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.     

Restriction Fragment Length Polymorphism (RFLP) for protein disulfide isomerase (PDI) gene sequences in Triticum and Aegilops species

RFLP variation revealed by protein disulfide isomerase (PDI) coding gene sequences was assessed in 170 accessions belonging to 23 species of Triticum and Aegilops. PDI restriction fragments were highly conserved within each species and confirmed that plant PDI is encoded either by single-copy sequences or by small gene families. The wheat PDI probe hybridized to single EcoRI or HindIII fragments in different diploid species and to one or two fragments per genome in polyploids. Four Aegilops species in the Sitopsis section showed complex patterns and high levels of intraspecific variation, whereas Ae. searsii possessed single monomorphic fragments. T. urartu and Ae. squarrosa showed fragments with the same mobility as those in the A and D genomes of Triticum polyploid species, respectively, whereas differences were observed between the hybridization patterns of T. monococcum and T. boeoticum and that of the A genome. The single fragment detected in Ae. squarrosa was also conserved in most accessions of polyploid Aegilops species carrying the D genome. The five species of the Sitopsis section showed variation for the PDI hybridization fragments and differed from those of the B and G genomes of emmer and timopheevi groups of wheat, although one of the Ae. speltoides EcoRI fragments was similar to those located on the 4B and 4G chromosomes. The similarity between the EcoRI fragment located on the 1B chromosome of common and emmer wheats and one with a lower hybridization intensity in Ae. longissima, Ae. bicornis and Ae. sharonensis support the hypothesis of a polyphyletic origin of the B genome. Received: 25 June 1999 / Accepted: 14 September 1999     

Wheat phylogeny determined by RFLP analysis of nuclear DNA. 3. Intra- and interspecific variations of five Aegilops Sitopsis species

The level of intra- and interspecific variations on nuclear DNA in five Aegilops species of the Sitopsis section were investigated using restriction fragment length polymorphism (RFLP) analysis. A total of 18 accessions, i.e. 7 of Ae. speltoides, 3 of Ae. longissima, 2 of Ae. searsii, 3 of Ae. sharonensis and 3 of Ae. bicornis, were used. One accession each of Triticum aestivum, T. durum, T. urartu and Ae. squarrosa was included as reference material. Five enzymes and 20 probes were used. Among the five Sitopsis species studied, Ae. speltoides had the largest intraspecific variation (=0.061), which was as high as the interspecific variation observed among the other four species. The section Sitopsis was divided into two distinct groups: one containing only Ae. speltoides and the other, Ae. longissima, Ae. searsii, Ae. sharonensis and Ae. bicornis. This grouping by RFLP analysis is in agreement with the taxonomical classification of the subsections.     

Genetic Diversity of the Cytoplasm in Triticum and Aegilops. VIII. Fraction I Protein of 39 Cytoplasms

The electrophoretic characteristics of the cytoplasmically controlled large subunit of the Fraction I protein of 36 alloplasmic and three euplasmic control lines are reported. These lines, representing the cytoplasms of 32 Triticum and Aegilops species, had either H- or L-type large subunits in their Fraction I protein; the diploid Triticum and most Aegilops species, including Ae. bicornis and Ae. sharonensis, had the L-type subunits; whereas, all the polyploid Triticum species (emmer, timopheevi, common wheats), Ae. speltoides, Ae. aucheri, and Ae. longissima had H-type subunits. Therefore, section Sitopsis of Aegilops exhibits interspecific heterogeneity. The H-type is believed to have originated in the Sitopsis section from an L-type subunit because of the prevalence of the latter among the diploid species.     

NADP-dependent aromatic alcohol dehydrogenase in polyploid wheats and their diploid relatives. On the origin and phylogeny of polyploid wheats

Summary The three major isoenzymes of the NADP-dependent aromatic alcohol dehydrogenase (ADH-B), distinguished in polyploid wheats by means of polyacrylamide gel electrophoresis, are shown to be coded by homoeoalleles of the locus Adh-2 on short arms of chromosomes of the fifth homoeologous group. Essentially codominant expression of the Adh-2 homoeolleles of composite genomes was observed in young seedlings of hexaploid wheats (T. aestivum s.l.) and tetraploid wheats of the emmer group (T. turgidum s.l.), whereas only the isoenzyme characteristic of the A genome is present in the seedlings of the timopheevii-group tetraploids (T. timopheevii s.str. and T. araraticum).The slowest-moving B³ isoenzyme of polyploid wheats, coded by the homoeoallele of the B genome, is characteristic of the diploid species Aegilops speltoides S.l., including both its awned and awnless forms, but was not encountered in Ae. bicornis, Ae. sharonensis and Ae. longissima. The last two diploids, as well as Ae. tauschii, Ae. caudata, Triticum monococcum s.str., T. boeoticum s.l. (incl. T. thaoudar) and T. urartu all shared a common isoenzyme coinciding electrophoretically with the band B² controlled by the A and D genome homoeoalleles in polyploid wheats. Ae. bicomis is characterized by the slowest isoenzyme, B⁴, not found in wheats and in the other diploid Aegilops species studied.Two electrophoretic variants of ADH-B, B¹ and B², considered to be alloenzymes of the A genome homoeoallele, were observed in T. dicoccoides, T. dicoccon, T. turgidum. s.str. and T. spelta, whereas B² was characteristic of T. timopheevii s.l. and only B¹ was found in the remaining taxa of polyploid wheats. The isoenzyme B¹, not encountered among diploid species, is considered to be a mutational derivative which arose on the tetraploid level from its more ancestral form B² characteristic of diploid wheats.The implication of the ADH-B isoenzyme data to the problems of wheat phylogeny and gene evolution is discussed.     

Studies on maternal inheritance in polyploid wheats with cytoplasmic DNAs as genetic markers

Summary Restriction fragment patterns of DNA fragments obtained after EcoRI cleavage of chloroplastic (cp) and mitochondrial (mt) DNAs isolated from different wheat species were compared. T. aestivum, T. timopheevi, Ae. speltoides, Ae. sharonensis and T. urartu gave species specific mt DNA patterns. Consequently, the cytoplasmic genomes of wheat cannot have originated from contemporary Ae. speltoides, Ae. sharonensis and T. urartu species. It is shown that cp and mt DNAs of Ae. ventricosa, a tetraploid used to transfer eyespot resistance into T. aestivum, contains cp and mt DNAs differing from DNAs isolated from T. aestivum and other wheats. In contrast, the cytoplasmic DNAs of Ae. ventricosa and Ae. squarrosa reveal an important homology, suggesting that Ae. squarrosa was the female parent of Ae. ventricosa. Disomic addition lines (T. aestivum — Ae. ventricosa) in both Ae. ventricosa cytoplasm and T. aestivum cytoplasm contained cytoplasmic DNAs identical to those of the maternal parent. Restriction patterns of the cp and mt DNAs isolated from eight lines of Triticale differing in their cytoplasm have been compared to those of the maternal parent. A strict maternal inheritance has been observed in each case.     

The Phylogeny of Triticum L. and Aegilops L. Inferred from Comparative Analysis of Nucleotide Sequences in rDNA Promoter Regions

The process of accumulation of knowledge on wheat and related wild species during the 20th century is briefly reviewed with special reference to the evidence of the recent years on evolution of polyploid wheats and the role of diploid species. The latter serve as potential donors of the genomes, detection of which is particularly important because of the continuing speciation in the tribe Triticeae and artificial development of synthetic forms. The arguments in favor of the donor role for various diploid wheat and aegilops species from the section Sitopsis are compared. It is stated that in the formation of the both lines of polyploid wheats turgidum–aestivumand timopheevi,diploid Aegilops speltoides acted as a maternal form. In addition to cytoplasmic genomes, this aegilops species introduced into them also the B and G nuclear subgenomes. A comparison of nucleotide sequences in the variable part of the promoter of evolutionary conserved rRNA genes in polyploid wheats with their counterparts in diploid wheats and aegilops species confirmed the accepted wheat phylogenies.     

Heterochromatin differentiation and phylogenetic relationship of the A genomes in diploid and polyploid wheats

Summary Heterochromatin differentiation, including band size, sites, and Giemsa staining intensity, was analyzed by the HKG (HCl-KOH-Giemsa) banding technique in the A genomes of 21 diploid (Triticum urartu, T. boeoticum and T. monococcum), 13 tetraploid (T. araraticum, T. timopheevi, T. dicoccoides and T. turgidum var. Dicoccon, Polonicum), and 7 cultivars of hexaploid (T. aestivum) wheats from different germplasm collections. Among wild and cultivated diploid taxa, heterochromatin was located mainly at centromeric regions, but the size and staining intensity were distinct and some accessions' genomes had interstitial and telomeric bands. Among wild and cultivated polyploid wheats, heterochromatin exhibited bifurcated differentiation. Heterochromatinization occurred in chromosomes 4A^t and 7A^t and in smaller amounts in 2A^t, 3A^t, 5A^t, and 6A^t within the genomes of the tetraploid Timopheevi group (T. araraticum, and T. timopheevi) and vice versa within those of the Emmer group (T. dicoccoides and T. turgidum). Similar divergence patterns occurred among chromosome 4A^a and 7A^a of cultivars of hexaploid wheat (T. aestivum). These dynamic processes could be related to geographic distribution and to natural and artifical selection. Comparison of the A genomes of diploid wheats with those of polyploid wheats shows that the A genomes in existing diploid wheats could not be the direct donors of those in polyploid wheats, but that the extant taxa of diploids and polyploids probably have a common origin and share a common A-genomelike ancestor.Contribution of the College of Agricultural Sciences, Texas Tech Univ. Journal No. T-4-233.     

Molecular analysis of the phylogenetic relationships among the diploid <Emphasis Type="Italic">Aegilops</Emphasis> species of the section <Emphasis Type="Italic">Sitopsis</Emphasis>

RAPD analysis was used to study the intraspecific variation and phylogenetic relationships of Sgenome diploid Aegilops species regarded as potential donors of the B genome of cultivated wheat. In total, 21 DNA specimens from six S-genome diploid species were examined. On a dendrogram, Ae. speltoides and Ae. aucheri formed the most isolated cluster. Among the other species, Ae. searsii was the most distant while Ae. longissima and Ae. sharonensis were the closest species. The maximum difference between individual accessions within one species was approximately the same (0.18–0.22) in Ae. bicornis, Ae. longissima, Ae. sharonensis, and Ae. searsii. The difference between the clusters of questionable species Ae. speltoides and Ae. aucheri corresponded to the intraspecific level; the difference between closely related Ae. longissima and Ae. sharonensis corresponded to the interspecific level.     

NAD-dependent aromatic alcohol dehydrogenase in wheats (Triticum L.) and goatgrasses (Aegilops L.): evolutionary genetics

Summary Evolutionary electrophoretic variation of a NAD-specific aromatic alcohol dehydrogenase, AADH-E, in wheat and goatgrass species is described and discussed in comparison with a NAD-specific alcohol dehydrogenase (ADH-A) and a NADP-dependent AADH-B studied previously. Cultivated tetraploid emmer wheats (T. turgidum s. l.) and hexaploid bread wheats (T. aestivum s. l.) are all fixed for a heterozygous triplet, E^0.58/E^0.64. The slowest isoenzyme, E^0.58, is controlled by a homoeoallelic gene on the chromosome arm 6AL of T. aestivum cv. Chinese Spring and is inherent in all diploid wheats, T. monococcum s. Str., T. boeoticum s. l. and T. urartu. The fastest isoenzyme, E^0.64, is presumably controlled by the B- and D-genome homoeoalleles of the bread wheat and is the commonest alloenzyme of diploid goat-grasses, including Ae. speltaides and Ae. tauschii. The tetraploid T. timopheevii s. str. has a particular heterozygous triplet E^0.56/E^0.71, whereas the hexaploid T. zhukovskyi exhibited polymorphism with electromorphs characteristic of T. timopheevii and T. monococcum. Wild tetraploid wheats, T. dicoccoides and T. araraticum, showed partially homologous intraspecific variation of AADH-E with heterozygous triplets E^0.58/E^0.64 (the commonest), E^0.58/E^0.71, E^0.45/E^0.58, E^0.48/E^0.58 and E^0.56/E^0.58 recorded. Polyploid goatgrasses of the D-genome group, excepting Ae. cylindrica, are fixed for the common triplet E^0.58/E^0.64. Ae. cylindrica and polyploid goatgrasses of the C^u-genome group, excepting Ae. kotschyi, are homozygous for E^0.64. Ae. kotschyi is exceptional, showing fixed heterozygosity for both AADH-E and ADH-A with unique triplets E^0.56/E^0.64 and A^0.49/A^0.56.     

Comparison of the chromosomes of Triticum timopheevi with related wheats using the techniques of C-banding and in situ hybridization

Summary The chromosomes of the tetraploid wheats Triticum timopheevi (Genome AAGG) and T. araraticum (Genome AAGG) were C-banded at mitosis. The identity of the banded and unbanded chromosomes was then established by firstly making comparisons with the hexaploid species T. zhukovskyi which has the genome formula AAAAGG. Secondly, the meiotic pairing in F₁ hybrids between T. timopheevi and diploid wheats was examined by means of C-banding. The results showed that the banded chromosomes belonged to the G genome, while the unbanded chromosomes belonged to the A genome. Only one of the two pairs of satellited chromosomes had strong heterochromatic bands. The relationship between the genomes of T. timopheevi and T. dicoccum (Genome AABB) was then assessed at meiosis in hybrids between these species, using the techniques of C-banding and in situ hybridisation of a cloned ribosomal RNA gene probe. It was concluded that there were differences both in the amount and distribution of heterochromatin and also translocation differences between the species.     

Development of a complete set of Triticum aestivum-Aegilops speltoides chromosome addition lines

Aegilops speltoides Tausch (2n = 2x = 14, SS) is considered as the closest living relative of the B and G genomes of polyploid wheats. A complete set of Triticum aestivum L. cv Chinese Spring-Ae. speltoides whole chromosomes and seven telosomic addition lines was established. A low pairing accession was selected for the isolation of the chromosome addition lines. Except for chromosomes 3S and 6S, which are presently only available as monosomic additions, all other lines were recovered as disomic or ditelosomic additions. The individual Ae. speltoides chromosomes isolated in the wheat background were assayed for their genetic effects on plant phenotype and cytologically characterized in terms of chromosome length, arm ratio, distribution of marker C-bands, and FISH sites using a Ae. speltoides-specific repetitive element, Gc1R-1, as a probe. The homoeology of the added Ae. speltoides chromosomes was established by using a standard set of RFLP probes. No chromosomal rearrangements relative to wheat were detected. Received: 28 June 1999 / Accepted: 16 November 1999     

A comparative analysis of the composition and organization of two subtelomeric repeat families in <Emphasis Type="Italic">Aegilops speltoides</Emphasis>Tausch. and related species

The structural organization and evolution of two tandemly repeated families, Spelt1 and Spelt52, located in the subtelomeric regions of Aegilops speltoides chromosomes were studied. The Spelt1 family of sequences with a monomer length of 178 bp was characterized by cloning and sequence analysis of polymerase chain reaction (PCR) products. Members of the Spelt1 family revealed sequence similarities exceeding 95\%. This conservation has remained despite divergence of species in Aegilops section Sitopsis and after independent multiple amplification events in the genome of Ae. speltoides. Sequences representing the Spelt52 family were cloned, sequenced and compared with other sequences in databases. The Spelt52 repeat family contains monomers of two types, Spelt52.1 and Spelt52.2. The two monomers share a homologous stretch of 280 bp and have two regions without sequence similarity of 96 bp and 110 bp, respectively. PCR analysis was conducted to 15 lines in Ae. speltoidesTausch., Ae. longissimaSchw.&Mushc.,Ae. sharonensisEig.,Ae. bicornis(Forssk)Jaub.&Sp., andAe. searsii Feld.&Kis. using primers to the homologous and non- homologous regions of Spelt52 family. Intraspecies and interspecies differences in the occurrence and abundance of combinations of Spelt52.1 and Spelt52.2 monomers were detected. The use of primers to telomeric and subtelomeric repeats followed by Southern hybridization, cloning, and sequence analysis demonstrated that Spelt1 and Spelt52 are localized close to each other and to telomeric repeats. The efficiency of a PCR approach for the analysis of telomeric/subtelomeric junction regions of chromosomes is discussed.     

Relationships betweenNor-loci from differentTriticeae species

TheNor-loci of polyploid wheats and their putative diploid progenitor species were assayed by probing isolated nuclear DNA with ribosomal DNA spacer sequences (spacer rDNA sequences, isolated by cloning), from theNor-loci of genomes B (Triticum aestivum), G (T. timopheevi), B (syn. S,T. speltoides), A (T. monococcum) and V (Dasypyrum villosum). DNA samples for analysis were digested with the restriction endonuclease Taq 1 and assayed by DNA-DNA hybridization under standard (37°C) and high stringency (64°C) conditions. The assay procedure emphasized differences between the divergent spacer sequences of the polyploid species and allowed relative homologies to the respective sequences in diploid species to be established. — The studies indicated thatT. timopheevi andT. speltoides contain different sets of spacer rDNA sequences which were readily distinguishable and, in the case ofT. timopheevi, assigned toNor-loci on different chromosomes. This contrast with the spacer rDNA sequences of the majorNor-loci on chromosomes 1 B and 6 B inT. aestivum, which were difficult to distinguish and were deduced to contain very similar sequences. Among the diploid progenitor species only the spacer rDNA fromT. speltoides shared close homology with polyploid wheat species. OneNor-locus inT. timopheevi (on chromosome 6 G) did not show close homology with any of the rDNA spacer probes available. — The data suggestsT. speltoides was the origin of someNor-loci for both theT. timopheevi andT. turgidum lines of tetraploid wheats. The possibility that the 6GNor-locus inT. timopheevi may have derived from an unknown diploid species by introgressive hybridization is discussed. The spacer rDNA sequence probe fromT. monococcum shared good homology with some accessions ofD. villosum and a line ofT. dicoccoides; the implications of this finding for evolution of present-day wheats are discussed.     

A comparative study of the mitochondrial genome organization in in vitro cultures of diploid, tetraploid, and hexaploid Triticum species

Southern-blot hybridizations of total DNA to mitochondrial DNA (mtDNA) probes were used to investigate the extent of mtDNA variability in cultures derived from immature embryos of diploid (Triticum monococcum, genomic formula: AA, T. tauschii, genomic formula: DD), allotetraploid (T. durum cv Creso, genomic formula: AABB), and allohexaploid (T. aestivum, genomic formula: AABBDD) wheat species. Similar distinct changes in mtDNA organization were observed in in vitro cultures of the derived tetraploid and the hexaploid species with related genomes. The tetraploid and hexaploid species share the B genome and mtDNA variability in in vitro culture is known to be under nuclear control. These results suggest that a study of B genome diploids and other polyploid combinations would now shed light on whether or not mtDNA variability in tissue cultures is under B-genome control.     

Genetic control of seed proteins in wheat

Summary Electrophoretic profiles of crude protein extracts from seed of F₁ hybrids and reciprocal crosses among diploid, tetraploid and hexaploid wheats were compared with those of their respective parental species. The electrophoretic patterns within each of three pairs of reciprocal crosses, T.boeoticum X T.urartu, T.monococcun X T. urartu and T.dicoccum X T. araraticum, were different from one another but were identical with those of their respective maternal parents. Protein bands characteristic of the paternal parents were missing in F₁ hybrid seed suggesting that the major seed proteins in wheat were presumably regulated by genotype of the maternal parent rather than by the seed genotype. However, in another three pairs of reciprocal crosses, T.boeoticum X T. durum, T.dicoccum X T.aestivum and T. zhukovskyi x T. aestivum, protein bands attributable to the paternal parents were present in the F₁ hybrid seeds indicating that the seed proteins were not always exclusively regulated by the maternal genotype. The expression of paternal genomes is presumably determined by dosage and genetic affinity of the maternal and paternal genomes in the hybrid endosperm. The maternal regulation of seed protein content is probably accomplished through the maternal control over seed size. The seed protein quality may, however, depend upon the extent of expression of the paternal genome.     

Electrophoretic survey of seedling esterases in wheats in relation to their phylogeny

Summary Evolutionary and ontogenetic variation of six seedling esterases of independent genetic control is studied in polyploid wheats and their diploid relatives by means of polyacrylamide gel electrophoresis. Four of them are shown to be controlled by homoeoallelic genes in chromosomes of third, sixth and seventh homoeologous groups.The isoesterase electrophoretic data are considered supporting a monophyletic origin of both the primitive tetraploid and the primitive hexaploid wheat from which contemporary taxa of polyploid wheats have emerged polyphyletically and polytopically through recurrent introgressive hybridization and accumulation of mutations. Ancestral diploids belonging or closely related to Triticum boeoticum, T. urartu, Aegilops speltoides and Ae. tauschii ssp. strangulata are genetically the most suitable genome donors of polyploid wheats. Diploids of the Emarginata subsection of the section Sitopsis, Aegilops longissima s.str., Ae. sharonensis, Ae. searsii and Ae. bicornis, are unsuitable for the role of the wheat B genome donors, being all fixed for the esterase B and D electromorphs different from those of tetraploid wheats.     

Intraspecific divergence in wheats of the Timopheevi group as revealed by in situ hybridization with tandem repeats of the Spelt1 and Spelt52 families

Fluorescent in situ hybridization (FISH) was used to study the distribution of the Spelt1 and Spelt52 repetitive DNA sequences on chromosomes of ten accessions representing three polyploid wheat species of the Timopheevi group: Triticum araraticum (7), T. timopheevii (2), and T. kiharae (1). Sequences of both families were found mostly in the subtelomeric chromosome regions of the G genome. The total number of Spelt1 sites varied from 8 to 14 in the karyotypes of the species under study; their number, location, and size differed among the seven T. araraticum accessions and were the same in the two T. timopheevii accessions and T. kiharae, an amphidiploid T. timopheevii-Aegilops tauschii hybrid. The Spelt52 tandem repeat was detected in the subtelomeric regions of chromosomes 1-4; its sites did not coincide with the Spelt1 sites. The chromosome distribution and signal intensity of the Spelt52 repeats varied in T. araraticum and were the same in T. timopheevii and T. kiharae. The chromosome distributions of the Spelt1 and Spelt52 repeats were compared for the polyploid wheats of the Timopheevi group and diploid Ae. speltoides, a putative donor of the G genome. The comparison revealed a decrease in hybridization level: both the number of sites per genome and the size of sites were lower. The decrease was assumed to result from repeat elimination during polyploidization and subsequent evolution of wheat and from the founder effect, since the origin of Timopheevi wheats might involve the genotype of Ae. speltoides, which is highly polymorphic for the distribution of Spelt1 and Spelt52 sequences and is similar in the chromosome location of the repeats to modern wheat.     

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.     

Evidence for AEGILOPS SHARONENSIS Eig as the Donor of the B Genome of Wheat

A number of lines of evidence are advanced for the candidacy of Aegilops sharonensis Eig as the donor of the B genome of wheat. The cytoplasm of Ae. sharonensis is compatible with tetraploid wheat Triticum turgidum dicoccoides, as evidenced by the high level of chromosome pairing and fertility of the amphiploid Ae. sharonensis x T. turgidum dicoccoides. Ae. sharonensis chromosomes exhibit high levels of pairing with those of the B genome of wheat in hybrids with Ph-deficient hexaploid wheat and low levels of homoeologous pairing with T. monococcum chromosomes.——The amphidiploid between Ae. sharonensis and T. monococcum is very similar to T. turgidum dicoccoides in spike, spikelet and grain morphology. The karyotype of Ae. sharonensis resembles more closely that of extrapolated B genome karyotypes of wheat than do the karyotypes of other proposed B-genome donor species of Aegilops. Because of distinctiveness in cytological affinity and karyotype morphology between Ae. sharonensis and Ae. longissima, a separate genome symbol S^sh is proposed for the former species.