Repetitive DNA, Genome and Species Relationships in Avena and Arrhenatherum(Poaceae)

Repetitive sequences have been widely used for examining genomeand species relationships by in situ and Southern hybridization.In the present study, double-stranded DNA sequences, from denaturedDNA reannealed to Cot = 1, from Avena strigosa(2 n = 2x = 14;A genome; referred to as CotA) and Avena sativa(2n = 6 x =42; ACD genome; referred to as CotACD) were isolated with ahydroxyapatite column, and were used for in situ hybridizationon hexaploid A. sativa chromosomes. Probe CotACD labelled allchromosomes evenly throughout their length at the same intensity.Probe CotA labelled the 28 A and D genome chromosomes stronglyand the 14 C genome chromosomes weakly. Three cloned repetitivesequences, pAvKB9 (126 bp), pAvKB26 (223 bp) and pAvKB32 (721bp) were characterized in the A, B, C and D Avena genomes andthe genus Arrhenatherum using molecular and cytological methods.Clones pAvKB9 and pAvKB26 were absent from the Avena C genome,while both could identify the presence of the D genome by Southernhybridization. In situ hybridization to diploid and tetraploidAvena species revealed that the probes showed a dispersed genomicorganization and that they are present on both arms of all chromosomes.These sequences were excluded from areas where tandem repeats,such as rRNA genes and telomeres, are present. These resultsindicate the close relationship between A and D genomes andthe presence of common DNA sequences between A and C Avena genomes.All three clones hybridized to Southern blots containingArrhenatherumdigested genomic DNA, indicating Arrhenatherum’s closeaffinity to A, B and D Avena genomes. Copyright 2000 Annalsof Botany Company Cereals, DNA, hydroxyapatite, in situ hybridization, oats, reassociation kinetics, repetitive DNA     

The Hybrid Origin of Two Cultivars of Crocus (Iridaceae) Analysed by Molecular Cytogenetics including Genomic Southern and in situ Hybridization

The origin of the two common cultivars of Crocus, C. 'Stellaris'(2n = 2x = 10) and C. 'Golden Yellow' (2n = 3x = 14) was investigatedby fluorescent in situ hybridization using both total genomicDNA and cloned DNA sequences as probes. The clear differentiationbetween the chromosomes after genomic in situ hybridizationsupports the proposals of a hybrid origin of the cultivars andshows that they have the same parental genomes originating fromC. flavus (2n = 8) and C. angustifolius (2n = 12). C. 'Stellaris'has four chromosomes of C. flavus origin and six chromosomesof C. angustifolius origin. C. 'Golden Yellow' has eight chromosomesof C. flavus origin and six chromosomes of C. angustifoliusorigin. The number and location of 18S-5·8S-26S rRNAgenes on the chromosomes of the hybrids and of the parentalspecies agree with the results from the genomic probings. Hybridizationto Southern membranes also supports the hybrid origin of C.'Golden Yellow'.Copyright 1995, 1999 Academic Press Taxonomy, cytology, rDNA sites, in situ hybridization, Southern hybridization, Crocus     

Polyploidy and Evolution in Wild and CultivatedDahliaSpecies

Observations on the chromosomes of nine species ofDahliaCav.(Asteraceae, Heliantheae—Coreopsidinae) show that somehave 2n=32, others 2n=64, with a third group having both chromosomenumbers in the same taxon. Karyotype investigations showed thatthe chromosomes can be divided into groups of 14 metacentricsplus two submetacentrics per set of 16 chromosomes.In situhybridizationusing an rRNA gene probe indicated that the 2n=32 species haveeight hybridization sites whilst the 2n=64 species have 16 sites.Silver nitrate staining of these regions showed that not allof these nucleolar organizers are active. Meiotic analysis atmetaphase I and pachytene, by synaptonemal complex spreading,shows that the 2n=32 species have exclusive bivalent formationwhereas the 2n=64 species have small numbers of univalents plusquadrivalents in addition to bivalents. This study proposesthatDahliaspecies with 2n=32 are allotetraploids whereas thosespecies and chromosome races with 2n=64 are their autopolyploidderivatives. We suggest that a bivalent-promoting mechanismin the 2n=32 species may account for their meiotic behaviouras their component genomes appear so similar, and that thismechanism is also responsible for the low number of quadrivalentsin the 2n=64 taxa.Copyright 1998 Annals of Botany Comapny Chromosome pairing,Dahlia, in situhybridization, karyotype analysis, polyploidy, synaptonemal complex analysis     

Chromosomal Variation in Crocus vernus Hill (Iridaceae) Investigated by in situ Hybridization of rDNA and a Tandemly Repeated Sequence

The physical localization of three tandemly-organized repetitiveDNA sequences was investigated byin situ hybridization to metaphasechromosomes of 11 Crocus vernus accessions. The sequences includedwere the 18S–25S rDNA, the 5S rDNA and a tandemly-repeatedsequence cloned from C. vernus(clone pCvKB8). Ten 2n = 8 karyotypesfrom accessions ranging across the Alps and the Pyrenees couldbe interpreted as variations of a standard karyotype. Polymorphismswere found involving size of the satellite chromosomes, extra5S rDNA sites, and extensive differences in size and numberof pCvKB8 loci. The 2 n = 16 type did not correspond to anypossible tetraploid derived from the 2 n = 8 types. Copyright2000 Annals of Botany Company Evolution, phylogeny, Crocus vernus Hill (Iridaceae), in situ hybridization, chromosomal polymorphism, karyotype evolution, repetitive DNA     

Effects on Growth and Development of Individual Chromosomes from Slow-growing Lophopyrum elongatum Love when Incorporated into Bread Wheat (Triticum aestivum L.)

Aspects of growth and development were evaluated in the fast-developingannual Triticum aestivum L. ‘Chinese Spring’, theslow-developing perennial Lophopyrum elongatum Löve, theiramphiploid, and chromosome addition and substitution lines ofL. elongatum into ‘Chinese Spring’. Relative growthrates (RGR) of shoots of L. elongatum and the amphiploid werelower than those of ‘Chinese Spring’ (34 and 13%respectively) and main stem development was also slower. Therewas no difference in shoot RGR of any of the chromosome additionor substitution lines and that of ‘Chinese Spring’when assessed between Haun stages 2.0 and 5.0. In contrast,several aspects of plant development were observed to differin the chromosome addition and substitution lines. SubstitutingE genome chromosomes (with the exceptions of 3E and 4E) forD genome chromosomes, or adding E genome chromosomes, slowedthe rate of main stem development, at least up to Haun stage5.0. Despite these differences in the rate of main stem development,the appearance of adventitious roots commenced at approximatelyHaun stage 2.0 in all genotypes. However, the numbers of adventitiousroots and tillers at the 5.0 Haun stage differed between someof the lines when compared to ‘Chinese Spring’.Although incorporation of some L. elongatum chromosomes alteredaspects of plant development, all lines showed more similarityto bread wheat than to L. elongatum, reflecting, in part, thegreater genetic contribution made by bread wheat to these lines.Copyright 2001 Annals of Botany Company Adventitious roots, chromosome addition and substitution lines, Haun stage, Lophopyrum elongatum, relative growth rate (RGR), Triticum aestivum(wheat)     

Expression of Thinopyrum distichum NORs in wheat×Thinopyrum amphiploids and their backcross generations

Summary The C-banding pattern of the satellited chromosomes in Thinopyrum distichum and Triticum durum was established. Both T. durum and Th. distichum contained two pairs of satellited chromosomes, which could be distinguished from one another. In the amphiploids [T. durum×Th. distichum (2x=56)] and in the backcross T. durum/(T. durum×Th. distichum)², BC₁F₃, and BC₁F₅ (2n = 42) the satellite was visible on only 1B and 6B of T. durum. The vector pTa 71 containing the rRNA gene from wheat hybridized to two pairs of chromosomes (four hybridization sites) in T. durum and Th. distichum, to eight sites in the amphiploid hybrid (2n=56), and to six sites in the backcross populations BC₁F₁. BC₁F₃, and BC₁F₅ (2n=42). The two satellite pairs in Th. distichum could be distinguished by the chromosomal location of the rRNA site (median or subterminal) and by the centromere position. One copy of each pair was present in the BC₁F₁, but in the BC₁F₃ and BC₁F₅ populations the pair with the subterminal location of rRNA genes was absent. Silver nitrate staining indicated that the rRNA genes of T. durum did not completely suppress those of Th. distichum. The octoploid amphiploid (2n = 56) contained a maximum of four large and four small nucleoli and the hexaploid BC₁s (2n=42), four large and two small nucleoli.     

Genomic origin and organization of the allopolyploid Primula egaliksensis investigated by in situ hybridization

Background and Aims: Earlier studies have suggested that the tetraploid Primula egaliksensis(2n = 40) originated from hybridization between the diploidsP. mistassinica (2n = 18) and P. nutans (2n = 22), which werehypothesized to be the maternal and paternal parent, respectively.The present paper is aimed at verifying the hybrid nature ofP. egaliksensis using cytogenetic tools, and to investigatethe extent to which the parental genomes have undergone genomicreorganization. Methods: Genomic in situ hybridization (GISH) and fluorescent in situhybridization (FISH) with ribosomal DNA (rDNA) probes, togetherwith sequencing of the internal transcribed spacer (ITS) regionof the rDNA, were used to identify the origin of P. egaliksensisand to explore its genomic organization, particularly at rDNAloci. Key Results: GISH showed that P. egaliksensis inherited all chromosomes fromP. mistassinica and P. nutans and did not reveal major intergenomicrearrangements between the parental genomes (e.g. interchromosomaltranslocations). However, karyological comparisons and FISHexperiments suggested small-scale rearrangements, particularlyat rDNA sites. Primula egaliksensis lacked the ITS-bearing heterochromaticknobs characteristic of the maternal parent P. mistassinicaand maintained only the rDNA loci of P. nutans. These resultscorroborated sequence data indicating that most ITS sequencesof P. egaliksensis were of the paternal repeat type. Conclusions: The lack of major rearrangements may be a consequence of theconsiderable genetic divergence between the putative parents,while the rapid elimination of the ITS repeats from the maternalprogenitor may be explained by the subterminal location of ITSloci or a potential role of nucleolar dominance in chromosomestabilization. These small-scale rearrangements may be indicativeof genome diploidization, but further investigations are neededto confirm this assumption.     

The Close Relationship Between the A and B Genomes in Avena L. (Poaceae) Determined by Molecular Cytogenetic Analysis of Total Genomic, Tandemly and Dispersed Repetitive DNA Sequences

The genusAvena L. (Poaceae) consists of diploid, tetraploid,and hexaploid species, with the B genome known only in tetraploidspecies and the D genome in the hexaploid species. DNA:DNAinsitu hybridization, using total genomic DNA from diploidAvenastrigosa Schreb. (A_sgenome) as a probe, labelled all 28 chromosomesof the AB tetraploidAvena vaviloviana (Malz.) Mordv. stronglyand uniformly, revealing the close relationship between thesetwo genomes. Comparison of patterns of size-separated DNA restrictionfragments between the diploidA. strigosa and the tetraploidA.vaviloviana , using 32 different restriction enzymes, revealedno differences. Southern hybridization using total AB genomicDNA as a probe also gave no differences in banding patternsbetween the two genomes, even when a large excess of A genomicDNA was used as a block. From anA. vaviloviana genomic library,1800 colonies were blotted and probed sequentially with A andAB genomic DNA, but no colony was identified to be B genomespecific. DNA digests of AB genome tetraploids with restrictionenzymeHae III gave a strong band at 4.2 kb. Clone pAbKB3, derivedfrom the 4.2 kb band, was found to be part of aTy1-copia -likeretrotransposon present in A and B genome chromosomes. ClonedrRNA genes were used forin situ hybridization and showed thatdiploidA. strigosa has four major sites for 18S-25S rDNA andtwo pairs of sites for 5S rDNA (pairs on the same satellitedchromosome, on different chromosome arms), while 4xA. vavilovianahas eight major sites for 18S-25S rDNA and four pairs of sitesfor 5S rDNA (pairs on the same satellited chromosome, on differentchromosome arms). A repetitive sequence from rye pSc119.2, showeddispersed hybridization, while the telomeric sequence in clonepLT11 hybridized to telomeres. Again no discrimination was possiblebetween A and B genome chromosomes. The molecular similaritiesbetween the diploidA. strigosa and thebarbata group tetraploidsclearly indicate that thebarbata group of tetraploids arosefrom A_sdiploids through autotetraploidization. Avena ; evolution; repetitive sequences; in situ hybridization; retrotransposons; genome organization     

Characterization of Genome and Chromosomes in Octoploid Wheat wheatgrass Amphiploid Zhong 2 Using Fluorescence in situ Hybridization and Chromosome Pairing Analysis

Genomic constitution of octoploid wheat-wheatgrass amphiploid Zhong 2 was analyzed by chromosome pairing and fluorescence in sim hybridization techniques. The results indicated that the octoploid wheatwheatgrass chromosomes in Zhong 2 were derived from the distant homologous genomes of wheatgrass ( Agropyron intermedium (Host) P.B. = Elytrigia intermedia (Host) Nevski = Thinotopyrum intermedium (Host) Barkworth and Dewey, and thew distant homologous genomes were not from the E geaome of T. elongatum 2x. Zhong 2 contained 12 wheatgrass chromosomes in which a pair of chromosomes was involved in translocation between wheatgrass and wheat chromosomes.     

应用荧光原位杂交和染色体配对研究八倍体小冰麦中2的染色体组构成及染色体特征

通过染色体配对分析和荧光原位杂交（ＦＩＳＨ）技术对八倍体小冰麦中２的染色体组构成进行分析,结果表明：八倍体小冰麦中２含有的冰草染色体是来自天蓝冰草（Ａｇｒｏｐｙｒｏｎ　ｉｎｔｅｒｍｅｄｉｕｍ（Ｈｏｓｔ）Ｐ．Ｂ．＝Ｅｌｙｔｒｉｇｉａ　ｉｎｔｅｒｍｅｄｉａ（Ｈｏｓｔ）Ｎｅｖｓｋｉ＝Ｔｈｉｎｏｐｙｒｕｍ　ｉｎｔｅｒｍｅｄｉｕｍ　（Ｈｏｓｔ）Ｂａｒｋｗｏｒｔｈ　ａｎｄ　Ｄｅｗｅｙ）具同亲关系的染色体组,但冰草的这种同亲关系的染色体组不同于二倍体长穗偃麦草（Ｔｈｉｎｏｐｙｒｕｍ　ｅｌｏｕｇａｔｕｍ　２Ｘ）的Ｅ组染色体。中２含有１２条冰草染色体,且有一对染色体为小麦（Ｔｒｉｔｉｃｕｍ　ａｅｓｔｉｖｕｍ　Ｌ．）染色体和冰草染色体之间易位所形成的。     

Cytogenetic and genomic relationships ofThinopyrum elongatum with twoPsathyrostachys species and withLeymus secalinus (Poaceae)

Intergeneric hybridizations were made betweenT. elongatum, and twoPsathyrostachys and fiveLeymus species. The seed set obtained onT. elongatum ×Leymus hybrids ranged from 5.65% to 20.00%, depending onLeymus species. The seed set obtained onT. elongatum ×Psathyrostachys hybrids ranged from 16.07% to 19.70%. Meiotic pairing at metaphase-I in JN diploid hybrids ofT. elongatum ×Psathyrostachys species revealed a very low level homology between the basic J and N genomes, and further demonstrated that the two genomes are quite diverged. Chromosome pairing in theT. elongatum ×Leymus secalinus hybrid averaged 15.19 univalents + 2.62 rod bivalents + 0.26 ring bivalents + 0.02 trivalents, suggesting that the partial J^e chromosomes ofT. elongatum has homology withLeymus secalinus genomes.L. secalinus might have 3–4 chromosomes originating from J^e genome.     

Repeated DNA sequences isolated by microdissection. II. Comparative analysis in Hordeum vulgare and Triticum aestivum

The genomic organization of two satellite DNA sequences, pHvMWG2314 and pHvMWG2315, of barley (Hordeum vulgare, 2n=14, HH) was studied by comparative in situ hybridization (ISH) and PCR analysis. Both sequences are members of different RsaI families. The sequence pHvMWG2314 is a new satellite element with a monomer unit of 73 bp which is moderately amplified in different grasses and occurs in interstitial clusters on D-genome chromosomes of hexaploid wheat (Triticum aestivum, 2n=42, AABBDD). The 331-bp monomer pHvMWG2315 belongs to a tandemly amplified repetitive sequence family that is present in the Poaceae and preferentially amplified in Aegilops squarrosa (2n=14, DD), H. vulgare and Agropyron elongatum. (2n=14, EE). The first described representative of this family was pAs 1 from Ae. squarrosa. Different sequences of one satellite DNA family were amplified from Ae. squarrosa, A. elongatum and H. vulgare using PCR. Characteristic differences between members of the D and H genome occurred in a variable region which is flanked by two conserved segments. The heterogeneity within this element was exploited for the cytogenetic analysis of Triticeae genomes and chromosomes. Comparative ISH with pHvMWG2315 identified individual wheat and barley chromosomes under low (75%) and high (85%) hybridization stringency in homologous and heterologous systems. We propose the designation Tas330 for the Triticeae amplified sequence (Tas) satellite family with a 330 bp average monomer length.     

Genomic rearrangement between wheat and Thinopyrum elongatum revealed by mapped functional molecular markers

Thinopyrum elongatum serves as an excellent gene pool for wheat improvement. Genes for resistance to many biotic and abiotic stresses have been transferred from Th. elongatum to wheat through chromosome manipulation. For breeding programs, molecular markers enable screening of a large number of genotypes for alien chromosome introgressions. The main objective of the present study was to develop and characterize EST (expressed sequence tags) and PLUG (PCR-based Landmark Unique Gene) markers that can distinguish Th. elongatum chromatin from the wheat genomes. A total of 258 mapped EST primer pairs and 46 PLUG primer pairs were tested on DNA from wheat Chinese Spring (CS) and CS-Th. elongatum addition lines. The results showed that 43 primer pairs could be effectively mapped to specific Th. elongatum chromosomes. Twenty-two of the 43 markers displayed similar homoeologous chromosome locations to hexaploid wheat. Nine markers mapped to different linkage groups between wheat and Th. elongatum, while 12 makers mapped on two or three different Th. elongatum chromosomes. A comparison of molecular marker locations indicated that Th. elongatum genome was closely related to the D genome of wheat, and chromosome rearrangements and duplication had occurred in Th. elongatum and the wheat genomes. The markers will be useful in comparative gene mapping, chromosome evolutionary analysis, and gene introgression for wheat improvement using Th. elongatum accessions as gene donors.     

Chromosome identification and nuclear architecture in triticale tritordeum F1 hybrids

In situ hybridization with cloned, repetitive DNA probes andtotal genomic DNA enables the parental origin of all chromosomesto be established in metaphases of triticale tritordeum F¹hybrids (2n=6x=42). Nuclei contain seven chromosomes of Hordeumchilense origin, seven from Secale cereale and 28 of wheat origin.When used as a probe, total genomic rye DNA labelled the ryechromosomes strongly and uniformly along their lengths, withbrighter regions coincident with the terminal heterochromatin.The probe labelled the wheat-origin chromosomes weakly and wasalmost undetectable on the H. chilense-origin chromosomes. Incontrast, under the same conditions, H. chilense DNA hybridizedstrongly to the H. chilense- and, with intermediate strength,to the S. cereale-origin chromosomes, excluding the subtelomericheterochromatin: it hybridized only weakly to the wheat chromosomes,in some experiments revealing characteristic bands on wheatchromosomes. Cloned repetitive DNA probes from rye and H. chilensewere used as probes to identify the linkage groups of all oftheir own-species chromosomes. Analysis of hybridization patternsof various probes to prophase and interphase nuclei indicatedthat there are many non-random features in the localizationof both repetitive DNA and whole chromosomes, although generalpatterns of nuclear organization have yet to emerge. Both theparticular lines used and the techniques developed here arelikely to be valuable for production and characterization ofplant breeding material. Key words: In situ hybridization, triticale, cytogenetics, plant breeding, Hordeum chilense     

Development of wheat–<Emphasis Type="Italic">Lophopyrum elongatum</Emphasis> recombinant lines for enhanced sodium ‘exclusion’ during salinity stress

Lophopyrum elongatum (tall wheatgrass), a wild relative of wheat, can be used as a source of novel genes for improving salt tolerance of bread wheat. Sodium ‘exclusion’ is a major physiological mechanism for salt tolerance in a wheat–tall wheatgrass amphiploid, and a large proportion (~50%) for reduced Na⁺ accumulation in the flag leaf, as compared to wheat, was earlier shown to be contributed by genetic effects from substitution of chromosome 3E from tall wheatgrass for wheat chromosomes 3A and 3D. Homoeologous recombination between 3E and wheat chromosomes 3A and 3D was induced using the ph1b mutant, and putative recombinants were identified as having SSR markers specific for tall wheatgrass loci. As many as 14 recombinants with smaller segments of tall wheatgrass chromatin were identified and low-resolution breakpoint analysis was achieved using wheat SSR loci. Seven recombinants were identified to have leaf Na⁺ concentrations similar to those in 3E(3A) or 3E(3D) substitution lines, when grown in 200 mM NaCl in nutrient solution. Phenotypic analysis identified recombinants with introgressions at the distal end on the long arm of homoeologous group 3 chromosomes being responsible for Na⁺ ‘exclusion’. A total of 55 wheat SSR markers mapped to the long arm of homoeologous group 3 markers by genetic and deletion bin mapping were used for high resolution of wheat–tall wheatgrass chromosomal breakpoints in selected recombinants. Molecular marker analysis and genomic in situ hybridisation confirmed the 524-568 recombinant line as containing the smallest introgression of tall wheatgrass chromatin on the distal end of the long arm of wheat chromosome 3A and identified this line as suitable for developing wheat germplasm with Na⁺ ‘exclusion’.     

Dissecting the U,M, S and C genomes of wild relatives of bread wheat (Aegilops spp.) into chromosomes and exploring their synteny with wheat

Goat grasses (Aegilops spp.) contributed to the evolution of bread wheat and are important sources of genes and alleles for modern wheat improvement. However, their use in alien introgression breeding is hindered by poor knowledge of their genome structure and a lack of molecular tools. The analysis of large and complex genomes may be simplified by dissecting them into single chromosomes via flow cytometric sorting. In some species this is not possible due to similarities in relative DNA content among chromosomes within a karyotype. This work describes the distribution of GAA and ACG microsatellite repeats on chromosomes of the U, M, S and C genomes of Aegilops, and the use of microsatellite probes to label the chromosomes in suspension by fluorescence in situ hybridization (FISHIS). Bivariate flow cytometric analysis of chromosome DAPI fluorescence and fluorescence of FITC‐labelled microsatellites made it possible to discriminate all chromosomes and sort them with negligible contamination by other chromosomes. DNA of purified chromosomes was used as a template for polymerase chain reation (PCR) using Conserved Orthologous Set (COS) markers with known positions on wheat A, B and D genomes. Wheat–Aegilops macrosyntenic comparisons using COS markers revealed significant rearrangements in the U and C genomes, while the M and S genomes exhibited structure similar to wheat. Purified chromosome fractions provided an attractive resource to investigate the structure and evolution of the Aegilops genomes, and the COS markers assigned to Aegilops chromosomes will facilitate alien gene introgression into wheat.     

Salt Tolerance in the Triticeae: K/Na Discrimination in Synthetic Hexaploid Wheats

Ion concentrations were measured in the leaves of synthetichexaploid wheats and their parents growing in saline hydroponicculture. The synthetic hexaploids contained genomes from a tetraploidwheat (Triticum diccocum, T. durum, T. araraticum or T. timopheevi)and from a diploid species (T. monococcum, T. urartu, T. boeoticumor Aegilops squarrosa). Leaf Na concentrations were low, andK concentrations high, in Ae. squarrosa, T. araraticum and allof the synthetic hexaploids, but high in T. dicoccum and T.durum. At low salinities leaf Na concentrations were particularlyhigh in T. durum in comparison with the other species. Theseresults suggest that the enhanced K/Na discrimination character,originally found in Ae. squarrosa and BBAADD genome hexaploidwheats, is also present in diploid wheat and in GGAA genometetraploid wheats. It is suggested that this character has beenlost in the evolution of the BBAA genome tetraploid wheats. Key words: Salt, ion transport, A genome, Triticum spp     

In Situ Localization of Parental Genomes in a Wide Hybrid

In situ hybridization enabled DNA originating from the two parentalgenomes to be distinguished in plant hybrids. A probe of biotinylatedtotal genomic DNA from Secale africanum labelled the chromosomesof S. africanum origin but not those from Hordeum chilense inroot-tip chromosome spreads of the sexual hybrid between thetwo species. Hybridization of total genomic DNA from S. africanumto DNA on filters (dot blots) confirmed the distinction betweenDNA from Hordeum and Secale. The total genomic probe hybridizedto the whole length of the chromosomes from S. africanum remarkablyuniformly, labelling both euchromatin and heterochromatin, exceptat the centromeric region. The probe binding was visualizedas a yellow colour by the fluorescein-coupled detection systemwhich contrasted with the red fluorescing counterstain of theunlabelled chromatin. The chromosomes originating from bothparents could be seen and distinguished as red and yellow fluorescenceat all stages of the cell cycle. At interphase and prophase,the chromatin originating from the two parental genomes didnot mix. Chromosomes or groups of chromosomes occupied distinctdomains and also tended to be arranged in a Rabl configurationwith the centromeres clustered at one end of the nucleus. Wepropose calling the technique using total genomic DNA as a probe‘genomic in situ hybridization.’ Hordeum chilense, Secale africanum, hybrids, genomic in situ hybridization, DNA, repetitive sequences, chromosomes, chromosome disposition, nuclear order     

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

Intergeneric hybrids (ABDJJ^sS 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, J^s, S and wheat ABD genomes in the hybrids. It was shown that in the hexaploid (ABDJJ^sS) 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 J^s-genome chromosomes at a high frequency. The frequency of heterologous pairing between S and J or S and J^s chromosomes was higher than those between J and J^s 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 J^s 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. Received: 23 August 2000 / Accepted: 5 September 2000