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Genetic and cytogenetic analyses of the A genome of Triticum monococcum. VI. Production and identification of primary trisomics using the C-banding technique

Publication: Genome
August 1990

Abstract

Cytogenetic studies in Triticum monococcum (2n = 2x = 14) are nonexistent. To initiate such investigations in this species, a series of primary trisomics was generated from autotriploids derived from crosses between induced autotetraploids and diploids. All trisomics differed phenotypically from their diploid progenitors. Only two of the seven possible primary trisomic types produced distinct morphological features on the basis of which they could be distinguished. The chromosomes in the karyotype were morphologically very similar and could not be unequivocally identified using standard techniques. Therefore, C-banding was used to identify the chromosomes and trisomics of this species. Ag–NOR staining and in situ hybridization, using rDNA probes, were used to substantiate these identifications. A comparison of the C-banding patterns of the chromosomes of T. monococcum with those of the A genome in Triticum aestivum permitted identification of five of its chromosomes, viz., 1A, 2A, 3A, 5A, and 7A. The two remaining chromosomes possessed C-banding patterns that were not equivalent to those of any of the chromosomes in the A genome of the polyploid wheats. When one of these undesignated chromosomes from T. monococcum var. boeoticum was substituted for chromosome 4A of Triticum turgidum, it compensated well phenotypically and therefore genetically for the loss of this chromosome in the recipient species. Because this T. monococcum chromosome appeared to be homoeologous to the group 4 chromosomes of polyploid wheats, it was designated 4A. By the process of elimination the second undesignated chromosome in T. monococcum must be 6A. Analysis of the trisomics obtained led to the following conclusions. (i) Trisomics for chromosome 3A were not found among the trisomic lines analyzed cytologically. (ii) Primary trisomics for chromosomes 2A, 4A, 6A, and 7A were positively identified. (iii) Trisomics for the SAT chromosomes 1A and 5A were positively identified in some cases and not in others because of polymorphism in the telomeric C-band of the short arm of chromosome 1A. (iv) Trisomics for chromosome 7A were identified on the basis of their distinct phenotype, viz., the small narrow heads and small narrow leaves. Because rRNA hybridizes lightly to nucleolus organizer regions on chromosome 1A and heavily to nucleolus organizer regions on chromosome 5A, our results indicate that trisomics in line 50 carry chromosome 1A in triple dose and trisomics in lines 28 and 51 carry chromosome 5A in triplicate. Variable hybridization of the rDNA probe to nucleolus organizer regions on chromosomes in triple dose in lines 7, 20, and 28 precluded the identification of the extra chromosome in these lines. Cytogenetic methods for unequivocally identifying trisomics for chromosomes 1A and 5A are discussed. Thus six of the series of primary trisomics have been identified. Telotrisomic lines are also being produced.Key words: Triticum monococcum, trisomics, C-banding, Ag-NOR staining, in situ hybridization, rDNA probes, plant morphology.

Résumé

Le Triticum monococcum (2n = 2x = 14) n'a pas encore fait l'objet d'études cytogénétiques. Pour amorcer de telles études chez cette espèce, une série de plantes trisomiques primaires a été produite à partir d'autotriploïdes dérivées de croisements entre des autotétraploïdes induites et des diploïdes. Toutes les trisomiques ont différé phénotypiquement de leurs parents diploïdes. Sur sept types de trisomiques primaires possibles, deux seulement ont produit des traits morphologiques distincts permettant de les distinguer. Dans les caryotypes, les chromosomes se sont révélés morphologiquement très semblables et n'ont pu être identifiés sans équivoque par les techniques standard. La coloration des bandes C a donc été utilisée pour identifier les chromosomes et les trisomiques de cette espèce. De plus, la coloration à l'argent des régions organisatrices des nucléoles, l'hybridation in situ et l'emploi de sondes pour l'ADNr, ont servi à appuyer ces identifications. Une comparaison des profils de bandes C des chromosomes de T. monococcum avec ceux du génome A de T. aestivum a permis d'identifier cinq de ses chromosomes, soit les 1A, 2A, 3A, 5A, et 7A, alors que les profils des deux chromosomes restants n'ont présenté aucune équivalence avec tout autre chromosome du génome A des blés polyploïdes. Lorsque l'un des chromosomes indéterminés de T. monococcum var. boeoticum a été substitué au chromosome 4A de T. turgidum, il y eut compensation phénotypique, et donc génétique, pour la perte du 4A chez l'espèce réceptrice. Comme ce chromosome de T. monococcum a semblé être un homéologue du groupe de chromosomes 4 des blés polyploïdes, il a été désigné 4A et par voie d'élimination, l'autre chromosome indéterminé devait être le 6A. L'analyse des trisomiques obtenues a conduit aux conclusions suivantes : (i) parmi les lignées trisomiques obtenues, il n'en a pas été trouvé pour le chromosome 3A; (ii) les trisomiques primaires pour les chromosomes 2A, 4A, 6A et 7A, ont été positivement identifiés; (iii) les trisomiques pour les chromosomes SAT 1A et 5A ont été positivement identifiés dans certains cas, mais non dans d'autres, en raison du polymorphisme des bandes C télomiques du bras court du chromosome 1A; (iv) les trisomiques pour le chromosome 7A ont été identifiés par leur phénotype distinct, savoir, de petites feuilles étroites et de petits épis étroits. Comme l'ARNr s'est hybridé légèrement avec les régions organisatrices des nucléoles sur le chromosome 1A et fortement sur le 5A, nos résultats indiquent que les trisomiques de la lignée 50 sont porteuses d'une triple dose du chromosome 1A et que les trisomiques des lignées 28 et 51 sont porteuses du chromosome 5A en triplicata. Une hybridation variable des sondes de l'ADNr avec les régions organisatrices des nucléoles sur les chromosomes à triple dose des lignées 7, 20 et 28, n'a pas permis l'identification des chromosomes surnuméraires de ces lignées. En définitive, six des séries de trisomiques ont été identifiées et des lignées télotrisomiques ont été produites. Les méthodes cytogénétiques propres à identifier avec certitude les trisomiques pour les chromosomes 1A et 5A sont discutées. Mots clés : Triticum monococcum, trisomiques, bandes C, coloration argent – organisateur nucléolaire, hybridation in situ, sondes de l'ADNr, morphologie des plantes.[Traduit par la revue]

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cover image Genome
Genome
Volume 33Number 4August 1990
Pages: 542 - 555

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Version of record online: 15 February 2011

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1. Triticum L.
2. References
3. VRN-1 gene- associated prerequisites of spring growth habit in wild tetraploid wheat T. dicoccoides and the diploid A genome species
4. A Set of Cytogenetic Markers Allows the Precise Identification of All A-Genome Chromosomes in Diploid and Polyploid Wheat
5. Phylogenetic relationships among Triticum L. and Aegilops L. species as genome progenitors of bread wheat based on sequence diversity in trnT-F region of chloroplast DNA
6. Identification of the full set of Fagopyrum esculentum trisomics by heterochromatin banding analysis and rDNA physical mapping
7. Single-copy gene fluorescence in situ hybridization and genome analysis: Acc-2 loci mark evolutionary chromosomal rearrangements in wheat
8. Karyotypic analysis of Triticum monococcum using standard repetitive DNA probes and simple sequence repeats
9. C-banded karyotype of Thinopyrum bessarabicum and identification of its chromosomes in wheat background
10. Chromosomal location in triticale of leaf rust resistance genes introduced from Triticum monococcum
11. Tools and methodologies for cytogenetic studies of plant chromosomes
12. Wheat Genetics Resource Center: The First 25 Years
13. Distinguishing A/A m chromosome substitutions in secondary tetraploid triticale strains with the complete A-genome
14. References
15. Genus-specific localization of the TaiI family of tandem-repetitive sequences in either the centromeric or subtelomeric regions in Triticeae species (Poaceae) and its evolution in wheat
16. Deviations from Basic Chromosome Numbers—Aneuploidy
17. Genome differentiation in Aegilops. 2. Physical mapping of 5S and 18S–26S ribosomal RNA gene families in diploid species
18. Cytological identification of some trisomics of Russian wildrye (Psathyrostachys juncea)
19. Cytogenetic investigation of Triticum timopheevii (Zhuk.) Zhuk. and related species using the C-banding technique
20. Cytological and molecular characterization of a chromosome interchange and addition lines in Cadet involving chromosome 5B of wheat and 6Ag of Lophopyrum ponticum
21. CHy-banding patterns and chromatin organization inAegilops andTriticum species (Poaceae)
22. Metaphase-I analysis of a Triticum aestivum x T. monococcum hybrid by the C-banding technique
23. Inheritance of Induced Morphological Mutants in Triticutn monococcum L.
24. C-banding pattern and polymorphism of Aegilops caudata and chromosomal constitutions of the amphiploid T. aestivum — Ae. caudata and six derived chromosome addition lines
25. Physical mapping of the 18S.26S rRNA multigene family in common wheat: Identification of a new locus

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