Frequency Of Multivalents Research Articles

Partial cytological diploidization of neoautotetraploid meiosis by induced cross-over rate reduction

Polyploids, which arise from whole-genome duplication events, have contributed to genome evolution throughout eukaryotes. Among plants, novel features of neopolyploids include traits that can be evolutionarily or agriculturally beneficial, such as increased abiotic stress tolerance. Thus, in addition to being interesting from an evolutionary perspective, genome duplication is also increasingly recognized as a promising crop improvement tool. However, newly formed (neo)polyploids commonly suffer from fertility problems, which have been attributed to abnormal associations among the multiple homologous chromosome copies during meiosis (multivalents). Here, we test the long-standing hypothesis that reducing meiotic cross-over number may be sufficient to limit multivalent formation, favoring diploid-like bivalent associations (cytological diploidization). To do so, we developed Arabidopsis thaliana lines with low cross-over rates by combining mutations for HEI10 and TAF4b. Double mutants showed a reduction of ~33% in cross-over numbers in diploids without compromising meiotic stability. Neopolyploids derived from the double mutant show a cross-over rate reduction of about 40% relative to wild-type neotetraploids, and groups of four homologs indeed formed fewer multivalents and more bivalents. However, we also show that the reduction in multivalents comes with the cost of a slightly increased frequency of univalents and that it does not rescue neopolyploid fertility. Thus, while our results do show that reducing cross-over rates can reduce multivalent frequency in neopolyploids, they also emphasize that there are additional factors affecting both meiotic stability and neopolyploid fertility that will need to be considered in solving the neopolyploid fertility challenge.

A novel allele of ASY3 is associated with greater meiotic stability in autotetraploid Arabidopsis lyrata.

In this study we performed a genotype-phenotype association analysis of meiotic stability in 10 autotetraploid Arabidopsis lyrata and A. lyrata/A. arenosa hybrid populations collected from the Wachau region and East Austrian Forealps. The aim was to determine the effect of eight meiosis genes under extreme selection upon adaptation to whole genome duplication. Individual plants were genotyped by high-throughput sequencing of the eight meiosis genes (ASY1, ASY3, PDS5b, PRD3, REC8, SMC3, ZYP1a/b) implicated in synaptonemal complex formation and phenotyped by assessing meiotic metaphase I chromosome configurations. Our results reveal that meiotic stability varied greatly (20–100%) between individual tetraploid plants and associated with segregation of a novel ASYNAPSIS3 (ASY3) allele derived from A. lyrata. The ASY3 allele that associates with meiotic stability possesses a putative in-frame tandem duplication (TD) of a serine-rich region upstream of the coiled-coil domain that appears to have arisen at sites of DNA microhomology. The frequency of multivalents observed in plants homozygous for the ASY3 TD haplotype was significantly lower than in plants heterozygous for ASY3 TD/ND (non-duplicated) haplotypes. The chiasma distribution was significantly altered in the stable plants compared to the unstable plants with a shift from proximal and interstitial to predominantly distal locations. The number of HEI10 foci at pachytene that mark class I crossovers was significantly reduced in a plant homozygous for ASY3 TD compared to a plant heterozygous for ASY3 ND/TD. Fifty-eight alleles of the 8 meiosis genes were identified from the 10 populations analysed, demonstrating dynamic population variability at these loci. Widespread chimerism between alleles originating from A. lyrata/A. arenosa and diploid/tetraploids indicates that this group of rapidly evolving genes may provide precise adaptive control over meiotic recombination in the tetraploids, the very process that gave rise to them.

Varietal variation and chromosome behaviour during meiosis in Solanum tuberosum

Naturally occurring autopolyploid species, such as the autotetraploid potato Solanum tuberosum, face a variety of challenges during meiosis. These include proper pairing, recombination and correct segregation of multiple homologous chromosomes, which can form complex multivalent configurations at metaphase I, and in turn alter allelic segregation ratios through double reduction. Here, we present a reference map of meiotic stages in diploid and tetraploid S. tuberosum using fluorescence in situ hybridisation (FISH) to differentiate individual meiotic chromosomes 1 and 2. A diploid-like behaviour at metaphase I involving bivalent configurations was predominant in all three tetraploid varieties. The crossover frequency per bivalent was significantly reduced in the tetraploids compared with a diploid variety, which likely indicates meiotic adaptation to the autotetraploid state. Nevertheless, bivalents were accompanied by a substantial frequency of multivalents, which varied by variety and by chromosome (7–48%). We identified possible sites of synaptic partner switching, leading to multivalent formation, and found potential defects in the polymerisation and/or maintenance of the synaptonemal complex in tetraploids. These findings demonstrate the rise of S. tuberosum as a model for autotetraploid meiotic recombination research and highlight constraints on meiotic chromosome configurations and chiasma frequencies as an important feature of an evolved autotetraploid meiosis.

Cytotaxonomic investigation and meiotic behavior of natural populations of genus Avena in Algeria

Karyotype and meiotic analysis were performed on forty-five natural populations of genus Avena sampled in contrasting bioclimatic areas of Northern Africa. The diploids (2n = 2x = 14) A. clauda, A. eriantha and A. hirtula are sporadic in hills and mountains of the Tellian Atlas only. A. wiestii (2x) are scattered in arid and semi-arid regions, of which an unexpected 4x population has been discovered. A. barbata (4x) and A. sterilis (6x) are widespread in all bioclimates while A. fatua (6x) is rather rare. Most populations show remarkable novelties in the intra and inter karyotype asymmetry indexes, particularly the 4x cytotype of the endemic A. macrostachya which has almost exclusively metacentric chromosomes. Both 2x, 4x and 6x annual species display regular meiosis with generally bivalent association. Univalents, multivalents, laggards, bridges, asynchronous divisions and micronuclei were often observed. Meiotic behavior observed for the first time in the locus classicus of A. macrostachya, indicate constant occurrence of one or two tetravalents. Meiotic features together with the main bioclimatic parameters, were submitted to a principal component analysis. Significant correlations were found particularly between frequencies of multivalents and laggards with the Mediterranean bioclimatic coefficient and the maximum temperature of the hottest month. These new cytogenetic data have been discussed in the context of the geographical distribution of diploids and polyploids and the aftermath of the local environmental stress conditions on the meiotic process within natural populations.

Competition for Chiasma Formation Between Identical and Homologous (But Not Identical) Chromosomes in Synthetic Autotetraploids of Arabidopsis thaliana.

Polyploid organisms provide additional opportunities to study meiosis in a more complex context since more than two potential homologous chromosomes are available. When the chromosome complement of a diploid individual is duplicated, each chromosome is accompanied by one identical and two homologous chromosomes within the same nucleus. In this situation, a competition in pairing/synapsis/chiasma formation between identical and homologous (but not necessarily identical) chromosomes can occur. Several studies have been conducted in different species to address whether there are preferences in crossover formation between identical rather than homologous chromosomes. In this study, multivalent and chiasma frequencies were cytologically analyzed in synthetic autotetraploids of Arabidopsis thaliana including the accessions Col, Ler, and the Col/Ler hybrid. Fluorescence in situ hybridization was conducted to identify each chromosome at metaphase I. The new Col and Ler tetraploids showed high multivalent frequencies, exceeding the theoretical 66.66% expected on a simple random end-pairing model, thus indicating that there are more than two autonomous synaptic sites per chromosome despite their small size. However, a significant excess of bivalent pairs was found in the Col/Ler hybrid, mainly due to the contribution of chromosomes 2 and 3. The mean chiasma frequencies of the three artificial autotetraploids were about twofold the corresponding mean cell chiasma frequencies of their diploid counterparts. The relative contribution of each chromosome to the total chiasma frequency was similar in the three genotypes, with the exception of a lower contribution of chromosome 3 in the hybrid. Preferences for chiasma formation between identical and homologous chromosomes were analyzed in Col/Ler 4x, taking advantage of the cytological differences between the accessions: variations in the size of the 45S rDNA region on the short arm of chromosome 2 and changes in the size and localization of the 5S rDNA region in chromosome 3. We observed a different behavior of chromosomes 2 and 3, i.e., random chiasma formation between identical and homologous chromosomes 2, and preferences for chiasma formation between homologous chromosomes 3. Hence, our results reveal the existence of chromosome-specific mechanisms responsible for these preferences.

Reporting of B-Chromosomes in Trachyspermum ammi (L.) Sprague (Ajwain)

To the best of our knowledge this is the first study regarding the reporting of B chromosomes in this plant species. During the meiotic study of Trachyspermum ammi (L.) Sprague, maximum two B chromosomes were reported in diploid plants which were retained in induced autotetraploid after the treatment of 0.2% colchicine at seedling stage. In the present study, the meiotic behaviour of B-chromosomes was analyzed in Trachyspermum ammi (L.) Sprague. The presence of B chromosomes and their number in the plant species of higher ploidy level is controversial. The existence of B chromosomes in polyploids varies from species to species. In the present case, no change has been observed in the number of B chromosomes despite the duplication of A chromosomes in autotetraploid plant. The unaffected number of B chromosomes represents their peculiar behaviour of inheritance. The plant species show adaptive mechanism for their retention in population. In the present study, significant changes (p < 0.05) have been observed in the chiasma frequency and pollen fertility of both diploid carrier plant as compare to non-carrier ones. Furthermore, the chromosomal associations have also been considered with observed number of B chromosomes in autotetraploid carrier plant. In autotetraploid carrier plant, the frequencies of multivalents were found to be quite low in comparison to diploid carrier plant.

Diverse morphological and cytogenetic variation and differentiation of the two subspecies in Aegilops geniculata Roth, a wild relative of wheat

Aegilops geniculata Roth, a wild relative of wheat (2n = 4x = 28, genome UUMM), is distributed over the Mediterranean basin and nearby areas. The species consists of two subspecies, subsp. geniculata and subsp. gibberosa (Zhuk.) Hammer. The former is distributed over the whole species area and has been genetically analyzed, and the latter is endemic to Spain and North Africa and has not been genetically evaluated. In this study, to clarify the genetic variation and delineation of the two subspecies from a biosystematic viewpoint, morphological variation among 23 accessions of subsp. geniculata and three of subsp. gibberosa and chromosome pairing at meiosis and fertility in their intra- and inter-subspecific F1 hybrids were examined. A principal component analysis based on the 11 spike characteristics clearly divided the 26 accessions into two groups representing the two subspecies. The inter-subspecific F1 hybrids showed significantly lower frequencies of chromosome pairing, significantly higher frequencies of multivalents, and significantly lower fertilities relative to those of the intra-subspecific F1 hybrids. It was concluded that wide-ranging cytogenetic variation is included in subsp. geniculata, that subsp. gibberosa, the intra-subspecific variation of which is small, is morphologically and cytogenetically differentiated from subsp. geniculata beyond the range of the intra-subspecific variation of subsp. geniculata, and that the two subspecies are effectively isolated reproductively by hybrid sterility. The results strongly suggested that western North Africa is one of the important diversity centers of Ae. geniculata, where two subspecies were differentiated in the past and grow together in the present.

Cytogenetic study and stripe rust response of the derivatives from a wheat - Thinopyrum intermedium - Psathyrostachys huashanica trigeneric hybrid.

To transfer multiple desirable alien genes into common wheat, we previously reported a new trigeneric hybrid synthesized by crossing a wheat - Thinopyrum intermedium partial amphiploid with wheat - Psathyrostachys huashanica amphiploid. Here, the meiotic behavior, chromosome constitution, and stripe rust resistance of F5 derivatives from the wheat - Th. intermedium - P. huashanica trigeneric hybrid were studied. Cytological analysis indicated the F5 progenies had chromosome numbers of 42-50 (average 44.96). The mean meiotic configuration was 1.28 univalents, 21.74 bivalents, 0.04 trivalents, and 0.02 tetravalents per pollen mother cell. In 2n = 42 lines, the average pairing configuration was 0.05 I + 19.91 II (ring) + 1.06 II (rod) + 0.003 IV, suggesting these lines were cytologically stable. Most lines with 2n = 43, 44, 46, 48, or 50, bearing a high frequency of univalents or multivalents, showed abnormal meiotic behavior. Genomic in situ hybridization karyotyping results revealed that 25 lines contained 1-7 Th. intermedium chromosomes, but no P. huashanica chromosomes were found among the 27 self-pollinated progenies. At meiosis, univalents (1-5) possessing Th. intermedium hybridization signals were detected in 19 lines. Bivalents (1-3) expressing fluorescence signals were observed in 12 lines. Importantly, 21 lines harbored wheat - Th. intermedium chromosomal translocations with various alien translocation types. Additionally, two homozygous lines, K13-668-10 and K13-682-12, possessed a pair of wheat - Th. intermedium small fragmental translocations. Compared with the recurrent parent Zhong 3, most lines showed high resistance to the stripe rust (Puccinia striiformis f. sp. tritici) pathogens prevalent in China, including race V26/Gui22. This paper reports a highly efficient technical method for inducing alien translocation between wheat and Th. intermedium by trigeneric hybridization. These lines might be potentially valuable germplasm resources for further wheat improvement.

The Double-Reduction Landscape in Tetraploid Potato as Revealed by a High-Density Linkage Map.

The creation of genetic linkage maps in polyploid species has been a long-standing problem for which various approaches have been proposed. In the case of autopolyploids, a commonly used simplification is that random bivalents form during meiosis. This leads to relatively straightforward estimation of recombination frequencies using maximum likelihood, from which a genetic map can be derived. However, autopolyploids such as tetraploid potato (Solanum tuberosum L.) may exhibit additional features, such as double reduction, not normally encountered in diploid or allopolyploid species. In this study, we produced a high-density linkage map of tetraploid potato and used it to identify regions of double reduction in a biparental mapping population. The frequency of multivalents required to produce this degree of double reduction was determined through simulation. We also determined the effect that multivalents or preferential pairing between homologous chromosomes has on linkage mapping. Low levels of multivalents or preferential pairing do not adversely affect map construction when highly informative marker types and phases are used. We reveal the double-reduction landscape in tetraploid potato, clearly showing that this phenomenon increases with distance from the centromeres.

Evaluation of cotton leaf curl virus resistance in BC1, BC2, and BC3 progenies from an interspecific cross between Gossypium arboreum and Gossypium hirsutum.

Cotton leaf curl virus disease (CLCuD) is an important constraint to cotton production. The resistance of G. arboreum to this devastating disease is well documented. In the present investigation, we explored the possibility of transferring genes for resistance to CLCuD from G. arboreum (2n = 26) cv 15-Mollisoni into G. hirsutum (2n = 52) cv CRSM-38 through conventional breeding. We investigated the cytology of the BC1 to BC3 progenies of direct and reciprocal crosses of G. arboreum and G. hirsutum and evaluated their resistance to CLCuD. The F1 progenies were completely resistant to this disease, while a decrease in resistance was observed in all backcross generations. As backcrossing progressed, the disease incidence increased in BC1 (1.7–2.0%), BC2 (1.8–4.0%), and BC3 (4.2–7.0%). However, the disease incidence was much lower than that of the check variety CIM-496, with a CLCuD incidence of 96%. Additionally, the disease incidence percentage was lower in the direct cross 2(G. arboreum)×G. hirsutum than in that of G. hirsutum×G. arboreum. Phenotypic resemblance of BC1 ∼BC3 progenies to G. arboreum confirmed the success of cross between the two species. Cytological studies of CLCuD-resistant plants revealed that the frequency of univalents and multivalents was high in BC1, with sterile or partially fertile plants, but low in BC2 (in both combinations), with shy bearing plants. In BC3, most of the plants exhibited normal bearing ability due to the high frequency of chromosome associations (bivalents). The assessment of CLCuD through grafting showed that the BC1 to BC3 progenies were highly resistant to this disease. Thus, this study successfully demonstrates the possibility of introgressing CLCuD resistance genes from G. arboreum to G. hirsutum.

Meiotic chromosome pairing behaviour of natural tetraploids and induced autotetraploids of Actinidia chinensis

Non-preferential chromosome pairing was identified in tetraploid Actinidia chinensis and a higher mean multivalent frequency in pollen mother cells was found in colchine-induced tetraploids of A. chinensis compared with naturally occurring tetraploids. Diploid and tetraploid Actinidia chinensis are used for the development of kiwifruit cultivars. Diploid germplasm can be exploited in a tetraploid breeding programme via unreduced (2n) gametes and chemical-induced chromosome doubling of diploid cultivars and selections. Meiotic chromosome behaviour in diploid A. chinensis 'Hort16A' and colchicine-induced tetraploids from 'Hort16A' was analysed and compared with that in a diploid male and tetraploid males of A. chinensis raised from seeds sourced from the wild in China. Both naturally occurring and induced tetraploids formed multivalents, but colchicine-induced tetraploids showed a higher mean multivalent frequency in the pollen mother cells. Lagging chromosomes at anaphase I and II were observed at low frequencies in the colchicine-induced tetraploids. To investigate whether preferential or non-preferential chromosome pairing occurs in tetraploid A. chinensis, the inheritance of microsatellite alleles was analysed in the tetraploid progeny of crosses between A. chinensis (4x) and A. arguta (4x). The frequencies of inherited microsatellite allelic combinations in the hybrids suggested that non-preferential chromosome pairing had occurred in the tetraploid A. chinensis parent.

Deep cytogenetics analysis reveals meiotic recombination depletion in species of Senecio (Asteraceae).

BackgroundSenecio is the largest genus in the Asteraceae family growing in all environments around the world. It displays taxonomic and systematical difficulties. Cytogenetic knowledge of this genus is ancient, scarce and mainly restricted to chromosome number records.ResultsIn this study we analyzed chromosome number, meiotic configuration, bivalent morphology, meiotic behavior and pollen grain stainability on 100 accessions of 27 different polyploid Senecio L. sect Senecio entities. Median, standard deviation and mode were calculated for number and position of chiasmata and meiotic recombination was statistically evaluated. Although high frequency of multivalents and associated meiotic irregularities are expected in high polyploids, bivalents predominance and, consequently, regular meiosis were observed, with normal sporogenesis and high pollen grain stainability.ConclusionDepletion in the total chiasmata was significant only in some species but the terminal position was preferential in all the entities analyzed, indicating significant reduction in recombination. The regular meiosis observed suggest that intra and intergenomic reorganization process occur quickly and efficiently in this genus. Mechanisms of diploidization, common to all polyploids, are reinforced by the strong reduction in crossing-over rushing polyploids stabilization.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-54-20) contains supplementary material, which is available to authorized users.

Molecular cytogenetic analysis of wheat – Elymus repens introgression lines with resistance to Fusarium head blight

Elymus repens (L.) Gould (2n = 6x = 42, StStStStHH) is a hexaploid perennial wheatgrass species from the tribe Triticeae, distantly related to bread wheat Triticum aestivum L. (2n = 6x = 42, AABBDD). As a potential source of resistance to Fusarium head blight (FHB), E. repens was crossed to common wheat to transfer resistance genes. The progeny were advanced to homozygosity by single seed descent. A total of eight BC(1)F(9) progeny lines were selected and characterized in this study. The chromosome numbers of these derived lines ranged from 42 to 56, including lines with 44, 52, and 54 chromosomes. All of the lines were cytologically stable in terms of meiotic chromosome behavior. The univalent frequency in the lines varied between 0.34 and 2.36 per cell. Similarly, the multivalent frequency did not exceed 1% in any of the lines. GISH analysis revealed that the number of intact wheat chromosomes in the various lines varied between 40 and 44. Numerous translocated chromosomes were detected in all lines. The translocations involved chromosomal segments from wheat, and the St and H genomes of E. repens. Furthermore, trigenomic translocated chromosomes were detected in some of the lines. The introgression into wheat chromosomes included not only terminal types but also interstitial segments. The Fusarium head blight resistance of the eight lines, following point inoculation, varied from 5.65% infected florets to 11.46% compared with the check cultivars T. aestivum 'Roblin' and T. aestivum 'Crocus' at 100% and 85%, respectively.

Meiotic nondisjunction in resynthesized Brassica napus and generation of aneuploids through microspore culture and their characterization

Meiotic nondisjunction during microsporegenesis can lead to aneuploid gametes formation and reduced pollen fertility in plants. This paper reports the prevalence of meiosis I nondisjunction in a resynthesized Brassica napus (AACC, 2n = 38) and its use for aneuploid production. Meiosis in the amphidiploids was characterized by high frequencies of univalents and multivalents per PMC at diakinesis/metaphase I and notably unbalanced chromosome segregations at anaphase I (AI). In all the plants observed, 18.95–44.3% of PMCs exhibited a segregation of 18:20 (n − 1:n + 1) at AI which was caused by nondisjunction of one bivalent or the distribution of two homologous univalents to the same pole. Meiosis proceeded normally after AI then, thus led to the formation of viable n − 1 and n + 1 gametes and high pollen fertility of these plants. Microspore culture was subsequently carried out using these plants in an attempt to isolate Brassica nullisomics. Four nullisomics (2n = 36), two nullihaploids (2n = 18) and one tetrasomic haploid (2n = 20) were identified cytologically and characterized morphologicaly and physiologically. Amplified fragment length polymorphism (AFLP) survey suggested that of the six nullisomics/nullihaploids, one nullihaploids lost one A-genome chromosome and the other five lost C genome chromosome(s). Altogether, different C-genome chromosomes were thought to have been lost in the nullisomics/nullihaploids. The mechanisms underlying the meiotic abnormalities and the implications of these B. napus nullisomics are discussed.

A comparative cytogenetic study of the rice (Oryza sativa L.) autotetraploid restorers and hybrids

We studied pollen fertility, seed set and cytogenetic characteristics of restorer lines and F1 hybrids of autotetraploid rice. T4002, T4063, T461A x T4002 and T461A x T4063 showed significantly higher pollen fertility and seed set than T4132 and T461A x T4132. Meiotic pairing configurations of T4002, T4063, T4132, T461A x T4002, T461A x T4063 and T461A x T4132 were 0.051 + 19.96II (9.89 rod + 10.07 ring) + 0.01III + + 2.00IV, 0.11I + 19.17II (8.90 rod + 10.37 ring) + 0.09III + 2.26IV + 0.01VI, 1.34I + 9.46II (4.50 rod + 4.96 ring) + 0.80III + 6.02IV + 0.09VI + 0.09VIII, 0.02I + 14.36II (6.44 rod + 7.91 ring) + 0.01III + 4.80IV + 0.01VIII, 0.06I + 17.67II (11.01 rod + 6.67 ring) + 0.06III + 3.10IV + 0.01VI and 1.11I + 11.31II (5.80 rod + 5.51 ring) + 0.41III + 5.63IV + 0.03VI + 0.03VIII, respectively. Configuration 16II + 4IV and 12II + 6IV occurred in the highest frequency among the autotetraploid restorers and hybrids. Meiotic chromosome behaviors were less abnormal in the tetraploids with high seed set than those with low seed set. The hybrids had fewer frequencies of bivalents, univalents, trivalents and multivalents than the restorers, but higher frequency of quatrivalents than the restorers at MI. The frequency of univalents at MI had the most impact on pollen fertility and seed set, i.e., pollen fertility decreased with the increase of univalents. The secondary impact factors were trivalents and multivalents, and bivalents and quatrivalents had no effect on pollen fertility and seed set. The correlative relationship between pollen fertility and cytogenetic behaviors could be utilized to improve seed set in autotetraploidy breeding.

Meiotic properties in populations of hexaploid Phleum pratense

The meiotic properties were studied in two Norwegian populations of Phleum pratense L. (Grindstad and Bodin), one Danish (Pajbjerg) and one Russian population (Rjadovaja). At diakinesis, multivalents in addition to bivalents were found in most of the sporocytes examined, and the mean frequency per sporocyte ranged from 1.09 in Bodin to 1.39 in Grindstad. The differences between populations were not statistically significant. First metaphase was unsuitable for determination of bivalents and multivalents because the chromosomes were clumped together on the equatorial plate. The frequency of MI's with univalents could, however, be determined with certainty, and the average per cent of cells with univalents was 8.7 in Rjadovaja, 18.4 in Pajbjerg, 20.9 in Grindstad and 33.1 in Bodin. Comparisons between the 4 populations showed that Rjadovaja had a significantly lower frequency of MI's with univalents than the others. The remaining populations, on the other hand, did not differ significantly, though the frequency of sporocytes with irregularities at MI and later stages generally was higher in Bodin than in Grindstad and Pajbjerg. The mean frequency of multivalents at diakinesis and first metaphase with univalents varied continuously among plants within populations, and the variation was of the same kind as that found for characters like earliness, plant height etc. Unpaired chromosomes at MI were the most common reason for irregularities at later stages of meiosis and in tetrads, whereas multivalents seemed to play a relatively minor role.

Cytogenetics, biogeography and biology ofSantolina ageratifoliaBarnades ex Asso (Asteraceae: Anthemideae)

Santolina ageratifolia Barnades ex Asso is a natural autohexaploid (2n = 6x = 54, 54 + 1B), endemic to Teruel Province, Spain and inhabits a substrate derived from sandstone, red limolite and quartzite. Three chromosome formulae are found: 30m + 12sm + 12st, present in 52% of the descendants (52 metaphase), 24m + 5m-1sm + 18sm + 6st in 39% of the descendants (39 metaphase) and 24m + 5m-1sm + 18sm + 6st + 1B in 9% of the descendants (9 metaphase). Chiasmata are mostly interstitial rather than terminal, giving rise to the formation of cruciform structures. The predominance of bivalent configurations in the meiosis and the exclusively bivalent formation in four individuals indicate that this species has a strong tendency towards diploidization. Secondary association of bivalents is observed in the number of 2, 4–6 chromosomes associated, the average being 4.21 ± 1.20 chromosomes. The variation in the chromosomal characteristics suggests chromosome translocation and/or inversions. This species is partially sterile, with a mean pollen fertility of 40.56% and a mean fructification of 34.24%. The frequencies of multivalents and pollen fertility have a strongly significant effect on fructification percentage. Phenotypic variation in habits is not correlated with karyotype characteristics. The cytogeography of the polyploid taxa of the Santolina rosmarinifolia aggregate is discussed.

Genome Analysis of Finger Millet E. coracana by Interspecific Hybridization among Diploid Wild Species of Eleusine (Poaceae)

Four species of Eleusine viz. E. intermedia, E. floccifolia, E. indica and E. tristachya are wild diploid taxa (2n=2x=18) and are presumed to have contributed to the evolution of finger millet, E. coracana, the amphidiploid with AABB genome (2n=2x=36) and an important minor millet grown in Africa and South Asia. E. indica is known to have contributed the A genome to E. coracana, while the information regarding the other genome donor species is not forthcoming. The present investigations were undertaken to clearly understand the genome homology of 3 species viz. E. intermedia, E. floccifolia and E. tristachya vis-a-vis the A genome of E. indica and to analyze the interspecific relationship among these diploid species and their possible contribution to the evolution of E. coracana. Interspecific F1 hybrids of E. intermedia×E. indica, E. intermedia×E. floccifolia and E. tristachya×E. intermedia were produced and studied for morphological and cytological details. The experimental data revealed a high degree of homology at the interspecific level among all 4 species resulting in high frequency of bivalents and a very low frequency of univalents and multivalents. Inspite of good chromosome pairing and bivalent formation, a significant reduction in pollen stainability (8–32%) has been recorded in the F1 hybrids. The data obtained on chromosome associations at diakinesis/ metaphase I of meiosis suggest that these diploid species form a close genetic assemblage within the genus Eleusine. Various factors affecting the pollen stainability and seed fertility are discussed in the light of available information on the subject.

Increase in Multivalent Frequency in F1, Hybrids of Zea Diploperennis × Z. Perennis by Colchicine Treatment

Studies of meiotic configurations of colchicine treated and untreated Zea diploperennis ( AdAd BdBd) and two F, synthetic Z. diploperennis x Z. perennis hybrids (2n = 30, ApAp’Ad BplBpZBd and 2n = 40, ApAp’AdAd Bpl Bp2BdBd) were made. Pre-zygotene colchicine treatment produces an increase in the frequency of multivalents (trivalents and quadrivalents respectively) in the F, hybrids, but hexavalents or octovalents were not observed. However, in several stems of Z. diploperennis treated with colchicine, quadrivalent formation was not observed. These results suggest that there are homoeologies within the A and B genomes, but little if any homoeology between them. Colchicine treatment may disrupt a bivalent promoting mechanism, probably due to the presence of Ph-like genes, thus revealing cryptic genome homologies.

Meiosis in Aneuploids of Tetraploid Lathyrus Odoratus and L. Pratensis

Meiosis was studied in one hypoploid (trisomic, 2n = 4x - 1 = 27) of an induced tetraploid (2n = 28) of Lathyrus odoratus and two hyperploids (single pentasomic, 2n = 4x + 1 = 29 and double pentasomic, 2n = 4x + 1 + 1 = 30, respectively) of an induced tetraploid of L. pratensis. Multivalent frequencies in the aneuploids were high, but the numbers of chiasmata were not sufficient to maintain all pairing configurations till metaphase I. Interstitial chbdsmata were relatively frequent. Chiasma frequencies were considerably reduced in all three aneuploids, compared with the eutetraploids. The two pentasomes (sets of five homologous chromosomes) of the double pentasomic were both present as a quinquivalent more frequently than expected when they would behave independently. The single pentasomic and the trisomic did not deviate much from expected, although, like in the eutetraploids, the multivalent frequencies were considerably higher than corresponds with the assumption that pairing initiation is restricted to the chromosome ends. The conclusion is that aneuploids of Lathyrus at the tetraploid level tend to behave similar to euploids, except that the chiasma frequency is considerably reduced. When maintained in the population their progeny will contain even more aneuploids than the euploids, not only because the aneuploidy will be perpetuated, but also because of lower chiasma frequencies leading to univalent formation. J. Sybenga, Fazantenlaan 4, NL-4351 RV Veere, The Netherlands