated that some of the recombinants carried resistance genes Lr19 and Bdv2 yet lacked the self-elimination trait associated with shortened T4 segments. We have also shown that the recombinant translocations are fixed and stable once removed from the influence of the ph1b. The molecular markers developed in this study will facilitate selection of individuals carrying recombinant Th. intermedium–Th. ponticum translocations (Pontin series) in breeding programs. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Molecular characterization of the genomic region harboring the BYDV-resistance geneBdv2 in wheat

Barley yellow dwarf virus (BYDV) can cause significant losses of wheat worldwide. The long arm segment ofThinopyrum intermedium chromosome 7Ai#1 carrying the BYDV resistance geneBdv2 was translocated to the distal region of the long arm of wheat chromosome 7D in translocation line Yw642. In this study, 40 wheat EST sequences located in the distal region of 7DL were explored to identify specific PCR markers for theBdv2 region on the basis of the homoeologous relationship between wheat chromosome 7D and Th.intermedium chromosome 7Ai# 1. Our results revealed 8 novel EST-PCR markers specific to theBdv2 region, including 5 EST-STS markers of BE404744, BE498985, BE591497, BG606695 and BQ161842, and 3 EST-SSCP markers of BE404953, BG312663 and BE498985. These EST-PCR markers could distinguishBdv2 from another BYDV-resistance gene located onTh.intermedium chromosome 2Ai-2. These specific bands for theBdv2 region were further cloned and sequenced. The sequencing analysis indicated that the specific sequences for theBdv2 region were highly homologous with the original wheat EST sequences that were used to design primers, and encode respectively a protein kinase, P450, centrin, transducin, and a hypothetical protein. This study created a starting point for eventual cloning of theBdv2 gene and understanding the defense mechanism.     

Molecular markers show a complex mosaic pattern of wheat-Thinopyrum intermedium translocations carrying resistance to YDV

Thinopyrum intermedium translocations derived from the wheat (Triticum aestivum L.) substitution line P-29 were previously characterized by RFLP. We have further analyzed these lines and additional related germplasm with publicly available STS and SSRs. Primers which showed a polymorphism between wheat and P-29, were tested in all recombinant and nulli-tetrasomic lines confirming their position on chromosome 7D. The resulting 7D/7E chromosome maps appeared as a mosaic of wheat and Th. intermedium chromatin sections. To verify the composition of the translocation lines suggested by the RFLP-PCR map, F₂ progeny of two crosses (CS/216-1 and CS/260-1) were analyzed with molecular markers. Both populations gave an unexpectedly diverse number of recombinant individuals, suggesting that interstitial translocations occur more frequently than previously thought. This analysis also showed that there is a wide range in the number and position of the interstitial translocations within a given line such as the mosaic chromosome in recombinant line 260-1/CS-26, which has four Th. intermedium chromosome segments. Phenotypic data of the two populations suggested the presence of one gene which we have called Bdv3 to differentiate it from the previously reported orthologous gene Bdv2. Using the PCR-based molecular markers identified in this study, 5 out of 12 elite lines that showed good yields and no YDV symptoms contained Th. intermedium chromatin. Due to the multiple components involved in the YDV disease complex, combining selection for YDV resistance with the molecular markers and maps identified in this study will increase the efficiency of introgressing Th. intermedium chromatin containing YDV resistance or other beneficial traits into elite wheat germplasm.     

Research progress in BYDV resistance genes derived from wheat and its wild relatives

Barley yellow dwarf virus （BYDV） may cause a serious disease affecting wheat worldwide. True resistance to BYDV is not naturally found in wheat. BYDV resistance genes are found in more than 10 wild relative species belonging to the genera of Thinopyrum, Agropyron, Elymus, Leymus, Roegneria, and Psathyrostachy. Through wide crosses combining with cell culture, use ofph mutants, or irradiation, 3 BYDV resistance genes in Th. intermedium, including Bdv2, Bdv3 and Bdv4, were introgressed into common wheat background. Various wheat-Th, intermedium addition and substitution, translocation lines with BYDV-resistance were developed and characterized, such as 7D-TAi#1 （bearing Bdv2）, 7B-7Ai#1, 7D-7E （beating Bdv3）, and 2D-2Ai-2 （bearing Bdv4） translocations. Three wheat varieties with BYDV resistance from Th. intermedium were developed and released in Australia and China, respectively. In addition, wheat-Agropyron cristatum translocation lines, wheat-Ag, pulcherrimum addition and substitution lines, and a wheat-Leymus multicaulis addition line （line24） with different resistance genes were developed. Cytological analysis, morphological markers, biochemical markers, and molecular markers associated with the alien chromatin carrying BYDV resistance genes were identified and applied to determine the presence of alien, chromosomes or segments, size of alien chromosome segments, and compositions of the alien chromosomes. Furthermore, some resistance-related genes, such as RGA, P450, HSP70, protein kinases, centrin, and transducin, were identified, which expressed specifically in the resistance translocation lines with Bdv2. These studies lay the foundations for developing resistant wheat cultivars and unraveling the resistance mechanism against BYDV.     

Development of novel PCR markers linked to the BYDV resistance gene <Emphasis Type="Italic">Bdv2</Emphasis> useful in wheat for marker-assisted selection

The distal segment of the long arm of the Thinopyrum intermedium chromosome 7Ai1 carries the barley yellow dwarf virus (BYDV) resistance gene Bdv2. This segment was transferred to the distal region of the long arm of wheat chromosome 7D in the Yw series of translocation lines by using the ph1b mutant to induce homoeologous pairing. To transfer Bdv2 to commercial varieties, we developed two resistance gene-analog polymorphism (RGAP) markers, Tgp-1₃₅₀ and Tgp-2₂₁₀, and one randomly amplified polymorphic DNA (RAPD) marker, OPD04₁₃₀₀. The diagnostic fragments of the RGAP marker Tgp-1₃₅₀ and the RAPD marker OPD04₁₃₀₀ were cloned, sequenced and converted into sequence-characterized amplified region (SCAR) markers, named SC-gp1 and SC-D04, respectively. SC-gp1 and SC-D04 were validated based on available translocation lines and segregating F₂ individuals. Our results indicated that the SCAR markers co-segregated with the BYDV resistance associated with Bdv2. Therefore, they can be used as a low-cost, high-throughput alternative to conventional phenotypic screening in wheat-breeding programs exploiting Bdv2. The marker-assisted selection for BYDV resistance was successfully performed in a wheat-breeding program.Electronic Supplementary Material Supplementary material is available for this article at     

Development and characterization of wheat lines carrying stem rust resistance gene Sr43 derived from Thinopyrum ponticum

Key message

Wheat lines carrying Ug99-effective stem rust resistance gene Sr43 on shortened alien chromosome segments were produced using chromosome engineering, and molecular markers linked to Sr43 were identified for marker-assisted selection.

Abstract

Stem rust resistance gene Sr43, transferred into common wheat (Triticum aestivum) from Thinopyrum ponticum, is an effective gene against stem rust Ug99 races. However, this gene has not been used in wheat breeding because it is located on a large Th. ponticum 7el₂ chromosome segment, which also harbors genes for undesirable traits. The objective of this study was to eliminate excessive Th. ponticum chromatin surrounding Sr43 to make it usable in wheat breeding. The two original translocation lines KS10-2 and KS24-1 carrying Sr43 were first analyzed using simple sequence repeat (SSR) markers and florescent genomic in situ hybridization. Six SSR markers located on wheat chromosome arm 7DL were identified to be associated with the Th. ponticum chromatin in KS10-2 and KS24-1. The results confirmed that KS24-1 is a 7DS·7el₂L Robertsonian translocation as previously reported. However, KS10-2, which was previously designated as a 7el₂S·7el₂L-7DL translocation, was identified as a 7DS-7el₂S·7el₂L translocation. To reduce the Th. ponticum chromatin carrying Sr43, a BC₂F₁ population (Chinese Spring//Chinese Spring ph1bph1b*2/KS10-2) containing ph1b-induced homoeologous recombinants was developed, tested with stem rust, and genotyped with the six SSR markers identified above. Two new wheat lines (RWG33 and RWG34) carrying Sr43 on shortened alien chromosome segments (about 17.5 and 13.7 % of the translocation chromosomes, respectively) were obtained, and two molecular markers linked to Sr43 in these lines were identified. The new wheat lines with Sr43 and the closely linked markers provide new resources for improving resistance to Ug99 and other races of stem rust in wheat.     

Development and characterization of a compensating wheat-Thinopyrum intermedium Robertsonian translocation with Sr44 resistance to stem rust (Ug99)

The emergence of the highly virulent Ug99 race complex of the stem rust fungus (Puccinia graminis Pers. f. sp. tritici Eriks. and Henn.) threatens wheat (Triticum aestivum L.) production worldwide. One of the effective genes against the Ug99 race complex is Sr44, which was derived from Thinopyrum intermedium (Host) Barkworth and D.R. Dewey and mapped to the short arm of 7J (designated 7J#1S) present in the noncompensating T7DS-7J#1L?7J#1S translocation. Noncompensating wheat-alien translocations are known to cause genomic duplications and deficiencies leading to poor agronomic performance, precluding their direct use in wheat improvement. The present study was initiated to produce compensating wheat-Th. intermedium Robertsonian translocations with Sr44 resistance. One compensating RobT was identified consisting of the wheat 7DL arm translocated to the Th. intermedium 7J#1S arm resulting in T7DL?7J#1S. The T7DL?7J#1S stock was designated as TA5657. The 7DL?7J#1S stock carries Sr44 and has resistance to the Ug99 race complex. This compensating RobT with Sr44 resistance may be useful in wheat improvement. In addition, we identified an unnamed stem rust resistance gene located on the 7J#1L arm that confers resistance not only to Ug99, but also to race TRTTF, which is virulent to Sr44. However, the action of the second gene can be modified by the presence of suppressors in the recipient wheat cultivars.     

Thinopyrum 7Ai-1-derived small chromatin with Barley Yellow Dwarf Virus (BYDV) resistance gene integrated into the wheat genome with retrotransposon

Thinopyrum intermedium is a useful source of resistance genes for Barley Yellow Dwarf Virus (BYDV), one of the most damaging wheat diseases. In this study, wheat/Th. intermedium translocation lines with a BYDV resistance gene were developed using the Th. intermedium 7Ai-1 chromosome. Genomic in situ hybridization (GISH), using a Th. intermedium total genomic DNA probe, enabled detection of 7Ai-1-derived small chro-matins containing a BYDV resistance gene, which were translocated onto the end of wheat chromosomes in the lines Y95011 and Y960843. Random amplified polymorphic DNA (RAPD) analyses using 120 random 10-mer primers were conducted to compare the BYDV-resistant translocation lines with susceptible lines. Two primers amplified the DNA fragments specific to the resistant line that would be useful as molecular markers to identify 7Ai-1-derived BYDV resistance chromatin in the wheat genome. Additionally, the isolated Th. intermedium-specific retrotransposon-like sequence pTi28 can be used to identify Th. intermedium chromatin transferred to the wheat genome.     

Molecular verification and characterization of BYDV-resistant germ plasms derived from hybrids of wheat with Thinopyrum ponticum and Th. intermedium

Twenty-five partial amphiploids (2n=8x=56), which were derived from hybrids of wheat (Triticum aestivum L.) with either Thinopyrum ponticum (Podpera) Liu & Wang, Th. intermedium (Host) Barkworth & D. Dewey, or Th. junceum (L.) A. Löve, were assayed for resistance to BYDV serotype PAV by slot-blot hybridization with viral cDNA of a partial coat protein gene. Three immune lines were found among seven partial amphiploids involving Th. ponticum. Seven highly resistant lines were found in ten partial amphiploids involving Th. intermedium. None of eight partial amphiploids or 13 addition lines of Chinese Spring — Th. junceum were resistant to BYDV. Genomic in situ hybridization demonstrated that all of the resistant partial amphiploids, except TAF46, carried an alien genome most closely related to St, whether it was derived from Th. ponticum or Th. intermedium. The two partial amphiploids carrying an intact E genome of Th. ponticum are very susceptible to BYDV-PAV. In TAF46, which contains three pairs of St- and four pairs of E-genome chromo somes, the gene for BYDV resistance has been located to a modified 7 St chromosome in the addition line L1. This indicates that BYDV resistance in perennial polyploid parents, i.e., Th. ponticum and Th. intermedium, of these partial amphiploids is probably controlled by a gene(s) located on the St-genome chromosome(s).     

Direct evidence for high level of autosyndetic pairing in hybrids of Thinopyrum intermedium and Th. ponticum with Triticum aestivum

 Genomic in situ hybridization (GISH) was used to distinguish autosyndetic from allosyndetic pairing in the hybrids of Thinopyrum intermedium and Th. ponticum with Triticum aestivum cv ‘Chinese Spring’ (CS). All hybrids showed high autosyndetic pairing frequencies among wheat chromosomes and among Thinopyrum chromosomes. The high autosyndetic pairing frequencies among wheat chromosomes in both hybrids suggested that Th. intermedium and Th. ponticum carry promoters for homoeologous chromosome pairing. The higher frequencies of autosyndetic pairing among Thinopyrum chromosomes than among wheat chromosomes in both hybrids indicated that the relationships among the three genomes of Th. intermedium and among the five genomes of Th. ponticum are closer than those among the three genomes of T. aestivum. Received: 19 September 1996 / Accepted: 18 April 1997     

Radiation-induced nonhomoeologous wheat-Agropyron intermedium chromosomal translocations conferring resistance to leaf rust

Summary The Agropyron intermedium chromosome 7Ai #2 is the source of the leaf rust resistance gene Lr38 which was transferred to wheat by irradiation. The chromosomal constitutions of eight radiation-induced rust-resistant wheat-Agropyron intermedium derivatives were analyzed by C-banding and genomic in-situ hybridization (GISH). Five lines were identified as wheat Ag. intermedium chromosome translocation lines with the translocation chromosomes T2AS·2AL-7Ai#2L, T5AL · 5AS-7Ai # 2L, T1DS · 1DL-7Ai # 2L, T3DL · 3DS-7Ai#2L, and T6DS · 6DL-7Ai#2L. The sizes of the 7Ai#2L segments in mitotic metaphases of these translocations are 2.42 m, 4.20 m, 2.55 m, 2.78 m, and 4.19 m, respectively. One line was identified as a wheat-Ag. intermedium chromosome addition line. The added Ag. intermedium chromosome in this line is different from 7Ai # 2. This line has resistance to leaf rust and stem rust. Based on the rust reactions, and the C-banding and GISH results, the remaining two lines do not contain any Ag. intermedium-derived chromatin.     

Molecular characterization of durum and common wheat recombinant lines carrying leaf rust resistance (Lr19) and yellow pigment (Y) genes from Lophopyrum ponticum

Chromosome 7E from Lophopyrum ponticum carries a valuable leaf rust resistant gene designated Lr19. This gene has not been widely used in common wheat breeding because of linkage with the yellow pigment gene Y. This gene tints flour yellow, reducing its appeal in bread making. However, a high level of yellow pigment is desirable in durum wheat breeding. We produced 97 recombinant chromosomes between L. ponticum transfer 7D.7E#1 and its wheat homoeologues, using the ph1b mutation that promotes homoeologous pairing. We characterized a subset of 37 of these lines with 11 molecular markers and evaluated their resistance to leaf rust and the abundance of yellow pigment. The Lr19 gene was mapped between loci Xwg420 and Xmwg2062, whereas Y was mapped distal to Xpsr687, the most distal marker on the long arm of chromosome 7. A short terminal 7EL segment translocated to 7A, including Lr19 and Y (line 1-23), has been transferred to durum wheat by backcrossing. The presence of this alien segment significantly increased the abundance of yellow pigment. The Lr19 also conferred resistance to a new durum leaf rust race from California and Mexico that is virulent on most durum wheat cultivars. The new durum lines with the recombinant 7E segment will be useful parents to increase yellow pigment and leaf rust resistance in durum wheat breeding programs. For the common wheat breeding programs, we selected the recombinant line 1-96, which has an interstitial 7E segment carrying Lr19 but not Y. This recombinant line can be used to improve leaf rust resistance without affecting flour color. The 7EL/7DL 1-96 recombinant chromosome did not show the meiotic self-elimination previously reported for a 7EL/7BL translocation.     

Introduction of Thinopyrum intermedium ssp. trichophorum chromosomes to wheat by trigeneric hybridization involving Triticum,Secale and Thinopyrum genera

Main conclusion

Fluorescence in situ hybridization and molecular markers have confirmed that several chromosomes from Thinopyrum intermedium ssp. trichophorum have been added to a wheat background, which originated from a cross between a wheat– Thinopyrum partial amphiploid and triticale. The lines displayed blue grains and resistance to wheat stripe rust.

Thinopyrum intermedium has been used as a valuable resource for improving the disease resistance and yield potential of wheat. With the aim to transfer novel genetic variation from Th. intermedium species for sustainable wheat breeding, a new trigeneric hybrid was produced by crossing an octoploid wheat–Th. intermedium ssp. trichophorum partial amphiploid with hexaploid triticale. Fluorescence in situ hybridization (FISH) revealed that Thinopyrum chromosomes were transmitted preferably and the number of rye chromosomes tended to decrease gradually in the selfed derivatives of the trigeneric hybrids. Four stable wheat–Th. intermedium chromosome substitution, addition and translocation lines were selected, and a 2J^S addition line, two substitution lines of 4J^S(4B) and 4J(4B), and a small 4J.4B translocation line were identified by FISH and molecular markers. It was revealed that the gene(s) responsible for blue grains may located on the FL0.60–1.00 of long arm of Th. intermedium-derived 4J chromosome. Disease resistance screenings indicated that chromosomes 4J^S and 2J^S appear to enhance the resistance to stripe rust in the adult plant stage. The new germplasm with Th. intermedium introgression shows promise for utilization of Thinopyrum chromosome segments in future wheat improvement.

     

The use of cell culture for subchromosomal introgressions of barley yellow dwarf virus resistance from Thinopyrum intermedium to wheat.

Barley yellow dwarf virus (BYDV) resistance has been transferred to wheat from a group 7 chromosome of Thinopyrum (Agropyron) intermedium. The source of the resistance gene was the L1 disomic addition line, which carries the 7Ai-1 chromosome. The resistance locus is on the long arm of this chromosome. BYDV resistant recombinant lines were identified after three or more generations of selection against a group 7 Th. intermedium short arm marker (red coleoptile) and selection for the presence of BYDV resistance. One recombinant line produced by ph. mutant induced homoeologous pairing and 14 recombinant lines induced by cell culture have been identified. Resistance in seven of the cell culture induced recombinants has been inherited via pollen according to Mendelian segregation ratios for up to eight generations. Meiotic analysis of heterozygotes indicates that the alien chromatin in the cell culture induced recombinants is small enough to allow regular meiotic behaviour. The ph-induced recombinant was less regular in meiosis. A probe, pEleAcc2, originally isolated from Th. elongatum and that hybridizes to dispersed repeated DNA sequences, was utilised to detect Th. intermedium chromatin, which confers resistance to BYDV, in wheat backgrounds. Quantification of these hybridization signals indicated that the translocations involved a portion of alien chromatin that was smaller than the complete long arm of 7Ai-1. Restriction fragment length polymorphism analysis confirmed the loss of the short arm of 7Ai-1 and indicated the retention of segments of the long arm of 7Ai-1. Two 7Ai-1L DNA markers always assorted with the BYDV resistance. A third 7Ai-IL DNA marker was also present in seven of eight recombinants. In all recombinants except TC7, the 7Ai-1L markers replaced the 7DL markers. None of the wheat group 7 markers was missing from TC7. It is concluded that all the resistant lines are the result of recombination with wheat chromosome 7D, except line TC7, which is the result of recombination with an unidentified nongroup 7 chromosome.     

Resistance to eyespot of wheat, caused by Tapesia yallundae, derived from Thinopyrum intermedium homoeologous group 4 chromosome

Thinopyrum intermedium was identified previously as resistant to Tapesia yallundae, cause of eyespot of wheat. Using GUS-transformed isolates of T. yallundae as inoculum, we determined that wheat lines carrying Th. intermedium chromosome 4Ai#2 or the short arm of chromosome 4Ai#2 were as resistant to the pathogen as the eyespot-resistant wheat- Th. ponticum chromosome substitution line SS767 (PI 611939) and winter wheat cultivar Madsen, which carries gene Pch1 for eyespot resistance. Chromosome 4E from Th. elongatum and chromosome 4J from Th. bessarabicum did not confer resistance to T. yallundae. Genome-specific PCR primers confirmed the presence of Thinopyrum chromatin in these wheat- Thinopyrum lines. Genomic in situ hybridization using an St genomic probe from Pseudoroegneria strigosa demonstrated that chromosome 4Ai#2 belongs to the J^s genome of Thinopyrum. The eyespot resistance in the wheat- Th. intermedium lines is thus controlled by the short arm of this J^s chromosome. This is the first report of resistance to T. yallundae controlled by a J^s genome chromosome of Th. intermedium.     

Molecular cytogenetic characterization of two high protein wheat-<Emphasis Type="Italic">Thinopyrum intermedium</Emphasis> partial amphiploids

Fluorescence and genomic in situ hybridization (FISH and GISH) were used to establish the cytogenetic constitution of two wheat × Thinopyrum intermedium partial amphiploids H95 and 55(1-57). Both partial amphiploids are high-protein lines having resistance to leaf rust, yellow rust and powdery mildew and have in total 56 chromosomes per cell. Repetitive DNA probes (pTa71, Afa family and pSc119.2) were used to identify the individual wheat chromosomes and to reveal the distribution of these probes within the alien chromosomes. FISH detected 6B tetrasomy in H95 and a null (1D)-tetrasomy (1B) in 55(1-57). GISH was carried out using biotin labeled Th. intermedium DNA and digoxigenin labeled Pseudoroegneria spicata DNA as probes, subsequently. GISH results revealed 44 wheat chromosomes and four Thinopyrum chromosome pairs, including three S and one J chromosome pairs in line H95. Line 55(1-57), contained 42 wheat chromosomes and six Th. intermedium pairs, including two S and one J^S pairs. Additionally, two identical translocated chromosome pairs with diminished affinity to the alien chromatin were detected in both amphiploids. Another two translocations were found in 55(1-57), with satellite sections from the Thinopyrum J genome.     

Molecular mapping of leaf rust resistance gene Lr15 in hexaploid wheat

Leaf rust is a widespread and commonly occurring rust disease of wheat. Genetic resistance is the most economical method of reducing losses due to leaf rust. Lr15 has been shown to be present on wheat chromosome 2D and is reported to be a seedling resistance gene. However, tightly linked markers associated with Lr15 have not been reported to date. To identify molecular markers linked to Lr15, an F₂ mapping population of Thatcher × Thatcher-Lr15 was generated. Available wheat simple sequence repeat markers were utilized in parental screening and polymorphic markers were used to analyze the entire population of 221 plants. Phenotypic evaluations of the F₂-derived F₃ progenies with Puccinia triticina Eriks. pathotype 162A (93R15) confirmed the monogenic inheritance of Lr15. The linkage group representing chromosome 2DS was constructed at LOD 4.0 which revealed the closest flanking markers Xgwm4562 and Xgwm102 at a distance of 3.1 and 9.3 cM, respectively. Furthermore, utilization of these flanking markers in combination has successfully identified wheat lines with or without Lr15. These markers could potentially be useful in gene pyramiding with other genes to enhance rust resistance in wheat.     

Molecular Cytogenetic Characterization and Stem Rust Resistance of Five Wheat−Thinopyrum ponticum Partial Amphiploids

Partial amphiploids created by crossing common wheat (Triticum aestivum L.) and Thinopyrum ponticum (Podp.) Barkworth & D. R. Dewey are important intermediates in wheat breeding because of their resistance to major wheat diseases. In this study, we examined the chromosome compositions of five Xiaoyan-series wheat−Th. ponticum partial amphiploids (Xiaoyan 68, Xiaoyan 693, Xiaoyan 784, Xiaoyan 7430, and Xiaoyan 7631) using GISH, multicolor-GISH, and multicolor-FISH. We found several chromosome changes in these lines. For example, wheat chromosomes 1B and 2B were added in Xiaoyan 68 and Xiaoyan 7430, respectively, while wheat chromosome 6B was eliminated from Xiaoyan 693 and Xiaoyan 7631. Chromosome rearrangements were also detected in these amphiploids, including an interspecific translocation involving chromosome 4D and some intergenomic translocations, such as A–B and A–D translocations, among wheat genomes. Analysis of the Th. ponticum chromosomes in the amphiploids showed that some lines shared the same alien chromosomes. We also evaluated these partial amphiploids for resistance to nine races of stem rust, including TTKSK (commonly known as Ug99). Three lines, Xiaoyan 68, Xiaoyan 784, and Xiaoyan 7430, exhibited excellent resistance to all nine races, and could therefore be valuable sources of stem rust resistance in wheat breeding.     

Comparative analysis of <Emphasis Type="Italic">Agropyron intermedium</Emphasis> (Host) Beauv 6Ag<Superscript>i</Superscript> and 6Ag<Superscript>i</Superscript>2 chromosomes in bread wheat cultivars and lines with wheat–wheatgrass substitutions

A comparative study of wheat–wheatgrass substituted cultivars and lines resistant to leaf rust developed by the Agricultural Research Institute for Southeast Regions (Multi 6R, Belyanka, Favorit, Voevoda, Lebedushka) and Samara Agricultural Research Institute (Tulaikovskaya 5, Tulaikovskaya 10, Tulaikovskaya 100, Tulaikovskaya Zolotistaya) breeding was conducted. A complex analysis using molecular cytogenetic (C-differential banding, fluorescent (FISH) and genomic (GISH) in situ hybridization), molecular (PLUG markers), and biochemical (electrophoretic analysis of gliadins) markers demonstrated that they have a substitition of wheat chromosome 6D by the chromosomes 6Agⁱ and 6Agⁱ2 belonging to the J(=E) Agropyron intermedium (Host) Beauv (=Thinopyrum intermedium (Host) Barkworth & D.R. Dewey) subgenome. In spite of the fact that the chromosomes 6Agⁱ and 6Agⁱ2 differ in the C-banding pattern and demonstrated minor differences in the blocks of gliadin components, they had the identical pattern of pSc119.2 and pAs1 probe distribution and conjugated between themselves with insignificant disturbance. Thus, it was demonstrated that 6Agi and 6Agⁱ2 are homologous chromosomes; however, the question about allelism of their leaf rust resistance genes between themselves requires special studies. Nevertheless, using STS and SCAR markers and taking into account the type of reaction to Puccinia triticina, their non-allelism to the Lr9, Lr19, Lr24, Lr29, Lr38, and Lr47 genes was established. It was revealed that the 6Agⁱ and 6Agⁱ2 chromosomes have a different level of transmission in hybrid F₂ populations depending on the hybrid combination gene background.