ABD Genomes Research Articles

Chromosome-specific painting in Thinopyrum species using bulked oligonucleotides.

Chromosome-specific painting probes were developed to identify the individual chromosomes from 1 to 7E in Thinopyrum species and detect alien genetic material of the E genome in a wheat background. The E genome of Thinopyrum is closely related to the ABD genome of wheat (Triticum aestivum L.) and harbors genes conferring beneficial traits to wheat, including high yield, disease resistance, and unique end-use quality. Species of Thinopyrum vary from diploid (2n = 2x = 14) to decaploid (2n = 10x = 70), and chromosome structural variation and differentiation have arisen during polyploidization. To investigate the variation and evolution of the E genome, we developed a complete set of E genome-specific painting probes for identification of the individual chromosomes 1E to 7E based on the genome sequences of Th. elongatum (Host) D. R. Dewey and wheat. By using these new probes in oligonucleotide-based chromosome painting, we showed that Th. bessarabicum (PI 531711, EbEb) has a close genetic relationship with diploid Th. elongatum (EeEe), with five chromosomes (1E, 2E, 3E, 6E, and 7E) maintaining complete synteny in the two species except for a reciprocal translocation between 4 and 5Eb. All 14 pairs of chromosomes of tetraploid Th. elongatum have maintained complete synteny with those of diploid Th. elongatum (Thy14), but the two sets of E genomes have diverged. This study also demonstrated that the E genome-specific painting probes are useful for rapid and effective detection of the alien genetic material of E genome in wheat-Thinopyrum derived lines.

Molecular Characterization and Marker Development of the HMW-GS Gene from Thinopyrum elongatum for Improving Wheat Quality

The quality of wheat primarily depends on its storage protein quality, especially in regards to gluten content and high-molecular-weight glutenin subunits (HMW-GS). The number of HMW-GS alleles is limited in bread wheat (Triticum aestivum L.), whereas it is abundant in wheat relatives. Therefore, HMW-GS alleles from wheat relatives could provide a potential for improving quality in wheat breeding. Thinopyrum elongatum (EE) is one of the relatives of wheat. The E genome is closely related to the ABD genome in wheat; therefore, Th. elongatum is often used as an excellent exogenous gene donor for wheat genetic improvement. In this study, the high-molecular glutenin subunit gene was cloned and sequenced from Th. elongatum. A specific molecular marker for identifying the Glu-1Ey subunit gene was developed and applied to detected wheat-Th. elongatum alien introgression lines. Quality analysis indicated that the substitution and addition lines containing Th. elongatum alleles significantly (p < 0.05) increased grain protein content by 3.76% to 5.11%, wet-gluten content by 6.55% to 8.73%, flour 8-MW by 0.25% to 6.35%, and bread volume value by 33.77 mL to 246.50 mL, in comparing it with Chinese Spring. The GMP content and lactic acid SRC showed significant positive correlations with flour processing quality and might be used as indicators for wheat quality. The results were expected to provide a novel route for improving processing quality in wheat quality breeding.

Assessment of Genetic Diversity in Triticum spp., Secale Cereale And Triticale Using Issr Markers And Sds-Page

Genetic diversity among some wild close relatives of wheat was estimated using inter simple sequence repeats (ISSR) and SDS-PAGE markers. Four Triticum, Secale cereale and Triticale genotypes including seven Triticum, Secale and Triticale accessions belonging to one diploid (Secale cereale), three tetraploid (Triticum durum (4x)) and two hexaploid (Triticale (6x)) in addition to one hexaploid wheat (Triticum aestivum) species sampled from different ecogeographical regions of Egypt; a durum wheat cultivars 'Baniswef 1 and 3 and Sohag 3', a local wheat cultivars growing in upper Egypt 'Giza 168', a bread wheat cultivar and two triticale strains beside one rye strain were evaluated. Genetic diversity among wheat accessions was estimated using 11 ISSR primers. Of the approximately 153 detected ISSR markers, 65 (42%) were polymorphic with 4 bands per used primer pair. Cluster analysis of 7 accessions belonging to the four species by UPGMA cluster analysis based on Jaccard’s similarity estimates for ISSR data divided all accessions into one major cluster and Secale cereale separated from the major cluster. two major sub-clusters reflecting almost their genome composition. The first one included wheat species having AB genomes ('Baniswef 1 and 3 and Sohag 3'), while second cluster included wheat species having ABD and ABR genomes. The genetic similarity coefficients ranged from 0.36 between Triticale 1 and rye accession and 0.84 between Triticale 1 (6x) and Triticale 2 (6x). Two Triticum durum species of were ranked as the second most related species (0.81). The results of SDS-PAGE revealed a total number of 145 bands with molecular weights (MW) ranging from about 17 kDa to 158 kDa, which were not necessarily present in the 7 genotypes. Data revealed seven common bands (monomorphic), six unique bands while the remaining 90 band were polymorphic with 62% polymorphism. The unique Bands at the molecular weight 158 and 41 kd were the distinguishable band of Baniswef 3. The unique Band at the molecular weight 64 kd was the distinguishable band detected of Sohag 3. The unique Bands at the molecular weight 62 and 55 kd were detected only in Rye. The unique Band at the molecular weight 17 kd was detected only in Baniswef 1.

Biosystematics and evolutionary relationships of perennial Triticeae species revealed by genomic analyses

AbstractUnderstanding the classification and biosystematics of species in Triticeae Dumort., an economically important tribe in the grass family (Poaceae), is not an easy task, particularly for some perennial species. Does genomic analysis facilitate the understanding of evolutionary relationships of these Triticeae species? We reviewed literature published after 1984 to address questions concerning: (1) genome relationships among the monogenomic diploid species; (2) progenitors of the unknown Y genome in Elymus polyploids, X genome in Thinopyrum intermedium, and Xm genome in Leymus; and (3) genome constitutions of some perennial Triticeae species that were unknown or misidentified. A majority of publications have substantiated the close affinity of the Eb and Ee genomes in Th. bessarabicum and Th. elongatum, supporting the use of a common basic genome symbol. The E genome is close to the St genome of Pseudoroegneria and ABD genomes of Triticum/Aegilops complex, providing an explanation for transferring genes from the E to ABD genomes with relative ease. Although the solid proof is still lacking, the W, P, and especially Xp genomes are possible origins for the Y genome of polyploid Elymus. The absence of the E genome and the allopolyploidy nature of tetraploid Leymus species have been unequivocally confirmed by both cytogenetic and molecular studies. However, the donor of the Xm genomes of Leymus was only speculated to be related to the P genome of Agropyron and F genome of Eremopyrum. Intermediate wheatgrass (Th. intermedium) has been extensively studied. The presence of the St (as the previously designated X) genome in Th. intermedium is now unequivocal. Its two more closely related E1 and E2 genomes are shown to be older versions of the E genome rather than the current Eb and Ee genomes. Speciation of Th. intermedium was similar to that of Triticum aestivum, in which the Js/Es (like B) genomes had the greatest differentiation from the current J (Eb) genome owning to repetitive sequences of the V genome, whereas its St (like D) had the least differentiation from the current St genome. Species with unknown or misidentified genomes have been correctly designated, including those with the ESt, StP, StPY, StWY, EStP, HW, StYHW, and NsXm genomes. Some of those species have been transferred to and renamed in appropriate genera.

Genetic Rearrangements of Six Wheat–Agropyron cristatum 6P Addition Lines Revealed by Molecular Markers

Agropyron cristatum (L.) Gaertn. (2n = 4x = 28, PPPP) not only is cultivated as pasture fodder but also could provide many desirable genes for wheat improvement. It is critical to obtain common wheat–A. cristatum alien disomic addition lines to locate the desired genes on the P genome chromosomes. Comparative analysis of the homoeologous relationships between the P genome chromosome and wheat genome chromosomes is a key step in transferring different desirable genes into common wheat and producing the desired alien translocation line while compensating for the loss of wheat chromatin. In this study, six common wheat–A. cristatum disomic addition lines were produced and analyzed by phenotypic examination, genomic in situ hybridization (GISH), SSR markers from the ABD genomes and STS markers from the P genome. Comparative maps, six in total, were generated and demonstrated that all six addition lines belonged to homoeologous group 6. However, chromosome 6P had undergone obvious rearrangements in different addition lines compared with the wheat chromosome, indicating that to obtain a genetic compensating alien translocation line, one should recombine alien chromosomal regions with homoeologous wheat chromosomes. Indeed, these addition lines were classified into four types based on the comparative mapping: 6PI, 6PII, 6PIII, and 6PIV. The different types of chromosome 6P possessed different desirable genes. For example, the 6PI type, containing three addition lines, carried genes conferring high numbers of kernels per spike and resistance to powdery mildew, important traits for wheat improvement. These results may prove valuable for promoting the development of conventional chromosome engineering techniques toward molecular chromosome engineering.

Population divergence in the wheat leaf rust fungus Puccinia triticina is correlated with wheat evolution.

Co-evolution of fungal pathogens with their host species during the domestication of modern crop varieties has likely affected the current genetic divergence of pathogen populations. The objective of this study was to determine if the evolutionary history of the obligate rust pathogen on wheat, Puccinia triticina, is correlated with adaptation to hosts with different ploidy levels. Sequence data from 15 loci with different levels of polymorphism were generated. Phylogenetic analyses (parsimony, Bayesian, maximum likelihood) showed the clear initial divergence of P. triticina isolates collected from Aegilops speltoides (the likely B genome donor of modern wheat) in Israel from the other isolates that were collected from tetraploid (AB genomes) durum wheat and hexaploid (ABD genomes) common wheat. Coalescence-based genealogy samplers also indicated that P. triticina on A. speltoides, diverged initially, followed by P. triticina isolates from durum wheat in Ethiopia and then by isolates from common wheat. Isolates of P. triticina found worldwide on cultivated durum wheat were the most recently coalesced and formed a clade nested within the isolates from common wheat. By a relative time scale, the divergence of P. triticinia as delimited by host specificity appears very recent. Significant reciprocal gene flow between isolates from common wheat and isolates from durum wheat that are found worldwide was detected, in addition to gene flow from isolates on common wheat to isolates on durum wheat in Ethiopia.

Proteomic analysis of the mature kernel aleurone layer in common and durum wheat

The aleurone layer (AL) is one of inner tissues removed from the grain with the wheat bran. It is the main source of vitamins, minerals and antioxidants of potential nutritional value in the wheat kernel. The AL of three varieties of each of the two main species of wheat, Triticum aestivum (ABD) and Triticum durum (AB), were manually dissected and analysed using two-dimensional gel-based proteomics. A total of 1258 and 1109 Coomassie-stained spots were detected in the AL of representatives of the ABD and AB genomes. In two varieties (T. aestivum Chinese Spring and T. durum Bidi17), grown in two different years with full fungicide protection, no quantitative or qualitative (presence/absence) differences in spots were detected, suggesting that AL proteome is strongly genetically controlled. Comparison within and between species revealed a total of 339 AL significant protein spots. Among these spots, 30.8% differed within T. aestivum and 56.5% within T. durum varieties, whereas only 12.7% differed between the two species. Among the 142 AL proteins identified using MALDI-TOF and LC-MS/MS, 57% were globulin type storage proteins (Glo-3, Glo-3B, Glo-3C, Glo-2), 16.2% were involved in carbohydrate metabolism and 17.6% in defence/stress pathways. These variations in AL proteome are discussed.

Production and identification of wheat-Agropyron cristatum 6P translocation lines

The narrow genetic background of wheat is the primary factor that has restricted the improvement of crop yield in recent years. The kernel number per spike is the most important factor of the many potential characteristics that determine wheat yield. Agropyron cristatum (L.) Gaertn., a wild relative of wheat, has the characteristics of superior numbers of florets and kernels per spike, which are controlled by chromosome 6P. In this study, the wheat-A. cristatum disomic addition and substitution lines were used as bridge materials to produce wheat-A. cristatum 6P translocation lines induced by gametocidal chromosomes and irradiation. The results of genomic in situ hybridization showed that the frequency of translocation induced by gametocidal chromosomes was 5.08%, which was higher than the frequency of irradiated hybrids (2.78%) and irradiated pollen (2.12%). The fluorescence in situ hybridization results of the translocation lines showed that A. cristatum chromosome 6P could be translocated to wheat ABD genome, and the recombination frequency was A genome > B genome > D genome. The alien A. cristatum chromosome 6P was translocated to wheat homoeologous groups 1, 2, 3, 5 and 6. We obtained abundant translocation lines that possessed whole-arm, terminal, segmental and intercalary translocations. Three 6PS-specific and four 6PL-specific markers will be useful to rapidly identify and trace the translocated fragments. The different wheat-A. cristatum 6P translocation lines obtained in this study can provide basic materials for analyzing the alien genes carried by chromosome 6P. The translocation line WAT33-1-3 and introgression lines WAI37-2 and WAI41-1, which had significant characteristics of multikernel (high numbers of kernels per spike), could be utilized as novel germplasms for high-yield wheat breeding.

Salinity tolerance and sodium exclusion in genus Triticum

The ability of plants to exclude sodium from the shoot is one of the major components of salinity tolerance. In this study, considerable variability in sodium exclusion within different species is demonstrated. The diploid species T. monococcum revealed a large (50-fold) variability in sodium exclusion in contrast to T. urartu, which was significantly less variable (10-fold). These species with the A genome are known to be salt sensitive, whilst T. (Aegilops) tauschii, a diploid species with the D genome, was very salt tolerant, but had only moderate variability in sodium exclusion (10-fold). The tetraploid species T. turgidum ssp. durum (both cultivated and landraces) and wild emmer T. dicoccoides (all with the AB genome) showed a range of variability in both salinity tolerance and sodium exclusion. The general pattern (from most sensitive and with highest Na+ accumulation) was as follows: durum (cultivated) < durum (landraces) < wild emmer. Cultivated durum wheats had minimal or no variability, whereas landraces of durum wheats had greater variability, two excellent genotypes having been identified which combine very low sodium accumulation with very high salinity tolerance. Wild emmer was extremely variable. Hexaploid bread wheat, T. aestivum with the ABD genome, is known to be more salt tolerant, having an effective mechanism for sodium exclusion but only low variability.

Acc homoeoloci and the evolution of wheat genomes

The DNA sequences of wheat Acc-1 and Acc-2 loci, encoding the plastid and cytosolic forms of the enzyme acetyl-CoA carboxylase, were analyzed with a view to understanding the evolution of these genes and the origin of the three genomes in modern hexaploid wheat. Acc-1 and Acc-2 loci from each of the wheats Triticum urartu (A genome), Aegilops tauschii (D genome), Triticum turgidum (AB genome), and Triticum aestivum (ABD genome), as well as two Acc-2-related pseudogenes from T. urartu were sequenced. The 2.3-2.4 Mya divergence time calculated here for the three homoeologous chromosomes, on the basis of coding and intron sequences of the Acc-1 genes, is at the low end of other estimates. Our clock was calibrated by using 60 Mya for the divergence between wheat and maize. On the same time scale, wheat and barley diverged 11.6 Mya, based on sequences of Acc and other genes. The regions flanking the Acc genes are not conserved among the A, B, and D genomes. They are conserved when comparing homoeologous genomes of diploid, tetraploid, and hexaploid wheats. Substitution rates in intergenic regions consisting primarily of repetitive sequences vary substantially along the loci and on average are 3.5-fold higher than the Acc intron substitution rates. The composition of the Acc homoeoloci suggests haplotype divergence exceeding in some cases 0.5 Mya. Such variation might result in a significant overestimate of the time since tetraploid wheat formation, which occurred no more than 0.5 Mya.

Assessment of genetic diversity in Triticum spp. and Aegilops spp. using AFLP markers

Genetic diversity among some wild relatives of wheat was estimated using amplified fragment length polymorphism (AFLP) and morphological markers. Thirty one Triticum and Aegilops genotypes including twenty-four Triticum and Aegilops accessions belonging to five diploid (Triticum baeoticum, Triticum monococcum, Aegilops umbellulata, Aegilops caudata and Aegilops tauschii), five tetraploid (Triticum dicoccoides, Triticum dicoccum, Aegilops crassa (4x), Aegilops cylindrica, Aegilops triuncialis) and two hexaploid (Triticum compactum, A. crassa (6x)) species sampled from different ecogeographical regions of Iran; a durum wheat cultivar 'Langdon', a local wheat cultivar 'Roshan', a wheat cultivar 'Chinese spring' and four synthetic hexaploid wheats were evaluated. Genetic diversity among wheat accessions was estimated using 14 PstI:MseI primer pair combinations. Of the approximately 414 detected AFLP markers, 387 (93.5%) were polymorphic with 28 bands per used primer pair. Cluster analysis of 31 accessions belonging to the 15 species by UPGMA cluster analysis based on Jaccard’s similarity estimates for AFLP data divided all accessions into two major clusters reflecting almost their genome composition. The first one included wheat species having A and AB genomes, while second cluster included wheat species having C, D, AB, CD, UC, DM, DDM and ABD genomes. The genetic similarity coefficients ranged from 0.12 between Ae. glabra and accession number 3 of T. monococcum and 0.57 between A. crassa (6x) and Ae. crassa (4x-6x). Two Aegilops species of A. umbellulata and A. caudata were ranked as the second most related species.

Attempts to induce homoeologous pairing between wheat and Agropyron cristatum genomes

Agropyron cristatum (2n = 4x = 28, PPPP) possesses potentially valuable traits that could be used in wheat (Triticum aestivum) improvement through interspecific hybridization. Homoeologous pairing between wheat chromosomes and P chromosomes added to wheat in a set of wheat - A. cristatum addition lines was assessed. First, the Ph-suppressing effect of P chromosomes (except 7P) was analyzed. It was concluded that this system is polygenic with no major gene, and consequently, has no prospect in the transfer of alien genes from wild relatives. In a second step, the potential of the deletion ph1b of the Ph1 gene for inducing P-ABD pairing was evaluated. Allosyndetic associations between P and ABD genomes are very rare. This very low level of pairing is likely due to divergence in the repeated sequences between Agropyron and wheat genomes. Development of translocation lines using ionizing radiation seems to be a more suitable technique than homoeologous recombination to exploit the A. cristatum genome in wheat improvement.

Molecular characterization of a wheat – Thinopyrum ponticum partial amphiploid and its derivatives for resistance to leaf rust

Leaf rust (caused by Puccinia triticina Eriks.) occurs annually in most wheat-growing areas of the world. Thinopyrum ponticum (Podp.) Z.-W. Liu & R.-C. Wang has provided several leaf rust resistance genes to protect wheat from this fungal disease. Three chromosome substitution lines, Ji806, Ji807, and Ji859, and two chromosome addition lines, Ji791 and Ji924, with a winter growing habit were developed from crosses between wheat (Triticum aestivum L. em Thell.) and the wheat - Th. ponticum partial amphiploid line 693. These lines were resistant to leaf rust isolates from China. Sequence-tagged site (STS) analysis with the J09-STS marker, which is linked to the gene Lr24, revealed that the partial amphiploid line 693 and all of the substitution and addition lines carried gene Lr24. Genomic in situ hybridization (GISH) analysis was carried out on chromosome preparations using total genomic DNA from Pseudoroegneria strigosa (M. Bieb) A. Löve (St genome, 2n = 14) as a probe in the presence of total genomic DNA from T. aestivum 'Chinese Spring' wheat (ABD genomes, 2n = 42). The GISH analysis demonstrated that these lines had a pair of chromosomes displaying the typical pattern of a Js genome chromosome. This indicates that the chromosome that carries gene Lr24 belonged to the Js genome of Th. ponticum. In addition to 40 wheat chromosomes, eight Js and eight J genome chromosomes were also differentiated by GISH in the partial amphiploid line 693. Since most sources of Lr24 have a red grain color, the white-colored seeds in all of these substitution and addition lines, together with high protein content in some of the lines, make them very useful as a donor source for winter wheat breeding programs.

Molecular cytogenetic evidence for a high level of chromosome pairing among different genomes in Triticum aestivum–Thinopyrum intermedium hybrids

Intergeneric hybrids (ABDJJsS genomes) were made between Triticum aestivum cv. Chinese Spring (CS) and Thinopyrum intermedium. Genomic in situ hybridization (GISH) using genomic DNA probes from Pseudoroegneria libanotica (Hackel) D.R. Dewey (genome S, 2n = 14) was used to study chromosome pairing among J, Js, S and wheat ABD genomes in the hybrids. It was shown that in the hexaploid (ABDJJsS) hybrids, high pairing occurred among wheat chromosomes and among Thinopyrum chromosomes. A closer relationship was observed among the three genomes of Th. intermedium than among the three genomes of T. aestivum. It was further discerned that S genome chromosomes paired with J- and Js-genome chromosomes at a high frequency. The frequency of heterologous pairing between S and J or S and Js chromosomes was higher than those between J and Js chromosomes, indicating that the S-genome was more closely related with these two genomes. Our results provided direct molecular cytogenetic evidence for the hypothesis that S-genome chromosomes are genetically similar to the J-genome chromosomes and, therefore, genetic exchange between these genomes is possible. The discovery of a close relationship among S, J and Js genomes provides valuable markers for molecular cytogenetic analyses using S-genomic DNA probes in monitoring the transfer of useful traits from Thinopyrum species into wheat.

Genomic in situ hybridization analysis of Thinopyrum chromatin in a wheat-Th. intermedium partial amphiploid and six derived chromosome addition lines

The genomic origin of alien chromosomes present in a wheat-Thinopyrum intermedium partial amphiploid TAF46 (2n = 8x = 56) and six derived chromosome addition lines were analyzed by genomic in situ hybridization (GISH) using S genomic DNA from Pseudoroegneria strigosa (2n = 2x = 14, SS) as a probe. The GISH analysis clearly showed that the chromosome complement of the partial amphiploid TAF46 consists of an entire wheat genome plus one synthetic genome consisting of a mixture of six S genome chromosomes and eight J (=E) genome chromosomes derived from Th. intermedium (2n = 6x = 42, JJJ(s)J(s)SS). There were no Js genome chromosomes present in TAF46. The J genome chromosomes present in TAF46 displayed a unique GISH hybridization pattern with the S genomic DNA probe, in which S genome DNA strongly hybridized at the terminal regions and weakly hybridized over the remaining parts of the chromosomes. This provides a diagnostic marker for distinguishing J genome chromosomes from Js or S genome or wheat ABD genome chromosomes. The genomic origin of the alien chromosomes present in the six derived chromosome addition lines were identified by their characteristic GISH hybridization patterns with S genomic DNA probe. GISH analysis showed that addition lines L1, L2, L3, and L5 carried one pair of J genome chromosomes, while addition lines L4 and L7 each carried one pair of S genome chromosomes. GISH patterns detected by the S genome probe on addition line of L1 were identical to those of the J genome chromosomes present in the partial amphiploid TAF46, suggesting that these chromosomes were not structurally altered when they were transferred from TAF46 to addition lines.

Absence of the J genome in Leymus species (Poaceae: Triticeae): evidence from DNA hybridization and meiotic pairing

To test the presence of a J genome in the type species of Leymus, L. arenarius, its total genomic DNA and that of tetraploids L. mollis, L. salinus ssp. salmonis, L. ambiguus, L. chinensis, L. secalinus, L. alaicus ssp. karataviensis, and L. innovatus were probed with the 277-bp insert of pLeUCD2, which can hybridize with the J, S, and P but not with the N, R, V, Q, I, T, and ABD genomes. The DNA probe hybridized with PalI- or TaqI-digested total DNAs from Thinopyrum elongatum (JeJe diploid) and T. elongatum x Psathyrostachys juncea (JeN hybrid), but not with those from L. arenarius (NNNNXXXX octoploid) and all tetraploid Leymus species (NNXX). Attempts to cross diploid Thinopyrum and tetraploid Leymus species yielded only one triploid hybrid, T. elongatum x L. salinus ssp. salmonis. Meiotic chromosome associations at metaphase I of pollen mother cells in the triploid hybrid averaged 19.69 univalents, 0.64 bivalents, and 0.01 trivalents per cell. Chromosome pairings in the tetraploid hybrids of L. mollis x L. salinus ssp. salmonis, and the reciprocal cross, indicate that L. mollis and L. salinus ssp. salmonis shae the same genomic constitution. Both the DNA probe and genome analysis results confirm the absence of the J genome in the seven additional Leymus species tested. Meiotic data indicated that tetraploid Leymus species could not have the genome formula N1N1N2N2; thus their genome formulas should remain as NNXX until the source of X is identified.

Mycorrhizal dependence of modern wheat cultivars and ancestors: a synthesis

To supplement previous studies, wheat ancestors with the A, S(B), D, and AB genomes and modern spring and winter wheat cultivars were vernalized for 42 days in a growth chamber prior to transplanting and growth in a greenhouse for 14 weeks. One-half of the seedlings were inoculated with a mixture of equal numbers of spores of six vesicular–arbuscular mycorrhizal fungi at transplanting. Dry weights of plants and component parts were determined. Percent colonization of roots was determined microscopically. Growth response and mycorrhizal dependence were calculated. However, no mycorrhizal dependence was observed in Triticum monococcum PI 266844 and PI 355520 (A genome), Aegilops speltoides 1773 (S(B) genome), or in the AB genome ancestors Triticum carthlicum 2825, Triticum polonicum 2808, Triticum dicoccum 1165, Triticum pyramidale 2809, Triticum orientale 2805, Triticum paleocolchicum 2807, and Triticum persidum 2811 and 2812. Mycorrhizal dependence in the D genome ancestors was more variable. Triticum tauschii var. typica accessions 1649, 1691, 2378, 2448, 2492, 2495, 2528, 2541, and 2567 lacked dependence, whereas T. tauschii var. meyeri 2529 and var. strangulata 2377 and 2452 were dependent on mycorrhizal symbiosis. The spring wheat cultivars Chinese Spring 3008, Spelta 2603, Pavon 76 2980, and Norin 29 3025 and the winter wheat cultivars TAM 200, Wrangler, Saluda, and Karl were not dependent on mycorrhizae, whereas winter wheat cultivars TAM 107 and Century were dependent. When these data are synthesized with previously tested ancestors, landraces, and cultivars, it appears that both dependent and nondependent diploid ancestors with the A, S(B), and D genomes existed, but dependence was lost in tetraploid ancestors. Since no dependence on mycorrhizae has been demonstrated in any AB genome ancestors, the presence of dependence in modern cultivars of the hexaploid ABD genome is probably derived from the D genome. The consistent dependence of wheat cultivars released before 1950 suggests that modern breeding practices have reduced dependence on mycorrhizal symbiosis. The implications of having mycorrhizal colonization in the absence of mycorrhizal dependence (benefit) are discussed. Key words: pathogenesis, growth response, vesicular – arbuscular mycorrhizae.

Inheritance of Cold Hardiness in Triticum aestivum × Synthetic Hexaploid Wheat Crosses

AbstractSynthetic hexaploid wheat, produced by combining tetraploid wheat (AB genome) with Triticum tauschii (D genome), was crossed to modern hexaploid wheat (Triticum aestivum ABD genome) in an attempt to introduce new cold hardiness genes into the common hexaploid wheat gene pool. The cold hardiness levels of F) hybrids ranged from similar to parental means to equal to the hardy parent, indicating that cold hardiness was controlled by both additive and dominant genes. As expected when dominant gene action is involved, differences between F2 and parental means were smaller than comparable differences in the F., Frequency distributions of F2—derived F3 lines also suggested that dominant genes were involved in the control of cold hardiness in some crosses. Heritability estimates for cold hardiness ranged from 63 to 70 % indicating that selection for cold hardiness should be effective in populations arising from crosses between common and synthetic hexaploid wheat. However, high selection pressure on the progeny of crosses that included the most hardy T. aestivum, T. durum, and T. tauschii accessions as parents did not identify transgressive segregates for improved cold hardiness. These observations indicate that the close wheat relatives, sharing common genomes with T. aestivum, are not promising sources of new genes to increase the maximum cold hardiness potential of common hexaploid wheat.

Enhanced meiotic chromosome pairing in intergeneric hybrids between Triticum aestivum and diploid Inner Mongolian Agropyron

Triticum aestivum cv. Chinese Spring (2n = 6x = 42, ABD genomes) was crossed with diploid Inner Mongolian Agropyron Gaertn. species A. cristatum and A. mongolicum and reciprocal hybrids between them (2n = 2x = 14, P genome, with or without B chromosomes). Intergeneric hybrids with 2n = 27, 28, 32, and 33 chromosomes were produced by the aid of embryo rescue. The extra chromosomes in two hybrids were assumed to be B chromosomes transmitted by the male Agropyron parent. Average meiotic pairing in the euploid hybrid with 28 chromosomes was 14.38 univalents + 4.92 bivalents + 1.26 trivalents. This level of pairing higher than expected was likely due to homeologous associations between wheat chromosomes. This data indicates that the P genome of diploid as well as tetraploid Agropyron originating from Inner Mongolia possess a genetic system interfering with 5B homoeologous restricting system of wheat.Key words: intergeneric hybrids, Triticum aestivum, diploid Agropyron species, chromosome pairing.

Production and cytogenetic analysis of the intergeneric hybrids between nine Elymus species and common wheat (Triticum aestivum L.)

Intergeneric hybridizations were performed between Triticum aestivum L. (2n=6x=42, AABBDD) and twelve Elymus species, ten tetraploids (2n=4x=28, SSYY) and two hexaploids (2n=6x=42, SSHHYY and SSYY??), namely, E. pendulinus (Nevski) Tzvelev, E. altissimus (Keng), Love, E. anthosachnoides (Keng) Love, E. brevipes (Keng) Love, E. dolichatherus (Keng) Love, E. parviglumis (Keng) Love, E. pseudonutans (Keng) Love, E. tibeticus (Melderis) G. Singh, E. semicostatus (Nees ex Steud.) Melderis, E. caucasicus (C. Koch) Tzvelev (tetraploids), and E. tsukushiensis Honda and E. tschimganicus (Drobov) Tzvelev (hexaploids). The hybrid seed sets in different combinations varied from 4.8%–72.2%, and embryo yields ranged from 3.2%–36.7%. Nine combinations produced adult hybrid plants, eight pentaploids and one hexaploid, through embryo rescue. The production of hybrid plants varied from 1.2%–30%. Chromosome pairing was analysed at metaphase I in the parental species and the hybrids. Average meiotic configurations of 33.51 I+0.74 II+0.03 III+0.001 IV were observed amongst the pentaploid hybrids although there was a large variation, and 31.42 I+5.21 II+0.04 III was recorded in the hexaploid hybrid. It is concluded from the study that: 1) very little pairing occurred between the ABD genomes in T. aestivum and the different genomes in the tetraploid Elymus species. even though the pairing behaviour varied in different combinations; 2) the hexaploid combination had distinctly higher chromosome pairing than the other pentaploid combinations, which could be due either to a low degree of homoeology between the T. aestivum and E. tschimganicus genomes or that the latter species contains, certain gene(s) which increase the meiotic pairing between genomes from the same parental species.