Genetic introgression between tetraploidDactylis glomerata subspp.reichenbachii andglomerata in the French Alps. Insight from morphological and allozyme variation

The morphology, phenology and allozyme polymorphism in seven tetraploidDactylis glomerata populations growing in the French Alps were studied. Based on habitat and morphological characteristics, two of the populations could be classified asD. glomerata subsp.reichenbachii, which is known to comprise diploid and tetraploid plants growing exclusively on dolomite, on south-facing meadows. This subspecies has been previously recorded in the Italian and Swiss Alps but not in the French Alps. The remaining five populations were morphologically intermediate but more similar to the cosmopolitanD. glomerata subsp.glomerata. On the basis of allozyme variation, all populations were more related to subsp.reichenbachii than to the cosmopolitan subsp.glomerata, suggesting that gene flow has occurred between the two tetraploid subspecies. The possibility that selection has acted differently on morphological and allozyme characters is discussed.     

Synthesis and transformations of a pyrazole containing <Emphasis Type="Italic">α</Emphasis>,<Emphasis Type="Italic">β</Emphasis>-didehydro-<Emphasis Type="Italic">α</Emphasis>-amino acid derivatives

Summary.  2H-Pyran-2-ones 1 were transformed with various hydrazines into (E)- or (Z)-α,β-didehydro-α-amino acid (DDAA) derivatives 4 (and 7) containing a highly substituted pyrazolyl moiety attached at the β-position. With heterocyclic hydrazines, the products 4 were accompanied also by decarboxylated enamines E-6. In order to separate (E/Z)-mixtures of acids, they were transformed to the corresponding methyl esters 9 and 10 by the application of diazomethane. Catalytic hydrogenation under high pressures with Pd/C as a catalyst resulted in the formation of racemic alanine derivatives 11. Received January 29, 2002 Accepted May 27, 2002 Published online December 18, 2002 RID="*" ID="*"  Dedicated with deep respect to Professor Waldemar Adam on the occasion of his 65^th birthday. Acknowledgements We thank the Ministry of Education, Science and Sport of the Republic of Slovenia for the financial support (P0-0503-103). Dr. B. Kralj and Dr. D. Žigon (Center for Mass Spectroscopy, “Jožef Stefan” Institute, Ljubljana, Slovenia) are gratefully acknowledged for the mass measurements. Authors' address: Prof. Marijan Kočevar, Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, SI-1000 Ljubljana, Slovenia, E-mail: marijan.kocevar@uni-lj.si     

Genome size variations within Dasypyrum villosum: correlations with chromosomal traits, environmental factors and plant phenotypic characteristics and behaviour in reproduction

 Feulgen/DNA cytophotometric determinations carried out in the root meristem of seedlings showed that substantial quantitative alterations in the nuclear genome are present between and within 15 natural populations of Dasypyrum villosum in Italy. When the most variant values are considered, there is a 17.6% difference between the mean genome size of the populations, and a 66.2% difference between the genome size of individual plants within a population. A highly significant, positive correlation was found to exist between the genome size of D. villosum plants and the altitude of their stations, and differences in DNA contents between individual plants were greater in populations from mountain sites. Karyological analyses showed all chromosome pairs to differ largely in size between plants with differing DNA contents. A highly significant, positive correlation was found to exist between genome size and both the length of the chromosome complement at metaphase and the length and arm ratio of pair VII. Significant correlations were also found between DNA content and certain phenotypic characteristics of the plants. The mean genome size of the populations was negatively correlated with the mean leaf length and width. In contrast, the genome size of individual plants was positively correlated with the weight of the seed from which they originated and their flowering interval. A large range of genome sizes was found in the half-sib progeny of a plant having a relatively large genome. In contrast, in the half-sib progeny of a plant having a small genome, the genome sizes of the individual plants were less divergent and similar to that of the mother plant. All siblings from crosses between plants with differing genome sizes had similar DNA contents, which were intermediate between those of the parental plants, even if closer to the DNA content of the parent plant having the smaller genome size. Size polymorphism within pairs was never observed in plants obtained from these crosses or in half-sibs whose genome size differed from that of the mother plant. The intraspecific alterations observed in the nuclear genome and their effects on plant development and phenotype are briefly discussed as evolutionary factors which allow D. villosum populations to withstand different environmental conditions as well as the variability of conditions in a given environment. Received: 6 October 1997 / Accepted: 28 October 1997     

Evolutionary history of the polyploid complex of Cardamine amara (Brassicaceae): isozyme evidence

 In samples from 56 populations of Cardamine amara, representing four diploid subspecies (subspp. amara, opicii, balcanica, and pyrenaea) and two tetraploid subspecies (subspp. austriaca and olotensis) from different parts of the European distribution area, four enzyme systems with 23 alleles were studied. These data, together with previous morphological and karyological data, suggest that the distribution and variation pattern within the species was strongly influenced by the last glacial period and postglacial migrations. Cardamine amara subsp. pyrenaea is monomorphic for a unique allele, and subsp. balcanica has a unique allele, too which, however, is not fixed in all populations of the taxon. Both taxa seem to be relic ones, although otherwise subsp. balcanica in respect of allelic spectrum much resembles subsp. amara. The other two diploid subspecies, subsp. amara and subsp. opicii, are not characterised by presence of unique alleles but differ in allele frequencies. The two tetraploid subspecies have different evolutionary histories. C. amara subsp. austriaca seems to be an autopolyploid derivative of subsp. amara which colonised open space offered by retreating glaciers in the Eastern Alps. C. amara subsp. olotensis from the Iberian Peninsula represents most probably a polyploid of preglacial time. Received June 22, 2001; accepted May 17, 2002 Published online: September 13, 2002     

Contribution to the taxonomy and phylogeny of Sarcocapnos DC. (Fumariaceae)

 To solve problems concerning the status of the taxa described in the genus Sarcocapnos, we have conducted a study using morphological, pollen morphology (light microscopy), cytogenetic and molecular techniques. Focusing on the last technique, we have sequenced ITS-1 and ITS-2 of nuclear rDNA. The species differ basically according to 5 morphological traits (leaf shape, flower spur, corolla colour, corolla size, and crest of the stigmatic surface). The cytogenetic analyses indicated n=16 to be the standard chromosome number. The ITS analyses showed that the genus is monophyletic, defining two main well-supported clades, one containing S. saetabensis and S. enneaphylla, and one containing the rest of the species. In this second clade, S. speciosa, S. pulcherrima, and S. baetica subsp. ardalii are related, as are S. integrifolia, S. crassifolia subsp. crassifolia, and S. crassifolia subsp. atlantis; S. baetica subsp. baetica forms a trichotomy with the foregoing groups. S. speciosa is shown to be a species separate from S. crassifolia subsp. crassifolia, as in the case of S. baetica with respect to S. integrifolia. Palynologically, the parameters used enabled us to establish clear differences between the taxa, often corroborating the macromorphological and genetic data. The flower spur has been reduced several times in different groups of the genus, for which the classifications established on the basis of this trait are paraphyletic. Received July 16, 2002; accepted December 11, 2002 Published online: March 31, 2003     

Cytogenetics of new Guizotia Cass. (Compositae) interspecific hybrids pertaining to genomic and phylogenetic affinities

 The following crosses were made using four recognized species/subspecies and a new population of Guizotia, referred to as Chelelu after the name of the locality in Ethiopia from which it was collected: G. scabra subsp. schimperi × Chelelu, Chelelu × G. scabra subsp. scabra, G. zavattarii × G. arborescens and Chelelu × G. zavattarii (all accessions with 2n=30). Plant morphology as well as mitotic and meiotic chromosome analysis confirmed the hybrid nature of the obtained progeny. At metaphase I of meiosis, the F₁ hybrid plants (2n=30) showed a mean of about 95%, 31%, 63% and 0.50% of the pollen mother cells with 15 bivalents, and a mean of about 14.95, 13.75, 14.40 and 7.86 bivalents per cell, respectively. The respective mean pollen stainability was about 67%, 19%, 31% and 2%. From the results it was concluded that Chelelu is more closely related to G. scabra subsp. schimperi than to G. scabra subsp. scabra but more to the latter than to G. zavattarii. Guizotia zavattarii and G. arborescens are closely related to each other. Based on the cytological observations made, the probable basic chromosome number for the genus is discussed. Received November 5, 1999 Accepted August 21, 2001     

Cytogenetic characterization of <Emphasis Type="Italic">Hydrangea involucrata</Emphasis> Sieb. and <Emphasis Type="Italic">H. aspera</Emphasis> D. Don complex (Hydrangeaceae)<Emphasis Type="Italic">:</Emphasis> genetic,evolutional, and taxonomic implications

The subsection Asperae of genus Hydrangea L. (Hydrangeaceae) has been investigated for three reasons: several ambiguous classifications concerning Hydrangea aspera have been published, unexpected differences in genome size among seven accessions have been reported Cerbah et al. (Theor Appl Genet 103:45–51, 2001), and two atypical chromosome numbers (2n = 30 for Hydrangea involucrata and 2n = 34 for H. aspera) have been found when all other species of the genus present 2n = 36. Therefore, these two species and four subspecies of Hydrangea in all 29 accessions were analyzed for their genome size, chromosome number, and karyotype features. This investigation includes flow cytometric measurements of nuclear DNA content and bases composition (GC%), fluorochrome banding for detection of GC- and AT-rich DNA regions, and fluorescent in situ hybridisation (FISH) for chromosome mapping of 5 S and 18 S-5.8 S-26 S rDNA genes. In the H. aspera complex, the genome size ranged from 2.98 (subsp. sargentiana) to 4.67 pg/2C (subsp. aspera), an exceptional intraspecific variation of 1.57-fold. The mean base composition was 40.5% GC. Our report establishes the first karyotype for the species H. involucrata, and for the subspecies of H. aspera which indeed present different formulae, offering an element of discrimination. FISH and fluorochrome banding revealed the important differentiation between these two species (H. involucrata and H. aspera) and among four subspecies of the H. aspera complex. Our results are in agreement with the Chinese classification that places the groups Kawakami and Villosa as two different species: Hydrangea villosa Rehder and Hydrangea kawakami Hayata. This knowledge can contribute to effective germplasm management and horticultural use.     

Study of Poaceae phenology in a Mediterranean climate. Which species contribute most to airborne pollen counts?

The present study sought to determine which of the common Poaceae species in the study area contribute most to the Poaceae pollen season curve, and to determine the phenological behaviour of the species studied. The different floral phenophases in thirty-three Poaceae species common in and around the city of Córdoba (SW Iberian Peninsula) were checked periodically over the period 2004–2006. Results showed that longer phenological ranges were recorded in the coolest and wettest year, and shorter ranges in the warmest and driest year. Moreover, ranges varied as a function of altitude: populations in lower-lying areas flowered earlier than those at higher altitudes. The results, taken in conjunction with the findings of preliminary research into potential pollen production, showed that probably only four of the Poaceae species studied—Dactylis glomerata, Lolium rigidum, Trisetaria panicea and Vulpia geniculata—were major contributors to the Poaceae airborne pollen curve.     

Impact of land use intensity and temperature on the reproductive performance of <Emphasis Type="Italic">Dactylis glomerata</Emphasis> populations in the southeastern Alps

An understanding of the processes and environmental conditions governing spatial variation in reproductive performance of plants can provide important information about the factors characterizing plant community structure and influencing fitness in natural plant populations, especially in the context of climate and land use change. In this study, 60 mountain populations of Dactylis glomerata distributed along a fertilization regime in varying grassland hay meadows were evaluated. Variations in field management, climate, soil fertility, vegetation structure, population density and species richness on reproductive performance were examined. The results indicated that field management and soil nutrient availability are the main variables influencing population density and reproductive output of D. glomerata. Moreover, the results show the effect of temperature on seed mass and resource investment in reproduction. Climate and soil change suggest a morphological differentiation of reproductive traits: (i) individuals grown on sites with higher soil nutrient availability or nutrient supply have larger inflorescences with a greater number and heavier seeds; (ii) individuals grown on warmer sites have heavier seeds. We conclude that if the climate warms and increases land use intensification in hay meadows in the Alps, this will have a pronounced positive impact on the reproductive performance of D. glomerata. Moreover, it can be hypothesized that the migration potential of D. glomerata towards higher altitudes may be likely in the near future in response to accelerated climate change.     

Accessory nucleoli in microsporocytes of hybrid Phlox

Studies were conducted on the number of nucleoli present during diplotene and diakinesis in plants adjacent to, at the edge, and at the center of a zone of secondary intergradation between Phlox pilosa subsp. pilosa and P. pilosa subsp. fulgida. Assessory nucleoli were present in some cells of about 75% of the plants examined. Nucleolar numbers varied from 1 to 5. Where 2 or more nucleoli were present they were usually attached to different chromosomes. As the number of nucleoli increased, the volume of single nucleoli decreased so that volume of all nucleoli was roughly that of a normal single nucleolus. — Only 1% of the microsporocytes from populations adjacent to the zone had accessory nucleoli as compared to 4.6% of the cells in populations at the edge of the zone, and 7.7% in populations in the center. The correlation between population hybridity and incidence of accessory nucleoli is r = 0.80.     

Archaeobotanical evidence for early agriculture at Ljubjansko barje (Ljubljana Moor), central Slovenia

Archaeobotanical evidence is presented for early agriculture at southwestern Ljubljansko barje (Ljubljana Moor), Slovenia. Archaeobotanical finds from the Eneolithic site at Hočevarica, and pollen records from an archaeological profile and from a nearby core were analysed. Numerous charred grains of cultivated cereals together with fossil seeds of Chenopodium sp. demonstrate that during the occupation of the settlement at Hočevarica, agriculture was well established. The majority of identified grains were of Hordeum vulgare (cultivated barley) and the rest were Triticum monococcum and T. turgidum ssp. dicoccum (cultivated wheats). Large amounts of cereal pollen and pollen of Chenopodiaceae also suggest strong human impact on the surrounding vegetation and landscape. Pollen and archaeobotanical data from Hočevarica show a large consistency in timing of the appearance of agriculture. In the pollen record from the core at Hočevarica a significant increase (up to 40%) in cereal pollen was detected at 4881 ± 50 B.P. (3770-3630 cal B.C.). Charred cereal grains were dated to 4800 ± 40 B.P. (3650-3520 cal B.C.). The grains of cultivated cereals from Hočevarica represent the oldest archaeobotanical evidence for agriculture in central Slovenia. Received February 18, 2002 / Accepted October 21, 2002     

Chromosomal differentiation and genome size in three European mountain Lilium species

 Three related and taxonomically close species of the genus Lilium (L. pyrenaicum Gouan, L. pomponium L. and L. carniolicum Bernh.), all of them with 2n=24 chromosomes, have been studied for chromosomal differentiation, using fluorochrome banding and fluorescence in situhybridization (FISH), and for genome size and GC percentage using flow cytometry. The total DNA content of L. pomponium (2C=70.26 pg) was about 5% higher than that of L. pyrenaicum (2C=67.74) and L. carniolicum (2C=67.37 pg), while GC percentage was higher in this last species (36.60%) than in L. pomponium (35.56%) and lower than in L. pyrenaicum (37.92%). Silver staining, fluorochrome banding with chromomycin A₃ (CMA) and fluorescence in situ hybridization (FISH) clearly pointed out the number of nucleoli, the number and position of GC-rich bands and the number and location of rDNA sites thus permitting distinction of the three species at chromosomal level. Two families of ribosomal genes, 18S-5.8S-26S (18S) and 5S rRNA genes, were separated onto different pairs in chromosome complements of examined species. Chromosome regions containing both kinds of rRNA genes were also GC-rich regions. The results revealed a clear interspecific differentiation at the chromosomal level and permitted the discussion about relationships among the species. Received June 21, 2002; accepted October 4, 2002 Published online: Febraury 7, 2003     

Geographic partitioning of chloroplast DNA variation in the genusDatisca (Datiscaceae)

Datisca (Datiscaceae) is a ditypic genus with an intercontinentally disjunct distribution. Chloroplast DNA restriction site data was obtained from 23 populations and four 10–20 year old herbarium specimens ofD. glomerata and three populations ofD. cannabina from throughout their geographic ranges in western North America and southwest-central Asia, respectively. InD. glomerata, plastome diversity is partitioned geographically. All populations from southern California have a common plastome, while most populations north of this region share a relatively divergent plastome (0.49% sequence divergence). Likewise, these plastomes are highly divergent (0.87% mean sequence divergence) from those found inD. cannabina. Biogeographic processes dating to the Pleistocene and Late Miocene may be responsible for these intra- and interspecific patterns of chloroplast DNA divergence.     

The effect of urea on growth of moulds and biomass yield in solid-state cultivation

Urea, added at 2 to 20 mg/g in solid bran medium supporting growth of Aspergillus oryzae and Rhizopus oligosporus, led to a higher concentration of NH₄ ⁺ and pH but a decrease in biomass production.The authors are with the Department of Food Science and Technology, Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, 61000 Ljubljana, Slovenia.     

Allelopathic potential of alkylphenols from Dactylis glomerata subsp. hispanica (Roth) Nyman

Eleven alkylphenols were isolated from the aerial parts of Dactylis glomerata subsp. hispanica, six of them described for the first time. The structural characterization of these compounds has been elucidated by 1D and 2D NMR techniques. The fragmentation patterns of the metabolites obtained by GC–MS analysis allowed the side chain to be elucidated. The allelopathic potential of three alkylphenols, representative of each homologous series of alkylphenols from D. glomerata subsp. hispanica, has been assayed on D. glomerata subsp. hispanica and an herbaceous coexisting species, Phleum subulatum. The bioassay results showed a high auto-stimulation values of germination and root and shoot elongation for D. glomerata subsp. hispanica at high concentrations.     

Seed germination in the Sicilian subspecies of Dianthus rupicola Biv. (Caryophyllaceae)

Abstract

Five populations belonging to three subspecies of Dianthus rupicola Biv. (D. rupicola subsp. rupicola, D. rupicola subsp. aeolicus, and D. rupicola subsp. lopadusanus) and growing in different geographical areas of Sicily were tested for seed germination at various temperatures. All populations showed high germination rates with an optimum temperature between 15°C and 25°C. Efficient seed germination might contribute significantly to the preservation of these subspecies which are currently exposed to several environmental threats.     

Comparison of the Giemsa C-banded karyotypes of the three subspecies ofPsathyrostachys fragilis,subspp.villosus (2x),secaliformis (2x, 4x), andfragilis (2x) (Poaceae), with notes on chromosome pairing

The karyotypes of diploidP. fragilis subsp.villosus (2n = 2x = 14) and tetraploid subsp.secaliformis (2n = 4x = 28) were studied by Giemsa C- and N-banding, and AgNO₃ staining and compared with the karyotype of subsp.fragilis (2x). The complements of subsp.villosus and subsp.fragilis were similar, with 8 metacentric and 6 SAT-chromosomes, one metacentric and two submetacentric pairs, with small to minute, polymorphic, heterochromatic satellites. The complement of subsp.secaliformis on the whole agreed with a doubling of the complement of diploidP. fragilis, suggesting autopolyploidy. Only the presence of 12 nucleoli in interphases identified 6 SAT-chromosome pairs. In subsp.villosus one or two extra micronucleoli indicated a chromosome pair with very low nucleolusforming activity, bringing the number of SAT-chromosome pairs to 4. This number may be a characteristc ofPsathyrostachys. Besides very small, inconsistently observed bands, the C-banding pattern consisted of 0–3 small bands per chromosome at intercalary and terminal locations, and at NORs. The level of banding pattern polymorphism was low, but enough to indicate that the taxa are outbreeders. Similarities in chromosome morphology and C-banding patterns identified homology of all chromosomes of subsp.villosus, but for 12 pairs only in subsp.secaliformis. Between plants, reliable identification of homology and homoeology (subsp.secaliformis) was possible only for the SAT-chromosomes and the shortest metacentrics. Chromocentres were very small and the amount of constitutive heterochromatin was low. N-banding stained chromosomes uniformly. The basic karyotypes of theP. fragilis taxa were similar to those ofP. juncea, P. lanuginosa, andP. stoloniformis supporting a close relationship and the presence of a common genome, N. NORs had different nucleolus-forming activities. Meiotic analysis demonstrated a high level of bivalent pairing in the three taxa. A chromosomal rearrangement was suggested in subsp.villosus. The low multivalent frequency in subsp.secaliformis indicates the presence of a pairing regulation mechanism. The majority of chiasmata were interstitial. Pollen grain size discriminated between diploid and tetraploid taxa. The existence of a diploid cytotype of subsp.secaliformis is supported by pollen measurements of herbarium material.     

Intraspecific variation and evolutionary trends in Capparis spinosa L. (Capparaceae)

 In order to investigate the variability of the polymorphic Capparis spinosa L., a comparative study was carried out in Sicily on subsp. spinosa and subsp. rupestris. Autecology, phenology, quantitative morphology, plant architecture and leaf development of several populations were examined. These data reveal a parapatric distribution of the two subspecies and support their present taxonomic treatment. Subsp. spinosa is widespread on clay soils and shows remarkable intrapopulational variation. It is characterized by shortened reproductive and vegetative periods, high shoot growth rate, winter-desiccating shoot system and stipular thorns. Subsp. rupestris, less variable and linked with carbonatic and volcanic outcrops, shows prolonged phenological patterns, slow growth rate, woody habit and caducous stipules. A noteworthy phenotypic convergence with subsp. rupestris was observed in individuals of subsp. spinosa growing in rocky habitats. The evolutionary trends of Capparis spinosa in the Mediterranean region are discussed. Received March 29, 2000 Accepted April 6, 2001     

RAPD variation in wild populations of four species of the genus Hordeum (Poaceae)

 The genetic variation of 102 natural populations of wild barley growing in Spain was assessed using RAPDs (random amplified polymorphic DNA). The plant material included the annual species H. marinum subsp. marinum (22 populations) and subsp. gussoneanum (14), H. murinum subsp. murinum (7) and subsp. leporinum (35), and the perennial species H. bulbosum (17) and H. secalinum (7). Ten of the tested 64 arbitrary 10-mer primers amplified polymorphic DNA in all taxonomic units. Analyses was performed within and between populations, species and subspecies. The primers gave a total of 250 RAPD products. The level of polymorphism varied between taxonomic units depending on the primers employed and the plant reproductive system. In general, the most variable were the allogamous species H. secalinum and H. bulbosum and the autogamous H. marinum subsp. marinum. Among the amplified bands, 69 (27%) were shared by at least two different taxonomic units. The remaining bands were specific. The results demonstrate differences in the degree of similarity between taxonomic units. Jaccard’s similarity coefficients for interval measure within and between populations were used to produce a cluster diagram using the unweighted pair-group method (UPGMA). The different populations of the species and subspecies of Hordeum fell into three groups. The first group contained the populations belonging to both subspecies of H. marinum, plus those of H. secalinum. The populations of H. marinum subsp. gussoneanum were very closely associated. Those of H. marinum subsp. marinum were grouped in a broad cluster. The second group, occupying the innermost position of the tree, was very closely associated with the populations of both subspecies of H. murinum. The third branch segregated H. bulbosum. A series of RAPD markers were investigated by cleaving the amplified products of the same size with restriction endonucleases that recognize targets of 4- or 6-bp. The production of equivalent fragments following cleavage by the same enzyme would seem to demonstrate their homology in samples from different individuals, populations or taxonomic units. Received: 18 May 1997 / Accepted: 22 August 1997     

Genome differentiation in Aegilops. 3. Evolution of the D-genome cluster

 Six polyploid Aegilops species containing the D genome were studied by C-banding and fluorescence in situ hybridization (FISH) using clones pTa71 (18S-5.8S-26S rDNA), pTa794 (5S rDNA), and pAs1 (non-coding repetitive DNA sequence) as probes. The C-banding and pAs1-FISH patterns of Ae. cylindrica chromosomes were identical to those of the parental species. However, inactivation of the NOR on chromosome 5D with a simultaneous decrease in the size of the pTa71-FISH site was observed. The N^v and D^v genomes of Ae. ventricosa were somewhat modified as compared with the N genome of Ae. uniaristata and the D genome of Ae. tauschii. Modifications included minor changes in the C-banding and pAs1-FISH patterns, complete deletion of the NOR on chromosome 5D^v, and the loss of several minor 18S-5.8S-26S rDNA loci on N^v genome chromosomes. According to C-banding and FISH analyses, the D^cr1 genome of Ae. crassa is more similar to the D^v genome of Ae. ventricosa than to the D genome of Ae. tauschii. Mapping of the 18S-5.8S-26S rDNA and 5S rDNA loci by multicolor FISH suggests that the second (X^cr) genome of tetraploid Ae. crassa is a derivative of the S genome (section Emarginata of the Sitopsis group). Both genomes of Ae. crassa were significantly modified as the result of chromosomal rearrangements and redistribution of highly repetitive DNA sequences. Hexaploid Ae. crassa and Ae. vavilovii arose from the hybridization of chromosomal type N of tetraploid Ae. crassa with Ae. tauschii and Ae. searsii, respectively. Chromosomal type T1 of tetraploid Ae. crassa and Ae. umbellulata were the ancestral forms of Ae. juvenalis. The high level of genome modification in Ae. juvenalis indicates that it is the oldest hexaploid species in this group. The occurrence of hexaploid Ae. crassa was accompanied by a species-specific translocation between chromosomes 4D^cr1 and 7X^cr. No chromosome changes relative to the parental species were detected in Ae. vavilovii, however, its intraspecific diversity was accompanied by a translocation between chromosomes 3X^cr and 3D^cr1. Received July 24, 2001 Accepted October 1, 2001