High Frequency Of Univalents Research Articles

The classification of tetraploid wheat by phylogenetic and cytogenetic analyses

Tetraploid wheat (Triticum turgidum L.) is an important species within the genus Triticum and harbors many desirable agronomic traits. The classification, origin, and evolution of tetraploid wheat remain confused and controversial, resulting in useless germplasm resources. Two classification systems for tetraploid wheat are widely used: 1) tetraploid wheat comprises two species; 2) all forms of tetraploid wheat are classified as one species. The present study aimed to reassess the classification of tetraploid wheat using phylogenetic analysis of nuclear rDNA internal transcribed spacer region (ITS) sequence data, fluorescence in situ hybridization (FISH) karyotyping, and observation of meiotic pairing behavior in F1 hybrids. Network analysis of ITS sequences indicates that tetraploid wheat was not closely related to other Triticeae species with the exception of Aegilops speltoides and Ae. sharonensis. Phylogenetic analysis of ITS sequences and FISH show that Triticum turgidum and T. timopheevii clustered on distinct branches, and meiotic pairing in F1 hybrids of these species showed a high frequency of univalents. Meiotic behavior of F1 hybrids among forms of T. turgidum revealed a low number of univalents (means < 2) except for T. turgidum ssp. dicoccoides. The significant variation on chromosomes 1A, 2A, 5A, 1B, 2B, 3B, and 6B in the FISH hybridization patterns were observed between T. turgidum ssp. dicoccoides and other T. turgidum accessions. Furthermore, the results of ITS phylogenetic analyses correspond closely with observations of meiotic behavior and FISH karyotyping. The present results indicate that T. turgidum and T. timopheevii are two distantly related species of different origins. Triticum turgidum ssp. dicoccoides should be maintained as a subspecies of T. turgidum whereas other forms of T. turgidum should be reclassified as varieties.

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.

Chromosome counts, chromosomal pairing, and pollen fertility in thirty-eight species of Asteraceae from Pangi Valley in District Chamba of Himachal Pradesh (India)

The current investigation includes detailed male meiotic studies, chromosomal counts, and pollen fertility on 38 species of family Asteraceae from the Pangi Valley, a part of cold desert Himalayas. The first-ever chromosome counts have been made for seven species viz. Aster albescens Wall. (n = 9), A. heterochaeta C. B. Clark (n = 9), Cirsium involucratum DC. (n = 34), Inula obtusifolia Kern. (n = 8), Saussurea piptathera Edgew. (n = 13), Senecio arnicoides (DC.) C. B. Clark, and Tanacetum robustum Hook f. et Thoms. (n = 9). Besides, new cytotypes are reported for Aster flaccidus Bunge (2n = 2x = 18), A. peduncularis Wall. ex Nees (2n = 2x = 18), and Youngia tenuifolia (Willd.) Babcock & Stebbbins (2n = 4x = 20). Out of the thirty-eight species, six species viz. Crepis multicaulis Ledeb., C. sancta (L.) Babcock, Erigeron multiradiatus (Lindl.) C. B. Clark, Scorzonera divaricata DC., S. arnicoides (DC.) C. B. Clark, and Taraxacum officinale Wigg., showed a number of meiotic abnormalities leading to reduction in pollen fertility and production of heterogeneous-sized pollen grains. The triploid cytotype of T. officinale Wigg. (2n = 24) depicted irregular meiotic course characterized by the presence of high frequency of univalents, abnormal sporads, and pollen malformation. B-chromosome has been reported for the first time in some individuals of S. arnicoides (DC.) C. B. Clark. Compiled information on the worked out species reveals the existence of considerable amount of chromosomal variations in some species involving the role of aneuploidy and polyploidy.

Chromosome numbers, characterization of chromosomal pairing during meiosis, origin and natural propagation in polyploid cytotypes (4x, 5x and 6x) of Agrimonia eupatoria L. (Rosaceae) in northwest Himalayas (India)

Despite the presence of intraspecific polyploidy (2x, 4x, 5x and 6x) in Agrimonia eupatoria, origin of these cytotypes has never been addressed adequately. The aim of the present study was to record the original chromosome counts and characterize chromosomal pairing during meiosis and microsporogenesis in the 5x cytotype, and discussing the hypothesis regarding the possible origin of polyploid cytotypes (4x, 5x and 6x) in the species. The geographical distribution pattern of cytotypes in the Indian Himalayas and elsewhere has also been analyzed. The present meiotic analysis revealed three chromosomes counts, the tetraploid (2n = 4x = 56), the pentaploid (2n = 5x = 70) and the hexaploid (2n = 6x = 84) cytotypes based on x = 14. Meiotic course was perfectly normal in the 4x and 6x cytotypes resulting into high pollen fertility (94-100 %). Meiotic course in the imbalanced 5x cytotype has been found to be irregular characterized by the presence of high frequency of univalents at diakinesis and metaphase-I. Abnormal meiotic course contributed towards high pollen sterility (74-88 %). Even the apparently fertile/stained pollen grains were of irregular shape and of heterogeneous sizes. Meiotic behaviour of the 5x cytotype is like typical of allopolyploid. Individuals of 5x cytotype did not produce seeds and propagate vegetatively (root suckers) while 4x and 6x cytotypes exploited sexual (seeds) as well as vegetative means for propagation. Chromosomal pairing in pentaploid cytotype is like typical of an allopolyploid and we assume that it might have originated owing to natural inter-cytotype hybridization between 4x and 6x cytotypes in a mixed population. Analysis of geographical distribution pattern of cytotypes shows that Indian Himalayas represent the most cytotype-diverse region for A. eupatoria with the existence of all the four cytotypes (2x, 4x, 5x, 6x). This shows the dynamic nature of the species at chromosomal level in this part of the world.

Induced desynaptic variation in poppy (Papaver somniferum L.)

Cytological investigation of EMS (ethyl methane sulphonate) treated population demonstrated enhanced univalent frequency per cell with unequal separation at Anaphase I. In contrast to controlled plants, medium strong type desynaptic plants were obtained from 0.6 % EMS treated set, revealing high frequency of univalents at Metaphase I, along with bivalents, which were loosely paired. The univalents remained unpaired till the end of meiosis, leading to formation of micronuclei and abnormal tetrads. These plants had high pollen inviability and sterile seeds. It might be possible that EMS had acted on some genes responsible for chiasma formation, resulting in early chiasma dissociation, which suggests that EMS can act as a potential tool in the development of male sterile lines. The study demonstrated the feasibility of chemical mutagenesis in mutation breeding programme on poppy (Papaver somniferum L.).

Generation of B. nigra–B. rapa chromosome addition stocks: cytology and microsatellite markers (SSRs) based characterization

To improve Brassica nigra, the B-genome donor for Brassica juncea through selective introgression of useful variation from A-genome chromosomes, B. nigra-B. rapa chromosome addition stocks were successfully synthesized for the first time. Resynthesized B. juncea was used as B-genome donor species and A-genome addition stocks were developed by hybridizing sesquidiploid plant (ABB) as female and using B. nigra as the male parent. Various cycles of backcrossing and/or selfing were utilized to isolate plants carrying addition of three A-genome chromosomes in the background of B. nigra. These chromosome addition stocks were characterized by chromosome counts, pollen and seed fertility and chromosome specific microsatellite (SSRs) markers. The chromosome number in different backcross/self generations ranged between 2n=26 and 2n=19 with relatively high frequency of univalents (8-10I) at in meiotic configurations observed, suggesting the role of preferential transmission of A-genome chromosomes. SSRs analysis revealed that B. rapa chromosomes 3 and 4 were the first to get eliminated followed by chromosome 10. Remaining chromosomes were maintained till BC(1)F(4). However, second cycle of backcrossing (BC(2)) led to the elimination of chromosome numbers 1 and 2. BC(2)F(2) plants carried the chromosome numbers 6, 7, 8 and 9. Generation BC(3) having plants with 2n=19 carried chromosome numbers 6, 7 and 8. It is possible that chromosomes 6, 7 and 8 had higher transmission frequency and these were better tolerated by the B. nigra genome.

Male Meiosis, Microsporogenesis and Pollen Grain Study in Inula cuspidata C. B. Clarke (Asteraceae)

Male meiosis, microsporogenesis and pollen grain studies have been made on 11 accessions of Inula cuspidata C. B. Clarke from the cold desert regions of the Kinnaur district, Himachal Pradesh, India. All the accessions share the same meiotic chromosome number n=10. Out of these, 10 accessions show regular chromosome pairing resulting into normal 10 bivalents formation. The meiotic analysis in these accessions reveals that 2 bivalents are of comparatively large size. These large-sized bivalents in 6 accessions show abnormalities in their disjunctions resulting into laggards/bridges during anaphases/telophases and micronuclei in tetrads and consequently some pollen sterility. In one of the accessions of I. cuspidata scored from Tapri, meiotic course is irregular due to the presence of a high frequency of univalents during the first meiosis. These univalent chromosomes during subsequent stages of meiosis fail to organize at the spindle plate and remain scattered in the cytoplasm. Consequently, the majority of the PMCs in the accession depict irregular anaphases/telophases, formation of multiple nuclei and abnormal sporads (dyads, triads, polyads and tetrads with micronuclei). The accession forms a large number of malformed pollen grains consisting of unstained/sterile and heterogeneous sized stained/fertile pollen grains. The accession showing such a abnormal meiotic behaviour could be attributed to its hybrid nature where the chromosome of the 2 putative parents is left unpaired during earlier stages of prophase I.

An Analysis of Univalent Segregation in Meiotic Mutants ofArabidopsis thaliana: A Possible Role for Synaptonemal Complex

During first meiotic prophase, homologous chromosomes are normally kept together by both crossovers and synaptonemal complexes (SC). In most eukaryotes, the SC disassembles at diplotene, leaving chromosomes joined by chiasmata. The correct co-orientation of bivalents at metaphase I and the reductional segregation at anaphase I are facilitated by chiasmata and sister-chromatid cohesion. In the absence of meiotic reciprocal recombination, homologs are expected to segregate randomly at anaphase I. Here, we have analyzed the segregation of homologous chromosomes at anaphase I in four meiotic mutants of Arabidopsis thaliana, spo11-1-3, dsy1, mpa1, and asy1, which show a high frequency of univalents at diplotene. The segregation pattern of chromosomes 2, 4, and 5 was different in each mutant. Homologous univalents segregated randomly in spo11-1-3, whereas they did not in dsy1 and mpa1. An intermediate situation was observed in asy1. Also, we have found a parallelism between this behavior and the synaptic pattern displayed by each mutant. Thus, whereas spo11-1-3 and asy1 showed low amounts of SC stretches, dsy1 and mpa1 showed full synapsis. These findings suggest that in Arabidopsis there is a system, depending on the SC formation, that would facilitate regular disjunction of homologous univalents to opposite poles at anaphase I.

Induced Desynaptic Male Sterile Lines in Soybean

In a study on soybean using gamma rays, we came across with some sterile mutants. Cytological studies of these mutants clearly revealed desynapsis in them. In these sterile plants only few bivalents and a high frequency of univalents have been recorded and they displayed a very high percentage of pollen sterility. Later meiotic stages were also found to be highly disturbed. The plants were identified as male sterile ones as few pods were formed. It might be possible that gamma rays have acted on some genes responsible for synapsis and chiasma formation and resulted in early chiasmate dissociation suggesting that gamma rays can act as a potential tool in the development of male sterile lines. Study of desynaptic mutants is a potentially important source of information on the chiasma maintenance mechanism. These mutants furthermore can provide useful cytological and genetical informations on the male sterility occured in higher plants.

Cytogenetic Studies in Ethiopian Landraces of Tetraploid Wheat (Tviticum Turgidum L.). II. Spontaneous Chromosome Translocations and Fertility

Meiosis was studied in seven tetraploid (2n =4x = 28) wheat (Triticum turgidum L.) landrace morphotypes of Ethiopian origin and one introduced durum variety, ‘Boohai’. The objectives were to detect the presence of chromosome structural rearrangements by using the variety ‘Senatore Cappelli’ (SC) as a reference and to investigate if the previously reported low fertility (seed set) of the landraces has a chromosomal basis. All the parents exhibited a normal bivalent pairing at metaphase I (MI) except one (CD-7) that showed a relatively high proportion of pollen mother cells (PMC) with univalents (0.40/PMC). ‘Boohai’ and two of the landraces from Ambo district were structurally similar to SC. The remaining five landraces each differed by one translocation from SC. These, in turn, differed from each other by one or two translocations while two of the landraces carried the same translocation. However, in some of the landrace x landrace hybrids there was a tendency of restricting the formation of more than one quadrivalent per PMC. Four different translocations involving four to six chromosomes are present in the material studied. Lack of pairing, as measured by univalent frequency, vaned for the different F, hybrids. Generally, however, it was lower in the F, hybrids between the landraces than in hybrids between the landraces and SC. In almost all cases, division stages following MI proceeded as normal. Inversions were absent or too small to be detected. Meiotic irregularities have little to do with the low fertility of most of the parental landraces. In the F, hybrids, on the other hand, high univalent frequency and multivalent associations impaired seed set depending upon the cross combination. The results indicate that chromosome structural Polymorphism for translocations may be common in Ethiopian tetraploid wheat landraces that might have played a role in maintaining their diversity by producing new linkage relationships. From breeding perspective, the bulk selection method and/or backcrossing to high fertility genotypes seem to be appropriate when these landraces are employed in hybridization programmes.

Homoeologous pairing and recombination in Solanum lycopersicoides monosomic addition and substitution lines of tomato.

We compared meiotic pairing and recombination between tomato ( Lycopersicon esculentum) and homoeologous Solanum lycopersicoides chromosomes in monosomic additions (MAs) and substitution lines (SLs), each representing a single chromosome of the nightshade in a tomato background. Three configurations of each alien chromosome and its two tomato homoeologues were detected by genomic in situ hybridization in MA-7, -8, and -10 at diakinesis/metaphase-I: 1 trivalent (III), 1 bivalent + 1 univalent (II+I), and 3 univalents (3I). The II+I category was by far the most common, and the univalent was from S. lycopersicoides 91-99.5% of the time, indicating a high degree of preferential (homologous) pairing. In the corresponding substitution lines, association of homoeologous chromosomes was much higher (up to 90% of the cells), presumably due to the absence of homologous partners. However, SL-10 showed a surprisingly high frequency of univalents (about 73%). Genome-wide analysis of chromosome pairing revealed a decrease in the average chiasma frequency for both monosomic additions and substitution lines. Recombination between tomato and the nightshade was restricted in all cases, the reduction being more severe in each monosomic addition than in the corresponding substitution line. Recombination rates in the substitutions were less than those observed for the same chromosomes in the first backcross generation. Chromosomes 8 and 10 showed the highest and the lowest rates of homoeologous recombination, respectively. No recombination was detected between markers on the long arm of chromosome 10, presumably due to the presence of a paracentric inversion differentiating the two genomes in this region. The frequency of homoeologous pairing at diakinesis/metaphase-I was significantly higher than the rate of homoeologous recombination detected in the progeny, suggesting a strong selection against recombinant products in meiotic or post-meiotic stages.

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.

Crossability of wild species of Oryza with O. sativa cvs PR 106 and Pusa Basmati 1 for transfer of bacterial leaf blight resistance through interspecific hybridization

Fourteen rice accessions resistant to bacterial leaf blight (BB), caused by Xanthomonas oryzae pv. oryza (Xoo) and belonging to nine wild Oryza species representing three genomic groups: AA (O. nivara, O. barthii, O. longistaminata, O. rufipogon and O. meridionalis), BBCC (O. punctata, O. malampuzhaensis and O. minuta) and CCDD (O. latifolia) were used to produce hybrids with two O. sativa (2n=24, AA) cultivars PR 106 and Pusa Basmati 1 (PB 1). The seed set in similar genome crosses ranged between 1·4 and 79% depending upon the rice cultivar used. In general, PR 106 showed better crossability with the wild species. Hybrids were obtained from intergenomic crosses with O. malampuzhaensis, O. latifolia and O. punctata, using embryo rescue. Morphologically, the hybrids were more vigorous than their parents and tended to resemble their male parent. Intragenomic hybrids showed little fertility (0·24–8·04%), while the intergenomic hybrids were completely sterile. Meiotic studies revealed irregularities in cell division, with a high frequency of univalents (12·17–18·75), fewer bivalents (2·43–5·80) and occasional multivalents, in intragenomic hybrids. The intergenomic hybrids were characterized by a very high frequency of univalents (34·98–35·35). The reaction of the hybrids to BB revealed the presence of both dominant and recessive genes in the wild gene pool. The hybrids with O. longistaminata, O. punctata, O. latifolia and O. malampuzhaensis showed resistance in the F1 generation, and hence they were likely to carry dominant genes for resistance, while the hybrids with O. barthii, O. nivara, O. meridionalis and O. rufipogon were susceptible and hence carried recessive genes for resistance.

Meiosis in the leek (Allium porrum L.) revisited. II. Metaphase I observations

A detailed analysis of metaphase I of meiosis in pollen mother cells of Allium porrum has confirmed that despite frequent quadrivalent pairing (71 per cent) at prophase I and a high mean chiasma frequency (3.5 per tetrasome), the majority of quadrivalents are resolved into bivalent associations at metaphase I. The present observations also support the view that quadrivalent resolution results from the pronounced proximal chiasma localization found in this species. However, neither chiasma localization nor quadrivalent resolution are as prevalent as most previous reports have indicated. About 2 per cent of chiasmata, considerably more than in previous studies, occur in nonproximal chromosome regions in this material, while 12.9 per cent of metaphase I cells contained one or more multivalents, again exceeding most previous estimates. Meiotic regularity in this material was also disturbed by an unexpectedly high frequency of univalents. Overall 25.8 per cent of cells contained one or more univalent pairs, giving an overall mean of 0.32 univalent pairs per cell. It appears that meiosis in the leek is less regular than previous reports have indicated. The implications for fertility, stability and uniformity are not trivial and ought to be considered in the context of leek production and breeding.

Cytological Abnormality Control Seed Set in Panicum repens L. in Egypt.

The cytology, meiotic behaviour and breeding system were investigated in this work for Panicum repens trying to find out its genetic situation with other Egyptian species and to study the reasons cause reduction in seed set and induce sterility. Mitotic counts of chromosomes shows 36 as tetraploid species based on 9 as basic number. Based on length and centromere position the karyotype formula shows 14 pairs of metacentric, 3 pairs of submetacentric and one pair of telocentric chromosomes. The mean chromosome length measure 0.97μm and arm ratio of 1.25. The heterogenity in chromosome set suggests the alloploid origin of the species.Meiotic behaviour of chromosomes was found somehow irregular with high frequency of univalents and low multivalents. The latter insures that the species is not autotetraploid in origin. Also the high level of univalents suggests the structural hybridity of the species. Irregular meiosis lead to form abnormal pollen and non functional gamets which directly decrease fertility and probably affect seed set either at open or self pollination. Cytological results indicate that the species is cytologically complex with alloploid origin and more self incompatible in breeding system.

Meiotic mutants of rye Secale cereale L. II. The nonhomologous synapsis in desynaptic mutants sy7 and sy10

We studied the expression and inheritance of two spontaneous mutations found in different populations of rye Secale cereale L. that cause high univalent frequency in meiosis and low fertility. Both mutations were inherited as monogenic recessives. For each of the mutations the corresponding gene symbols (sy7 and sy10) were suggested although their allelism has not been studied. These mutants differ in chiasma frequency and in the number of univalents per meiocyte. Electron microscopy of the wholemount surface-spread synaptonemal complexes (SCs) from microsporocytes of both mutants revealed that during meiotic prophase I random synapsis began and progressed that involved not only homologous but also nonhomologous chromosomes. SCs were formed with frequent changes of pairing partners (switches) and intrachromosomal foldbacks of unpaired axial elements. As a result, incompletely synapsed, non-homologous and multivalent SCs were formed in mutants by the stage analogous to pachytene in normal plants. In sy7 a maximum in the number of switches and foldbacks were observed at zygotene, whereas in sy10 this occurred at pachytene. We suggest that it is the process of recognition of homology that is impaired in both mutants. This leads to indiscriminate synapsis and prevents chiasma formation. Both mutants may be classified as desynaptic.

Intergeneric Hybridization between Species of Leymus, Psathyrostachys and Hordeum (Poaceae, Triticeae)

A total of 132 intergeneric crossing attempts (49 combinations) involving species of Leymus Hochst., Psathyrostachys Nevski and Hordeum L. were performed, of which 103 were between Hordeum and Leymus. Embryo rescue was used throughout the experiment. Hybrids between Leymus and Psathyrostachys were difficult to obtain. Hybrid progeny were relatively easily obtained when crossing Hordeum and Leymus. Plants from 20 different combinations were obtained. Nineteen of these have not previously been reported. Meiotic analysis of three hybrid combinations of Hordeum × Leymus is reported. The high frequency of univalents in meiotic interphase (MI) indicates that allosyndetic chromosome pairing did not occur, supporting the assumption that the genomes of Leymus are non-homologous to the H genomes of Hordeum.

Cytogenetical studies in Rhoeo spathacea (Commelinaceae). I. A desynaptic and second division restitution mutant

A mutant causing partial desynapsis (dissociation of paired chromosomes), and consequently a high frequency of univalents at metaphase 1, was found in Rhoeo spathacea among the selfed progeny of a wild-collected ring-forming complex interchange heterozygote. All the plants were diploid, 2n = 2x = 12. The mutant formed univalents in all microsporocytes (range 2–12; average 7.56/cell), and 23.69% of the pollen mother cells contained the maximum of 12 univalents at metaphase I. There was no significant difference in pollen fertility between the mutant and parental plants. The desynaptic mutant produced microspores with chromosome numbers of n = 6–14 in the same anther. Unreduced pollen was formed at telophase II by second division restitution and comprised 52.74% of the pollen grains. By selfing, diplandrogynous tetraploid progeny (2n = 4x = 24) of 12 seedlings were obtained. The results demonstrate that both male and female gametes are unreduced.Key words: Rhoeo, desynapsis, univalent, second division restitution, tetraploid.

Induced Synaptic Mutant from Mesophyll Cell Protoclones of Dihaploid Solanum tuberosum

Summary A synaptic mutant showing a very abnormal meiotic chromosome pairing was individuated among plants regenerated from protoplasts treated with 0.025 % EMS, which results in an abnormally high frequency of univalents at diakinesis and metaphase I. As a consequence of univalent formation, the chiasma frequency was greatly reduced and the later stages of meiosis were highly irregular, resulting in high pollen sterility.

Effects of B-Chromosomes on Recombination inCylinbrotettix Obscurus(Leptysminae: Acrididae)

SUMMARYThe grasshopper Cylindrotettix obscuras (Leptysminae: Acrididae) is polymorphic for a mitotically stable supernumerary isochromosome (Iso B) and a small, mitotically unstable B-chromosome (BT); both B-chromosomes significantly increase abnormal sperm formation, as determined by CONFALONIERI and BIDAU (1986). In the present work 87 male individuals of C. obscurus from Misiones, Argentina, were analysed for total (T), proximal (P), interstitial (I) and distal (D) chiasma frequency with the aim of detecting effects of those B-chromosomes on recombination in this species. It was evident that the Iso B significantly raise T and P chiasma frequency; this effect was more evident in the carriers of two Iso B's. T and P chiasma frequencies descend in follicles with 1 BT with respect to 0 BT ones, and then increase gradually with 2, 3, 4 and 6 BT's; the regression of T and P on BT number was significant. However, the simultaneous presence of both B-chromosomes produces a marked decrease of T and P frequencies, yielding in some cases a high univalent frequency. The effects of both B-chromosomes are discussed in relation with other similar cases in closely related species. It is suggested that the rise of chiasma frequency in both cases would be due to reduced interference; on the contrary, the interaction effect would be due to asynapsis or desynapsis rather than to increased interference.