Introgression Of Chromatin Research Articles

Triticum durum Desf. is a valuable source for spring bread wheat genetic diversity enhancement

Background. Enhancement of the Triticum aestivum L. genetic diversity by means of alien chromatin, including that from Triticum durum Desf., is an important element in the breeding of bread wheat cultivars that meet modern requirements.Materials and methods. The study included the L153, L154 and L155 introgressive spring bread wheat lines produced from crosses between the spring bread wheat cultivars ‘L503’ and ‘L505’ and spring durum wheat cultivars ‘Yazi10’ and ‘Tarro’ developed in Mexico. Evaluation of these introgressive lines included phytopathological, phenological, genetic, and breadmaking analyses carried out with conventional methods both under open-air and laboratory conditions. Seventeen DNA markers were used to identify genes for resistance to Puccinia triticina Erikss. f. sp. tritici in the lines. The obtained data were statistically analyzed using the Agros-2.10 package of breeding and genetic programs.Results. Studying introgressive spring bread wheat lines L153, L154 and L155, developed with the participation of durum wheat cvs. ‘Yazi10’ and ‘Tarro’, showed that leaf rust resistance of these lines was induced by the Lr genes from durum wheat cultivars. The effect of the gene donor and the recipient cultivars on a number of useful agronomic traits was identified. The recipient cv. ‘L505’ was noted for its good combining abilities.Conclusion. Introgression of chromatin from durum wheat cultivars into the spring bread wheat gene pool made it possible to produce lines resistant to the local P. triticina population, as well as to some test clones of this pathogen. Such lines can be used as donors of the Lr genes. In addition, the L154 introgressive line combined good grain productivity and baking quality.

Comparative transmission genetics of introgressed chromatin in reciprocal advanced backcross populations in Gossypium (cotton) polyploids.

Introgression is a potential source of valuable genetic variation and interspecific introgression lines are important resources for plant breeders to access novel alleles. Experimental advanced-generation backcross populations contain individuals with genomic compositions similar to those resulting from natural interspecific hybridization and provide opportunities to study the nature and transmission pattern of donor chromatin in recipient genomes. Here, we analyze transmission of donor chromatin in reciprocal backcrosses between G. hirsutum and G. barbadense. Across the genome, recurrent backcrossing in both backgrounds yielded donor chromatin at slightly higher frequencies than the Mendelian expectation in BC5F1 plants, while the average frequency of donor alleles in BC5F2 segregating families was less than expected. In the two subgenomes of polyploid cotton, the rate of donor chromatin introgression was similar. Although donor chromatin was tolerated over much of the recipient genomes, 21 regions recalcitrant to donor alleles were identified. Only limited correspondence is observed between the recalcitrant regions in the two backgrounds, suggesting the effect of species background on introgression of donor segments. Genetic breakdown was progressive, with floral abscission and seed inviability ongoing during backcrossing cycles. Regions of either high or low introgression tended to be in terminal chromosomal regions that are generally rich in both genes and crossover events, with long stretches around the centromere having limited crossover activity resulting in relatively constant low introgression frequencies. Constraints on fixation and selection of donor alleles highlights the challenges of utilizing introgression breeding in crop improvement.

Precise Identification of Chromosome Constitution and Rearrangements in Wheat-Thinopyrum intermedium Derivatives by ND-FISH and Oligo-FISH Painting.

Thinopyrum intermedium possesses many desirable agronomic traits that make it a valuable genetic source for wheat improvement. The precise identification of individual chromosomes of allohexaploid Th. intermedium is a challenge due to its three sub-genomic constitutions with complex evolutionary ancestries. The non-denaturing fluorescent in situ hybridization (ND-FISH) using tandem-repeat oligos, including Oligo-B11 and Oligo-pDb12H, effectively distinguished the St, J and JS genomes, while Oligo-FISH painting, based on seven oligonucleotide pools derived from collinear regions between barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.), was able to identify each linkage group of the Th. intermedium chromosomes. We subsequently established the first karyotype of Th. intermedium with individual chromosome recognition using sequential ND-FISH and Oligo-FISH painting. The chromosome constitutions of 14 wheat–Th. intermedium partial amphiploids and addition lines were characterized. Distinct intergenomic chromosome rearrangements were revealed among Th. intermedium chromosomes in these amphiploids and addition lines. The precisely defined karyotypes of these wheat–Th. intermedium derived lines may be helpful for further study on chromosome evolution, chromatin introgression and wheat breeding programs.

The Pros and Cons of Rye Chromatin Introgression into Wheat Genome

Rye is one of the most commonly used sources of elite genes in wheat improvement programs. Due to the high collinearity of the genomes of both cereal species, it is possible to obtain interspecific chromosomal translocations and substitution lines. Rye chromatin is used to transfer numerous genes for resistance to biotic and abiotic stresses into the wheat genome. Introgression has also resulted in improved agronomic traits. However, despite the numerous advantages, the transfer of large fragments or whole chromosomes has been quite often accompanied by a decrease in end-use quality. This paper presents an overview of the benefits and drawbacks of using rye as a source of variability in wheat breeding.

Molecular cytogenetic characterization of a novel wheat-Thinopyrum intermedium introgression line tolerant to phosphorus deficiency

Thinopyrum intermedium has been used as a resource for improving resistance to biotic and abiotic stresses and yield potential in common wheat. Wheat line SN304 was derived from a cross between common wheat cultivar Yannong 15 and Th. intermedium. Genomic in situ hybridization (GISH) produced no hybridization signal in SN304 using Th. intermedium genomic DNA as a probe, but fluorescence in situ hybridization (FISH) using oligonucleotides AFA-3, AFA-4, pAs1-1, pAs1-3, pAs1-4, pAs1-6, pSc119.2-1, and (GAA)10 as probes detected hybridization signals on chromosomes 2A, 7A, 2B, 3B, 6B, and 7B in SN304 that differed from Yannong 15. Results of specific markers also indicated that there were Th. intermedium chromatin introgressions on different chromosomes in SN304. In a hydroponic culture experiment, SN304 not only produced more biomass and higher stem and leaf dry weight but also accumulated more phosphorus than Yannong 15 under phosphorus-deficiency stress. Moreover, SN304 produced a lower pH and released more organic acids, especially oxalic acid, than Yannong 15, which suggests that SN304 exudates enabled more absorbance of P than Yannong 15 under comparable conditions. The results indicate that SN304 is a wheat-Th. intermedium introgression line with tolerance to phosphorus-deficiency stress.

Characterization of Resistance to Cereal Cyst Nematode, Agronomic Performance, and End-Use Quality Parameters in Four Perennial Wheat-Thinopyrum intermedium Lines.

Perennial wheat is considered to be a practical way to increase the flexibility and profitability of sustainable agricultural system, as it can be either a forage grass or a grain crop. Four perennial wheat lines SX12-480, SX12-787, SX12-1150, and SX12-1269 were developed from a series of interspecific crosses between common wheat (Triticum aestivum, 2n = 42) or durum wheat (T. turgidum var. durum, 2n = 28) and the intermediate wheatgrass (Thinopyrum intermedium, 2n = 42). These lines were characterized by the vigorous regrowth for at least 3 years. The one- and 2-year-old plants had higher grain yield potential than the 3-year-old perennial plants. The decline of grain yield was associated with plant age-related effects on yield components. The perennial wheat lines were all resistant to both Heterodera avenae and H. filipjevi, the two distinct cereal cyst nematode species that occur in China, except that line SX12-787 exhibited moderate resistance only to H. avenae. The dual-purpose perennial wheat lines were evaluated for quality values of both defoliated grass and harvested grains in the form of amino acid profile, mineral concentration, and contents of protein and fiber. Difference in the quality profile was observed between the perennial lines. These perennial lines had an overall improved quality levels over those of the perennial wheat control Montana-2 (T. turgidum × Th. intermedium) and the annual wheat cultivar Jinchun 9. The amplification profiles of the molecular markers provided molecular evidence for the introgression of alien chromatin. Genomic in situ hybridization detected 16, 14, 14, and 12 Th. intermedium chromosomes in lines SX12-480 (2n = 48), SX12-787 (2n = 56), SX12-1150 (2n = 56), and SX12-1269 (2n = 54), respectively, in addition to either 32 or the complete set of wheat chromosomes. The four perennial wheat-Th. intermedium lines described here provide valuable sources of perennial wheat for the dual-purpose application of both grain and forage.

Development of RNA-seq-based molecular markers for characterizing Thinopyrum bessarabicum and Secale introgressions in wheat.

Sequence-based markers have added a new dimension in the efficiency of identifying alien introgressions in wheat. Expressed sequence tag-sequence tagged sites (EST-STS) markers have proved useful in tracing alien chromatin. In this study, we report the development of Thinopyrum bessarabicum- and Secale anatolicum-specific EST-STS markers and their application in tracing respective alien chromatin introgressions in wheat. The parental lines, Chinese Spring (CS), ISR991.1 (CS/Th. bessarabicum amphidiploid), and ISR1049.2 (CS/Secale anatolicum amphidiploid), were used as core experimental materials. Using comparative analysis of RNA-Seq data, 10 903 and 10 660 candidate sequences specific to Th. bessarabicum and S. anatolicum, respectively, were assembled and identified. To validate the genome specificity of these candidate sequences, 68 and 64 EST-STS markers were developed from randomly selected candidate sequences of Th. bessarabicum and S. anatolicum, respectively, and tested on sets of alien addition lines. Fifty-five and 53 markers for Th. bessarabicum and S. anatolicum chromatin, respectively, were assigned to chromosomal location(s), covering all seven chromosomes. Approximately 83% of S. anatolicum-specific markers were transferable to S. cereale. The genome-specific candidate sequences identified and the EST-STS markers developed will be valuable resources for exploitation of Th. bessarabicum and Secale species diversity in wheat and triticale breeding.

Genome-wide impacts of alien chromatin introgression on wheat gene transcriptions

Agronomic characteristics and tolerance to biotic and abiotic stresses in hexaploid wheat can be drastically improved through wheat-alien introgression. However, the transcriptional level interactions of introduced alien genes in the wheat genetic background is rarely investigated. In this study, we report the genome-wide impacts of introgressed chromosomes derived from Ae. longissima on gene transcriptions of the wheat landrace Chinese Spring. RNA-seq analyses demonstrated 5.37% and 4.30% of the genes were significantly differentially expressed (DEGs) in CS-Ae. longissima disomic 3Sl#2(3B) substitution line TA3575 and disomic 6Sl#3 addition line TA7548, respectively when compared to CS. In addition, 561 DEGs, including 413 up-regulated and 148 down-regulated or not transcribed genes, were simultaneously impacted by introgressed chromosomes 3Sl#2 and 6Sl#3, which accounts for 41.25% of the DEGs in TA3575 and 38.79% in TA7548. Seventeen DEGs, annotated as R genes, were shared by both introgression lines carrying chromosomes 3Sl#2 and 6Sl#3, which confer resistance to powdery mildew. This study will benefit the understanding of the wheat gene responses as result of alien gene(s) or chromosome intogression and the plant defense response initiated by powdery mildew resistance genes in chromosomes 3Sl#2 and 6Sl#3.

Introgression Analysis and Morphological Characterization of an Arachis hypogaea × A. diogoi Interspecific Hybrid Derived Population

Cultivated peanut (Arachis hypogaea L.) is an economically important crop grown around the world. Compared with the entire Arachis genus, cultivated peanut germplasm has low levels of genetic diversity for several economically important traits, resulting in the need for alternative sources of favorable alleles. Wild diploid species of Arachis are a source of such alleles to improve cultivated peanut for many economically important traits. An A. hypogaea × A. diogoi Hoehne introgression population was produced via the triploid–hexaploid method; the fourth generation after tetraploidy was used to initiate this study. The introgression lines were genotyped using a single nucleotide polymorphism (SNP) marker array to estimate the percentage of A. diogoi chromatin introgression. Morphologically, the introgression lines varied for an array of measured traits, with the majority being intermediate to the two parents. The average amount of A. diogoi genome introgressed was 8.12% across the tetraploid genome and ranged from 3.00 to 18.14% on individual chromosomes. The average A. diogoi introgression across all lines was 7.70% and ranged from 0.17 to 51.12%. Principal component analysis of morphological data and SNP markers revealed similarities and groupings of introgression lines. This introgression population demonstrates the potential of using wild diploid Arachis species for peanut improvement and has great potential for use in cultivated peanut breeding programs.

Complex characterization of oat (Avena sativa L.) lines obtained by wide crossing with maize (Zea mays L.).

BackgroundThe oat × maize addition (OMA) lines are used for mapping of the maize genome, the studies of centromere-specific histone (CENH3), gene expression, meiotic chromosome behavior and also for introducing maize C4 photosynthetic system to oat. The aim of our study was the identification and molecular-cytogenetic characterization of oat × maize hybrids.MethodsOat DH lines and oat × maize hybrids were obtained using the wide crossing of Avena sativa L. with Zea mays L. The plants identified as having a Grande-1 retrotransposon fragment, which produced seeds, were used for genomic in situ hybridization (GISH).ResultsA total of 138 oat lines obtained by crossing of 2,314 oat plants from 80 genotypes with maize cv. Waza were tested for the presence of maize chromosomes. The presence of maize chromatin was indicated in 66 lines by amplification of the PCR product (500 bp) generated using primers specific for the maize retrotransposon Grande-1. Genomic in situ hybridization (GISH) detected whole maize chromosomes in eight lines (40%). All of the analyzed plants possessed full complement of oat chromosomes. The number of maize chromosomes differed between the OMA lines. Four OMA lines possessed two maize chromosomes similar in size, three OMA—one maize chromosome, and one OMA—four maize chromosomes. In most of the lines, the detected chromosomes were labeled uniformly. The presence of six 45S rDNA loci was detected in oat chromosomes, but none of the added maize chromosomes in any of the lines carried 45S rDNA locus. Twenty of the analyzed lines did not possess whole maize chromosomes, but the introgression of maize chromatin in the oat chromosomes. Five of 66 hybrids were shorter in height, grassy type without panicles. Twenty-seven OMA lines were fertile and produced seeds ranging in number from 1–102 (in total 613). Sixty-three fertile DH lines, out of 72 which did not have an addition of maize chromosomes or chromatin, produced seeds in the range of 1–343 (in total 3,758). Obtained DH and OMA lines were fertile and produced seeds.DiscussionIn wide hybridization of oat with maize, the complete or incomplete chromosomes elimination of maize occur. Hybrids of oat and maize had a complete set of oat chromosomes without maize chromosomes, and a complete set of oat chromosomes with one to four retained maize chromosomes.

RNA-seq facilitates development of chromosome-specific markers and transfer of rye chromatin to wheat

Transcriptome shotgun sequencing (RNA-seq) provides an abundant resource for developing molecular markers specifically related to functional genes. In this study, transcriptomes of Chinese rye cultivar Jingzhouheimai (JZHM) challenged with powdery mildew pathogen Bgt (Blumeria graminis f. sp. tritici) were obtained and used to develop expressed sequence tag (EST)-based simple sequence repeat (SSR) and sequence-tagged site (STS) markers. A total of 866 primer sets for EST-SSRs and STSs were designed, from which we developed 401 rye-specific markers. The highest level of polymorphism was observed in EST-SSRs (56.73%) followed by STS2 (49.07%) designed via rye-specific contigs and STS1 (35.90%) primers designed from upregulated contigs. Genotyping with newly developed markers along with cytogenetic techniques allowed us to identify nine wheat alien chromosome lines from the cross of Zhoumai 18/Jinghui 1 (Jinghui 1 is an amphiploid of wheat landrace Huixianhong and JZHM) carrying rye chromosome 6R or 6R segments of different length, which permitted preliminary location of the powdery mildew resistance gene PmJZHM6RL and 12 specific markers to 6RL FL 0.51–1.0. 5R-specific markers and genomic in situ hybridization/fluorescence in situ hybridization detected MtA5RL and T5AS·5AL-5RL chromosomes among 41 F5 plants from the cross CS ph1bph1b/MA5R, and aberrations permitted the location of the hairy peduncle gene (Hp) and marker XLFZ3473 to the region 5RL FL 0.78–1.0 with another nine markers locating to 5RL 0.0–0.78. The chromosome-specific markers and chromosome aberrations developed in this study will facilitate the introgression of rye chromatin into wheat.

A resource of large-scale molecular markers for monitoring Agropyron cristatum chromatin introgression in wheat background based on transcriptome sequences

Agropyron cristatum is a wild grass of the tribe Triticeae and serves as a gene donor for wheat improvement. However, very few markers can be used to monitor A. cristatum chromatin introgressions in wheat. Here, we reported a resource of large-scale molecular markers for tracking alien introgressions in wheat based on transcriptome sequences. By aligning A. cristatum unigenes with the Chinese Spring reference genome sequences, we designed 9602 A. cristatum expressed sequence tag-sequence-tagged site (EST-STS) markers for PCR amplification and experimental screening. As a result, 6063 polymorphic EST-STS markers were specific for the A. cristatum P genome in the single-receipt wheat background. A total of 4956 randomly selected polymorphic EST-STS markers were further tested in eight wheat variety backgrounds, and 3070 markers displaying stable and polymorphic amplification were validated. These markers covered more than 98% of the A. cristatum genome, and the marker distribution density was approximately 1.28 cM. An application case of all EST-STS markers was validated on the A. cristatum 6 P chromosome. These markers were successfully applied in the tracking of alien A. cristatum chromatin. Altogether, this study provided a universal method of large-scale molecular marker development to monitor wild relative chromatin in wheat.

Segregation distortion and genome-wide digenic interactions affect transmission of introgressed chromatin from wild cotton species

This study reports transmission genetics of chromosomal segments into Gossypium hirsutum from its most distant euploid relative, Gossypium mustelinum . Mutilocus interactions and structural rearrangements affect introgression and segregation of donor chromatin. Wild allotetraploid relatives of cotton are a rich source of genetic diversity that can be used in genetic improvement, but linkage drag and non-Mendelian transmission genetics are prevalent in interspecific crosses. These problems necessitate knowledge of transmission patterns of chromatin from wild donor species in cultivated recipient species. From an interspecific cross, Gossypium hirsutum × Gossypium mustelinum, we studied G. mustelinum (the most distant tetraploid relative of Upland cotton) allele retention in 35 BC3F1 plants and segregation patterns in BC3F2 populations totaling 3202 individuals, using 216 DNA marker loci. The average retention of donor alleles across BC3F1 plants was higher than expected and the average frequency of G. mustelinum alleles in BC3F2 segregating families was less than expected. Despite surprisingly high retention of G. mustelinum alleles in BC3F1, 46 genomic regions showed no introgression. Regions on chromosomes 3 and 15 lacking introgression were closely associated with possible small inversions previously reported. Nonlinear two-locus interactions are abundant among loci with single-locus segregation distortion, and among loci originating from one of the two subgenomes. Comparison of the present results with those of prior studies indicates different permeability of Upland cotton for donor chromatin from different allotetraploid relatives. Different contributions of subgenomes to two-locus interactions suggest different fates of subgenomes in the evolution of allotetraploid cottons. Transmission genetics of G. hirsutum × G. mustelinum crosses reveals allelic interactions, constraints on fixation and selection of donor alleles, and challenges with retention of introgressed chromatin for crop improvement.

Chromosomal location of genes for resistance to powdery mildew in Agropyron cristatum and mapping of conserved orthologous set molecular markers

Agropyron cristatum exhibits resistance to Blumeria graminis f. sp. tritici. Disomic and ditelosomic chromosome addition lines of A. cristatum in ‘Chinese Spring’ wheat were utilized to determine which A. cristatum chromosomes carry resistance gene(s). Resistance is conferred by gene(s) on chromosome arms 2PL and 6PL. The availability of molecular markers capable of detecting these chromosome arms in a wheat background would be very useful for marker-assisted introgression of 2PL and 6PL chromatin into common wheat. With this aim, 170 wheat conserved orthologous set (COS) markers (92 and 78 from wheat homoeologous groups 2 and 6 respectively) were assessed for their utility in A. cristatum. A total of 116 (68.2%) COS markers successfully amplified product in A. cristatum and 46 (40.0%) of these markers were polymorphic between A. cristatum and common wheat. From marker loci mapping on wheat homoeologous group 2 chromosomes, 23 markers (34.9%) were polymorphic between A. cristatum and common wheat and from them 13 markers were assigned to chromosome arm 2PL and six markers were mapped to chromosome 4P of A. cristatum showing that this chromosome is related to wheat homoeologous group 2. From marker loci mapping on wheat homoeologous group 6 chromosomes, 23 (46.0%) markers were polymorphic between A. cristatum and common wheat and from them 17 markers were located on chromosome 6P, six of them were mapped to chromosome arm 6PS and five to chromosome arm 6PL, respectively. The specific COS markers allocated on the long arms of chromosomes 2P and 6P may have a role in marker-assisted screening in wheat breeding for powdery mildew disease resistance.

Heterosis, transmission genetics, and selection for increased growth rate in a N. tabacum × synthetic tobacco cross

Cultivated tobacco (Nicotiana tabacum L.) is a classic amphidiploid, and hybrids between this cultivated species and closely related diploid Nicotiana relatives often exhibit heterotic effects for growth rate and yield. Crosses between N. tabacum and synthetic tobaccos, 4x(Nicotiana sylvestris × Nicotiana otophora) or 4x(N. sylvestris × Nicotiana tomentosiformis), may provide superior routes for genome-wide introgression from diploid relatives and allow increased potential to capitalize on heterotic effects in tobacco. Significant levels of mid-parent heterosis were observed for yield and growth rate in F1 hybrids between synthetic tobaccos and a standard tobacco cultivar. Microsatellite marker genotyping of an F2 population derived from a K326 × [4x(N. sylvestris × N. otophora)] cross was carried out to preliminarily investigate the relative importance of different types of gene action on observed heterosis in the original interspecific cross. Results suggested a role for both partial dominance and overdominance. Marker genotyping also indicated an overall reduced level of recombination in the N. tabacum × synthetic tobacco cross relative to a N. tabacum × N. tabacum cross but no evidence of genomic regions with severely restricted levels of recombination. Results suggest that populations derived from N. tabacum × synthetic tobacco crosses may be more efficient for introgressing germplasm from diploid relatives, as compared to populations derived from crosses between N. tabacum and diploid forms where preferential pairing between N. tabacum homologues can reduce the potential for introgression of alien chromatin. Such materials may be useful as sources of favorable alleles influencing quantitative characters in tobacco.

Advanced Backcross Quantitative Trait Loci (QTL) Analysis of Oil Concentration and Oil Quality Traits in Peanut (Arachis hypogaea L.)

Peanut seed oil is an important commodity worldwide and breeding efforts have been to improve both the quality and quantity of oil produced. Identifying sources of variation and elucidating the genetics of oil concentration and quality in peanut is essential to advancing the development of improved genotypes. The objective of this study was to discover QTLs for oil traits in an advanced backcross population derived from a cross between a wild-species derived amphidiploid, TxAG-6, and a cultivated genotype, Florunner. A BC1F1 population was developed for genetic mapping and an advanced backcross BC3F6 population was phenotyped in three environments and genotyped using SSR markers. Composite interval mapping results identified three genomic regions associated with oil concentration in a combined analysis. Marker PM36, associated with oil concentration and multiple fatty acids in this study, mapped directly to a HD-ZIP transcription factor in diploid Arachis genome sequences. For fatty acid concentrations, results suggested 17 QTLs identified in two or more environments, 15 of which were present across environments. Fourteen genomic regions on 13 linkage groups contained significant QTLs for more than one trait, suggesting that same genes or gene families are responsible for multiple phenotypes. QTLs and the genes identified in this study could be effective tools in marker-assisted breeding targeted at pyramiding seed oil alleles from wild-species while minimizing introgression of non-target chromatin.

A new 2DS·2RL Robertsonian translocation transfers stem rust resistance gene Sr59 into wheat.

A new stem rust resistance gene Sr59 from Secale cereale was introgressed into wheat as a 2DS·2RL Robertsonian translocation. Emerging new races of the wheat stem rust pathogen (Puccinia graminis f. sp. tritici), from Africa threaten global wheat (Triticum aestivum L.) production. To broaden the resistance spectrum of wheat to these widely virulent African races, additional resistance genes must be identified from all possible gene pools. From the screening of a collection of wheat-rye (Secale cereale L.) chromosome substitution lines developed at the Swedish University of Agricultural Sciences, we described the line 'SLU238' 2R (2D) as possessing resistance to many races of P. graminis f. sp. tritici, including the widely virulent race TTKSK (isolate synonym Ug99) from Africa. The breakage-fusion mechanism of univalent chromosomes was used to produce a new Robertsonian translocation: T2DS·2RL. Molecular marker analysis and stem rust seedling assays at multiple generations confirmed that the stem rust resistance from 'SLU238' is present on the rye chromosome arm 2RL. Line TA5094 (#101) was derived from 'SLU238' and was found to be homozygous for the T2DS·2RL translocation. The stem rust resistance gene on chromosome 2RL arm was designated as Sr59. Although introgressions of rye chromosome arms into wheat have most often been facilitated by irradiation, this study highlights the utility of the breakage-fusion mechanism for rye chromatin introgression. Sr59 provides an additional asset for wheat improvement to mitigate yield losses caused by stem rust.

Cytological and morphological characterization of rye-wheat derivatives for important agronomic traits

Ninety two derivatives derived from rye-wheat crosses were analyzed for their rye chromosome/chromatin constitution using molecular cytogenetic tools FISH and GISH, to detect targeted rye chromatin introgression with minimum linkage drag. Of the 92 recombinants lines analyzed, 17 exhibited one pair of rye chromosome substituting different chromosomes of A, B, and D genomes, 10 lines showed substitution and translocations at the same time and 55 lines had 1BL.1RS translocations. Four lines that had more than 10 chromosomes from rye were alike triticale, whereas remaining six lines exhibited no rye chromatin/chromosome. These lines were evaluated for different agronomic traits such as days to maturity, type of spike, colour of spike, compactness of spike etc. for ascertaining correlation between rye chromatin with morphological traits.

Marker Assisted Transfer of Two Powdery Mildew Resistance Genes PmTb7A.1 and PmTb7A.2 from Triticum boeoticum (Boiss.) to Triticum aestivum (L.).

Powdery mildew (PM), caused by Blumeria graminis f. sp. tritici, is one of the important wheat diseases, worldwide. Two PM resistance genes, designated as PmTb7A.1 and PmTb7A.2, were identified in T. boeoticum acc. pau5088 and mapped on chromosome 7AL approximately 48cM apart. Two resistance gene analogue (RGA)-STS markers Ta7AL-4556232 and 7AL-4426363 were identified to be linked to the PmTb7A.1 and PmTb7A.2, at a distance of 0.6cM and 6.0cM, respectively. In the present study, following marker assisted selection (MAS), the two genes were transferred to T. aestivum using T. durum as bridging species. As many as 12,317 florets of F1 of the cross T. durum /T. boeoticum were pollinated with T. aestivum lines PBW343-IL and PBW621 to produce 61 and 65 seeds, respectively, of three-way F1. The resulting F1s of the cross T. durum/T. boeoticum//T. aestivum were screened with marker flanking both the PM resistance genes PmTb7A.1 and PmTb7A.2 (foreground selection) and the selected plants were backcrossed to generate BC1F1. Marker assisted selection was carried both in BC1F1 and the BC2F1 generations. Introgression of alien chromatin in BC2F1 plants varied from 15.4 - 62.9 percent. Out of more than 110 BC2F1 plants showing introgression for markers linked to the two PM resistance genes, 40 agronomically desirable plants were selected for background selection for the carrier chromosome to identify the plants with minimum of the alien introgression. Cytological analysis showed that most plants have chromosome number ranging from 40-42. The BC2F2 plants homozygous for the two genes have been identified. These will be crossed to generate lines combining both the PM resistance genes but with minimal of the alien introgression. The PM resistance gene PmTb7A.1 maps in a region very close to Sr22, a stem rust resistance gene effective against the race Ug99. Analysis of selected plants with markers linked to Sr22 showed introgression of Sr22 from T. boeoticum in several BC2F1 plants. Thus, in addition to PM resistance, these progeny might also carry resistance to stem rust race Ug99.

Development and utilization of new sequenced characterized amplified region markers specific for E genome of Thinopyrum

Species containing E genome of Thinopyrum offered potential to increase the genetic variability and desirable characters for wheat improvement. However, E genome specific marker was rare. The objective of the present report was to develop and identify sequenced characterized amplified region (SCAR) markers that can be used in detecting E chromosome in wheat background for breeding purpose. Total 280 random amplified polymorphic DNA (RAPD) primers were amplified for seeking of E genome specific fragments by using the genomic DNA of Thinopyrum elongatum and wheat controls as templates. As a result, six RAPD fragments specific for E genome were found and cloned, and then were converted to SCAR markers. The usability of these markers was validated using a number of E- genome-containing species and wheat as controls. These markers were subsequently located on E chromosomes using specific PCR and fluorescence in situ hybridization (FISH). SCAR markers developed in this research could be used in molecular marker assisted selection of wheat breeding with Thinopyrum chromatin introgressions.