Inheritance of seed colour in turnip rape (Brassica campestris L.)

Summary A high gene frequency for ps (parallel spindles) is expected in cultivated tetraploid potatoes, S. tuberosum Group Tuberosum, if 2n pollen produced by ancestral diploid plants which were psps was involved in the origin and evolution of the potato. Fifty-six North American cultivars (varieties and advanced selections) were pollinated by diploid clones, either W 5295.7 or W 5337.3 which are homozygous recessive for ps. The segregation ratios in regard to 2n pollen production in derived tetraploid progenies, from 4x×2x crosses, reveal the genotype of ps in the cultivars. Microsporogenesis of 2n pollen producing 4x progeny was observed to avoid an overestimation of the frequency of 2n pollen producing plants due to mechanisms other than parallel spindles. More than 50% of the 56 cultivars are simplex (Pspspsps), since in each of these cultivars about 50% of their progeny produced 2n pollen. The ps gene frequency in the 56 cultivars was estimated as high as 0.69. The high frequency of ps in the tetraploid cultivars clearly supports the hypothesis that 2n pollen produced by plants homozygous recessive for ps have been involved in the origin of cultivated tetraploid potatoes, since a higher frequency of ps in the tetraploid than in the ancestral diploid population can be expected from sexual polyploidization but not from somatic doubling. The importance of meiotic mutants such as ps for the successful evolution of polysomic polyploids is emphasized.     

The occurrence and frequency of 2n pollen in three diploid solanums from Northwest Argentina

Summary A group of wild, tuber-bearing species from Northwest Argentina, belonging to the series Tuberosa, Solarium spegazzini Bitt. (spg, 2n=2x=24), S. gourlayi Hawkes (grl, 2n=2x=24 and 2n=4x=48) and S. oplocense Hawkes (opl, 2n=6x=72), and Cuneolata, S. infundibuliforme Phil (ifd, 2n=2x=24), is being used to investigate the mode of origin of polyploids in the genus Solanum. 2n gametes have been detected in the diploid species ifd and spg and in a diploid race of grl, using cytological and breeding approaches. Twenty-two introductions of spg, 8 of grl and 26 of ifd have been tested for 2n pollen; 59%, 63% and 54% of them, respectively, had at least one 2n pollen producing plant. These introductions comprised 238, 76 and 235 plant respectively, of which 20, 16, and 32 plant produced 5% or more 2n pollen. The mechanism of 2n pollen formation was determined in several plant of 2x spg, 2x grl and 2x ifd. All of them were found to form diplandroids via parallel spindles. This mechanism, which gives meiotic products genetically equivalent to first division restitution gametes, is under control of the Mendelian recessive ps. The results suggest that the allele ps is widely distributed in natural populations of the three diploids, and that its frequency is very high. These species are seen as valuable material for population genetic studies, and for the eventual incorporation into a breeding scheme involving sexual polyploidization via 2n gametes.     

Occurrence of 2n pollen and ps gene frequencies in cultivated groups and their related wild species in tuber-bearing Solanums

Summary The gene frequency for parallel spindles (ps) was estimated from the frequency of plants producing 2n pollen in three cultivated groups: 2x Phureja (phu), 2x Stenotomum (stn), and 4x Andigena (adg), as well as in four related wild taxa: 2x Solanum brevicaule (brc), 2x S. sparsipilum (spl), 4x S. gourlayi (grl) and 4x S. gourlayi-S. infundibuliforme hybrids (grl-ifd). Plants with more than 1% large pollen were considered as 2n pollen producers. Observations of meiosis in a sample of 2n pollen-producing plants indicated that parallel spindles is the mechanism of 2n pollen formation. The number of plants with 2n pollen among the total examined was 228 plants (15.5%) of 1,473 in 2x spl, 31 (26.7%) of 116 in 2x brc, 92 (17.4%) of 528 in 2x stn, 665 (22.1%) of 3,008 in 2x phu, 731 (51.4%) of 1,421 in 4x adg, 591 (41.2%) of 1,436 in 4x grl, and 36 (64.3%) out of 56 in 4x grl-ifd. The ps gene frequencies assuming Hardy-Weinberg equilibrium were: 0.393 for 2x spl, 0.462 for 2x brc, 0.417 for 2x stn, 0.470 for 2x phu, 0.847 for 4x adg, 0.801 for 4x grl, and 0.895 for 4x grl-ifd. Twenty-five adg clones were randomly selected from a large population and were crossed with 2x clone W5295.7, which produces 2n pollen by parallel spindles (ps). The 4x progenies from 4x×2x crosses were used to determine the genotypes at the ps locus by screening 10–20 plants in each family for 2n pollen. Based on chromosome segregation at the ps locus, 9, 14, 1, and 1 clones were nulliplex, simplex, simplex or duplex, and duplex, respectively. The frequency of the ps gene in the adg population was estimated to be 0.825 and 0.815 for chromosome and chromatid segregation, respectively. The high frequencies of 2n pollen and the ps gene in cultivated 2x and 4x groups, and in wild taxa closely related to them, provide evidence for sexual polyploidization in the tuber-bearing Solanums.Paper No. 3032 from the Laboratory of Genetics. Research supported by the College of Agriculture and Life Sciences; International Potato Center; USDA, SEA, CGRO 84-CRCR-1-1389; and Frito Lay, Inc.     

Desynaptische Mutanten mit Unterschieden im Univalentenverhalten

After application of neutrons on dry seeds ofPisum sativum three recessive mutants were isolated showing irregularities in the course of meiosis. A cytogenetical analysis showed that at metaphase I, a varying number of univalents are formed, most likely as a result of reduced chiasma frequencies. At anaphase I, some univalents divide precociously in mutant 2982 but none do so in mutants 2989 and 2552. As a consequence, most cells of 2989 and 2552 built up more than two spindles at anaphase II, whereas the majority of cells in 2982 form two spindles. This situation is reflected in the frequency distribution of gones per PMC at tetrad stage. The discussion deals with the possible causes of univalent formation at meiotic prophase and the variability of univalent behaviour at anaphase I.     

The use of Endosperm Balance Number and 2n gametes to transfer exotic germplasm in potato

Summary A triploid hybrid (2n=3x=36) between a colchicine-induced 4x(2EBN) Solanum brevidens (a non-tuber-bearing species) and 2x(2EBN) S. chacoense (a tuber-bearing species) was used as a vehicle for germplasm transfer to S. tuberosum Group Tuberosum. The use of 2n gametes from the triploid allowed the unique opportunity for transferring exotic germplasm from Series Etuberosa to Gp. Tuberosum material. The triploid hybrid used had a pollen stainability of less than 0.1%. Observations of microsporogenesis revealed that metaphase I pairing configurations were primarily 12 bivalents and 12 univalents with occasional trivalents. Anaphase I separations were irregular, often with lagging univalents. Meiotic observations and pollen morphology suggest that the stainable pollen produced by the hybrid was 2n=3x=36. A single pentaploid hybrid (2n=5x=60) was produced by the fertilization of a rare 2n egg from the triploid with a normal male gamete from the clone Wis AG 231 (2n=4x=48). Limited crosses to other 1, 2 and 4EBN species and cultivars were unsuccessful. The pentaploid hybrid had a more regular meiosis than the triploid and dramatically improved pollen stainability (37% stainable pollen). Stylar blocks prevented estimates of male fertility in crosses. Female fertility in 47 crosses with nine cultivars averaged 19 seeds per fruit. Although S. brevidens is non-tuber-bearing, and the triploid produced only stolons, the pentaploid hybrid tuberized well under field conditions, despite being very late. Results suggest that the tuberization response is a dosage and/or threshold effect. This approach to the incorporation of 1EBN germplasm indicates the utility of the EBN concept coupled with 2n gametes. Further, it demonstrates a means for the introgression of 1EBN species genes into Gp. Tuberosum material.     

Meiosis in a triploid hybrid of <Emphasis Type="Italic">Gossypium</Emphasis>: high frequency of secondary bipolar spindles at metaphase II

Studies on meiosis in pollen mother cells (PMCs) of a triploid interspecific hybrid (3x = 39 chromosomes, AAD) between tetraploid Gossypium hirsutum (4n = 2x = 52,AADD) and diploid G. arboreum (2n = 2x = 26,AA) are reported. During meiotic metaphase I, 13 AA bivalents and 13 D univalents are expected in the hybrid. However, only 28% of the PMCs had this expected configuration. The rest of the PMCs had between 8 and 12 bivalents and between 12 and 17 univalents. Univalents lagged at anaphase I, and at metaphase II one or a group of univalents remained scattered in the cytoplasm and failed to assemble at a single metaphase plate. Primary bipolar spindles organized around the bivalents and multivalents. In addition to the primary spindle, several secondary and smaller bipolar spindles organized themselves around individual univalents and groups of univalents. Almost all (97%) of the PMCs showed secondary spindles. Each spindle functioned independently and despite their multiple numbers in a cell, meiosis I proceeded normally, with polyad formation. These observations strongly support the view that in plant meiocytes bilateral kinetochore symmetry is not required for establishing a bipolar spindle and that single unpaired chromosomes can initiate and stabilize the formation of a functional bipolar spindle.     

Cytological analysis of tetraploid hybrids between sweet potato and diploid Ipomoea trifida (H. B. K.) Don.

Summary Tetraploid F₁ hybrids between Ipomoea batatas, sweet potato (2n = 6x = ca. 90), and diploid (2n = 2x = 30) I. trifida (H. B. K.) Don. showed various degrees of fertility reduction. The present study aimed to clarify its causes by cytological analysis of meiotic chromosome behavior in the diploid and sweet potato parents and their tetraploid hybrids. The diploid parents showed exclusively 15 bivalents, and the sweet potato parents exhibited almost perfect chromosome pairing along with predominant multivalent formation. Their hybrids (2n = 4x= 57–63) formed 2.6–5.0 quadrivalents per cell, supporting the autotetraploid nature. The meiotic aberratios of the hybrids were characterized by the formation of univalents, micronuclei, and abnormal sporads (monad, dyad, triad, and polyad). The causes underlying these aberrations were attributed in part to the multivalent formation, and in part to a disturbance in the spindle function. Three hybrids showing serious meiotic aberrations were very low in fertility. The utilization of the sweet potato-diploid I. trifida hybrids for sweet potato improvement is described and, further, the role of interploidy hybridization in the study of the sweet potato evolution is discussed.     

Cytological evidences of SDR-FDR mixture in the formation of 2n eggs in a potato diploid clone

Summary Macrosporogenesis and microsporogenesis were investigated in a diploid S. tuberosum x S. chacoense potato hybrid, characterized by more than 50% 2n egg formation. Fifty-five percent of dyad formation of 2n macrospores is ascribed to two meiotic abnormalities: omission of the second meiotic division, occurring at a frequency of 38%, and irregular spindle axis orientation at metaphase I at a frequency of 16%: These abnormalities give origin to a mixture of 2n eggs, composed of mostly second division restitution (SDR) and a small portion of first division restitution (FDR). Microsporogenesis showed rare dyads of 2n microspores depending on parallel spindles observed in anaphase II.Contribution no. 53 from the Center of Vegetable Breeding, CNR, Portici, Italy     

Genome relationships between Hordeum procerum (6x) and H. lechleri (6x)

Investigations on the meiotic behaviour of chromosomes in interspecific hybrids (2n=6x=42) between Hordeum lechleri (6x) and H. procerum (6x) and in their component haploids have been utilized to assess the nature of pairing and the extent of genome homology between the two species. In the F₁ hybrids an average of 25 (60%) chromosomes associated at metaphase I, mostly as bivalents. A majority (60%) of the pollen mother cells (PMCs) in H. procerum haploids (2n=3x=21) displayed 21 univalents and even in the remainder, a maximum of two rod bivalents were formed resulting in an average of 0.52 bivalents per cell. In haploids of H. lechleri (2n=3x=21) however, 30% of chromosomes pair. The sum of the chromosomal associations in the component haploids represents only 17% of the complement, far below the observed frequency (60%) in the hybrids. Thus, the pairing displayed in hybrids between H. lechleri and H. procerum was mostly allosyndetic and suggestive of two genomes being common in these species.In haploid H. procerum 1/3 of the PMCs displayed a tripolar organisation of chromosomes leading to triad and hexad formation after divisions I and II respectively. The significance of hexad formation in the trihaploid H. procerum and a possible suppression of homoeologous pairing in H. procerum haploids are discussed.     

Use of 2n pollen-producing triploid hybrids to introduce tetraploid Mexican wild species germ plasm to cultivated tetraploid potato gene pool

Summary Tetraploid (2n=4x=48) 2EBN Mexican wild species in the series Longipedicellata, which consists of Solanum fendleri, S. hjertingii, S. papita, S. polytrichon, and S. stoloniferum, were crossed with two 2EBN cultivated diploid (2n=2x=24) clones. The resulting triploid hybrids (2n=3x=36) produced 2n pollen (triplandroids) by the mechanism of parallel orientation of anaphase II spindles. The percentage of stainable pollen in 520 triploids ranged between 0 and 23.5%, with a mean of 2.7%. Triploids producing between 13.0 and 23.5% stainable pollen were crossed as staminate parents to the tetraploid cultivars, resulting in abundant pentaploid (2n=5x=60) and near-pentaploid hybrid progeny. Crosses of triploids with lower percentage of stainable pollen as pollen parent to the tetraploid cultivars did not yield fruit, unless rescue pollen from a tetraploid cultivar was added 2 days later. Pentaploid hybrids were selected among selfed tetraploid progenies using morphological and isoxyme markers transmitted from their cultivated diploid parents. These pentaploid hybrids were vigorous and had uniformly sterile pollen. They were female fertile and were crossed with tetraploid cultivars, yielding an average of 19 seeds per fruit. Triplandroids provide the opportunity of transferring 2EBN tetraploid Mexican wild species in the series Longipedicellata germ plasm into the 4EBN cultivated potatoes.Cooperative investigations of the ARS, USDA, and the Washington State University Agricultural Research Center, Prosser, WA 99350, USA. H/LA Paper No. 90-03, College of Agriculture and Home Economies Research Center, Washington State University, Pullman, WA 99164, USA     

Formation of first division restitution (FDR) 2n-megaspores through pseudohomotypic division in ds-1 (desynapsis) mutants of diploid potato: routine production of tetraploid progeny from 2xFDR × 2xFDR crosses

Summary The level and mode of 2n megaspore formation was studied in full-sib diploid potato clones with either normal or desynaptic (ds-1ds-1) meiosis. Cytological analysis revealed that functional 2n megaspores produced by normal and desynaptic clones originate exclusively from second division restitution (SDR) and first division restitution (FDR), respectively. SDR 2n megaspores resulted from the omission of the second meiotic division following chromosome doubling after anaphase I, whereas FDR 2n megaspores resulted from a direct equational division of univalent chromosomes at anaphase I (pseudohomotypic division). Comparative data strongly indicated that the observed mechanisms of SDR and FDR 2n megaspore formation are extremes of a continuum that is being brought about by common genes for precocious chromosome division. Depending on the relative timing of cell cycle and chromosome division, this precocious chromosome division may impose postreductional (SDR) or prereductional (FDR) restitution of the sporophytic chromosome number under normal synaptic and desynaptic conditions, respectively. The observed frequencies of 2n megaspores closely correlated with seed set, following pollination by tetraploid varieties and by desynaptic diploid clones with exclusive FDR 2n pollen formation. Up to 54.0 and 21.5 seeds/ fruit were obtained from normal synaptic (SDR) and desynaptic (FDR) progeny, respectively. The high frequency of segregants with either SDR or FDR 2n megaspore formation (78.0 and 45.2%, respectively) supports the hypothesis that sexual polyploidization is the driving force behind the origin and evolution of polyploid Solanum species. The present identification of diploid potato clones with consistent FDR 2n megaspore formation extends the opportunities for direct transfer of enhanced diploid germ plasm to tetraploids, and particularly advocates the feasibility of 2x(ds-1; FDR)×2x(ds-1; FDR) breeding schemes in cultivar development and the production of relatively vigorous and uniform true potato seed (TPS) varieties. Its potential value and limitations for breeding and the experimental induction of diplosporic apomixis are discussed.     

Efficiency of potato breeding using FDR 2n gametes for multitrait selection and progeny testing

Summary The objective of this research was to compare the efficiency of the 4x×2x breeding scheme with the traditional 4x×4x method with respect to potato improvement. The basis for such a comparison was the parental value of four 2x and four 4x male parents from the International Potato Center (CIP) as measured by multitrait selection and progeny testing. The 2x parents produced 2n pollen by parallel spindles at anaphase II, which is genetically equivalent to a first division restitution (FDR) mechanism. Both 2x and 4x parents were crossed with four common 4x female parents. Thus, 32 families were evaluated over 2 years at four Peruvian locations. A selection index which considered tuber yield, tuber number, average tuber weight and specific gravity was used for multitrait selection. Three FDR 2x parents had better selection index scores than the 4x parents over the four locations. Estimates of broad-sense heritability for total yield using different number of replications and locations were calculated by using the variance components. The 4x × 2x breeding scheme was found to be better than the traditional 4x × 4x method since fewer replications and locations are required to evaluate tuber yield in 4x × 2x progenies than in 4x × 4x progenies. The FDR 2x parents were also better material than the 4x parents for testing combining ability for tuber yield of the 4x progenitors. This could be the result of the mode of FDR 2n pollen formation. The pollen of FDR 2x parents is more heterozygous, but more homogenous than n pollen from 4x parents.Paper from the Laboratory of Genetics. Research supported by the College of Agricultural and Life Sciences; International Potato Center; USDA-CRGO-88-37234 3619, and Frito-Lay, Inc., USA     

Genetic Collection of Meiotic Mutants of Rye <Emphasis Type="Italic">Secale cereale</Emphasis> L.

Genetic collection of meiotic mutants of winter rye Secale cereale L. (2n = 14) was created. Mutations were detected in inbred F₂ generations after self-fertilization of the F₁ hybrids, obtained by individual crossing of rye plants (cultivar Vyatka) or weedy rye with plants from autofertile lines. The mutations cause partial or complete plant sterility and are maintained in collection in a heterozygous state. Genetic analysis accompanied by cytogenetic study of meiosis has revealed six mutation types. (1) Nonallelic asynaptic mutations sy1 and sy9 caused the formation of only axial chromosome elements in prophase and anaphase. The synaptonemal complexes (SCs) were absent, the formation of the chromosome “bouquet” was impaired, and all chromosomes were univalent in meiotic metaphase I in 96.8% (sy1) and 67% (sy2) of cells. (2) Weak asynaptic mutation sy3, which hindered complete termination of synapsis in prophase I. Subterminal asynaptic segments were always observed in the SC, and at least one pair of univalents was present in metaphase I, but the number of cells with 14 univalents did not exceed 2%. (3) Mutations sy2, sy6, sy7, sy8, sy10, and sy19, which caused partially nonhomologous synapsis: change in pairing partners and fold-back chromosome synapsis in prophase I. In metaphase I, the number of univalents varied and multivalents were observed. (4) Mutation mei6, which causes the formation of ultrastructural protrusions on the lateral SC elements, gaps and branching of these elements. (5) Allelic mutations mei8 and mei8-10, which caused irregular chromatin condensation along chromosomes in prophase I, sticking and fragmentation of chromosomes in metaphase I. (6) Allelic mutations mei5 and mei10, which caused chromosome hypercondensation, defects of the division spindle formation, and random arrest of cells at different meiotic stages. However, these mutations did not affect the formation of microspore envelopes even around the cells, whose development was blocked at prophase I. Analysis of cytological pictures of meiosis in double rye mutants reveled epistatic interaction in the mutation series sy9 > sy1 > sy3 > sy19, which reflects the order of switching these genes in the course of meiosis. The expression of genes sy2 and sy19 was shown to be controlled by modifier genes. Most meiotic mutations found in rye have analogs in other plant species.     

Meiotic analysis of haploid and doubled haploid forms of Nicotiana otophora and N. tabacum

Detailed meiotic studies were conducted on anther-derived haploids of Nicotiana otophora (n = 12) and N. tabacum (n = 24). At midpachytene stages the non-homologous chromosomes apparently remain unpaired. However, since the spreading of chromosomes at this stage was poor, the possible partial pairing, if any, between non-homologues could not be determined with certainty. One to two univalents rarely exhibited partial foldback pairing involving a single arm or the intercalary regions of the same chromosome. — At diakinesis the bivalent-like structures ranged from 0–2 in Otophora and 0–7 per cell in Tabacum haploids. The bivalent-like configurations (mostly rod types with chromatin connections of varying thickness) observed at meta-anaphase I varied from 0 to 1 and 0 to 5 per cell in haploids of Otophora and Tabacum respectively. The various types of secondary associations of univalents at meta-anaphase I were also studied in different haploids. — The probable origin and significance of bivalent-like configurations and secondary associations observed in Nicotiana haploids is briefly discussed. Based on our results, it is concluded that there is very little intra- or intergenomic pairing, if any, in Nicotiana haploids studied. — The meiotic behavior of chromosomes in doubled haploids (N. tabacum) obtained by leaf mid-rib culture, root culture and spontaneous chromosome doubling was remarkably regular with a stable chromosome number of 2n = 48. The meiotic stability of the doubled haploids permits using these materials directly in the breeding program.Contribution from the Department of Agronomy, University of Kentucky. The investigation reported in this paper (72-3-51) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director.     

Meiotic behavior of pollen mother cells in relation to ploidy level of somatic hybrids between Solanum tuberosum and S. chacoense

Potato somatic hybrids obtained by protoplast fusion between Solanum tuberosum (4x) and Solanum chacoense (2x) were investigated for genome stability and meiotic behavior associated with the pollen viability in order to elucidate the mechanism influencing the fertility of the somatic hybrids. The ploidy level detections conducted in 2004 and 2007 demonstrated that 68 out of 108 somatic hybrids had their ploidy level changed to be uniform and euploidy after successive in vitro subcultures, which mainly occurred in octaploids, aneuploids, and mixoploids, while 74% hexaploids were still stable in their genome dosage in 2007. Different types of abnormal meiotic behavior were observed during the development of pollen mother cells (PMCs) including the formation of univalents, multivalents, laggard chromosomes, and chromosomal bridges, as well as triads and polyads. A higher proportion of abnormal meiosis seemed to be accompanied with a genome dosage higher than the hexaploids expected in this study. A significant positive correlation between defective PMCs and the number of small pollen grains and negative correlation between number of small pollen grains and pollen viability strongly suggested that abnormal meiosis could be a causal factor influencing the fertility of the somatic hybrids. The hexaploids with stable genome dosage and a certain level of fertility will have great potential in a potato breeding program.     

Pollen markers for gene-centromere mapping in diploid potato

The utility of two pollen genetic markers for estimating the extent of meiotic recombination between the centromere and a marker gene was tested in 2n pollen of diploid potato clones. One of these markers was the distal locus amylose-free (amf) on chromosome 8 and the other was the isozyme locus alcohol dehydrogenase (Adh-1) on chromosome 4. In the case of the amf locus, the gene-centromere distance was estimated in a normal synaptic and a desynaptic genotype. In both cases the genetic analysis was confined to: (1) a direct estimation of the phenotypic (blue vs red) segregation ratios in FDR (first-division restitution) 2n pollen and (2) a classification of the 4 x progeny from 4x (nulliplex amf) x 2x (Amf/amf) crosses into duplex, simplex and nulliplex classes. The recombination frequency between the centromere and the amf locus in the normal synaptic genotype B92-7015-4 corresponded to a gene-centromere distance of 48.8 cM, whereas this distance amounted to 13.3 cM in the desynaptic genotype RS93-8025-1. Hence desynapsis reduced crossing-over by 73%. The observed genetic distance of 48.8 cM in the normal synaptic clone, B92-7015-4, is the highest gene-centromere distance reported so far in potato and this could be explained on the assumption of absolute chiasma interference. For the Adh-1 locus, it was found that heterozygous 2n pollen grains could be detected in pollen samples of the diploid clones, because of the occurrence of a heterodimeric band of the isozyme. Unlike the amf locus, the genecentromere distance for the Adh-1 locus was estimated only on the basis of the duplex, simplex and nulliplex classes in the progenies from 4x (nulliplex Adh-1 ² )x B92-7015-4 (Adh-1 ¹ /Adh-1 ² )crosses and was found to be 19.4 cM. Because the accurate positions of centromeres in relation to other loci are not available in the existing genetic maps of potato, which are saturated with molecular markers, halftetrad analysis is a promising additional approach to the basic genetics of this crop.     

Chromosome numbers, meiotic behavior, and pollen viability of species of Vriesea and Aechmea genera (Bromeliaceae) native to Rio Grande do Sul, Brazil

Chromosome number, meiotic behavior, and pollen viability were analyzed in 15 species of two genera, Vriesea and Aechmea, native to Rio Grande do Sul, Brazil. This study is the first cytogenetic analysis of these taxa. The chromosome numbers are all n = 25, consistent with the proposed base number of x = 25 for Bromeliaceae. All examined taxa displayed regular bivalent pairing and chromosome segregation at meiosis. Observed meiotic abnormalities include univalents in metaphase I; missing or extra chromosomes and precocious division of centromeres in metaphase II; laggards in telophase I and anaphase II/telophase II. The high pollen viability (>88%) reflects a regular meiosis.     

Studies on triploid Allium triquetrum

This work describes the relationship between the univalents seen at metaphase I and the distribution of dyads at anaphase I in the pollen mother cells of triploid Allium triquetrum. The orientation of the centromeres within the trivalents and bivalents at metaphase I towards the two poles of the pollen mother cells is random. The distribution of polar univalents towards the two poles at metaphase I is also random, as is the distribution of dyads at anaphase I in low univalent frequency collections. However, in a high univalent frequency collection, the distribution of dyads at anaphase I is non-random. There is an excess of cells with the most equal dyad distribution (13–14) and a paucity of cells with a 12–15 distribution. In low univalent frequency collections, the equatorial univalents are believed to remain in the equatorial region during anaphase I and are seen as laggards at late anaphase I. The remaining chromosomes move according to the metaphase I orientation of their centromeres to give a random distribution of dyads at anaphase I. In high univalent frequency collections it is argued that the non-random dyad distribution seen at anaphase I is the result of non-random movement of some of the equatorial univalents away from the equatorial region during anaphase I. The remaining equatorial univalents remain in the equatorial region and are seen as laggards at late anaphase I.     

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

Summary 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.     

Cytology of lepidoptera VIII. Acetylation of α-tubulin in mitotic and meiotic spindles of two Lepidoptera species,Ephestia kuehniella (Pyralidae) andPieris brassicae (Pieridae)

Summary The microtubular spindle in spermatocytes of Lepidoptera is unconventional in that the bulk of the microtubules (MTs) ends relatively abrupt about halfway between the spindle equator and the centrosomes from late prometaphase through early anaphase. Membranous elements separate the MT ends from the centrosomes. In the present study, the question is addressed whether MTs in meiotic spindles of male Lepidoptera are — as typical of spindle MTs in other systems — highly dynamic or whether they represent a more stable MT population. To this end, primary spermatocytes of two Lepidoptera species,Ephestia kuehniella (Pyralidae) andPieris brassicae (Pieridae), were probed with a widely used antibody, 6–11B-1, directed against acetylated -tubulin. Tubulin acetylation is believed to indicate the presence of long-lived MTs. In late telophase spermatocytes of both species, spindle MTs were highly acetylated. This is in keeping with observations in other systems: MT dynamics decreases towards telophase. The labeling intensity in younger spermatocytes differed, however, between both species. InE. kuehniella only flagella were labeled, whereas inP. brassicae also the kinetochore MTs and small MT arrays around the centrosomes were detected by the antibody against acetylated -tubullin. The findings are compatible with the suggestion that spindle MTs are dynamic in prometaphase to anaphase spermatocytes ofE. kuehniella. In fact, treatment with taxol, a MT-stabilizing drug, leads to high acetylation of -tubulin throughout spindle MTs ofE. kuehniella in this period. Meiotic spindles inP. brassicae are longer by a factor of 1.3 than those ofE. kuehniella. The shorter MTs inE. kuehniella may turnover completely and cannot accumulate acetylated portions, whereas segments of MTs in the longer spindles ofP. brassicae persist and become post-translationally acetylated. Spermatogonial mitosis was also studied in both species and spindle MTs were found highly acetylated throughout mitosis. Thus, mitotic and meiotic spindles in males of Lepidoptera differ with respect to MT turnover.Abbreviations BSA bovine serum albumin - DAPI 4,6-Diamidino-2-phenylindole-2 HC1 - EGTA ethylene glycol-bis (-aminoethyl ether)-N,N-tetraacetic acid - PBS phosphate-buffered saline - PIPES piperazine-N,N-bis (2-ethane sulfonic acid) - MT microtubule