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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Systematic study on Davalliaceae in Peninsular Malaysia

Kader Maideen, Haja Maideen January 2008 (has links)
The results presented in this thesis show moderate to strong support for the paraphyly of genera in Davalliaceae, especially in Peninsular Malaysia. The results were incongruent with the latest classification based on morphology but congruent with a preliminary study based on molecular data. the phylogeny showed that <i>Leucostegia </i>should not be in Davalliaceae. Six clades were recognised in Davalliaceae, namely the <i>Ariaostegia </i>clade (AC); <i>Davallia </i>with four clades: denticulate clade (DC1), dimorpha-divaricata clade (DCII), scyphularia-solida clade (DCIII), trichomanoides clade (DCIV); and the <i>Humata </i>clade (HC). Maximum parsimony and Bayesian analyses of <i>rps4-trnS </i>and combined three regions produced congruent topologies, but the topologies of <i>rbcL </i>and <i>trnL-F </i>produced only slight differences. The combined <i>rbcL</i> data also showed that all species were fully resolved without having a separated/regional clade. In general the molecular phylogenetic reconstruction of Davalliaceae based on <i>trnL-F </i>and <i>rps4-trnS </i>regions showed additional support that no genera in this family are monophyletic. However, the results produced could have been interpreted with more confidence if species from <i>Davallodes </i>(not reported in Peninsular Malaysia) and species from other parts of the world were included in the study. Most genera of Davalliaceae in the study area were characterized by having a single base chromosome number, x = 40, except for <i>Leucostegia </i>which has x = 41. All plants studied were diploids except for <i>Humata vestita </i>which was polyploid (hexaploid). Spores of Davallioid ferns are monolete (ellipsoid) and have verruculate ornamentation. Davalliaceae in Peninsular Malaysia comprises fifteen species in two genera, <i>Araiostegia </i>(1 species) and <i>Davallia </i>(14 species).

Experimental taxonomy in some annual species of Senecio from the Mediterranean area

Alexander, James Crynan Murray January 1975 (has links)
No description available.

Hybridization in sub-arctic willow scrub in Scotland

Forrest, Alan January 2006 (has links)
Molecular and morphological markers were used to clarify the species and hybrid taxonomy of sub-arctic <i>Salix </i>species in Scotland, and to investigate the extent of hybridization and introgression in sub-arctic willow scrub communities. The utility of molecular and morphological markers for the identification of hybrids between pairs of species was compared. A detailed study of hybridization between <i>S.</i> <i>arbuscula </i>and <i>S. lapponum </i>was conducted at two sites. The potential for differences in phenology to act as a reproductive barrier between the species was estimated. The results were used to determine the importance of hybridization and introgression in the systematics of montane <i>Salix, </i>and to provide guidance for conservation programmes aimed at restoring sub-arctic willow scrub communities. The six morphologically circumscribed montane species considered in this study (<i>S.</i> <i>arbuscula, S. herbacea, S. lanata, S. lapponum, S. myrsinites, S. reticulata) </i>can be distinguished clearly with nuclear AFLP markers, but not with chloroplast DNA markers. A relationship between the occurrence and frequency of hybridization and genetic distance between species pairs was detected. At two locations in central Scotland (Meall nan Gabhar, Meall Ghaordie) <i>S. arbuscula </i>and <i>S. lapponum </i>can be distinguished clearly with morphometric analysis of six foliar characters. They maintain their molecular differentiation but to a lesser degree than in allopatric reference populations. A significant but low correlation (Meall nan Gabhar <i>r</i><sup>2</sup><i> </i>= 0.173; Meall Ghaordie <i>r</i><sup>2</sup> = 0.095) between morphological distance and molecular distance in individuals was detected. Bayesian assignment analysis based on AFLP data was, however, unable to resolve distinct parental species groups at these two sites, suggesting a significant level of genetic exchange between the taxa. Morphological differentiation was site independent, whereas molecular differentiation was site dependent and showed considerable mixing of the species gene pools when considering both sites together. Despite this evidence for genetic exchange, flowering asynchrony was found to constitute a strong barrier to inter-specific gene flow at both sites (RI<sub>phen</sub> = 0.778 at Meall nan Gabhar, and 0.702 at Meall Ghaordie) with <i>S. lapponum </i>flowering before <i>S. arbuscula. </i>A relationship between flowering onset and altitude contributes to spatio-temporal isolation between species. This barrier is slightly weaker at one site (Meall Ghaordie) and more morphological hybrids were detected at this site. This case study represents a situation where rare hybridization has led to the widespread introgression of neutral markers while diagnostic morphological traits remain differentiated. In the final chapter, the information obtained about the extent of hybridization and introgression is used to provide guidance for conservation management strategies for sub-arctic willow scrub in Scotland.

A taxonomic revision of the genus Matthiola R.Br. (Cruciferae) and related genera

Gowler, Zoe R. January 1998 (has links)
A global taxonomic review of the Cruciferae genera <I>Matthiola</I> R.Br., <I>Lonchophora </I>Durieu, <I>Diceratella</I> Boiss. and <I>Morettia</I> DC. is presented. The fifty species of <I>Matthiola</I> were investigated taxonomically, with the aim of improving their classification and giving a better understanding of their relationships and evolution. The species are widely distributed over Macaronesia, the Mediterranean, NE Africa, the Middle East and SW Asia, with one species in S Africa. Exploratory work in the fields of cytology, anatomy and molecular biology was undertaken to determine the usefulness of such techniques in producing new taxonomic characters and to establish techniques that are suitable for this group of plants. A major part of the investigation was to determine and clarify the generic limits, especially with reference to the monotypic genus <I>Lonchophora </I>and the genus <I>Microstigma </I>Trautv., both of which were formerly included in <I>Matthiola.</I> The genera <I>Diceratella</I> and <I>Morettia</I> were also included in the investigation as there has been much movement of species between these genera by taxonomists in recent years. Nine informally designated species-groups of <I>Matthiola</I> are recognised and supported by the phenetic numerical analysis, although only two species-groups are fully supported by the cladistic analysis. Intuitive, phenetic and cladistic analyses all confirm that <I>Lonchophora </I>is a part of <I>Matthiola, </I>belonging to Species-Group LONGIPETALA, and that <I>Microstigma </I>is closely allied to <I>Matthiola</I>, but remains distinct. <I>Diceratella </I>and <I>Morettia</I> are very close to each other but somewhat more distantly related to <I>Matthiola</I>. Three species of <I>Matthiola</I> are reduced to synonymy, two of which are reduced to subspecific level. A new subspecies of <I>Matthiola montana</I> Boiss. is recognised.

Primordial development in Phaseolus

Aleixo Pereira, Maria de Fatima D. January 1978 (has links)
No description available.

Plant cell lines resistant to environmental stresses

Dix, Philip J. January 1975 (has links)
Cell cultures initiated from Nicotiana sylvestris and Capsicum annuum were used in studies on mutation and the selection of variants. Both diploid and haploid derived cultures of N. sylvestris were used, but the genetic instability of these cultures invariably resulted in the application of selection pressures to cultures of mixed ploidy. No haploid material of C. annuum could be obtained, so diploid derived cultures alone were used for this species. A plating method was devised in which small aggregates from the cell suspensions were incorporated into a thin layer of agar medium in Petri dishes, and exposed to the selection pressures in this form. Using these methods, lines of both species were selected with improved chilling tolerance, high temperature tolerance and high salt resistance, in some cases chemical mutagens were shown to increase the yield of lines selected as tolerant. Many tolerant lines were maintained in culture for a number of passages and a proportion of them maintained their tolerance through extended periods in the absence of the selection pressures. For three chilling tolerant lines of N. sylvestris, fertile plants were regenerated and two of these exhibited the maintenance of an improved tolerant phenotype in the seedlings. Metabolic and anatomical aspects of the suspension cultures of variant lines were examined and certain characteristics were found which could relate to the improved tolerance. These included changes in the temperature dependance of respiration, associated with chilling tolerance and ultrastructural changes associated with high salt resistance.

Plant selection for green roofs in the UK

Nagase, Ayako January 2008 (has links)
The use of green roofs is increasing in many countries because of their benefits to the urban environment. However, only a few plant selection studies for green roofs have been carried out and little information on plant performance on roof environments is available in the UK climate. As a result, only a limited range of plants such as Sedum spp. are commonly used for green roofs, especially for shallow substrate green roofs. Therefore, this thesis investigates plant selection for extensive green roofs in the UK. The work in this thesis focused on the following objectives. (1) To identify groups of plants that have potential for use on green roofs, with regard to tolerance of rooftop conditions, (2) To investigate establishment methods for diverse, attractive, flowering green roof vegetation, with attention to seedling techniques, (3) To test survival and performance of a selected range of species and cultivars from the previously identified groups (annuals and geophytes) at different substrate depths, irrigation regimes and covering plants treatments, (4) To compare green roof performance (water management and drought tolerance) between different vegetation types and drought tolerance with different percentages of organic matter in the growing substrate, (5) To investigate the performance of plants as well as their aesthetic appeal, seasonal interest over time and what is required for maintenance (weed Invasion and self-seeding). The direct sowing of perennial and grass mixtures, the use of annual plant seed mixtures and the use of geophytes could be useful techniques for the quick establishment, long flowering, their beautiful colour of flowers, cost effectiveness and providing food resources for biodiversity in an extensive green roof. Germination testing revealed that many perennial and grasses which have potential for use in extensive green roofs did not require chilling for germination and had high germination rates in spring. The results suggested that spring might be the best season for direct sowing on the roofs for quick establishment. In annual plant meadows, it was shown that a low sowing density could be better than high density to reduce competition, resulting in good individual plant growth when there was sufficient watering. However, a high sowing density was recommended for the dry conditions. For geophytes, growth, survival rate, regeneration and flowering were more successful in a deeper substrate rather than a shallow substrate. The vegetation cover by Sedum seemed to work as a protection layer and the overall emergence was encouraged with Sedum, especially in the shallow substrate. In the study of amount of water runoff from different vegetation types, it was shown that grass species may be the most effective for reduction of water runoff followed by forbs and sedums. The size and structure of plants significantly influenced the amount of water runoff, however, species richness did not affect the amount of water runoff significantly. In the study of the drought tolerance of different vegetation types, the forbs and grasses groups used in this study reached permanent wilting point after two to three weeks of no watering and they were required to be watered once a week to maintain their visually attractive forms. Sedum spp. were able to survive well and maintain good visual quality even after three weeks of no watering. There was a tendency that overall survival increased as species richness increased. The diversity in vegetation reduced the vigor potential dominant species. In the investigation of the relationship between percentage of organic matter of substrate and plant growth, it was concluded that about 10% (about 14% in total) of organic matter was the best because the plants showed stable growth regardless of the watering regime. In wet conditions, increased organic matter resulted in increased growth, whereas in the dry conditions, increased organic matter did not result in increased growth. In the investigation of plant growth and performance on an existing semi-extensive green roof it was shown that it is possible to create low-input green roofs which have long flowering and seasonal interest with a little maintenance and supplemental irrigation if appropriate plants were chosen. Plant species diversity might affect overall flowering succession and dynamic change and planting density might affect interaction between plants. In areas of high plant species diversity, there were more possibilities to have a longer flowering term, more seasonal interest and dynamic change than low plant species diversity. In areas of low planting density, individual plants generally produced the better growth than those in high planting density. Moreover, plant growth had more interaction between species in the higher planting density. The tendency was observed that the plants had better growth in the NE and the SE. Also, longer flower duration was shown in the NW whereas many species started flower from the SE. The combination of low plant species diversity and high planting density appeared to reduce weeds effectively. Using a gravel mulch in the shallow substrate could reduce the number of weeds significantly.

Conservation and molecular systematics of the genus Cedrus

Semaan, Myrna January 2000 (has links)
Cedrus is a long-lived forest tree whose extant distribution is limited to a disjunct occurrence at the southern margin of the wide expansion range of its family Pinaceae. Its taxonomy is marked with conflicting inferences. The position of Cedrus within Pinaceae is unresolved between the major subfamily groupings. The infrageneric classification of Cedrus taxa, which is based on indistinct phenotypic characters, remains highly controversial. Within its narrow geographical boundaries, Cedrus has long been, and is still, threatened with a diversity of degrading pressures that raise questions on the viability of the dispersed remnant populations. The unsettled taxonomic dispute, compounded with gaps and uncertainties in the information available on the genus, impede potential efforts toward the conservation and sustainable management of this ancient heritage. This study employed molecular systematics to establish a better understanding of the phylogenetic relationships of Cedrus at the different organizational levels from genus to species and populations. The phylogeny of Pinaceae, reconstructed from chloroplast DNA sequences, establishes Cedrus as a monophylum and resolves its position as sister to the rest of the Pinaceae genera. A DNA-based phylogeny of the interrelationships within Cedrus delimits five evolutionary units which are recognized as species, emphasizing the significance of their geographical disjunction. The evolutionary sequence of these units defines an east-west migration trend from the Himalayas toward the Mediterranean. At the population level, fingerprinting of the genetic diversity in the remnant Cedrus isolates of Lebanon infers a substantial level of diversity distributed within populations with no indication of interpopulation divergence. These findings are instrumental at defining the future conservation of Cedrus as a genetic resource

Studies in the systematic anatomy, embryology and morphology of the Umbelliferae tribe Caucalideae

Al-Attar, Adnan January 1974 (has links)
No description available.

The identification and characterisation of diacylglycerol acyltransferases (DGATS) in microalgae

Chen, Jit Ern January 2014 (has links)
No description available.

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