Inter- and intra-genomal chromosome pairing in an interspecific hybrid and its bearing on basic chromosome number inPennisetum

Meiosis in the interspecific hybrid betweenPennisetum typhoides (2n=14; genomeAA) andP. purpureum (2n=28; genomesA′A′BB) has been studied with particular reference to allosyndetic and autosyndetic pairing of chromosomes. Although up to nine bivalents occurred in the hybrid, never more than five were observed to be (heteromorphic)AA′ bivalents (range 1–5). It has been concluded thatA andA′ genomes are onlypartially homologous. It has further been inferred that the two genomes are evolutionarily related and could have arisen from a common progenitor withx=5 chromosomes or from related species withx=5 chromosomes. Autosyndetic pairing of chromosomes within thetyphoides complement (A genome) and within theA′ genome ofpurpureum have been reported here for the first time. Intra-haploid pairing to a probable maximum of two bivalents within each of the three genomes of the hybrid, viz.,A, A′ andB, further suggestsx=5 as the phyletically basic number in the genusPennisetum. It has been inferred thatx=7 is a secondarily basic number, having been derived fromx=5. The occurrence of a species withn=5 inPennisetum, viz.,P. ramosum, substantiates this view. Further support in favour of this conclusion comes from the secondary association of bivalents in dipoidP. typhoides. Thus, the apparently diploid species,Pennisetum typhoides with2n=14 chromosomes is considered to be a “secondary diploid” having a secondarily balanced number ofx=7. On the basis of the results obtained by the author is conjunction with the available evidence from the literature, it is suggested thatx=5 may be the original basic number for the entire grass family and seven, the most preponderant number in it, and other higher numbers derived from it subsequently during the course of evolution.     

Cytological studies on diploid and polyploid taxa of the genus Pennisetum Rich

The cytology of thirteen taxa and two hybrids in the genus Pennisetum indicated the distribution of the taxa among the four basic chromosome numbers 5, 7, 8 and 9. The diploid nature of P. ramosum and P. typhoides and the genomic allotetraploid status of P. purpureum was further confirmed. P. massaicum (2n=32), P. orientale (2n=36) and P. subangustum (2n=36) suggested probable autotetraploid nature and the three hexaploids (2n=54) investigated (P. polystachyon, P. longistylis and P. squamulatum) revealed allohexaploid constitution. The natural triploid, P. ruppellii (2n=27) and pentaploid P. villosum (2n=45) were found to be apomicts and they were allotriploid and allopentaploid respectively. The tetraploid-hexaploid complex of P. pedicellatum showed them to be cytotypes only. The cytogenetical behaviour of the hybrid, P. typhoides x P. purpureum with 2n=21 and the trispecies hybrid (P. typhoides x P. purpureum) x P. squamulatum with 2n=48 brought out the homology within the genomes of x=7 and x=9 and also between the genomes with x=7 and x=9. The significance of the inter- and intragenomic chromosome pairing had been brought out from the interspecific hybrids and the natural allotriploid and allopentaploid species having one genome in the haploid condition.The morphological sections of this genus did not correspond with the cytological groups. A high degree of evolutionary specialization was evident in species of the section Gymnothrix. A complete series of polyploids and high degree of heterogeneity from the morphological point of view was brought out in species with x=9.     

Telo aneuploids in pearl millet

Summary Nomenclature and chromosome constitution for twenty different aneuploids with telocentrics in Pennisetum typhoides are presented.     

The Relationship between Embryo and Endosperm in Interspecific Hybrids in PennisetumL. Rich

In the interspecific cross [diploid Pennisetum typhoides X hexaploid(P. typhoides X P. purpureum)] X diploid P. typhoides, embryosand endosperms in the same ovule may respond differently totreatment with the growth substance gibberellic acid, as maydo different genotypes. Size of embryo and size of its endospermare positively correlated in some genotypes but not in others.Large fully developed normal embryos may be associated withnormal, retarded, degenerate or even no endosperm at all. Conversely,large normal endosperms, even in mature seeds, may contain large,small, or no embryos. Fully developed embryos may be viableregardless of whether they had been associated with normal,retarded or degenerate endosperm, or even no endosperm at all. It is concluded that the embryo is not always dependent on theendosperm during its early development and that a degeneratingendosperm need not have a detrimental effect on the developmentof its embryo or on the viability of the latter.     

Multiple chromosomal interchanges in pearl millet

Summary Intercrossing and irradiation were successfully used in pearl millet (Pennisetum typhoides) to develop multiple interchanges involving up to the total complement of all the chromosomes in one complex. In interchange heterozygotes showing 12 + 1 II and 14, 90.9 and 87.8 per cent of the cells, respectively, had chromosome configurations other than that of 12 and 14 chromosomes. In general, the frequency of such cells resulting from breakdown of the expected complex configuration increased with the increase in the number of translocated chromosomes in the complex. The higher the number of chromosomes involved in the interchange ring, the higher were the pollen and ovule sterility. The results indicated that meiotic instability, deficiency-duplication gametes, and unequal distribution of chromosomes account for increased sterility of multiple interchange heterozygotes. Even though interchanges in pearl millet predominantly show the alternate type of segregation, sterility seems to be the major barrier for the exploitation of the multiple interchange method for gamete selection and the establishment of homozygous lines in this plant species.     

柊叶和象草波式潜流人工湿地的对比研究

为探索柊叶和象草在人工湿地中的应用及其净化机理,该研究以柊叶和象草为人工湿地植物分别构建了波式潜流人工湿地系统,分析了柊叶和象草波式潜流人工湿地对生活污水中COD_(cr)、TN和TP的净化效果,观察了柊叶和象草两种植物在不同季节的生长状况。结果表明:经过15个月的连续运行,在表面水力负荷约0.3 m·d~(-1)的条件下,柊叶和象草波式潜流人工湿地平均去除率是COD_(cr)分别为66.1%和70.1%,TN分别为60.4%和63.7%,TP分别为74.1%和75.1%。两种植物生长良好,根系发达,象草的地上生物量是柊叶的2.1倍,地下生物量相当;冬季象草生长缓慢,柊叶部分叶片的四周干枯,但二者都不会枯亡。这说明两个人工湿地对COD_(cr)、TN和TP都具有较好的去除效果,但无显著性差异,柊叶和象草能明显提高潜流人工湿地的净化效果。     

A translocation tester set in pearl millet

Summary Sixteen translocation stocks developed in pearl millet, Pennisetum typhoides (Burm.) S.&H. (2 n = 14) were inter-crossed and the meiotic configurations of f₁'s analysed. A translocation tester set comprising five translocation stocks, each involving two non-homologous chromosomes has been developed.     

Origin of the main class of repetitive DNA within selected Pennisetum species

In an attempt to identify relationships among genomes of the allotetraploid Pennisetum purpureum Schumach and closely related Pennisetum species with which it can be successfully hybridized, repetitive DNA sequences were examined. Digestion with KpnI revealed two highly repetitive fragments of 140 by and 160 bp. The possibility that these sequences could be used as genome markers was investigated. Average sequences were determined for the 140 by and 160 by KpnI families from P. purpureum and P. squamulatum Fresen. Average sequences (based upon four or five repeats) were determined for the P. glaucum (L.) R. Br. 140 by KpnI family and the diploid P. hohenackeri Hochst. ex Steud. 160 bp KpnI family. The average sequences of the 160 by KpnI families in P. purpureum and P. squamulatum differ by only nine bases. The 140 by KpnI families of the three related species, P. purpureum, P. squamulantum, and P. glaucum are nearly identical, and thus likely represent a recent divergence from a common progenitor or a common genome. Each repetitive sequence may contain internal duplications, which probably diverged following amplification of the original sequence. The 140 by KpnI repeat probably evolved from the 160 by KpnI repeat since the missing 18 by segment is part of the internal duplication that is otherwise conserved in the subrepeats. Tandemly arrayed repetitive sequences in plants are likely to be composed of subrepeats which have been duplicated and amplified.Florida Aqricultural Experiment Station series #R-02758     

Haploid meiosis and its bearing on the phylogeny of pearl millet,Pennisetum typhoides stapf et hubb.

Meiotic chromosome associations in a spontaneously originated haploid plant of pearl millet have been studied and their phyletic significance discussed. Chromosome pairing could be observed at pachytene and diplotene. Out of a total of 285 PMC's studied at diakinesis-metaphase 1, 43 showed one bivalent and 7 had two bivalents per cell. Both rod- and ring-bivalents were observed. Apart from synapsis accompanied by chiasma formation, close associations of univalent chromosomes were observed. Out of 150 cells without true bivalents, 41 showed 1 s-s association and five, 2 s-s pairs per cell. On the basis of the realization of a maximum of two bivalents per cell, as also of a maximum of 2 s-s pairs, it has been inferred that the chromosome complement ofP. typhoides (n=7) has evolved from a basic set ofn=5 chromosomes. Other available evidence supporting this inference is also discussed.     

Effect of wild grasses planted as border rows on stemborer infestations in maize in Uganda)

The presence of wild grasses in the vicinity of maize fields has been associated with reduced stemborer incidence on the maize crop. This study evaluated the impact of border rows with wild grasses on stemborer infestations and parasitism. Field trials were conducted in East and Central regional Agricultural Research Institutes in Uganda for three seasons. The four grass species planted as border rows included Pennisetum purpureum Schumach, Pennisetum polystachion (L.) Schult, Panicum maximum Jacq. and Sorghum arundinaceum (Desv.) Stapf. (Poaceae) were used. A pure maize stand without a grass border was planted as control. Busseola fusca Fuller (Lepidoptera: Noctuidae) and Chilo partellus Swinhoe (Lepidoptera: Crambidae) were the major stemborers found. Maize with P. purpureum and P. maximum borders reduced stemborer infestations and damage compared to the pure maize stand. The results were however, not consistent for all the three seasons. Yield per plot was higher in pure maize stand compared to plots with grass borders. The usefulness of this technique in stemborer management is discussed.     

Cytogenetics for the model system Arabidopsis thaliana

A detailed karyotype of Arabidopsis thaliana is presented using meiotic pachytene cells in combination with fluorescence in situ hybridization. The lengths of the five pachytene bivalents varied between 50 and 80 μm, which is 20–25 times longer than mitotic metaphase chromosomes. The analysis confirms that the two longest chromosomes (1 and 5) are metacentric and the two shortest chromosomes (2 and 4) are acrocentric and carry NORs subterminally in their short arms, while chromosome 3 is submetacentric and medium sized. Detailed mapping of the centromere position further revealed that the length variation between the pachytene bivalents comes from the short arms. Individual chromosomes were unambiguously identified by their combinations of relative lengths, arm-ratios, presence of NOR knobs and FISH signals with a 5S rDNA probe and chromosome specific DNA probes. Polymorphisms were found among six ecotypes with respect to the number and map positions of 5S rDNA loci. All ecotypes contain 5S rDNA in the short arms of chromosomes 4 and 5. Three different patterns were observed regarding the presence and position of a 5S rDNA locus on chromosome 3. Repetitive DNA clones enabled us to subdivide the pericentromeric heterochromatin into a central domain, characterized by pAL1 and 106B repeats, which accommodate the functional centromere and two flanking domains, characterized by the 17 A20 repeat sequences. The upper flanking domains of chromosomes 4 and 5, and in some ecotypes also chromosome 3, contain a 5S rDNA locus. The detection of unique cosmids and YAC sequences demonstrates that detailed physical mapping of Arabidopsis chromosomes by cytogenetic techniques is feasible. Together with the presented karyotype this makes Arabidopsis a model system for detailed cytogenetic mapping.     

Chromosome polymorphism of teosinte

Florida teosinte from Honduras and Guanajuato teosinte have most of their knobs internally located and a common inversion in the short arm of chromosome 8. Teosintes from northern Guatemala, Huixta and Monajil, have all their knobs terminally located and do not have any inversions. Therefore, Florida teosinte from Honduras appears to be phylogenetically closer to Guanajuato teosinte than it is to Guatemalan teosintes.——The presence of B chromosomes and an In 8 in Guanajuato teosinte and Florida teosinte from Honduras may constitute evidence of introgression between maize and teosinte.     

Cytogenetics of pearl millet

Summary The somatic karyotype of pearl millet Pennisetum americanum (L.) Leeke. (2n = 14) has been studied in several cultivars, but few cytological markers have been discovered which could help in the easy identification of the chromosomes. Analysis of pachytene bivalents permits such identification but is feasible only in a few cultivars. Recently, several lines having telocentric chromosomes have been produced and classified but their potentialities as cytogenetic tools have yet to be explored. Some African populations of pearl millet carry B-chromosomes in their karyotype. Cytogenetics of B-chromosomes has been reported in great detail. Bs undergo spontaneous changes to produce deficient- and iso-chromosomes. The main effect of B-chromosomes is on chiasma frequency which is exerted by the relative amounts of chiasma promoting euchromatin and the chiasma depressing heterochromatin in the Bs. Haploid plants occur occasionally and sometimes show a low degree of seed set, offering a possibility of establishing homozygous inbred lines. Cytogenetics of several spontaneous and induced autotetraploids have been reported. In general quadrivalent formation between the seven sets of four homologues was random. Seed set of the autotetraploids could be improved by selection; improved seed fertility was found to be associated with increased chiasma frequency, increased quadrivalent frequency and regular distribution of chromosomes at anaphase I. Genes controlling morphological characters of plant phenotype segregate independent of those controlling fertility and in pearl millet polyploidy per se is not limiting to plant vigour. Primary trisomics represent the best studied among the aneuploids of pearl millet. All the seven primary trisomics have been identified and described. Some were used in assigning genes to specific chromosomes but in general trisomies have poor vigour and fertility, and show low frequency of transmission. Apart from B-chromosomes, cytogenetics of interchanges has been the best studied aspect of pearl millet. The frequency of co-orientation of an interchange complex at metaphase I, which determines the fertility or sterility of the interchange heterozygote, is influenced by the genetic background and thus is theoretically amenable for selection leading to improved fertility of the heterozygote. Interchange tester-stocks have been assembled which can be used to identify the chromosomes involved in any newly obtained interchange. A complex interchange line involving all the chromosomes of the complement has also been produced, but the ring-of-fourteen produces total male and female sterility.Genotypic control of mitosis and meiosis has been reported, with reference to chromosome numerical mosaicism, multiploid sporocytes, desynapsis and chromosome fragmentation, and male sterility. Pearl millet being a largely outbreeding species, forced inbreeding was mainly found to result in loss of morphological vigour and reduction in mean chiasma frequency per PMC. Interspecific hybrids between pearl millet and several related species have been cytologically investigated and homology of the seven chromosomes of pearl millet with seven of the fourteen chromosomes of P. purpureum has been demonstrated. Cytogenetic evidence from haploids, autopolyploids and interspecific hybrids has indications to suggest that the haploid number of x = 7 is derived from x = 5, but the evidence is inconclusive and needs critical evaluation.     

Mitochondrial DNA variation in pearl millet and related species

Summary Mitochondrial DNA (mtDNA) restriction endonuclease fragment patterns and patterns of mtDNA hybridized by mitochondrial gene probes were used to study phylogenetic relationships of seven Pennisetum species, including five P. americanum (pearl millet) ecotypes and a reference species from the distantly related genus, Panicum. The restriction patterns of the pearl millet ecotypes were uniform with the exception of the ecotype collected in Ethiopia. The probe hybridization method revealed more variability, with both the Rhodesian and Ethiopian ecotypes differing from the others and from each other. Considerable restriction pattern polymorphism was noted among different species of Pennisetum, and Panicum. Significant relationships were noted of Pennisetum polystachyon to P. pedicellatum and of P. purpureum to P. squamulatum using the restriction pattern method. In addition to those relationships, the hybridization method showed relationships of pearl millet to P. purpureum and to P. squamulatum. The relationships noted between species by the hybridization method agreed more closely to the cytological data than those indicated by the restriction pattern method. Therefore, the hybridization method appeared to be the preferred method for studying species relationships. The mitochondrial genome size of pearl millet was calculated to be 407 kb and the mitochondrial genome sizes of other Pennisetum species ranged from 341 to 486 kb.Florida Agricultural Experiment Station Journal Series No. 8485.     

Multicolor FISH mapping of the dioecious model plant,<Emphasis Type="Italic"> Silene latifolia</Emphasis>

Silene latifolia is a key plant model in the study of sex determination and sex chromosome evolution. Current studies have been based on genetic mapping of the sequences linked to sex chromosomes with analysis of their characters and relative positions on the X and Y chromosomes. Until recently, very few DNA sequences have been physically mapped to the sex chromosomes of S. latifolia. We have carried out multicolor fluorescent in situ hybridization (FISH) analysis of S. latifolia chromosomes based on the presence and intensity of FISH signals on individual chromosomes. We have generated new markers by constructing and screening a sample bacterial artificial chromosome (BAC) library for appropriate FISH probes. Five newly isolated BAC clones yielded discrete signals on the chromosomes: two were specific for one autosome pair and three hybridized preferentially to the sex chromosomes. We present the FISH hybridization patterns of these five BAC inserts together with previously described repetitive sequences (X-43.1, 25S rDNA and 5S rDNA) and use them to analyze the S. latifolia karyotype. The autosomes of S. latifolia are difficult to distinguish based on their relative arm lengths. Using one BAC insert and the three repetitive sequences, we have constructed a standard FISH karyotype that can be used to distinguish all autosome pairs. We also analyze the hybridization patterns of these sequences on the sex chromosomes and discuss the utility of the karyotype mapping strategy presented to study sex chromosome evolution and Y chromosome degeneration.Communicated by J.S. Heslop-Harrison     

Karyotype characterisation of Brazilian species of the genus <Emphasis Type="Italic">Psychotria</Emphasis> L. — subfamily Rubioideae (Rubiaceae)

The pantropical genus Psychotria L., probably the largest among angiosperms, occurs in different Brazilian vegetal formations. This work determined the chromosome numbers and karyotypic characteristics of ten species of Brazilian Psychotria. The chromosome numbers ranged from 2n = 22, in five species (P. hoffmannseggiana (Willd. ex Roem. & Schult.) Müll. Arg., P. lupulina Benth., P. marginata Sw., P. tenerior (Cham.) Müll. Arg., and P. trichophora Müll. Arg.), to 2n = 40, in P. mapourioides DC., and 2n = 44 in four other species (P. carthagenensis Jacq., P. gracilenta Müll. Arg., P. longipes Müll. Arg. and P. suterella Müll. Arg.). In addition to these differences, great variations in chromosome lengths and karyotypic formulae were also observed among these species. Chromosome length varied from 5.59 μm to 0.90 μm and no relationship was detected between chromosome numbers and lengths in any species. Chromosomes are principally metacentric, except for P. mapourioides that presents mainly submetacentric chromosomes. Karyotypic asymmetry rate (TF%) ranged from moderate (TF% = 38.83) to highly symmetric (TF% = 50.00). The difference in chromosome numbers of Psychotria carthagenensis (2n = 44) and P. mapourioides (2n = 40) is very important to taxonomists, because these have great difficulty in identifying and differentiating these two species with the sole use of morphological characteristics, since some individuals have intermediate characteristics between both species. Although this study does not allow for a consistent cytotaxonomic analysis, not even to delimit P. subgen. Psychotria and P. subgen. Heteropsychotria, this karyotype analysis of some Brazilian species, along with their morphology, may contribute to a better knowledge of the genus.     

Curvularia leaf blight of bajra (pennisetum typhoides Stapf.) in India

Summary The symptoms of leaf blight of bajra (Pennisetum typhoides Stapf.) from India, its cause which has been identified asCurvularia penniseti (Mitra)Boedijn var.poonensis n. var. together with the morphology and host range of the fungus etc. have been given.Part of the work submitted by ShriP. L. Patil for M. Sc. (Agric.), University of Poona, under the guidance of Dr.N. B. Kulkarni.The authors express their sincere thanks to Prof.M. Sulaiman for providing necessary facilities for this work.     

Photochemical Characteristics of Mesophyll and Bundle Sheath Chloroplasts from C4 Plants

Mesophyll and bundle sheath chloroplasts were isolated by differential grinding from the leaves of two NADP-ME C₄ plants, Setaria italica Beauv. cv. H-1, Pennisetum typhoides S & H. cv. AKP-2, and a NAD-ME C₄ species Amaranthus paniculatus L. The mesophyll chloroplasts of C₄ plants possessed slightly lower K_m for ADP and Pi than those of bundle sheath chloroplasts. The Hill reaction activities and noncyclic photophosphorylation rates of the bundle sheath chloropiasts from S. italica and P. typhoides were less than one-fifth of those by the mesophyll chloroplasts. But the bundle sheath chloroplasts of A. paniculatus exhibited high rates of Hill reaction, cyclic as well as noncyclic photophosphorylation. The pigment- and eyiochrome composition suggested a relative enrichment of PS 1 in bundle sheath chloroplasts of S. italica and P. typhoides. The chain exists in both mesophyll and bundle sheath chloroplasts. As much as 35–52% of leaf chlorophyll was located in the bundle sheath chloroplasts. The photochemical activities of bundle sheath chloroplasts are significant though a major part of leaf photochemical potential is associated with the mesophyll chloroplasts.     

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.     

Mitotic evidence for the tetraploid nature of Glycine max provided by high quality karyograms

The high number, very small size and morphological similarity of the chromosomes, and low metaphasic indexes obtained in root meristems have hindered the progress in cytogenetic and evolutionary studies of Glycine max. In order to contribute to the solving of these problems, we have developed a method based on the use of DNA synthesis inhibiting and anti-microtubule solutions and enzymatic maceration and air-drying techniques. Besides, we have employed a digital image analysis system tool. This method provided prometaphasic and metaphasic chromosomes showing well-defined primary and secondary constrictions, which facilitated the pairing of homologues and assembly of the first karyogram for G. max. This species possesses twenty chromosome pairs, being six metacentric and fourteen submetacentric. The karyograms support its tetraploid nature (4x = 40), specifically for the presence of chromosomes with identical morphology, and suggest that chromosome rearrangements may have occurred during the speciation of G. max.