Phylogeny and genetic diversity of D-genome species of Aegilops and Triticum (Triticeae, Poaceae) from Iran based on microsatellites, ITS, and trnL-F

Cereal species of the grass tribe Triticeae are economically important and provide staple food for large parts of the human population. The Fertile Crescent of Southwest Asia harbors high genetic and morphological diversity of these species. In this study, we analyzed genetic diversity and phylogenetic relationships among D genome-bearing species of the wheat relatives of the genus Aegilops from Iran and adjacent areas using allelic diversity at 25 nuclear microsatellite loci, nuclear rDNA ITS, and chloroplast trnL-F sequences. Our analyses revealed high microsatellite diversity in Aegilops tauschii and the D genomes of Triticum aestivum and Ae. ventricosa, low genetic diversity in Ae. cylindrica, two different Ae. tauschii gene pools, and a close relationship among Ae. crassa, Ae. juvenalis, and Ae. vavilovii. In the latter species group, cloned sequences revealed high diversity at the ITS region, while in most other polyploids, homogenization of the ITS region towards one parental type seems to have taken place. The chloroplast genealogy of the trnL-F haplotypes showed close relationships within the D genome Aegilops species and T. aestivum, the presence of shared haplotypes in up to three species, and up to three different haplotypes within single species, and indicates chloroplast capture from an unidentified species in Ae. markgrafii. The ITS phylogeny revealed Triticum as monophyletic and Aegilops as monophyletic when Amblyopyrum muticum is included.     

Insight into the genetic variability analysis and relationships among some Aegilops and Triticum species,as genome progenitors of bread wheat,using SCoT markers

We assessed the molecular genetic diversity and relationships among some Aegilops and Triticum species using 15 start codon-targeted (SCoT) polymorphism markers. A total of 166 bands amplified, of which 164 (98.79%) were polymorphic. Analysis of molecular variance and inter-population differentiation (Gst) indicated high genetic variation within the studied populations. Our analyses revealed high genetic diversity in T. boeoticum, Ae. cylindrica, T. durum and Ae. umbellulata, low diversity in Ae. crassa, Ae. caudata and Ae. speltoides, and a close relationship among Ae. tauschii, T. aestivum, T. durum, T. urartu, and T. boeoticum. Cluster analysis indicated 180 individuals divided into 8 genome homogeneous clades and 11 sub-groups. T. aestivum and T. durum accessions were grouped together, and accessions with the C and U genomes were grouped into the same clade. Our results support the hypothesis that T. urartu and Ae. tauschii are two diploid ancestors of T. aestivum, and also that Ae. caudata and Ae. umbellulata are putative donors of C and U genomes for other Aegilops species that possess these genomes. Our results also revealed that the SCoT technique is informative and can be used to assess genetic relationships among wheat germplasm.     

Introgression of wheat DNA markers from A, B and D genomes in early generation progeny of Aegilops cylindrica Host × Triticum aestivum L. hybrids

Introgression from allohexaploid wheat (Triticum aestivum L., AABBDD) to allotetraploid jointed goatgrass (Aegilops cylindrica Host, CCDD) can take place in areas where the two species grow in sympatry and hybridize. Wheat and Ae. cylindrica share the D genome, issued from the common diploid ancestor Aegilops tauschii Coss. It has been proposed that the A and B genome of bread wheat are secure places to insert transgenes to avoid their introgression into Ae. cylindrica because during meiosis in pentaploid hybrids, A and B genome chromosomes form univalents and tend to be eliminated whereas recombination takes place only in D genome chromosomes. Wheat random amplified polymorphic DNA (RAPD) fragments, detected in intergeneric hybrids and introgressed to the first backcross generation with Ae. cylindrica as the recurrent parent and having a euploid Ae. cylindrica chromosome number or one supernumerary chromosome, were assigned to wheat chromosomes using Chinese Spring nulli-tetrasomic wheat lines. Introgressed fragments were not limited to the D genome of wheat, but specific fragments of A and B genomes were also present in the BC1. Their presence indicates that DNA from any of the wheat genomes can introgress into Ae. cylindrica. Successfully located RAPD fragments were then converted into highly specific and easy-to-use sequence characterised amplified regions (SCARs) through sequencing and primer design. Subsequently these markers were used to characterise introgression of wheat DNA into a BC1S1 family. Implications for risk assessment of genetically modified wheat are discussed.     

Phylogenetic Relationships and Intraspecific Variation of D-Genome Aegilops L. as Revealed by RAPD Analysis

RAPD analysis was carried out to study the genetic variation and phylogenetic relationships of polyploid Aegilops species, which contain the D genome as a component of the alloploid genome, and diploid Aegilops tauschii, which is a putative donor of the D genome for common wheat. In total, 74 accessions of six D-genome Aegilops species were examined. The highest intraspecific variation (0.03–0.21) was observed for Ae. tauschii. Intraspecific distances between accessions ranged 0.007–0.067 in Ae. cylindrica, 0.017–0.047 in Ae. vavilovii, and 0–0.053 inAe. juvenalis.Likewise, Ae. ventricosaand Ae. crassa showed low intraspecific polymorphism. The among-accession difference in alloploidAe. ventricosa (genome D^vN^v) was similar to that of one parental species, Ae. uniaristata (N), and substantially lower than in the other parent, Ae. tauschii (D). The among-accession difference in Ae. cylindrica(C^cD^c) was considerably lower than in either parent, Ae. tauschii (D) orAe. caudata (C). With the exception of Ae. cylindrica, all D-genome species—Ae. tauschii (D),Ae. ventricosa (D^vN^v), Ae. crassa (X^crD^cr1 and X^crD^cr1D^cr2), Ae. juvenalis (X^jD^jU^j), andAe. vavilovii (X^vaD^vaS^va)—formed a single polymorphic cluster, which was distinct from clusters of other species. The only exception, Ae. cylindrica(C^cD^c), did not group with the other D-genome species, but clustered withAe. caudata (C), a donor of the C genome. The cluster of these two species was clearly distinct from the cluster of the other D-genome species and close to a cluster of Ae. umbellulata (genome U) and Ae. ovata (genome U^gM^g). Thus, RAPD analysis for the first time was used to estimate and to compare the interpopulation polymorphism and to establish the phylogenetic relationships of all diploid and alloploid D-genome Aegilops species.     

Phylogenetic analysis of the dimeric alpha-amylase inhibitor sequences from an orthologous region in 21 different genomes of the tribe Triticeae (Poaceae)

Six hundred and thirty gene sequences from 21 different genomes in Triticeae tribe were obtained and subjected to phylogenetic analysis. The sequences showed high homology in both nucleotide sequences and length variation, and had a common conserved cysteine skeleton C–Xn–C–Xn–C–Xn–CC–Xn–C–X–C–Xn–C–Xn–C–Xn–C. The sequences from common wheat formed three clusters; two were close to Aegilops tauschii and Aegilops speltoides sequences, respectively, and the third cluster was complex with sequences from Ae. speltoides, Aegilops searsii, and Aegilops bicornis. Different S genome(s) of Aegilops contributed α-amylase inhibitor loci to polyploid wheat by gene introgression in interspecific hybridizations. No sequence from common wheat was similar to that from einkorn wheat. We conclude that the occurrence of multiple chromosomal translocations or inversions in the different genomes of Triticeae had not dramatically affected the primary structure of dimeric α-amylase inhibitors. The results revealed important information on genome shaping events and processes occurring at the dimeric α-amylase inhibitor genes loci and their bearing on the phylogenetic relationships in the tribe Triticeae (Poaceae).     

Unreduced gamete formation in wheat × <Emphasis Type="Italic">Aegilops</Emphasis> spp. hybrids is genotype specific and prevented by shared homologous subgenomes

Key message

The presence of homologous subgenomes inhibited unreduced gamete formation in wheat × Aegilops interspecific hybrids. Unreduced gamete rates were under the control of the wheat nuclear genome.

Abstract

Production of unreduced gametes is common among interspecific hybrids, and may be affected by parental genotypes and genomic similarity. In the present study, five cultivars of Triticum aestivum and two tetraploid Aegilops species (i.e. Ae. triuncialis and Ae. cylindrica) were reciprocally crossed to produce 20 interspecific hybrid combinations. These hybrids comprised two different types: T. aestivum × Aegilops triuncialis; 2n = ABDU^tC^t (which lack a common subgenome) and T. aestivum × Ae. cylindrica; 2n = ABDD^cC^c (which share a common subgenome). The frequency of unreduced gametes in F₁ hybrids was estimated in sporads from the frequency of dyads, and the frequency of viable pollen, germinated pollen and seed set were recorded. Different meiotic abnormalities recorded in the hybrids included precocious chromosome migration to the poles at metaphase I and II, laggards in anaphase I and II, micronuclei and chromosome stickiness, failure in cell wall formation, premature cytokinesis and microspore fusion. The mean frequency of restitution meiosis was 10.1 %, and the mean frequency of unreduced viable pollen was 4.84 % in T. aestivum × Ae. triuncialis hybrids. By contrast, in T. aestivum × Ae. cylindrica hybrids no meiotic restitution was observed, and a low rate of viable gametes (0.3 %) was recorded. This study present evidence that high levels of homologous pairing between the D and D^c subgenomes may interfere with meiotic restitution and the formation of unreduced gametes. Variation in unreduced gamete production was also observed between T. aestivum × Ae. triuncialis hybrid plants, suggesting genetic control of this trait.

     

Homoeologous relationships of Aegilops speltoides chromosomes to bread wheat

 Homoeologous pairing at metaphase I was analysed in the standard-type, ph2b and ph1b hybrids of Triticum aestivum (AABBDD) and Aegilops speltoides (SS). Data from relative pairing affinities were used to predict homoeologous relationships of Ae. speltoides chromosomes to wheat. Chromosomes of both species, and their arms, were identified by C-banding. The Ae. speltoides genotype carried genes that induced a high level of homoeologous pairing in the three types of hybrids analyzed. All arms of the seven chromosomes of the S genome showed normal homoeologous pairing, which implies that no apparent chromosome rearrangements occurred in the evolution of Ae. speltoides relative to wheat. A pattern of preferential pairing of two types, A-D and B-S, confirmed that the S genome is very closely related to the B genome of wheat. Although this pairing pattern was also reported in hybrids of wheat with Ae. longissima and Ae. sharonensis, a different behaviour was found in group 5 chromosomes. In the hybrids of Ae. speltoides, chromosome 5B-5S pairing was much more frequent than 5D-5S, while these chromosome associations reached similar frequencies in the hybrids of Ae. longissima and Ae. sharonensis. These results are in agreement with the hypothesis that the B genome of wheat is derived from Ae. speltoides. Received: 8 January 1998 / Accepted: 4 February 1998     

Metaphase I-bound arms frequency and genome analysis in wheat-Aegilops hybrids. 3. Similar relationships between the B genome of wheat and S or S l genomes of Ae. speltoides,Ae. longissima and Ae. sharonensis

The meiotic behaviour of Triticum aestivum × Aegilops speltoides, T. aestivum × Ae. sharonensis and T. aestivum × Ae. longissima tetraploid hybrids (genome constitution ABDS, ABDS ^l , and ABDS ^l , respectively) has been analysed by the C-banding technique. Of the six types of pairing normally occurring, at metaphase I three were recognized: A-D, AD-BS/AD-BS ^l and B-S/B-S ^l . The relative order observed in the low pairing hybrid, A-D> B-S ^l >AD-BS ^l , as well as that found in high-pairing Chinese Spring × Ae. speltoides hybrids, A-D>AD-BS>ß-S, revealed the existence of preferential pairing patterns among the different genomes that are in competition. In all of the hybrids analysed the mean number of bound arms per cell for the A-D type was significantly higher than the mean number of associations between the B and S/S ^l genomes. Usually the relative contribution of each type of pairing is maintained among hybrids with different Aegilops species. These results indicate that the genomes of Ae. speltoides, Ae. sharonensis and Ae. longissima show a similar affinity with the genomes of hexaploid wheat; therefore none of these species can be considered to be a distinct donor of the B genome of wheats.     

A high-density genetic linkage map of Aegilops tauschii, the D-genome progenitor of bread wheat

 Aegilops tauschii is the diploid D-genome progenitor of bread wheat (Triticum aestivum L. em Thell, 2n=6x=42, AABBDD). A genetic linkage map of the Ae. tauschii genome was constructed, composed of 546 loci. One hundred and thirty two loci (24%) gave distorted segregation ratios. Sixty nine probes (13%) detected multiple copies in the genome. One hundred and twenty three of the 157 markers shared between the Ae. tauschii genetic and T. aestivum physical maps were colinear. The discrepancy in the order of five markers on the Ae. tauschii 3DS genetic map versus the T. aestivum 3D physical map indicated a possible inversion. Further work is needed to verify the discrepancies in the order of markers on the 4D, 5D and 7D Ae. tauschii genetic maps versus the physical and genetic maps of T. aestivum. Using common markers, 164 agronomically important genes were assigned to specific regions on Ae. tauschii linkage, and T. aestivum physical, maps. This information may be useful for map-based cloning and marker-assisted plant breeding. Received: 23 March 1998 / Accepted: 27 October 1998     

Additive genetic variance and covariance between relatives in synthetic wheat crosses with variable parental ploidy levels

Cultivated bread wheat (Triticum aestivum L.) is an allohexaploid species resulting from the natural hybridization and chromosome doubling of allotetraploid durum wheat (T. turgidum) and a diploid goatgrass Aegilops tauschii Coss (Ae. tauschii). Synthetic hexaploid wheat (SHW) was developed through the interspecific hybridization of Ae. tauschii and T. turgidum, and then crossed to T. aestivum to produce synthetic hexaploid wheat derivatives (SHWDs). Owing to this founding variability, one may infer that the genetic variances of native wild populations vs improved wheat may vary due to their differential origin and evolutionary history. In this study, we partitioned the additive variance of SHW and SHWD with respect to their breed origin by fitting a hierarchical Bayesian model with heterogeneous covariance structure for breeding values to estimate variance components for each breed category, and segregation variance. Two data sets were used to test the proposed hierarchical Bayesian model, one from a multi-year multi-location field trial of SHWD and the other comprising the two species of SHW. For the SHWD, the Bayesian estimates of additive variances of grain yield from each breed category were similar for T. turgidum and Ae. tauschii, but smaller for T. aestivum. Segregation variances between Ae. tauschii—T. aestivum and T. turgidum—T. aestivum populations explained a sizable proportion of the phenotypic variance. Bayesian additive variance components and the Best Linear Unbiased Predictors (BLUPs) estimated by two well-known software programs were similar for multi-breed origin and for the sum of the breeding values by origin for both data sets. Our results support the suitability of models with heterogeneous additive genetic variances to predict breeding values in wheat crosses with variable ploidy levels.     

Reproductive and genetic roles of the maternal progenitor in the origin of common wheat (Triticum aestivum L.)

Common wheat (Triticum aestivum L., AABBDD genome) is thought to have emerged through natural hybridization between Triticum turgidum L. (AABB genome) and Aegilops tauschii Coss. (DD genome). Hybridization barriers and doubling of the trihaploid F₁ hybrids’ genome (ABD) via unreduced gamete fusion had key roles in the process. However, how T. turgidum, the maternal progenitor, was involved in these mechanisms remains unknown. An artificial cross‐experiment using 46 cultivated and 31 wild T. turgidum accessions and a single Ae. tauschii tester with a very short genetic distance to the common wheat D genome was conducted. Cytological and quantitative trait locus analyses of F₁ hybrid genome doubling were performed. The crossability and ability to cause hybrid inviability did not greatly differ between the cultivars and wild accessions. The ability to cause hybrid genome doubling was higher in the cultivars. Three novel T. turgidum loci for hybrid genome doubling, which influenced unreduced gamete production in F₁ hybrids, were identified. Cultivated T. turgidum might have increased the probability of the emergence of common wheat through its enhanced ability to cause genome doubling in F₁ hybrids with Ae. tauschii. The ability enhancement might have involved alterations at a relatively small number of loci.     

Ecological distribution and species diversity of Aegilops L. genus in Bulgaria

The genus Aegilops has an important potential utilization in wheat improvement because of its resistance to different biotic and abiotic stresses and close relation with the cultivated wheat. Therefore, a better knowledge of the eco-geographical distribution of Aegilops species and their collection and conservation are required. A total of 297 Aegilops accessions representing nine (five tetraploid and four diploid) species were collected in different regions of Bulgaria, and the ecological characteristics of the 154 explored sites were recorded. The distribution of the diploid species (Ae. caudata L., Ae. speltoides Tausch, Ae. umbellulata Zhuk. and Ae. comosa Sibth. and Sm.) was limited to specific environments in south-central Bulgaria. Tetraploid species were present in harsher environments than diploid species and showed wider adaptation and distribution. Species–environment relationships were analysed by considering the worldwide distribution of the species and their physiological resistance to abiotic stress. Aegilops cylindrica Host was more frequently found in northern Bulgaria and at high altitudes. Its distribution was closely related to its tolerance to low temperatures. Aegilops geniculata Roth and Ae. neglecta Req. ex Bertol. were absent in the north of Bulgaria, but widely distributed in low rainfall areas. Aegilops neglecta, more frost resistant than Ae. geniculata, was present at higher altitude. Aegilops biuncialis Vis. and Ae. triuncialis L. showed adaptation to a wide range of climatic conditions. The study of Aegilops species ecology and distribution in Bulgaria provided useful information for the future collection and for the genetic resource management in this region.     

Genetic structure of <Emphasis Type="Italic">Aegilops cylindrica</Emphasis> Host in its native range and in the United States of America

Chloroplast and nuclear microsatellite markers were used to study genetic diversity and genetic structure of Aegilops cylindrica Host collected in its native range and in adventive sites in the USA. Our analysis suggests that Ae. cylindrica, an allotetraploid, arose from multiple hybridizations between Ae. markgrafii (Greuter) Hammer. and Ae. tauschii Coss. presumably along the Fertile Crescent, where the geographic distributions of its diploid progenitors overlap. However, the center of genetic diversity of this species now encompasses a larger area including northern Iraq, eastern Turkey, and Transcaucasia. Although the majority of accessions of Ae. cylindrica (87%) had D-type plastomes derived from Ae. tauschii, accessions with C-type plastomes (13%), derived from Ae. markgrafii, were also observed. This corroborates a previous study suggesting the dimaternal origin of Ae. cylindrica. Model-based and genetic distance-based clustering using both chloroplast and nuclear markers indicated that Ae. tauschii ssp. tauschii contributed one of its D-type plastomes and its D genome to Ae. cylindrica. Analysis of genetic structure using nuclear markers suggested that Ae. cylindrica accessions could be grouped into three subpopulations (arbitrarily named N-K1, N-K2, and N-K3). Members of the N-K1 subpopulation were the most numerous in its native range and members of the N-K2 subpopulation were the most common in the USA. Our analysis also indicated that Ae. cylindrica accessions in the USA were derived from a few founder genotypes. The frequency of Ae. cylindrica accessions with the C-type plastome in the USA (~24%) was substantially higher than in its native range of distribution (~3%) and all C-type Ae. cylindrica in the USA except one belonged to subpopulation N-K2. The high frequency of the C-type plastome in the USA may reflect a favorable nucleo-cytoplasmic combination.     

Production of intergeneric hybrid between dwarfing polish wheat (<Emphasis Type="Italic">Triticum polonicum</Emphasis> L.) and <Emphasis Type="Italic">Aegilops tauschii</Emphasis> Cosson. with reference to wheat origin

Dwarfing polish wheat is a dwarfing accession of Triticum polonicum L. from Xinjiang of China. In the present study, the artificial hybridization between dwarfing polish wheat and two accessions of Aegilops tauschii Cosson. (AS60 and AS65) was carried out, and the F₁ hybrids were obtained successfully without using embryo rescue techniques for the first time. The crossabilities of hybrids T. polonicum × Ae. tauschii (AS60) and T. polonicum × Ae. tauschii (AS65) were 1.67% and 0.60% respectively. Only the hybrids of T. polonicum × Ae. tauschii (AS60) germinated well, and 24 F₁ hybrid plants were obtained. All the F₁ hybrid plants grew vigorously, and the morphological traits were similar to bread wheat. The F₁ plants had some obvious traits inherited from T. polonicum and Ae. tauschii and were completely sterile. Chromosome pairing in the hybrid was characterized by a large number of univalents, with an average of 20.56 and 0.22 bivalents per PMC, and no ring bivalents and multivalents were observed. Furthermore, the potential value of the F1 hybrids between T. polonicum and Ae. tauschii for studying wheat origin and breeding are discussed. The article is published in the original.     

Characterization of genetic variation in and phylogenetic relationships among diploid<Emphasis Type="Italic"> Aegilops</Emphasis> species by AFLP: incongruity of chloroplast and nuclear data

Intra- and inter-specific genetic variation was investigated in seven diploid Aegilops species using the amplified fragment length polymorphism (AFLP) technique. Of the seven species, the cross-pollinating Aegilops speltoides and Aegilops mutica showed high levels of intraspecific variation whereas the remaining five self-pollinating species showed low levels. Aegilops bicornis, Aegilops searsii and Ae. speltoides formed one cluster in the dendrograms, while Aegilops caudata and Aegilops umbellulata formed another. Relationships among the species inferred were more consistent with the relationships inferred from studies of chromosome pairing in interspecific hybrids, and previous molecular phylogenetic reconstructions based on nuclear DNA, than they were with those based on molecular plasmon analysis, suggesting that the nuclear genome has evolved differently from the cytoplasmic genome in the genus Aegilops.Communicated by J. Dvorak     

Amylase protein inhibitors and the role of Aegilops species in polyploid wheat speciation

Protein inhibitors extracted with water from seeds of Triticum and genetically related species were characterized according to their apparent molecular weights, electrophoretic mobilities and their specificities in inhibiting α-amylases from human saliva and Tenebrio molitor L. larvae. No detectable amylase inhibition activity was found in extracts from diploid wheats, whereas in all tetraploid and hexaploid wheats as well as in the Aegilops species tested we found several amylase inhibitor groups of different molecular weights. In each group, several inhibitor components slightly different in their electrophoretic mobilities, but identical in their inhibition behaviour toward amylases from different origins have been shown. Both from the qualitative and quantitative standpoints, amylase protein inhibitors from hexaploid wheats were the summation of those from tetraploid wheats plus the ones from Aegilops squarrosa. Amylase inhibitors from Aegilops speltoides largely differed from those extracted from tetraploid wheats as well as from all the amylase inhibitors described in plant seeds up to now. These results indicate a relevant homology between the amylase inhibitor coding genes of the D wheat genome and those of the D Aegilops genome and confirm that Ae. squarrosa is the donor of the whole D genome to hexaploid wheats. They also suggest that Ae. speltoides is not the donor of the B genome to polyploid wheats, although a not yet identified Aegilops species might be such a donor.     

Development of chromosome 6D-specific markers for α-gliadin genes and their use in assessing dynamic changes at the Gli-2 loci

To develop chromosome 6D-specific point mutation (PM) markers for α-gliadin genes, 79 α-gliadin sequences cloned from Aegilops tauschii and another 40 α-gliadin genes with known chromosome locations were used in multi-sequence alignment and phylogenic analysis. Additional multiple alignment adjustments were performed manually to facilitate discovery of putative chromosome 6D-specific point mutations. A total of 85 PM primers were designed to detect 68 candidate chromosome 6D-specific point mutations. Experimental tests revealed 11 chromosome 6D-specific PM markers by using genomic DNA from homoeologous group 6 nullisomic–tetrasomic lines of Chinese Spring and putative diploid and tetraploid ancestors of hexaploid wheat as PCR templates. Detection of PM markers in one synthetic hexaploid wheat and its parental lines indicated that some α-gliadin genes were lost from Gli-2 loci during the formation of hexaploid wheat by amphidiploidization of the genomes of Triticum turgidum and Ae. tauschii. Detection of these PM markers in Ae. tauschii, T. aestivum and its four subspecies indicated that at least two genetically distinct sources of Ae. tauschii contributed germplasm to the D genome of T. aestivum.     

Gene flow from wheat (Triticum aestivum L.) to jointed goatgrass (Aegilops cylindrica Host.), as revealed by RAPD and microsatellite markers

In order to estimate the potential of gene flow between wheat (Triticum æstivum L.) and jointed goatgrass (Aegilops cylindrica Host.), we carried out mixed pollinations in experimental and natural conditions. A set of species-specific RAPD (random amplified polymorphic DNA) and microsatellite markers were used to detect the presence of parental markers in the progeny of the plants used in these experiments. No hybrids were found within the offsprings of the plants used for the greenhouse experiments, while 85 Ae. cylindrica×T. æstivum hybrids were found within 2400 analyzed F₁ plants resulting from the field pollinations. The hybridization rates for individuals of different populations of the wild species differed considerably: 1% for two populations known for more than 90 years versus 7% for a newly discovered population. Most of the hybrids were completely sterile, but five of them produced 13 seeds (BC₁) by backcross with Ae. cylindrica. Twelve seeds germinated and generated viable and partly fertile plants. About 25% of the wheat specific RAPD markers were found in the BC₁ plants, indicating that introgression of wheat DNA into Ae. cylindrica is possible. In addition, one microsatellite marker, known to be situated on the D genome (a genome shared by both species), was also found in the BC₁ plants.     

BAC libraries of Triticum urartu, Aegilops speltoides and Ae. tauschii, the diploid ancestors of polyploid wheat

Triticum urartu, Aegilops speltoides and Ae. tauschii are respectively the immediate diploid sources, or their closest relatives, of the A, B and D genomes of polyploid wheats. Here we report the construction and characterization of arrayed large-insert libraries in a bacterial artificial chromosome (BAC) vector, one for each of these diploid species. The libraries are equivalent to 3.7, 5.4 and 4.1 of the T. urartu, Ae. speltoides, Ae. tauschii genomes, respectively. The predicted levels of genome coverage were confirmed by library hybridization with single-copy genes. The libraries were used to estimate the proportion of known repeated nucleotide sequences and gene content in each genome by BAC-end sequencing. Repeated sequence families previously detected in Triticeae accounted for 57, 61 and 57% of the T. urartu, Ae. speltoides and Ae. tauschii genomes, and coding regions accounted for 5.8, 4.5 and 4.8%, respectively.