High Frequency Of Bivalents Research Articles

Synthesis and characterization of interspecific trigenomic hybrids and allohexaploids between three cultivated Brassica allotetraploids and wild species Brassica fruticulosa

Interspecific reciprocal crosses between three cultivated Brassica allotetraploids and one wild species Brassica fruticulosa (FF, 2n =16) were made and the trigenomic hybrids were produced only with embryo rescue. From the crosses with Brassica juncea (AABB, 2n = 36) and Brassica napus (AACC, 2n = 38), hybrids (F.AB, 2n = 26; F.AC, 2n = 27) were obtained only with B. fruticulosa as female, but the reciprocal crosses with Brassica carinata (BBCC, 2n = 34) gave rise to hybrids (F.BC/BC.F, 2n = 25). These hybrids showed an intermediate morphology and were sterile for male and female except those with B. carinata . All the triploids showed high frequency of bivalents during diakinesis and metaphase I (MI) of meiosis. The allohexaploids (FF.AABB, 2n = 52; FF.AACC, 2n = 54; BBCC.FF, 2n = 50) were synthesized by colchicine treatments of respective hybrids in vitro , which showed growth vigor and had larger stature than the hybrids, but were male sterile except one (FF.AABB). They produced progenies with the expected chromosome complements (F.AABB, 2n = 44; F.AACC, 2n = 46; BBCC.F, 2n = 42) after pollination by respective Brassica allotetraploids . In these allohexaploids, chromosomes were mainly paired as bivalents at diakinesis and segregated equally at anaphase I (AI) during meiosis of pollen mother cells (PMCs). These allohexaploids and progenies were valuable for the breeding of Brassica crops. Key words : Brassica allotetraploids, Brassica fruticulosa, interspecific hybrids, crossability, morphology, genomic affinity.

Hybridizing Brassica rapa with wild crucifers Diplotaxis erucoides and Brassica maurorum

Two wide hybrids, Diplotaxis erucoides (2n = 14) × Brassica rapa (2n = 20) and B. maurorum (2n = 20) × B. rapa, were developed using the sequential ovary–ovule culture. Reciprocal crosses failed, possibly as a consequence of strong unilateral incompatibility. The F1 hybrids in each combination were completely male sterile and morphologically intermediate to the respective parents. DNA marker polymorphism and chromosome counts confirmed their hybrid nature. High frequency of bivalents in the F1 and the presence of trivalents/quadrivalents in the derived amphiploids suggested genomic duplications and homoeology of the parental genomes. Up to three homoeologous pairs between the D. erucoides (DeDe) and B. rapa (AA) genomes, and one between B. maurorum (BmBm) and B. rapa genomes were observed. Successful synthesis of the F1 hybrids and amphiploids of B. rapa with D. erucoides and B. maurorum, and allosyndetic chromosome pairing are expected to permit introgressions of desirable loci into the cultivated Brassica germplasm, especially for resistance to Alternariabrassicae and Albugo candida.

Characterization of Amphiploid Hybrids between Bluebunch and Thickspike Wheatgrasses

An amphiploid derivative from hybrids between bluebunch wheatgrass (2n = 2x = 14) [Pseudoroegneria spicata (Pursh) A. Love] and thickspike wheatgrass (2n = 4x = 28) [Elymus lanceolatus (Scribner and Smith) Gould] was developed to compare cytological, morphological, anatomical, and seed characteristics between the triploid F1 hybrids (2n = 3x = 21) and their colchicine induced hexaploid (2n = 6x = 42) derivative (C0). The amphiploid population produced an average of 3.1 seeds spikelet−1 and pollen stainability averaged 85.5%. Seed set under self‐pollination in the amphiploids ranged from <1% to >99% with an average of 50%. Fifty‐eight of the 103 plants studied were hexaploid (2n = 6x = 42). The remaining plants had chromosomes ranging from 2n = 39 to 2n = 44 and were less fertile than the euploids. Meiosis in the euploid plants was regular and typical of a segmental autoallohexaploid St1St1St2St2HH. The most common meiotic chromosome configuration was 21 bivalents. A high frequency of bivalents and a low frequency of quadrivalents indicate that the St genomes of the two parental species have diverged. The amphiploids had thicker culms, more leaves per culm, and longer and wider leaves than either parental species. Multivariate analysis demonstrated that the amphiploids, though morphologically similar to the parental species, was distinct. In general, C0 hybrids were less vigorous than the F1 from which they were derived. Through amphiploidy, genetic introgression between the two species is possible.

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.

Meiotic irregularities and pollen viability inPassiflora edmundoiSacco (Passifloraceae)

Abstract Meiotic and pollen viability studies were conducted in Passiflora edmundoi Sacco (n = x = 9). For meiotic studies anthers were squashed in a drop of 1% acetic carmine. For analysis of pollen viability, pollen grains of flowers at anthesis were stained with two stains, lugol and Alexander stain. At diakinesis frequency of bivalents was high (86% of pollen mother cell observed) and it was observed other pairing patterns (7 II + 1 IV; 5 II + 2 IV; and 18 I). The average number of chiasmata per cell was 9.3, in concordance with high frequency of bivalents. Meiotic phases showed the presence of spindle irregularities, asynchrony, and other abnormalities as laggard chromosomes and anaphase bridges. Different post‐meiotic products were observed and the frequency of triads was higher than monads, dyads, and polyads; however the meiotic index was 97.2% and the pollen viability was 97.9% suggesting meiotic stability. Sterile pollen was sorted in two categories: empty (60.3%) and shrunken (contracted cytopl...

Direct measurement of recombination frequency in interspecific hybrids between Hordeum vulgare and H. bulbosum using genomic in situ hybridization.

Two different genotypes of diploid Hordeum vulgare x H. bulbosum hybrids, which differ in their pattern of meiotic metaphase pairing behaviour, were investigated at MI and AI by genomic in situ hybridization (GISH). One hybrid, 102C2, showed a high frequency of bivalents at metaphase I whereas the other, 103K5, showed a high frequency of univalents. The GISH analysis of both hybrids established that pairing occurred only between chromosomes of different parental genomes and revealed that pairing frequency greatly exceeded recombination. Hybrid 102C2 had a significantly higher recombination frequency than 103K5, but in both hybrids recombination involved only distal chromosome regions. However, an interesting finding is that the ratio of recombination to pairing frequency in 103K5 (1:8.9) is twice as high compared with 102C2 (1:17). The hybrids also differed in chromosome stability; little chromosome elimination occurred in 102C2 but 103K5 showed extensive chromosome loss. It appears that the high frequency of bound arms at MI favours retention of H. bulbosum chromosomes and maintains stability of chromosome numbers in PMCs. Various ideas are put forward to explain the discrepancy between meiotic pairing frequency and recombination in these hybrids.

Rhizomatous Lotus corniculatus L.: III. Introgression of Rhizomes into Autogamous Germplasm

Introduction of genes for rhizomes from wild Lotus corniculatus L. germplasm into domesticated germplasm may be an important step towards improving persistence of cultivated L. corniculatus, normally a cross-pollinated herbage crop. This study was initiated to determine if rhizomes could be transferred to a L. corniculatus germplasm that sexually reproduces via autogamy. Autogamy is an unusual reproductive expression in this typically self-incompatible species. Compatibility was high between the autogamous germplasm AG-S4 and five wild Moroccan accessions with rhizomes. Higher crossing success was obtained when AG-S4 was used as a maternal parent. Most seeds produced were normal in appearance and size and had high germination. The resulting F1 progeny were morphologically intermediate between the parents for size and shape of leaf and floral characters, but appeared more similar to their Moroccan parents. Differences between reciprocal crosses were not evident. Hybridity of progeny was confirmed by random amplified polymorphic DNA (RAPD) analysis using eight primers. Fertility of F1 progeny was low relative to their parents. Meiosis of parental genotypes was characterized by a high frequency of bivalents, but the meiotic behavior of their F1 hybrids was more irregular. The frequency of univalents varied from 0 to 8 with an average 2.4 per ceil, indicating homology of chromosomes between AG-S4 and Moroccan accessions was not complete. Rhizomes were successfully expressed in F1 hybrids and a small number were found to also be autogamous. The autogamous hybrids will be important tools to elucidate the inheritance of rhizomes in L. corniculatus. Selection among the hybrids could lead to autogamous, rhizomatous cultivars of L. corniculatus.

Chromosome doubling inTurnera ulmifolia (Turneraceae) induced by regeneration of plants from in vitro cultured leaf explants

Plants were regenerated from cultured excised leaf segments ofTurnera ulmifolia (2n = 6x = 30). Cytological studies have demonstrated that chromosome doubling occurred in 100% of the regenerated plants. Probably it was produced by endomitosis, induced by excess of auxins in relation to cytokinins. High bivalent and low quadrivalent frequency, and univalents to octovalents were observed in metaphase I; lagging chromosomes were also found. Probably, the presence of multivalents may be due to the pairing among homoeologous chromosomes because the mother plant is a segmental allohexaploid. The high bivalent frequency may have been caused by preferential pairing of identical chromosomes against the homologous.

Cytogenetics of fertility improvement in artificial autotetraploids of Hyoscyamus niger L.

Genetically stable artificial autotetraploids with over 90% seed set were obtained by colchicine treatment of the solanaceous species Hyoscyamus niger L. (4x = 68). The tetraploids were vigorous and had earlier been shown to yield considerably more tropane alkaloid per individual than the source diploids. The tetraploids had high bivalent frequencies at meiosis, and high fertility as a result of the formation of genetically balanced gametes. There was a systematic and significant decrease in quadrivalent frequency and an increase in bivalent frequency in three subsequent generations tested (C0, C1, C2). Possible causes of high bivalent frequency are discussed. Seed fertility can probably be increased in advanced generations by further selection for fertility and maximization of heterozygosity.Key words: Hyoscyamus niger, autotetraploid, meiosis, bivalents, fertility, selection.

Chromosome Association and Behaviour in Autotetraploid Delphinium ajacis L.

Meiotic chromosome association showed uni- and bivalents and complete lacking of multivalents in C1 generation of autotetraploid D. ajacis. Present observations suggests that genetic factor is responsible for controlling the multivalent formation not chromosome size. Meiotic abnormalities were frequently observed as univalents, laggards, bridges and micronuclei in the induced autotetraploid despite high bivalent frequency in C1 generation. Cytogenetical irregularities affecting pollen as well as seed fertility in the present study.

Cytogenetics of decaploid Agropyron elongatum (Elytrigia elongata) (2n = 70). I. Frequency of decavalent formation

The multivalents that appeared in the decaploid strain of Agropyron elongatum (2n = 10x = 70), a relative of wheat, ranged from trivalent to decavalent. Few univalents occurred. The metaphase I chromosome association in 12 cells where all configurations could clearly be identified averaged 0.42 ring X + 0.17 chain X + 0.42 ring VIII + 0.17 branched VIII + 0.25 chain VIII + 0.17 chain VII + 1.17 ring VI + 0.33 branched VI + 0.5 chain VI + 1.67 ring IV + 0.42 branched IV + 0.58 chain IV + 0.08 branched III + 0.17 chain III + 12.58 ring II + 3.75 open II + 0.25 I. The occurrence of decavalents, up to two in one cell, and of a cell with five multivalents, each of which involved more than five chromosomes, and many multivalents of ring shape indicated that the strain is autodecaploid.The chromosome associations of each cell can be interpreted as seven groups of 10 homologous chromosomes. The high frequency of bivalents indicated a tendency toward reduced multivalent formation, for which an explanation is suggested.Key words: Agropyron elongatum, meiotic configuration, decaploid, multivalent.

Chiasma Localization in Four South African Grasshopper Species (Acridinae: Orthoptera)

SUMMARYThe chiasma distribution patterns of 4 Acridinae species were studied. The preliminary results show that in Parga xanthoptera the chiasmata are mostly located in the distal and proximal regions of the bivalents. Due to a relatively high frequency of bivalents with 2 chiasmata, the chiasma frequency was relatively high (15.8/cell). Gymnobothrus cruciatus, Machaeridia bilineata and Cannula gracilis all show proximal localization in the 8 longer chromosome pairs. Chiasma distribution in the 3 smaller pairs seemed to be random. One C. gracilis individual was also heterozygotic for an extra heterochromatic supernumerary segment on the distal end of chromosome 11. This caused a redistribution of chiasmata in the carrier bivalent as well as an increase in chiasma frequency. The mean cell chiasma frequency for G. cruciatus was 11.00, for M. bilineata 11.13, for C. gracilis (basic karyotype) 12.06 and for the individual with the extra segment 13.86.

SUPERNUMERARY CHROMOSOMES IN TRADESCANTIA II. EFFECT OF COLCHICINE ON MEIOTIC ISOCHROMOSOME CONFIGURATIONS

The effect of colchicine on meiotic pairing and configuration frequencies of three homologous isosupernumerary chromosomes was investigated. In the absence of colchicine, the three isochromosomes displayed a high degree of interchromosomal pairing and chiasma formation. As a consequence, a high frequency of bivalents and trivalents were observed at diakinesis‐metaphase I. The unique structure of isochromosomes enables them to pair intrachromosomally (i.e., foldback pairing) yet the preferential occurrence of interchromosomal pairing suggests that all six arms of the three isosupernumerary chromosomes were in close association prior to or upon initiation of synapsis. Supernumerary chromosomes in microsporocytes treated during presynapsis or early synapsis with colchicine exhibited a significant reduction (P < 0.001) in the number of bivalents and trivalents at diakinesis. However, there was no reduction in overall chiasma frequency among supernumeraries due to the induction of increased intrachromosomal pairing and chiasma formation. A colchicine‐sensitive association or alignment of homologues preceding effective pairing has been demonstrated in standard chromosomes of a number of plant species. This study provides the first evidence to indicate that at least certain supernumerary chromosomes may display presynaptic association as well. The results also support the strongly held contention that colchicine is not directly preventing or inhibiting the actual formation of chiasmata, since no reduction in chiasma frequency was observed in the isochromosomes.

Microsporogenesis in hexaploid Morus serrata Roxb.

Detailed microsporogenesis of hexaploid Morus serrata has been studied. This is the first record of natural hexaploidy (2n=6x=84) in the species. Meiosis has been found regular with high frequency of bivalents. The frequency of hexa-, penta-, tetra- and trivalents is considerably less suggesting its allopolyploid nature. Diploid like behaviour of this species with high frequency of bivalents, regular meiosis and high pollen stainability are discussed in relation to its evolution.

Implications of chromosome pairing in a monohaploid and its colchidiploid of Solanum tuberosum (x = 12)

A monohaploid (x = 12) of Solanum tuberosum, its colchidiploid and their 2n parent clone have been cytologically examined. The meiotic analysis of the monoploid shows a certain degree of pairing at pachytene with a high frequency of bivalents at metaphase I. The bivalent frequency ranges from 2.07 to 3.0 per pollen mother cell (PMC). The most frequent classes are 3II + 6I and 2II + 8I. Several PMCs show secondary associations. At anaphase I (AI), the chromosomes distribute frequently in groups of 7 to 5 (32% of PMCs) and 6 to 6 (30% of PMCs). Occasionally, however, both disjunct chromosomes and univalents remain at the equatorial plane and divide with or without segregation, resulting in the formation of dyads or monads. The PMCs with a regular AI show a parallel orientation of spindles as well as a normal one, a situation that ends at telophase II with dyads, triads, and tetrads but 0% pollen fertility. The overall frequency of monads, dyads, triads, and tetrads is equal to 13, 69, 7 and 11%, respectively. Both in the parent clone and in the 2n colchidiploid clone, chromosome pairing is normal. The pairing behaviour in the monohaploid suggests the presence of duplicated sequences in the chromosome complement. An alteration of genes controlling the level of pairing is excluded.Key words: monohaploid, colchidiploid, chromosome pairing, meiosis.

Cytogenetics of Tephrosia VI. Meiotic systems in some taxa.

Male meiosis was studied in sixteen species. Thirteen species were diploids. In T. purpurea and T. hamiltonii both diploid and tetraploid races were meiotically investigated. The present data together with the earlier data show that the gametic numbers recorded in the genus so far are n=10, 11, 18 and 22. Taking mitotic data also into consideration the series runs as n=10, 11, 12, 16, 18 and 22. It is important to note, however, that barring T. hookeriana all the 32 species, inves-tigated have one gametic number n=11 in common. The unrelated numbers (n=10, 12, 16, 18) are considered to be wrong reports or at the most study of one time aberrant plants and it is concluded that the genus Tephrosia is monobasic with x=11.The occurrence of 2-6 univalents in a few PMCs in eight species has been ascribed to early separation of synapsed homo/homeologues and/or precocious separation of rod bivalents. The presence of 0-22 univalents and their overall average of 5.37 per cell in T. uniflora ssp. petrosa has been attributed to desynapsis. Very low quadrivalent average and high bivalent frequency per cell in the three tetraploid species (T. purpurea, T. pumila, T. hamiltonii) is indicative of their hybrid origin.Besides gene mutation, the divergence and evolution of Tephrosia species was accompanied by chromosomal repatterning. The mechanisms responsible for detectable and undetectable chromosomal repatterning are peri- and paracentric inversions, cryptic structural hybridity, deletion and translocations. Hybridization is another important factor responsible for divergence. Polyploidy, present only in a few taxa, has played role in the stabilization of hybrids.

Cytogenetics of double cross hybrids between Pennisetum americanum — P. purpureum amphiploids and P. americanum x Pennisetum squamulatum interspecific hybrids

Pearl millet, Pennisetum americanum L. Leeke-napiergrass, Pennisetum purpureum Schum. amphiploids (2n=42) were crossed with pearl millet X Pennisetum squamulatum Fresen. interspecific hybrids (2n=41) to study the potential of germplasm transfer from wild Pennisetum species to pearl millet. These two interspecific hybrids were highly cross-compatible and more than two thousand trispecific progenies were produced from 17 double crosses. All doublecross hybrids were perennial and showed a wide range of morphological variations intermediate to both parents in vegetative and inflorescence characteristics. Some crosses resulted in sublethal progenies. Chromosomes paired mainly as bivalents (¯x15.88) or remained as univalents. At metaphase I, trivalents, quadrivalents, an occasional hexavalent and a high frequency of bivalents indicated some homeology among the genomes of the three species. Delayed separation of bivalents, unequal segregation of multivalents, lagging chromosomes, and chromatin bridges were observed at anaphase I. Although approximately 93% of the double-cross hybrids were male-sterile, pollen stainability in male-fertile plants ranged up to 94%. Seed set ranged from 0 to 37 seed per inflorescence in 71 plants under open-pollinated conditions. Apomictic embryo sac development was observed in double-cross progenies when crosses involved a pearl millet x P. squamulatum apomictic hybrid as pollen parent. These new double-cross hybrids may serve as 'bridging hybrids' to transfer genes controlling apomixis and other plant characteristics from the wild Pennisetum species to pearl millet.

Cytogenetics of Cucumis L. IV. Comparative study of natural and induced polyploids.

Colchiploids were raised in C. melo var. momordica and C. prophetaranm. Morphologically autotetraploids were vigorous with a little increase in fruit size, though with decrease in number of fruits per vine and seeds per fruit.A comparative meiotic analysis of colchiploids and four natural polyploids, C. pustulatus, C. membranifolius, C. meeusei and C. heptadactylis revealed that C. pustulatus and C. membranifolius with regular bivalent assoication are allopolyploids, while C. meeusei and C. heptadactylis with a few multivalent assoications are autopolyploids, may be segmental allopolyploids. A higher frequency of biva-lents in C. heptadactylis compared to earlier reports suggests that either selection of mutants ensuring bivalent association or diplontic gametes are evolving these species to diplontic behaviour. A high bivalent frequency comparative to natural polyploids observed in colchiploids suggest that they can attain diplontic behaviour like natural polyploids with generation advance and later may stabilise cytologically, sexually and agronomically.

Synaptonemal complex analysis of X-7 translocations in male mice. I. R3 and R5 quadrivalents.

The synaptonemal complexes of surface-spread spermatocytes of mice heterozygous for one of two reciprocal translations (R3 and R5) between the X and chromosome 7 have been examined by light and electron microscopy (EM). The break points of R3 were determined to be at 70% of chromosome 7, as measured from the centromere, and at 22% of the X. Translocation quadrivalents were formed almost exclusively. The break points of R5 were at 21% of chromosome 7 as measured from the centromere, and at 83% of the X. There was little indication that the break in the X interfered with sex-chromosome synapsis between the 7X and Y. Univalent Y's were not observed in R3, and only seldom observed (8-14%) in R5. However, in contrast to R3, R5 formed quadrivalents relatively rarely (20% in the EM study of 100 nuclei), and heteromorphic bivalents of 7X-Y and X7-7 quite frequently (72%). Possible causes of this high bivalent frequency are discussed. Light-microscope (LM) analysis alone was found to be inadequate for interpreting synaptic configurations (quadrivalents vs. bivalents) in R5. The LM analysis was further complicated by the occurrence of nonhomologous synapsis in the heteromorphic bivalents of R5, a phenomenon easily recognized and interpreted in the EM portion of the study.

MEIOSIS IN 8-CHROMOSOME BARLEY HAPLOIDS

Meiosis was studied in four 8-chromosome haploid plants produced from Wiebe's barley (2n = 14 + 2 centric fragments) (Hordeum vulgare L.) in which the extra chromosome had lost its telomeres and was one-third the length of a normal chromosome. Although secondary associations occurred, pairing between the normal and fragmented chromosome was rare despite the presence of homologous segments between them, indicating that the deletion of the telomeres restricted chromosome synapsis. A high bivalent frequency was attributed to a translocation between a long and short chromosome of the normal complement that persisted through the haploidization process.