Quadrivalent Frequency Research Articles

Induction and evaluation of colchitetraploids of two species of Tinospora Miers, 1851.

Autotetraploidy, both natural and/or induced, has potential for genetic improvement of various crop species including that of medicinal importance. Tinospora cordifolia (Willdenow, 1806) Miers, 1851 ex Hooker et Thomson, 1855 and T. sinensis (Loureiro, 1790) Merrill, 1934 are two diploid species, which are dioecious, deciduous and climbing shrubs with high medicinal importance. Among the three methods used for induction of polyploidy by colchicine treatment, it was cotton swab method which successfully induced the polyploidy in both species. The morphological and cytogenetical features of the synthetic tetraploids were compared with their diploid counterparts. The tetraploids were morphologically distinct from diploid plants. They exhibited larger organs, such as stem, leaves, inflorescence, fruits, flowers and seeds. The tetraploids were characterized by the presence of low quadrivalent frequency and high bivalent average. Unequal distribution of chromosomes at anaphase I was found in 60% cells. The present study provides important information on the superiority of autotetraploids as compared to diploid counterparts in both species.

Cytogenetic and molecular evidences revealing genomic changes after autopolyploidization: a case study of synthetic autotetraploid Phlox drummondii Hook.

Polyploidy is known to be common in plants; indeed most of the world's economically important crop plants are polyploids. Recent studies revealed extensive genomic changes in synthetic polyploids after genome doubling, although most of the information available is with regards to allopolyploids and little information have been generated in autopolyploids. In the present study, we used Phlox drummondii Hooker (2n=2x=14) as a model plant to observe genomic changes, if any, in synthetic autopolyploids. Colchitetraploids were produced and followed through different generations (C0, C1, C2 and C3). Male meiosis analysis showed differences between the frequency of both quadrivalents and bivalents from C0 to C2 generations. RAPD analysis revealed 2.8, 1.6, 2.1 and 3.2% polymorphism in C0, C1, C2 and C3 colchitetraploids respectively. The polymorphic fragments were further characterized after cloning. Dot blot assay was performed to confirm high copy/low copy nature of fragments showing variation. The analysis revealed changes in both repetitive and non-repetitive regions. Out of the six fragments only one fragment T01 was found to be of high copy, while four fragments were of the moderate copy and one fragment of the low copy nature.

Characterization of recombinants of the Aegilops peregrina-derived Lr59 translocation of common wheat.

A compensating, recombined Lr59 translocation with greatly reduced alien chromatin was identified. Microsatellite locus Xdupw217 occurs within the remaining segment and can be used as a co-dominant marker for Lr59. In earlier studies, leaf rust (caused by Puccinia triticina Eriks.) resistance gene Lr59 was transferred from Aegilops peregrina (Hackel) Maire et Weiler to chromosome arm 1AL of common wheat (Triticum aestivum L.). The resistance gene was then genetically mapped on the translocated chromosome segment following homoeologous pairing induction. Eight recombinants that retained the least alien chromatin apparently resulted from crossover within a terminal region of the translocation that was structurally different from 1AL. These recombinants could not be differentiated by size, and it was not clear whether they were compensating in nature. The present study determined that the distal part of the original translocation has group 6 chromosome homoeology and a 6BS telomere (with the constitution of the full translocation chromosome being 1AS·1L(P)·6S(P) ·6BS). During the allosyndetic pairing induction experiment to map and shorten the full size translocation, a low frequency of quadrivalents involving 1A, the 1A translocation, and two 6B chromosomes was likely formed. Crossover within such quadrivalents apparently produced comparatively small compensating alien chromatin inserts within the 6BS satellite region on chromosome 6B of seven of the eight recombinants. It appears that the Gli-B2 storage protein locus on 6BS has not been affected by the recombination events, and the translocations are therefore not expected to affect baking quality. Simple sequence repeat marker results showed that Lr59-151 is the shortest recombinant, and it will therefore be used in breeding. Marker DUPW217 detects a homoeo-allele within the remaining alien chromatin that can be used for marker-assisted selection of Lr59.

Karyotype and meiotic analysis of five species in the genusArtemisia

Abstract The karyotypes and meiotic behaviour of five species in Artemisia are investigated. The results are concluded as following: A. absinthum Linn., A. sieversiana Ehrhart ex Willd. and A. annua Linn. are diploids; while A. abrotanum Linn. and A. japonica Thumb. are tetraploids. Their karyotypes consist mainly of median centromere and submedian centromere chromosomes, except that A. sieversiana, A. abrotanum and A. japonica have one, one and two pairs of subterminal centromere chromosomes. One pair of satellited chromosomes is respectively observed in A. annua, A. sieversiana and A. absinthum. All the species have a 2A type karyotype. The mean configurations per the pollen mother cells (PMCs) of A. absinthum, A. sieversiana and A. annua are 0.03I + 8.82II + 0.08IV, 1.16I + 8.26II + 0.03III + 0.06IV and 2.15I + 7.78II + 0.04III + 0.04IV; the mean configurations of A. abrotanum and A. japonica are 0.11I + 16.83II + 0.08III + 0.50IV and 0.17I + 16.67II + 0.07III + 0.57IV, respectively. The meiotic behaviour in the PMCs of all species is generally normal, however, higher frequencies of univalents are observed both in A. annua and A. sieversiana. A low frequency of quadrivalents (and trivalents) and chromosome bridges/lagging chromosomes is observed.

Cytogenetical investigations in colchicine-induced tetraploids of Cyamopsis tetragonoloba L.

Successful induction of autotetraploidy has been achieved in five accessions of Cyamopsis tetragonoloba L. The diploid seedlings of these accessions were treated with different concentrations of aqueous colchicine using the cotton-swab method for 10–18 hours within 2–3 days. The highest percentage of success was recorded when the seedlings were treated with 0.2% colchicine for 10 h within two days. The synthesized plants showed remarkable enhancement in several morphological and floral characters making them more robust and better plants from the food and feed aspect. Cytologically, quadrivalent frequency ranging from 3.18 to 5.45 and univalent frequency ranging from 0.08 to 1.10 were characteristic of the colchicine-induced tetraploids. Among all the associations, bivalent chromosome associations were observed more frequently (2.95 to 6.04). The anaphase I and II disjunction of bivalents/chromosomes was leading more or less regularly and equally to the formation of at least few seeds from some of the synthesized plants. Significant enhancement in morphological traits as revealed in colchicine-induced tetraploid plants having a better food and feed value and normal meiotic behaviour of synthesized autotetraploids leading to a good seed set may ultimately result in the genetic improvement of Cyamopsis tetragonoloba.

Selection in tetraploid rye

A comparative study of two populations selected for both seed set and meiosis regularity, and an unselected population, showed variable relationships in euploid plants between chiasma frequency and the frequencies of metaphase-I configurations. In the population selected for high seed set and meiosis regularity, quadrivalent frequency had a significant positive regression on the frequency of chiasmata. In the unselected population an increase in chiasma frequency was associated with a significant increase in bivalent frequency. In the population selected for low seed set and irregular meiosis the regression, based on individual plant means, of chiasma frequency on quadrivalents was negative and on bivalents was positive and significant. The same regressions, when based on cell population means showed the opposite relationships. That is the chiasma frequency had a significant positive regression on quadrivalent frequency and a negative regression on bivalent frequency. These results are discussed in relation to chromosomal differentiation within the sets of four homologous chromosomes of an autotetraploid.

Karyotype and meiotic analyses of six species in the subtribe Chrysantheminae

The karyotypes and meiotic behaviour of six Chrysantheminae species are investigated. Pyrethrum coccineum (Willd.) Worosch. is a tetraploid, while the other five species (Argyranthemum frutescens (L.) Sch.-Bip., Opisthopappus taihangensis (Ling) shih, Crossostephium chinense (L.) Makino, Tanacetum vulgare L. and P. parthenium (L.) Sm.) are all diploids. Their karyotypes consist mainly of median centromere and submedian centromere chromosomes, although C. chinense also has two terminal centromere chromosomes, and P. parthenium two subterminal centromere chromosomes. No satellited chromosomes are observed in any of the six species. All the species have a 2A type karyotype, except for P. coccineum which is 3A. The meiotic behaviour in the pollen mother cells (PMCs) of all six species is essentially normal, with metaphase I chromosome pairing configurations in the diploid species predominantly showing 9II, while P. coccineum shows 18II. A low frequency of quadrivalents (and trivalents) and chromosome bridges/lagging chromosomes is observed.

Natural hybrids in Senecio (Asteraceae): new records from Argentina

Hybridisation is very common within Senecio. It is considered a fundamental mechanism of speciation and also a major feature causing systematic complexity. Morphological features are the preliminary characteristics used to identify hybrids; however this approach is usually not sufficient when this is the case chromosome studies represent a valuable tool for reinforcing the observations. Two natural homoploid interspecific hybrids are reported here: Senecio × lulioi M. G. López et Xifreda (S. brasiliensis (Spreng.) Less. × S. grisebachii Baker) and Senecio × piepaloensis M. G. López et Xifreda (S. ragonesei Cabrera × S. sectilis Griseb.). Classic cytogenetic analysis and pollen stainability were performed to evaluate hybrid origins and to designate the putative parents. S. × lulioi presented a low frequency of quadrivalents and heteromorphic bivalents, both strong evidences of hybridisation between closely related species. S. × piepaloensis exhibited a high frequency of meiotic irregularities, and reduced pollen stainability, certain characteristics of hybrids. This analysis is discussed in relation to the role of hybridisation in the evolution of the genus, and its systematic significance.

Meiotic behaviour in reciprocal tetraploid hybrids between perennial and Italian ryegrasses

Chromosome associations and chiasma frequencies at first metaphase (MI) were studied in allotetraploid reciprocal hybrids between perennial ryegrass (Lolium perenne, Lp) and Italian ryegrass (L. multiflorum, Lm), and parent autotetraploid perennial ryegrass. Preferential chromosome pairings were assessed in Lp × Lm and Lm × Lp hybrids. The reciprocal hybrids were found to have significantly higher frequencies of bivalent pairing and lower frequencies of quadrivalent pairing and chiasmata. The mean frequencies of total bivalents at MI were 6.820, 9.885 and 10.040 and total quadrivalent frequencies were 3.320, 1.775 and 1.760 in the autotetraploid parent and the Lp × Lm and Lm × Lp hybrids, respectively. The frequencies of chiasmata were 25.075, 23.455 and 23.315 in the parent and the Lp × Lm and Lm × Lp hybrids, respectively. The frequencies of preferential chromosome pairing in the Lp × Lm and Lm × Lp hybrids were 42.69 and 44.85%, respectively and the results indicate a significant degree of preferential bivalent association in the hybrids. An inverse relationship was found between the frequency of total bivalent and quadrivalent associations in the parent and the Lp × Lm and Lm × Lp hybrids. These reciprocal hybrids are potentially important breeding materials for developing new hybrid cultivars.

Cytogenetic data for Paspalum notatum Flügge accessions

Several species of the genus Paspalum L. are important forages, due their to quality, productivity and tolerance to environmental stresses. Chromosome numbers, meiotic configurations and pollen fertility were evaluated in a collection of 85 accessions of Paspalum notatum Flügge and in seven accessions of Pensacola (P. notatum var saurae). All P. notatum accessions were tetraploid, with 2n = 4x = 40, except one diploid accession, considered as an escape of Pensacola. All Pensacola plants had 2n = 2x = 20. Meiotic configurations at diakinesis and metaphase I varied among tetraploid accessions, from plants with only bivalents to plants with high frequency of quadrivalents. Pollen fertility varied from 82.5 to 95.9% among diploid accessions and from 72.4 to 97.9% among the tetraploids. Due to the apomictic mode of reproduction of tetraploid P. notatum, meiotic irregularities can be maintained by plants without harming their propagation. At the same time, pollen fertility should be high enough to assure endosperm development, since the species is pseudogamous. Wild diploid P. notatum populations, apart from the endemic P. notatum var saurae, are very rare. From a plant breeding point of view, all the examined tetraploid accessions are potentially male-fertile and could be used as males in crosses.

Cytogenetic studies on two F1 hybrids of autotetraploid rice varieties showing extremely high level of heterosis

Mechanisms of two F1 hybrids (D46A × DTP-4 and D46A × Dminghui63) of autotetraploid rice (2n = 4x = 48) showing extremely high pollen fertility 87.40% and 85.97%, respectively, seed set 82.00% and 79.00%, respectively and extremely high level of heterosis were analyzed cytologically. The chromosome pairing of D46A × DTP-4 and D46A × Dminghui63 was normal at metaphase I(MI), and had almost no I or III, with an average of 0.020I +14.36 II 6.44rod+7.91ring) +0.01III + 4.80 IV + 0.01VIII and 0.06 I + 17.67 II (11.01rod + 6.67ring)] + 0.06 III +3.10IV+0.01VI, respectively. The most frequent chromosome configurations were 10II+7IV and 12II+bIV. The bivalent frequency was less frequent in hybrids than that in restoring parents, and the same results were gained from univalents, trivalent and multivalents. However, the quadrivalent frequency was significantly higher in hybrids than that in restoring parents at MI. The other meiotic phases progressed normally, except for low percentages of PMCs with lagging chromosomes at AI and low percentages of PMCs with micronuclei at telophaseI (TI) and telophaseII (TII). PMCs with lagging chromosomes at AI and PMCs with micronuclei at TI and TII showed negative correlation between pollen fertility and seed set. Above 90% of the PMCs could form normal microspores, which resulted in the production of viable pollen grains, abnormal microspores were observed including penta-fission and hexa-fission. Based on these results we suggest that the two F1 hybrids had better behaviors of chromosome pairing and genetic stability than autotetraploid rice and other autotetraploid plants ever studied.

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.

Gamma-rays induced reciprocal translocation inNigella damascenaL. (Love-in-a-mist)

AbstractGamma irradiations (5, 10, 15 and 20 kR) to Nigella damascena L. (love-in-a-mist; family: Ranunculaceae) seeds (moisture content: 8.7%) induced three viable translocation heterozygotes (P-3 and P-15 from 5 kR and P-25 from 10 kR) which on selfing yielded progeny heterozygotes in subsequent generations (R2, R3 and R4; however, P-15 could only be assessed upto R2 generation) exhibiting the formation of either a ring or a chain of four chromosomes in 14.8–54.6% meiocytes. Mean quadrivalent frequency per cell was assessed to be 0.40–0.66 in P-3, 0.43–0.64 in P-15 and 0.15–0.47 in P-25. Configuration and orientation of the multiples in the heterozygotes assessed over the generations indicated a possible genetic control over the mechanism. Normal 6/6 separation of chromosomes at AI (55.86–100.00%) of the heterozygotes did not correlate significantly (r = 0.29,27 DF) with pollen fertility (6.98–46.38%). Pollen fertility showed negative and insignificant correlation (r = -0.20,27 DF) with seed set per pla...

Interspecific crossability and cytogenetic analysis of sexual progenies of Mexican wild diploid 1EBN speciesSolanum pinnatisectum andS. cardiophyllum

Mexican wild diploid species,Solanum pinnatisectum (S. pnt) (2n=2x=24, 1EBN: endosperm balance number) is a useful germplasm source of late blight and Colorado potato beetle (CPB) resistance in potato improvement. However, it is very difficult to cross this species with other 1EBNSolanum species. Sexual hybrids among three accessions ofS. pnt and two accessions ofS. cardiophyllum (S. cph) (2n=2x=24, 1EBN) were studied. There were large differences in the cross-compatibility among the genotypes and accessions from these two 2x-1EBN species. Interspecific incompatibility existed in the crosses betweenS. pnt andS. cph, in whichS. cph functioned only as the male parent. The crosses with accessions PI 275236 ofS. pnt produced 35 hybrids following the conventional propagation procedures. Seven hybrids were obtained with theS. pnt accession PI 275233 with the aid of embryo rescue, while hybridization involving accession PI 253214 resulted in no fruit. The cytogenetic analysis indicated that all of the hybrids derived from crosses of accession PI 275233 ofS. pnt withS. cph had 2n = 24 chromosomes and were pollen fertile. Crosses involving accession PI 275236 ofS. pnt produced both 2x (2n=24) and 3x (2n=36) hybrids. Meiotic analysis at metaphase I of pollen mother cells (PMCs) showed a fairly high rate of chromosome pairing that averaged between 10.10 and 11.10 bivalents per cell in most of the 2x hybrids, indicatingS. pnt andS. cph have the similar genome. A high frequency of trivalents and quadrivalents were observed in 3x hybrids derived fromS. pnt 2 ×S. cph 1, indicating homology exists among these chromosomes. These results suggest that specific gene(s) and not either differences between genomes or EBN controlled interspecific crossability and embryo development. The disease and insect tests on the 2x and 3x hybrids revealed that all have high levels of resistance to both late blight and CPB. Thus it could appear that selection of genotypes is a key for successful interspecific hybridization when using Mexican wild diploid species as a source of economic important traits.

Evaluation of the effect of pollen irradiation on karyotype variability in cotton plants

The effect of pollen irradiation at dose rates of 10, 15, 20, and 25 Gy on variability in cotton plants Gossypium hirsutum L. was studied. The modified plants showed a reduced fertility, mainly caused by chromosomal rearragements and genomic mutations during meiosis. The genomic mutations involved primary and tertiary monosomics, monotelodisomics, and a haploid plant. The decrease in meiotic index and pollen fertility in the cotton aneuploids was related not only to aberrations in chromosome pairing but also to genetic features of the original plants. It was found that heterozygosity for interchromosomal exchanges found in M1 plants resulted in the formation of multivalent associations of chromosomes of various forms and types of segregation from translocation complexes. Another result was high variability in pollen fertility. An increase in irradiation dose rate caused an increase in the number of translocants with a high frequency of quadrivalents. The results suggest that the great diversity of forms observed in M1 after pollination with irradiated pollen is determined, first, by elimination of some chromosomes or their arms or the whole paternal genotype and second, by interchromosomal rearrangements. The high variability in pollen fertility of translocants hampers using this trait as a marker of heterozygosity for exchanges in cotton.

Synapsis in a natural autotetraploid

To test assumptions of the autotetraploid chromosome pairing model regarding events during synapsis, whole-mount spreads of synaptonemal complexes (SCs) of Machaeranthera pinnatifida (=Haplopappus spinulosus) (Asteraceae) (2n = 4x = 16) were analyzed by electron microscopy. On the assumption of one synaptic initiation per chromosome arm, each pachytene quadrivalent is expected to have one partner switch (PS), and the frequency of pachytene quadrivalents for each chromosome is predicted to be 2/3 (or 0.67). However, to the contrary, we observed a range of one to four PSs per pachytene quadrivalent with an overall mean of 1.56. This suggests that the number of synaptic initiations is greater than one per chromosome arm (or >two per chromosome), and the predicted frequency of pachytene quadrivalents should be >8/9 (based on a minimum of three initiations per chromosome). However, in close agreement with the model, the observed pachytene quadrivalent frequency from SCs in this study was 0.69. To explain the apparent discrepancy between the observed frequency of PSs and the observed frequency of quadrivalents, the possibility of nonindependent synaptic initiations and presynaptic alignment are discussed in the context of their potential influence on quadrivalent frequency. Recombination nodules (RNs), which were scored in about half the SC spreads, occurred at a frequency (9.6 per nucleus) comparable with the chiasma frequency at diakinesis (9.3 per nucleus). The frequency of RNs as well as their distribution is consistent with the hypothesis that RNs occur at sites of crossing over and chiasma formation.Key words: autopolyploid, Machaeranthera pinnatifida, meiosis, recombination nodules, synaptonemal complex.

Differences in the synaptic pattern in two autotetraploid cultivars of rye with different quadrivalent frequencies at metaphase I

Synaptic behaviour of the two tetraploids rye cultivars Gigantón (G) and Tetrapico (T) displaying significant differences in their quadrivalent frequencies at metaphase I was analyzed by electron microscopy in surface-spread prophase I nuclei. A different behaviour was observed between the two cultivars; the synaptonemal complex (SC) quadrivalents frequency being significantly higher in G than in T at prophase I. Moreover, the G SC quadrivalents had more synaptic partner exchanges (SPEs) and their location was more distal than the T SC quadrivalents. However, inverse findings were found at metaphase I, the quadrivalent frequency was higher in T than in G. The role that different factors, mainly the number and location of the SPEs and the frequency and distribution of chiasmata, could play in the evolution from prophase I to metaphase I in both cultivars is discussed.Key words: autotetraploid rye, synaptonemal complex, spreading.

Synapsis in a natural autotetraploid

To test assumptions of the autotetraploid chromosome pairing model regarding events during synapsis, whole-mount spreads of synaptonemal complexes (SCs) of Machaeranthera pinnatifida (=Haplopappus spinulosus) (Asteraceae) (2n = 4x = 16) were analyzed by electron microscopy. On the assumption of one synaptic initiation per chromosome arm, each pachytene quadrivalent is expected to have one partner switch (PS), and the frequency of pachytene quadrivalents for each chromosome is predicted to be 2/3 (or 0.67). However, to the contrary, we observed a range of one to four PSs per pachytene quadrivalent with an overall mean of 1.56. This suggests that the number of synaptic initiations is greater than one per chromosome arm (or >two per chromosome), and the predicted frequency of pachytene quadrivalents should be >8/9 (based on a minimum of three initiations per chromosome). However, in close agreement with the model, the observed pachytene quadrivalent frequency from SCs in this study was 0.69. To explain the apparent discrepancy between the observed frequency of PSs and the observed frequency of quadrivalents, the possibility of nonindependent synaptic initiations and presynaptic alignment are discussed in the context of their potential influence on quadrivalent frequency. Recombination nodules (RNs), which were scored in about half the SC spreads, occurred at a frequency (9.6 per nucleus) comparable with the chiasma frequency at diakinesis (9.3 per nucleus). The frequency of RNs as well as their distribution is consistent with the hypothesis that RNs occur at sites of crossing over and chiasma formation.Key words: autopolyploid, Machaeranthera pinnatifida, meiosis, recombination nodules, synaptonemal complex.

Differences in the synaptic pattern in two autotetraploid cultivars of rye with different quadrivalent frequencies at metaphase I

Differences in the synaptic pattern in two autotetraploid cultivars of rye with different quadrivalent frequencies at metaphase I

Influence of Ploidy Levels on Phenotypic and Cytogenetic Traits in Maize and Zea perennis Hybrids.

The aim of this work was to analyse : a) the phenotypic and cytogenetic differences of Zea mays and Zea perennis hybrids 2n=30 and 40; b) the effect of colchicine on their chromosomes pairing in meiosis. The plant materials used for these studies were Z. mays (Zm20) 2n=20, Z. mays (Zm40) 2n=40 and Z. perennis (Zp) 2n=40 and the hybrids Zm20 ×Zp (MP30) 2n=30 and Zm40 × Zp (MP40) 2n=40. Some characteristics of Z. perennis such as rhizomes, distic ears, perennially and profuse tillering were only observed in MP40 plants. In the other hand, MP30 plants had maize like phenotype; they were annual, with 4 round ears and low tillering. Therefore, phenotypic expression of several traits depends upon the dose of genes from each parent in the hybrid. The genomic formulae proposed for these species and hybrids were Zm20 : AmAm BmBm; Zm40 : AmAmAmAm BmBmBmBm; Zp : ApApApAp Bp1Bp1 Bp2Bp2; MP30 : AmApAp Bp1Bp2 Bm; MP40 : AmAmApAp BmBm Bp1Bp2. Prezigotene colchicine treatment increased the frequency of quadrivalents in Zm20, Zp and Mp40 and trivalents in MP30. These results suggest homoeology between Bm and Bp1Bp2 genomes from maize and Zp, respectively.