Quadrivalent Frequency Research Articles

A Cytogenetic Study of Triploids and Aneuploids in Job's Tears, <i>Coix lacryma-jobi</i> L

In Job's tears (Coix lacryma-jobi L.) autotriploids (3n=30), hypo-triploids (3n=29) and hyper-triploids (3n=31) were produced by crossing diploids and colchicine induced autotetraploids. Trisomics (2n=21), double trisomics (2n=22) and multiple trisomics (2n=27) were obtained in the progenies of triploids. In none of the trisomics or double trisomics, the nucleolar chromosome was involved in trisomy. In each of the chromosome classes, meiotic behaviour, fertility and transmission of extra chromosomes to the progenies were studied. The average frequency of trivalents for a set of 3 chromosomes in triploids and aneuploids varied between 0.62 and 0.92, which is much higher compared to the average frequency of quadrivalents for a set of 4 chromosomes in the tetraploids (including hypo- and hyper-tetraploids) which varied between 0.49 and 0.58. These apparently indicate that the frequency of multivalents tends to decrease as the number of homologues of a chromosome in the complement increases. The average chiasma frequency per cell in triploid was significantly less than one-and-half times that in diploid. Although this depression in chiasmata in triploid is difficult to explain, some probable causes were mentioned. In general, aneuploids were lower in fertility compared to diploids, and both hypo- and hyper-triploids were less fertile than triploids. Transmission of extra chromosomes to the progenies occurred more frequently through the female gametes than male gametes.

THE SIGNIFICANCE OF CHROMOSOME ASSOCIATION IN AN ADVANCED POPULATION OF TETRAPLOID RYE

Chromosome pairing was studied in a population of tetraploid spring rye (Secale cereale L.) 20 years after the chromosomes were doubled. Cytogenetically the population was heterogeneous as revealed by significant differences between plants for chiasma frequency, the proportions of regular MI cells and regular quartets. Compared to early C generations meiotic behavior in the population improved by an increase in quadrivalent frequency, mainly at the expense of trivalents and univalents. However, quadrivalent frequency failed to correlate with all other meiotic features; instead bivalent frequency had significant positive correlations with the features of meiotic regularity including chiasma frequency. Furthermore, the average quadrivalent frequency in the population was considerably less than that of inbred lines. These facts led to the conclusion that disomic association dominated the chromosome association pattern in this random mating population, whereas in inbred materials the chromosome association pattern is predominantly tetrasomic. This was further proved by a test against the theoretically expected chromosome association pattern in a true autotetaploid.

Allopolyploid of tetraploid phaseolus species × p. calcaratus cross

Allopolyploids were raised by oolchicine treatment of vegetative buds in the triploid hybrid of tetraploidPhaseolus species xP. calcaratus cross. They had 70 per cent pollen fertility and produced many viable seeds. The average chromosome configuration per cell at MI in them was 1.56IV + 0.01m + 29.30II + l.llr. It has been concluded that the increased fertility in allopolyploids was due to more regular meiosis and the low frequency of quadrivalents indicated the occurrence of preferential pairing.

Effect of inbreeding and selection for vigour and fertility on meiotic behaviour in autotetraploid job's tears, Coix lacryma-jobi L.

Meiotic behaviour of the colchicine-induced "raw" autotetraploid (4n = 40) Job's tears (Coix lacryma-jobi L.) was compared with that of the tetraploid envolved from it through selection for vigour and fertility over a 4 year period and selfing of the selected plants for 3 generations. A significant decrease in quadrivalent frequency and an increase in bivalent frequency per cell, greater frequency of ring quadrivalents, more cells with regular separation of chromosomes and fewer cells with laggards at anaphase I, fewer irregularities in meiosis II, fewer pollen quartets with micronuclei and fewer aneuploids in the progenies were found in evolved tetraploid. The average chiasma frequency per cell, per quadrivalent and per bivalent were more or less the same in both tetraploids. All these facts indicate that inbreeding and selection for vigour and fertility have brought about a shift towards regular meiosis in the evolved tetraploid. The increase in fertility during the period of selection was not, however, significant, suggesting that its response to selection is slow, that a number of factors are probably involved and that, besides multivalents, genic factors also govern sterility in the tetraploid.

GENOME RELATIONSHIPS IN BROMUS ERECTUS, B. PUMPELLIANUS SSP. DICKSONII AND B. PUMPELLIANUS

Chromosome pairing was studied in hexaploid (2n = 42) hybrids of B. erectus (2n = 28) × B. pumpellianus (2n = 56) and B. pumpellianus ssp. dicksonii (2n = 28) × B. pumpellianus. Chromosome pairing in the B. erectus × B. pumpellianus hybrid was complete with predominantly bivalent formation and a low frequency of quadrivalents. The pairing results support the contention that B. pumpellianus is an autoalloploid with an AAAABBBB genome formula. The B. pumpellianus ssp. dicksonii × B. pumpellianus hybrid has an AAABBB genome formula. The presence of quadrivalents, hexavalents and cells containing a total number of bivalents or bivalents plus trivalents in excess of 14 indicated pairing between the A and B genomes. However, a high univalent frequency showed that the A and B genomes were homoeologous rather than homologous. Evidence for genetic control of homoeologous chromosome pairing and homoeologous differentiation between the genomes of the species is discussed.

Cytogenetics of cultivated Bougainvilleas. V. Induced tetraploidy and restoration of fertility in sterile cultivars

Induced tetraploidy restores fertility in sterile cultivars of Bougainvillea. However, like the fertile diploid cultivars induced tetraploids are self-incompatible, but set seeds readily on crossing. Diploid progenitors show irregular meiosis, while in tetraploid counterparts there is predominant bivalent pairing. Low frequency of quadrivalents at 4x level implies that pairing at diploid level is between chromosomes heterozygous for cryptic structural changes. This also accounts for lower number of chiasmata per chromosome in diploids in comparison with their tetraploid counterparts. Sterility at 2x level appears to be due to recombination of cryptic structural differences and/or unequal distribution or aberrant behaviour of univalents. Predominant bivalent pairing accompanted by high fertility is a strong pointer towards preferential pairing in induced tetraploids.

Effects of Ionizing Radiations on Roses

A comparative study of the male meiosis in the rose cultivar ‘Pink Parfait’ and its two, Deep and Light pink flowered mutants was conducted. ‘Pink Parfait’ was found to be a segmental allotetraploid. The frequency of univalents and quadrivalents at metaphase I was higher in the mutants. Anaphase I revealed a higher incidence of lagging chromosomes in Deep pink mutant and an increased frequency of chromosome bridges in both the mutants. The deleterious effects of radiations were evident from the higher percentage of chromosomal aberrations and pollen sterility found in mutants as compared with the control.

Double-bridge hybrids of Solanum bulbocastanum and cultivars of Solanum tuberosum

Solanum bulbocastanum (2n=2x=24) has valuable characters for potato breeding, but cannot be hybridized directly with S. tuberosum cultivars. Both S. acaule (2n=4x) and S. phureja (2n=2x) were used as bridging species. Triploid S. acaule × S. bulbocastanum were doubled with colchicine and the resulting fertile hexaploid F1's crossed with S. phureja. The triple hybrids obtained were tetraploid or nearly so. The two genomes of S. acaule in these triple hybrids probably pair preferentially, which may provoke pairing and possibly crossing over between the chromosomes of S. bulbocastanum and S. phureja. More than 20000 pollinations of the triple hybrids with four potato cultivars had to be made to produce 40 quadruple hybrids. These highly vigorous hybrids varied greatly in many morphological characters, resistance to Phytophthora infestans, fertility and crossability. The chromosome numbers are 48 (24 hybrids), 49 and 46, but some higher ploidy levels (65, 66, 72 chromosomes) were found as well. Their origin is to be sought in the fusion of an unreduced egg cell from triple hybrids (either euploid or hypoploid) and a reduced male gamete from the cultivars. This view is corroborated by their extreme resistance to Phytophthora. Also some 48-chromosome hybrids are highly resistant, which may indicate introgression from S. bulbocastanum. Most quadruple hybrids are readily inter-crossable and crossable as females with cultivars; several also as males. Two could be hybridized with S. bulbocastanum, but the few seeds dit not germinate. Studies of pachytene stage of meiosis revealed the presence of a S. bulbocastanum chromosome in at least one tetraploid hybrid, which is highly resistant to Phytophthora. At metaphase I of meiosis chromosome associations higher than quadrivalents were not found. Except in one hybrid, the frequency of quadrivalents did not exceed one per cell and the average proportion of chromosomes associated as bivalents amounted to 90%. The quadruple hybrids (‘double-bridge’ hybrids) appear good starting material for breeding programmes aimed at introducing genes from S. bulbocastanum into S. tuberosum cultivars.

CHROMOSOME PAIRING IN HEXAPLOID HYBRIDS FROM BROMUS ERECTUS (2n = 28) × B. INERMIS (2n = 56)

Meiotic chromosome pairing was studied at metaphase I of B. erectus (2n = 28), B. inermis (2n = 56) and interspecific hybrids from B. erectus × B. inermis (2n = 42). The B. erectus material averaged 2.08 IV + 0.11 III + 9.51 II + 0.35 I and B. inermis 0.05 VIII + 0.06 VI + 0.02 V + 2.25 IV + 0.11 III + 22.95 II + 0.25 I. The hybrid plants (2n = 42) averaged 0.18 VI + 1.90 IV + 0.19 III + 16.10 II + 0.39 I and one hybrid with 2n = 41 averaged 0.08 VI + 0.02 V + 0.95 IV + 0.50 III + 17.42 II + 0.72 I. Karyotype evidence supported the conclusion that B. erectus was an autotetraploid. The karyotype contains four large satellites and four subterminal chromosomes but the other four groups of four are median, with one group possibly a submedian. Since chromosome pairing in the hybrids was complete and the quadrivalent frequency in the parents and hybrids was similar, it was concluded that the genomic formula of B. erectus, B. inermis, and the hybrid was AAAA, AAAABBBB, and AAAABB, respectively.

THE SIGNIFICANCE OF MEIOTIC CHROMOSOME PAIRING IN TETRAPLOID (2n = 28) BROMUS PUMPELLIANUS SCRIBN. SSP. DICKSONII

Bivalent formation was predominant at meiosis in B. pumpellianus ssp. dicksonii. The average in 15 plants ranged from 11.38 to 13.77 bivalents per cell. The high chiasma frequency (23.41-26.74) was a reflection of the high frequency of ring bivalents (9.48-12.42). A low frequency of quadrivalents occurred (0.06-1.22). A karyotype of this species was presented from both a highly contracted and moderately contracted cell and the differences between these two were noted. Four satellites were found, two large and two minute. There were 3-5 submedian and 5-7 median chromosomes depending on the cell studied. In addition two subterminal chromosomes were present. The meiotic and karyotype analysis suggest a deviation from an autotetraploid behaviour, but the presence of quadrivalents and similarities between pairs in the karyotype suggested closely related genomes. Alternatively it was considered that the quadrivalents could be due to translocation heterozygotes. The implications of these results were discussed in relation to the reported meiotic events in the octoploids, B. inermis and B. pumpellianus.

CHROMOSOME ASSOCIATIONS AT PACHYTENE AND METAPHASE INMEDICAGO SATIVA

Chromosome associations were analyzed at pachytene and metaphase I from six plants of Medicago sativa L. (2n = 4x = 32). Quadrivalent frequency at pachytene ranged from 0.89 to 2.93. These values are considerably below theoretical expectations for an autotetraploid. The chromosome associations at metaphase I did not entirely reflect differences in quadrivalent frequency at pachytene, although there was a general tendency for plants with higher quadrivalent frequencies at pachytene to have a higher trivalent and univalent frequency at metaphase I. However, there were obvious differences in the amount and kind of pachytene quadrivalent dissociation that occurred, which are probably a result of small differences in chiasma frequency and distribution.

MEIOTIC CHROMOSOME BEHAVIOR IN INDUCED AUTOTETRAPLOIDS AND AMPHIDIPLOIDS IN THE LOTUS CORNICULATUS GROUP

A comparative meiotic study was conducted on 12 induced Lotus autotetraploids (2n = 4x = 24; L. alpinus, L. japonicus, L. filicaulis, L. schoelleri, L. krylovii, L. tenuis and L. corniculatus var. minor), and 22 amphidiploids (2n = 4x = 24) obtained by doubling the chromosome number of 12 diploid interspecific hybrids. Meiocytes of the autoretraploids were characterized by a rather high frequency of bivalents (average 8.79 per cell) and a low occurrence of quadrivalents (average 0.77 per cell). In many of the amphidiploids there was a relatively high frequency of bivalents (mean 9.92 per cell) and a low number of multivalents (mean 0.39 per cell) providing evidence for the structural differentiation of the chromosomes and preferential pairing. Homology of the chromosomes of the parental species was indicated by the presence of trivalents and quadrivalents, and the occurrence of inversion bridges with accompanying fragments in the amphidiploids. It appears that the chromosomes of L. japonicus and L. alpinus have considerable homology since the amphidiploid (L. japonicus × L. alpinus)2 exhibited a high frequency of quadrivalents in comparison with the number of quadrivalents observed in L. japonicus (4x) and L. alpinus (4x), A comparison of a) the pollen stainability and b) the frequencies of multivalent configurations in the autoretraploids and the amphidiploids indicated that both multiple gene substitution and cryptic structural changes of the chromosomes are important in differentiating the diploid species.

Cytology of the TetraploidAllium RubellumBieb.

SUMMARYAllium rubellum Bieb. so far known as a diploid and a triploid has been collected in the tetraploid form (2 n=4x=32) from the saffron fields and mud built house tops of Kashmir valley. Tetraploidy has caused gigantism in the size of the plant and the flower head. Root tip cells bear 32 chromosomes with median or submedian centromeres. Eight of the chromosomes are secondarily constricted. These do not match into pairs. Meiosis is characterized by a high frequency of quadrivalents ranging in number from 8 (maximum number possible) to 2 per cell. Anaphase distribution is regular in almost half of the microspore mother cells and only slightly irregular (17:15) in the rest. The subsequent course of meiosis is perfectly normal and as a consequence healthy pollen grains are produced. Though the high quadrivalent frequency points to autopolyploidy, in view of the karyotypic heteromorphicity the taxon seems to have arisen through hybridization at the varietal level.

Reproduction and Cytology of Trifolium uniflorum1

Among the 36 T. uniflorum plants studied, 30 plants were highly self‐incompatible, two were highly self‐compatible, and tour were intermediate. The average number of ovules per pod was 7.9 and the average number of seeds per pod following cross‐pollination of emasculated florets was 3.2. Tripping was not necessary for seed production on a self‐compatible plant.Somatic cells of T. uniflorum contained 28 submetacentric and four subtelocentric chromosomes. The subtelocentric chromosomes possessed satellites. The chromosomes formed almost exclusively quadrivalents and bivalents at metaphase I. The high frequency of quadrivalents (4.46 per microsporocyte) suggests an autotetraploid origin.

Effect of the Mutagens Hydroxylamine, Ethyl Methane Sulphonate and Gamma Rays Separately and in Combination on Meiotic Chromosomes

SUMMARYThe effects of the mutagens hydroxylamine, ethyl methane sulphonate and gamma rays separately and in combination were studied on the meiotic chromosomes in the M1 generation of an inbred strain of Pennisetum typkoides. The significant findings were as follows:When hydroxylamine followed 20 kR gamma ray-treatment the quadrivalent frequency was brought down from 22.03 to 1.81%, giving support to the view that hydroxylamine inhibits rejoining and restitution of chomosomal breaks. But when it followed 30 kR gamma ray-treatment actually the restitution and rejoining frequency increased and the highest frequency of quadrivalents, 34.26% was observed besides 0,92% hexavalents and 2.31% trivalents. Thus, hydroxylamine seemed to act either as an inhibitor or promotor of restitution and rejoining depending upon the intensity of the ionizing radiation.Ethyl methane sulphonate which attacks the guanine-cytosine base pair, like hydroxylamine, also acts as an inhibitor of restitution and rejoining since it broug...

Cytological Studies in the Tribe Paniceae, Gramineae

Chromosome numbers were determined during microsporogenesis in strains belonging to 21 species and 8 genera of Paniceae. These include 4 new reports. Intraspecific chromosome races were found in Brachiaria brizantha, Cenchrus ciliaris, Digitaria adescendens, D. eriantha, Eriochloa nubica, Panicum maximum, Paspalum, orbiculare, P. plicatulum, Pennisetum pedicellatum, Urochloa mosambicensis and U. panicoides.Meiosis was studied in all species. Chromosome pairing was regular in diploids but irregular in polyploids and aneuploids. It is suggested that polyploidy and meiotic irregularities are mechanisms which favor apomictic mode of reproduction in the members of Paniceae studied herein. The frequencies of quadrivalents observed in strains of Cenchrus ciliaris, Paspalum plicatulum and Paspalum simplex seem to be high enough to suggest their autoploid origin. In the rest of the species with low quadrivalent frequency, the factors favoring the accumulation of chromosome structural changes seem to be in operation.Of special interest was a plant of Digitaria eriantha, which exhibited the phenomenon of breakdown of meiosis. The pollen mother cells at early prophase were without well differentiated cell walls, due to which several nuclei formed cenocytes. A few cells showed fragmentation of chromosomes. The metaphase stage was never reached. The fragmented chromosomes formed restitution nuclei. A few cells formed multiple spindles. The pollen fertility was very low.The significance of the cytological findings was discussed.

Octoploidy inCoffea arabica

Morphology and cytology of three octoploid forms ofCoffea arabica were studied. A comparison of the morphological characters of natural allotetraploids and the derived octoploids indicates that there is a reduction in size from tetraploidy to octoploidy. The inferiority in vegetative vigour and high sterility of the octoploids suggests that the optimum chromosome number has been reached in nature at the tetraploid level. Occurrence of a high frequency of quadrivalents in meiosis of the octoploids presently studied is contrary to the reports of earlier workers where quatrivalents were not observed. The significance of quadrivalent formation is discussed.

Apomixis and Tetraploidy in Pennisetum orientate Rich.1

Five accessions of Pennisetum orientate Rich were tetraploid with 2N = 36. Pairing at diakinesis and metaphase I was generally normal, as was anaphase I disjunction. Quadrivalent frequency per cell ranged from zero to eight, but was usually three to five. Pollen sterility was about 28% and due, in part, to laggards, rare unequal disjunction, and univalent misdivision. Embryo development was aposporous. Development of nucellar embryo sacs was accompanied by degeneration of sexual tissue. multiple embryos were not found.

HEXAPLOID ALFALFA,MEDICAGO SATIVAL.: ORIGIN, FERTILITY AND CYTOLOGY

Two spontaneously occurring hexaploids, 6-1 and 6-2, 2n = 6x = 48, were discovered among tetraploid plants of the variety 'Saranac'. They were selfed, crossed with each other and with diploid (2x), triploid (3x), and tetraploid (4x) alfalfa. Self and cross progeny of 6-1 and 6-2 were all hexaploid; 2x-6x crosses produced a plant with 32 chromosomes; 3x-6x crosses produced hexaploids probably due to unreduced triploid gametes; and 4x-6x crosses produced plants with 32, 34, 35, 36, 37, 38, 40, and 56 chromosomes. Thus many additional hexaploids, two pentaploids, 2n = 40, and a septaploid, 2n = 56, were obtained.Chromosome associations were mostly bivalents, with a low frequency of univalents and quadrivalents in hexaploids with six sativa genomes or five sativa and one falcata genome. Pollen stainability was in excess of 95%, ovule number averaged 12 per carpel, and several grams of hexaploid seed were produced from hand crosses. Five different hexaploid synthetics with narrow and wide genetic bases were produced for future seed increase and field testing. The value of hexaploids in breeding and cytogenetic research was discussed.

Cytology of Autotetraploids of Linum Usit Atissimum L. and Linum Angustifolium Huds. and their Amphidiploid Hybrids1

Quadrivalent frequencies at metaphase I in amphidiploids of Linum usitatissimum L. X Linum angustifolium Huds. were comparable to those of autotetraploids of the two parental taxa. Conclusions from this study support previous evidence that the genomes of the two taxa are closely homologous.