Cytogenetic studies on natural intergeneric hybridization inAster alliances

Natural intergeneric hybrids betweenAster ageratoides subsp.ovatus (2n=36) andKalimeris incisa (2n=72) were found. All of the hybrids studied were found to have 2n=72, 18 more chromosomes than a regular F₁ hybrid. The hybrids were found to be of two types: one having 18 large chromosomes ofovatus, and the other having 9 large chromosomes of the same subspecies. In meiosis of the PMCs of the hybrid with 18 large chromosomes, a regular chromosome configuration, 36_II, was observed. In PMCs of the hybrid with 9 large chromosomes an irregularity of chromosome pairings was observed, showing varied chromosome configurations: 35_II+2_I, 34_II+4_I, 33_II+6_I, I_III+33_II+3_I, 1_IV+32_II+4_I, 32_II+8_I, 31_II+10_I, 29_II+14_I, 3_III+29_II+5_I. Most univalents were large, but a few were small. The hybrids with 18 large chromosomes were found to be partial amphidiploid and possessing double chromosome complements ofovatus. The hybrids with 9 large chromosomes were found to be the first backcrossed generation between the hybrid with 18 large chromosomes andK. incisa.     

Cytogenetic studies on natural intergeneric hybridization inAster alliances

Intergeneric hybrids ofAster ageratoides subsp.ovatus (2n=36)×Kalimeris pinnatifida (2n=18) were produced artificially. The chromosomes of the hybrid were found to be 2n=27, and to consist of 9 large chromosomes and 18 small chromosomes. In meiosis of the PMCs of the hybrid, a chromosome configuration of 9_II+9_I was regularly observed. While all the univalents were large, and all the bivalents were comparatively small. The large and small chromosomes ofA. ageratoides subsp.ovatus were found to be rather distant in homology, and the small chromosomes of the subspecies and the chromosomes ofK. pinnatifida were found to have a high degree of homology. The tetraploidovatus was concluded to be an amphidiploid, composed of the large chromosomes ofAster and the small chromosomes ofKalimeris.     

Embryo-callus-regenerated hybrids and their colchicine-induced amphiploids between Elymus canadensis and Secale cereale

Summary Intergeneric hybrids recovered through plant regeneration from embryo callus culture and their colchicine-induced amphiploids were obtained from a cross of Elymus canadensis with Secale cereale (cv Gazeller). The embryo-callus-regenerated F₁ plants grew vigorously to maturity and regrew well after clipping, while the embryo-rescued F₁ died of hybrid necrosis before maturity. Most of the morphological characters of the sterile F₁ hybrids were intermediate between the parents, but tiller number and dry matter yield were higher than the parents. Amphiploids from these F₁ plants had improved fertility but were less vigorous than the F₁ plants. The predominance of univalents in the F₁ and bivalents in the amphiploids indicated that the genomes S, H, and R were distinct. However, the occasional occurrence of multivalents reflected a random, intergenomic or intragenomic pairing. The mean chromosome associations of the F₁ (2n=21, SHR), the C₀ amphiploids (2n=42, SSHHRR), and the C₁ amphiploid (2n=40) at metaphase I (MI) were 16.51_I+2.05_II+0.06_III+0.02_IV+0.02_V, 2.20_I+19.87_II +0.02_IV, and 7.10_I+16.37_II+0.04_III+0.02_IV, respectively. These amphiploids could be exploited as new germplasm for forage crop improvement by controlled introgression and backcrosses to the parents.     

Interspecific hybrids of Antheraea roylei and A. pernyi — a cytogenetic reassessment

Summary A rare case of interspecific hybridization between the Indian oak feeding silkworm Antheraea roylei (n=31) and Chinese oak feeding silkworm A. pernyi (n=49) yielding fertile and vigorous offspring is reported. The F₁ and the backcross (A. roylei X A. pernyi X A. pernyi male individuals of the above cross and the F₂₃ and F₃₂ male offspring derived from an earlier cross between another race of A. roylei (n=30) and A. pernyi (n=49) were cytogenetically analysed in order to study their chromosome dynamics. The F₁ hybrids showed 18 trivalents and 13 bivalents in the first meiotic prophase and metaphase. The backcross individuals possessed either 9 trivalents and 31 bivalents or 49 bivalents, in Metaphase I cells. The F₂₃ and F₃₂ individuals were karyotypically alike and exhibited 49 bivalents. The following conclusions were drawn from the above observations: (a) in spite of allopatry and karyotypic divergence in number, a high degree of homology exists between the chromosomal complements of the two species; (b) A. pernyi possibly evolved from A. roylei, during the course of which 18 chromosomes of the latter underwent fission to give rise to the 36 chromosomes of the former. This is demonstrated by trivalent formation and pairing affinities in F₁ hybrids; (c) selection has favoured the elimination of large A. roylei chromosomes which participated in trivalent formation in successive generations of inbred hybrids to establish a stable Karyotype like that of A. pernyi.     

Cytogenetics of a Hordeum vulgare x Elymus patagonicus hybrid (n=4x=28)

Summary Hordeum vulgare L. (2n=2x=14) was hybridized with Elymus patagonicus Speg. (2n=6x=42). The hybrid had 28 chromosomes, genomically represented as HSH₁H₂, and was perennial with a codominant phenotype. The chromosomes were meiotically associated as 19.6 univalents + 0.004 ring bivalents + 2.6 rod bivalents + 0.8 trivalents + 0.14 quadrivalents in 1,129 meiocytes, with a chiasma frequency of 4.77 per cell. The bivalent pairing presumably is an autosyndetic but modified expression of the H₁H₂ genomes of E. patagonicus, since ring bivalents were rare. This does not preclude the association of the H. vulgare H genome chromosomes with either H₁ and/or H₂ genomes of E. patagonicus to form bivalent or multivalent associations. A further evaluation of the genome homologies of H. vulgare, H. bogdanii, E. canadensis and E. patagonicus is proposed.     

Molecular analysis and mapping of two genes encoding maize glutathione S-transferases (GST I and GST II)

Maize glutathione S-transferase (GST) isozymes are encoded by a gene family comprising at least five genes, three of which (Gst I, II andIII) have recently been isolated and sequenced. The enzymes are active as homo or heterodimers and exhibit intraspecific polymorphism including a “null” variant for the two major isoforms expressed in roots. Northern blot analyses performed on total root RNA from “null” and “plus” genotypes, usingGst I- andGst II-specific probes, indicated that theGst I gene controls the expression of the two major GST isoforms expressed in roots.Gst I andGst II were mapped by RFLP analysis using an F₂ population of 149 individuals previously characterized.Gst I was localized on the long arm of chromosome 8, while two putativeGst II loci were mapped to chromosomes 8 (70 cM fromGst I) and 10, respectively.     

Autosyndetic pairing in Gibasis (Commelinaceae) hybrids revealed by C-banding

Two closely related species of Gibasis, G. karwinskyana and G. consobrina, and their F₁ hybrids were studied cytologically at the diploid and tetraploid level. Despite similarity in their basic karyotype, pairing was extremely limited in the diploid hybrid and almost exclusively autosyndetic in the tetraploid, except for multivalent formation due to interchange heterozygosity. The analysis was considerably facilitated by the use of C-banding techniques at meiosis, by which the chromosomes of each species could be readily identified. In the parents, quadrivalents were formed between homologous but non-identical chromosomes, which also formed autosyndetic bivalents in the hybrids. Meiotic pairing in the hybrids was unaffected by polytypy for C-bands among different populations of the parental species.     

Cytogenetic studies on natural intergeneric hybridization inAster alliances

In addition to various types of natural hybrids betweenAster ageratoides subsp.ovatus andKalimeris incisa reported earlier, a new backcross type has been discovered. This new type, characterized by the chromosomes of 2n=27L+54S, was most probably produced through fertilization of a normally-reduced gamete of the F₁ plant (2n=72=18L+54S) and an unreduced gamete of subsp.ovatus (2n=36=18L+18S).     

Genome relationships between Hordeum vulgare L. and H. bulbosum L.

Interrelationships between H. vulgare (2x=14) and H. bulbosum (2x=14; 4x=28) were estimated on the basis of the karyotypes and the pairing behaviour of the chromosomes in diploid, triploid and tetraploid hybrids obtained with the aid of embryo culture. — A comparison of the karyotypes of the two species revealed similarities as well as differences. It was concluded that at least 4 or more of the chromosomes were similar in morphology and probably closely related. — Diploid and tetraploid hybrids are rarely obtained and their chromosome numbers tend to be unstable whereas triploid hybrids (1 vulgare + 2 bulbosum genomes) were stable and relatively easy to produce. In the diploid hybrid only 40% of the meiotic cells contained 14 chromosomes while the numbers ranged from 7 to 16 in other cells. All hybrids exhibited pairing between the chromosomes of the two species. Diploid hybrids had a mean of 5.0 and a maximum of 7 bivalents per cell in those cells having 14 chromosomes. Triploid hybrids from crosses between 2x H. vulgare and 4x H. bulbosum exhibited a mean of 1.5 and a maximum of 5 trivalents per cell. In a hexaploid sector found following colchicine treatment of a triploid the mean frequencies of chromosome associations per cell were: 5.5_I+8.0_II+0.7_III+3.7_IV+0.3_V+0.4_VI. One unstable 27 chromosome hybrid obtained from crosses between the autotetraploid forms had a mean of 1.1 and a maximum of 4 quadrivalents per cell. The chromosome associations observed in these hybrids are consistent and are taken as evidence of homoeologous pairing between the chromosomes of the two species. Interspecific hybridization between these two species also reveals that chromosome stable hybrids are only obtained when the genomes are present in a ratio of 1 vulgare2 bulbosum. Based upon the results obtained, the possibility of transferring genetic characters from H. bulbosum into cultivated barley is discussed.     

Cytogenetical studies on artificial hybrids amongElymus sibiricus,E. dahuricus andAgropyron tsukushiense in the tribe Triticeae,Gramineae

To explore the cytogenetical relationships ofElymus andAgropyron of the tribe Triticeae, Gramineae, two species of AsiaticElymus, E. sibiricus (2n=28) andE. dahuricus (2n=42), and a JapaneseAgropyron, A. tsukushiense (2n=42) were crossed. Pentaploid and hexaploid F₁ hybrids were vigorous. All pollen grains were aborted and none of the hybrids produced seed. For the crossE. sibiricus × A. tsukushiense, the average chromosome pairing per cell at the MI of the PMCs in the F₁ was 16.38 univalents, 8.93 bivalents, 0.25 trivalents and 0.01 quadrivalents; for the crossE. dahuricus × A. tsukushiense, it was 4.41 univalents, 17.67 bivalents, 0.32 trivalents, 0.28 quadrivalents and 0.04 quinquevalents; and for the crossE. dahuricus × E. sibiricus, it was 17.11 univalents, 8.74 bivalents, 0.04 trivalents and 0.07 quadrivalents. From the present results, it is concluded thatE. sibiricus contains one genome andE. dahuricus contains two genomes, which are homologous to those ofA. tsukushiense, and that the third genome ofE. dahuricus might be partially homologous to the remaining genome ofA. tsukushiense. This conclusion is also supported by the cytogenetical analysis ofE. dahuricus × E. sibiricus. Contribution No. 27 from the Plant Germ-plasm Institute, Faculty of Agriculture, Kyoto University, Kyoto, Japan.     

ORIGIN OF FRAGARIA POLYPLOIDS. II. UNREDUCED AND DOUBLED-UNREDUCED GAMETES

Offspring from natural hybrids between octoploid Fragaria chiloensis (2n = 56) and diploid F. vesca (2n = 14) backcrossed under natural conditions to F. chiloensis were studied. The natural F₁ hybrids themselves were of three kinds: (1) The expected pentaploids which resulted from the union of normally reduced gametes of diploid F. vesca and octoploid F. chiloensis; (2) A hexaploid F₁ hybrid which resulted from the union of an unreduced gamete from diploid F. vesca with a normally reduced gamete from octoploid F. chiloensis; and (3) A 9-ploid F₁ hybrid which probably arose from the union of an unreduced gamete of the octoploid F. chiloensis with a normally reduced gamete of diploid F. vesca. The progenies that resulted from the natural backcrossing of each of the three sorts of F₁ hybrids to F. chiloensis were as follows: The pentaploid F₁ hybrids (2n = 35) yielded mostly 9-ploid offspring from unreduced 5X gametes; a relatively high percentage of 14-ploid plants arising from doubled-unreduced 10 X gametes and a few 2N = ±46 aneuploids from reduced gametes. The hexaploid F₁ hybrid (2n = 42) on backcrossing yielded over 50% 10-ploid offspring with the rest 2n = ±50 aneuploids from reduced gametes. The 9-ploid F₁ hybrid (2n = 63) on backcrossing yielded mostly aneuploids normally distributed about a modal 2n = 59 chromosome class resulting from a 31 chromosome gamete, with a few 2n = 56 and 2n = 63 euploids. The 9-ploids may facilitate diploid Å octoploid introgression. Screening of the open-pollinated offspring from F. chiloensis revealed almost 2% 12-ploid (2n = 84) offspring from the union of the reduced and unreduced F. chiloensis gametes. The probable genomic constitution of the observed novel ploidy levels and those that theoretically may be generated from the known hybrids are presented. The origin of the existing polyploids from diploids through simple unreduction is postulated.     

Ordering selected Zn(II), Cu(II), Pd(II) and Co(III) complex compounds: their separately and combinedly antibacterial therapy and DNA-binding studies

Abstract

In this study, four Co(III)-, Cu(II)-, Zn(II)- and Pd(II)-based potent antibacterial complexes of formula K₃[Co(ox)₃]·3H₂O (I), [Cu(phen)₂Cl]Cl·6.5H₂O (II), [Zn(phen)₃]Cl₂ (III) and [Pd(phen)₂](NO₃)₂ (IV) (where ox is oxalato and phen is 1,10-phenanthroline) were synthesized. They were characterized by elemental analysis, molar conductivity measurements, UV–vis, Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance (¹H-NMR) techniques. These metal complexes were ordered in three combination series of I+II, I+II+III and I+II+III+IV. Antibacterial screening for each metal complex and their combinations against Gram-positive and Gram-negative bacteria revealed that all compounds were more potent antibacterial agents against the Gram-negative than those of the Gram-positive bacteria. The four metal complexes showed antibacterial activity in the order I > II > III > IV, and the activity of their combinations followed the order of I+II+III+IV > I+II+III > I+II. The DNA-binding properties of complex (I) and its three combinations were studied using electronic absorption and fluorescence (ethidium bromide displacement assay) spectroscopy. The results obtained indicated that all series interact effectively with calf thymus DNA (CT-DNA). The binding constant (K_b), the number of binding sites (n) and the Stern–Volmer constant (K_sv) were obtained based on the results of fluorescence measurements. The calculated thermodynamic parameters supported that hydrogen bonding and van der Waals forces play a major role in the association of each series of metal complexes with CT-DNA and follow the above-binding affinity order for the series.

Communicated by Ramaswamy H. Sarma     

Cytogenetics of ditelotetrasomics for short arms of four chromosomes of barley (Hordeum vulgare L.)

Summary Plants with a pair of extra homologous telocentric chromosomes in addition to the normal chromosome complement are called ditelotetrasomics. Six types of ditelotetrasomics of barley have been obtained. Four types obtained in the selfed progenies of telotrisomics (Triplo 2S, Triplo 5S, Triplo 6S, and Triplo 7S) are reported in this paper. The ditelotetra 2S showed a stronger expression of the diagnostic characteristics of Triplo 2S. It was weak and small, with narrow, short, dark-green leaves, and was almost completely pollen and seed sterile. However, three other ditelotetrasomics (ditelotetra 5S, 6S, and 7S) did not show specific diagnostic characteristics and were similar to normal diploid plants, with the exception of ditelotetrasomic 5S, which showed some effects. At meiotic diakinesis and metaphase I, these ditelotetrasomic plants showed chromosome configurations of 6_II+1_IV, 7_II+1 telo_II, 6_II+1_III+1telo_I, or 7_II+2 telo_I. Most of the sporocytes at anaphase and telophase in the first and second meiotic divisions showed almost normal chromosome behavior. Quartets were mostly normal with no micronuclei. Approximately 30% of the selfed progenies of these three ditelotetrasomics were ditelotetrasomics and almost 50% were telotrisomics, indicating a high percentage of male and female transmission of the extra telocentric chromosomes.     

Intergeneric hybridization between Brassica napus and Sinapis pubescens,and the cytology and crossability of their progenies

The cytological possibility of gene transfer from Sinapis pubescens to Brassica napus was investigated. Intergeneric hybrids between Brassica napus (2n = 38) and Sinapis pubescens (2n = 18) were produced through ovary culture. The F₁ hybrids were dihaploid and the chromosome configurations were (0–1) _III + (2–11) _II + (5–24) _I . One F₂ plant with 38 chromosomes was obtained from open pollination of the F₁ hybrid. Thirty-one seeds were obtained from the backcross of the F₂ plant with B. napus. Five out of seven plants had 38 chromosomes, and the pollen stainability ranged from 0% to 81.4%. In the B₂ plants obtained from the backcross of B₁ plants with B. napus, 66.7% of the plants examined had 38 chromosomes. S. pubescens may become a gene source for the improvement of B. napus.     

Introgression of chromosomes of Festuca arundinacea var. glaucescens into Lolium multiflorum revealed by genomic in situ hybridisation (GISH)

An F₁ hybrid (n=4x=28) between the tetraploid species Festuca arundinacea var. glaucescens (GGG′G′) and a synthetic tetraploid Lolium multiflorum (LmLmLmLm) was backcrossed to diploid L. multiflorum to produce triploid (2n=3x=21) BC₁ hybrids (LmLmG). At metaphase I of meiosis the triploids had a preponderance of ring bivalents and univalents with some linear and frying-pan trivalents. Genomic in situ hybridisation (GISH) differentiated the Festuca chromosomes from Lolium and revealed that the bivalents were exclusively between Lolium homologues, while the univalents were Festuca. Despite the limited amount of homoeologous chiasmata pairing in the triploids, some recombinant chromosomes were recovered in the second backcross when the hybrids were further crossed to diploid L. multiflorum. The progeny from the second backcross was predominantly diploid. Genotypes with recombinant chromosomes and chromosome additions involving an extra Festuca chromosome were identified using GISH. Changes in plant phenotype were related to the presence of Festuca chromatin. Received: 20 September 2000 / Accepted: 05 January 2001     

The ‘A’ genome donor of Eleusine coracana (L.) Gaertn. (Gramineae)

Summary In an attempt to discover A and B genome donor(s) to finger millet, Eleusine coracana, or its progenitor species, E. africana (both allotetraploid 2n=4x=36), five diploid species, E. Indica, E. Floccifolia, E. multiflora, E. tristachya and E. intermedia, were crossed to finger millet and its progenitor taxon. Crosses were successful only with E. coracana. Three combinations of triploid hybrids E. coracana x E. indica, E. coracana x E. floccifolia, and E. coracana x E. multiflora were obtained and analysed. Meiotic behaviour was perfectly normal in parental species. The regular number of 18 bivalents in E. coracana, 9 bivalents in E. indica, E. intermedia, E. tristachya and E. floccifolia and 8 bivalents in E. multiflora were invariably noticed. In E. coracana x E. indica hybrids a mean chromosome pairing of 8.84_I+8.80_II+0.03_III+0.10_IV per cell was found. About 86.5% of the cells showed the typical 9_I+9_II configuration, suggesting that E. indica (AA) is one of the diploid genome donors to cultivated species E. coracana. A mean chromosome pairing of 11.08_I+7.63_II+0.16_III+0.04_IV per cell was found in E. coracana x E. floccifolia hybrids. Two to ten bivalents and varying numbers of univalents were seen in 55% of the cells. About 45% of the cells showed the 9_I+9_II configuration. Various evidence suggests that perennial E. floccifolia is a primitive member of the A genome group of Eleusine species, and it may not be a genome donor to E. coracana. In E. coracana x E. multiflora hybrids (2n=26) mean chromosome pairing of 21.45_I+1.97_II+0.13_III+0.04_IV per cell was found. About 91% of the cells were observed to have 20–26 univalents. Only a small percentage of the cells contained bivalents or multivalents. This pairing behaviour indicates that E. multiflora lacks genomic homology with the A or B genome of E. coracana. Genomically E. multiflora is a distinct species and a genomic symbol of C is assigned to it. Identification of the B genome donor species to cultivated millet. E. coracana remains elusive.     

Low temperature spectral properties of subchloroplast fractions purified from spinach

Spinach (Spinacia oleracea L.) chloroplasts solubilized by digitonin were separated into five fractions by sucrose density gradient centrifugation. Three of the fractions, F_I, F_II, and F_III, corresponding to photosystem I, photosystem II, and the chlorophyll a/b complex, were purified further by two steps of diethylaminoethyl-cellulose chromatography followed by electrofocusing on an Ampholine column. The polypeptide patterns of the fractions were examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and the spectral properties of the fractions at −196 C determined by absorption spectra, fourth derivative curves of the absorption spectra, fluorescence emission spectra, and fluorescence excitation spectra. The activity of purified F_II (photosystem II) was also assayed by the photoreduction of dichlorophenol-indophenol at room temperature using 1,5-diphenylcarbohydrazine as the electron donor and by the photoreduction of C-550 at −196 C. The different fractions showed unique polypeptide patterns and unique sets of low temperature-absorbing forms of chlorophyll. The fluorescence emission spectra of F_I, F_II, and F_III at −196 C were also unique with maxima at 734, 685 and 681 nm, respectively. F_I showed negligible emission at wavelengths shorter than 700 nm and the long wavelength tails of F_II and F_III in the 730 nm region were relatively small (approximately 10% of emission of their wavelength maxima). Addition of 0.1% Triton to F_I and F_II caused the longer wavelength absorbing forms of chlorophyll to shift to 670 nm and the fluorescence emission maxima (of both fractions) to shift to 679 nm at −196 C with an increase in the yield of fluorescence especially in the case of F_I.     

大鹅观草与蛇河披碱草属间杂种的细胞遗传学研究

为探讨大鹅观草(Roegneria grandis,2n=4x=28)的染色体组组成,为其正确的分类处理提供细胞学依据。该研究通过人工远缘杂交,成功获得3株大鹅观草与蛇河披碱草(Elymus wawawaiensis,2n=4x=28)属间杂种F1植株。杂种植株形态介于两亲本之间,不育。亲本及杂种经I2-IK溶液染色后进行花粉育性检测,结果显示Roegneria grandis和Elymus wawawaiensis的花粉可育,育性高达94.6%和90.5%;杂种F1不育。花粉母细胞减数分裂中期I染色体配对结果显示,亲本花粉母细胞配对正常,均形成14个二价体,以环状二价体为主,Roegneria grandis有频率很低(0.04/细胞)的单价体出现;杂种F1平均每个花粉母细胞形成6.46个二价体,变化范围为5~8;在观察的83个花粉母细胞中,有35.2%的花粉母细胞形成了7个二价体,形成6个二价体的细胞占42.59%,较少细胞形成8个二价体;平均每个细胞形成14.66个单价体,变化范围为10~18;平均每细胞观察到0.14个三价体;杂种花粉母细胞染色体构型为14.66 I+6.46 II+0.14 III;平均每细胞交叉数为9.83,C值为0.35。结果表明:(1)R.grandis与Elymus wawawaiensis有一组染色体组同源的St染色体组,另外一组染色体组不是St或者H染色体组,Roegneria grandis的染色体组组成不是St Stg;(2)较低频率的三价体(平均0.14个/细胞),可能是由于R.grandis的St和Y染色体组间具有一定的同源性,也可能是染色体易位等原因导致,对于Y染色体组的起源还需深入地研究;(3)在不同地理来源的披碱草属和鹅观草属物种中St染色体组同源性不同,R.grandis与来自于北美的Elymus lanceolatus与E.wawawaiensis的St染色体组较与分布于亚洲的E.sibiricus和E.caninus的St染色体组同源性反而更高,其原因还需要进一步地研究。     

Cytological relationships in theConvolvulus pluricaulis complex

InConvolvulus pluricaulis Chois. two forms (2n=18, 36) along with one colchicine-autotetraploid have been investigated morphologically and cytologically. The diploid regularly formed 9_II although in the “off-season” plants certain irregularities were observed including formation of unreduced pollen grains. The natural tetraploid and the colchicine-autotetraploid had mean frequencies of configurations of 1.56_IV+14.04_II+1.48_I and 2.95_IV+0.56_III+11,43_II+0.8_I, respectively. The mode of chromosome association in the two types of tetraploids was comparable. A comparison of the morphological characters of the two tetraploid types, further, suggested close similarity. In addition they were indistinguishable from the diploid from except being gigas. From these data it is inferred that the natural tetraploid presumably arose as a result of direct duplication of the diploid form, through the chance fusion of unreduced spores. The lower quadrivalent frequency of the natural polyploid is ascribed to a gradual shift towards bivalent association accompanying natural selection for fertility. The taxonomic status of the two forms (2x, 4x) is discussed and the varietal status accorded to the tetraploid form is supported.     

Cytogenetics of a new type of barley with 16 chromosomes

In the progeny of a trisomic type for chromosome 6, Purple, a 16-chromosome type was obtained, which had a pair of new metacentric chromosome 6 in excess. The new metacentric chromosome 6 was shorter than any of the 14 chromosomes of normal barley complement and showed a heteropycnotic nature at late prophase in somatic mitosis. At metaphase I in the plants with 14+one metacentric chromosome 6 (2n=15) the chromosome configuration was exclusively 7_II+1_I indicating that the extra metacentric chromosome 6 could not associate with the normal chromosome 6. At diakinesis and metaphase I in the new 16-chromosome plants most of the sporocytes showed 8_IIor 7_II+2_I. Neither tetravalents nor trivalents were observed at meiosis. The chromosome behaviour at anaphase I and later stages of meiosis was regular in general, resulted in a fairly high pollen fertility of about 61 per cent. Seed fertility however, was very low. The transmission rate of the new metacentric chromosome 6 through the pollen was extremely low in 16-chromosome plants. Possible origin of new basic number and B-chromosome in diploid level through trisomic condition was suggested (Summary see p. 138).Contribution No. 141 of the Department of Plant Science, University of Manitoba.