No description available.

No description available.

No description available.

We formulate a stochastic spatio-temporal model for the spread of infectious diseases in plants. Studying the behaviour of a model which takes into account stochasticity and spatial extension usually involves intractable mathematics and requires the use of simulation. A challenging objective is to develop analytical methods for general application which provide predictions for the expected behaviour of the model. The individual-based model comprises primary and secondary infection and recovery processes. Using stochastic simulation we study the expected behaviour and variability of the epidemic size, and characterise the disease patterns through spatial correlation. Both stationary and transient behaviour are analysed over the parameter space. Simulation is also used to test empirical extensions of non-spatial models which attempt to account for heterogeneous mixing of susceptibles and infecteds. Analytical methods based on cluster approximations are commonly used for predicting the dynamics of stochastic models characterised by nearest neighbour (NN) interactions. On the other hand, for models with more general interactions, the rather simplistic and non-spatial Mean Field approximation has been extensively used. We propose an alternative general approach, built on individual-based ODEs and closure approximations, for predicting the behaviour of spatial models in which the individuals interact according to a generic function of their distance. The approximations, which take into account the development of correlations in the spatial distribution of the population, are tested against the simulation results showing excellent agreement in most of the parameter space. We also test the ability of cluster approximations to capture the effects of the anisotropic spread of the disease. To this end, we formulate a generalised NN model in which the dispersal of propagules depends on the direction of spread and use simulation to assess the performance of different approximations.

This work is divided into two main parts, the first looking at <i>Rhododendron</i> growth on limestone soils, both domestic (horticultural) and Chinese (wild), and the second looking at taxonomic trends in the leaf wax hydrocarbons of subsection Taliensia using Gas Chromatography. Analysis of <i>Rhododendron </i>plants growing on limestone soils was carried out using ICP-AES to look at levels of eight elements in the leaves and their availability in soils. Results showed that Ca and Mg concentrations and pH were correlated closely and loosely inverse to these were Cu, Fe and Mn concentrations (although Mn is not always predictable). Unrelated to these is another correlation, organic content is correlated to K, P and Zn levels. This is generally what one would expect from soils. In the leaves, Ca and Mg are correlated and Fe and P are also correlated, but unrelated to Ca and Mg concentrations. With few exceptions there is little or no correlation between leaf and soil, except in highly alkaline soils. Also related to this some work was carried out on annual trend in levels of nutrient in <i>Rhododendron </i>leaves. This showed that there may be a taxonomic annual trend in nutrient levels in <i>Rhododendron</i> and those <i>Rhododendron</i> suited to alkaline conditions have the most stable levels of Ca and Mg. The second part of the thesis presents an interpretation of patterns of leaf wax hydrocarbons in subsection Taliensia as a taxonomic guide. Analysis of data from gas chromatography of leaf wax extracts allowed a key to be developed in which separate taxa can be distinguished on the basis of their leaf wax compositions. This method is particularly useful when applied to hybrid populations where the parentage is in dispute or to species where the identity of a particular specimen is in question.

The tribe Hedychieae (ginger lily) is the second largest in the ginger family, Zingiberaceae. I carried out a phylogenetic analysis of the Hedychieae using nuclear ribosomal DNA (ITS1, 5.8S and ITS2) and chloroplast DNA (<i>trn</i>L (UAA) 5' exon to <i>trn</i>F (GAA)). The results of these two data sets are in accordance, though with differing levels of resolution. Hedychieae is confirmed to include Zingibereae, the true gingers, and is monophyletic. However, the genera <i>Boesenbergia </i>and <i>Curcuma </i>are apparently not monophyletic. Two major clades are recognised to Hedychieae namely, the '<i>Curcuma </i>clade' and the '<i>Hedychium</i> clade'. The '<i>Curcuma</i> clade' comprises <i>Camptandra, Pyrgophyllum, Stahlianthus </i>and a set of four morphologically very similar genera: <i>Curcuma, Hitchenia, Paracautleya </i>and <i>Smithatris</i>. In this clade, a subclade of <i>Camptandra/Pyrgophyllum</i> is the sister group to a very strongly supported '<i>Curcuma </i>complex': <i>Curcuma, Hitchenia, Paracautleya, Smithatris</i> and <i>Stahlianthus. Smithatris</i> may be recognised as a distinct genus and sister group to the others in the complex. <i>Curcuma</i> is paraphyletic. Two subclades are found in the complex namely, <i>Stahlianthus/Curcuma </i>subg. <i>Hitcheniopsis,</i> and <i>Hitchenia/Paracautleya/Curcuma </i>subg. <i>Curcuma. </i>The dorsifixed versatile anther of the <i>Curcuma </i>complex has been lost independently in <i>Hitchenia</i> and <i>Stahlianthus</i>, while the basifixed versatile anther has arisen independently in <i>Camptandra</i> and <i>Cautleya/Roscoea. </i>Scanning electron micrographs of anther development in <i>Cautleya spicata </i>show that the appendages develop from the joint connective tissue and thus the anther with the appendages is versatile in mature plant. Observation of the appendages in <i>Curcuma </i>and <i>Paracautleya</i> reveals that the anther is dorsifixed and the appendages are derived from the thecae of the anther.

No description available.

<I>Phylica </I>L. (Rhamnaceae) consists of about 150 species, most of which are found in Cape Province, South Africa. A number of species are found on islands off southern Africa such as St Helena, Tristan da Cunha, New Amsterdam, Mauritius, Reunion and Madagascar. <I>Phylica</I> has two close relatives, <I>Nesiota </I>Hook. f. (a monotypic genus from St Helena) and <I>Noltea</I> Riechb. (a monotypic genus from South Africa). Most of the species on the mainland are ericoid shrubs, whereas some of the island species and the genera <I>Nesiota </I>and <I>Noltea</I> are broad-leaved trees or shrubs that have retained other putatively primitive characteristics. I assessed tribal relationships in Rhamnaceae and relationships of the family itself using DNA sequences from two regions of the plastid genome, <I>rbc</I>L and <I>trn</I>L-F. This revealed that the closest relatives of Rhamnaceae are Dirachmaceae and Barbeyaceae. The plastid trees support the monophyly of the family and provide the basis for a new tribal classification. Three major strongly supported clades are identified, but morphological characters could not be found to underpin a formal taxonomic description of these three clades as subfamilies. A morphological phylogenetic analysis of Rhamnaceae using 18 characters provided less resolution than analysis of molecular characters. Sequences of <I>trn</I>L-F and internal transcribed spacer nuclear ribosomal DNA (ITS) showed that the genera <I>Nesiota </I>and <I>Noltea</I> are sister to <I>Phylica</I> and palaeoendemic within the context of the tribe Phyliceae and the island species of <I>Phylica </I>form an 'island group' embedded within the genus together with the widespread mainland species <I>P. paniculata</I>.

The phylogenetic position of <i>Lathyrus </i>relative to the rest of tribe Fabeae was estimated based on sequence data from the chloroplast <i>matK </i>region. This study included 24 species of <i>Lathyrus </i>(including 19 newly sequenced). A clade containing <i>Lathyrus, Pisum </i>and <i>Vavilovia </i>is strongly supported as monophyletic. The results support the existing morphologically based hypothesis that <i>Pisum </i>and <i>Vavilovia </i>are sister genera. To study relationships within <i>Lathyrus, </i>accessions representing 53 of its species were sequenced for the internal transcribed spacers and 5.8S-coding region of nuclear ribosomal DNA (ITS), and the chloroplast <i>trnL-F </i>and <i>trnS-G </i>regions. Within <i>Lathyrus,</i> the majority of the sections are centred on the Mediterranean region, which appears to be the area of origin for the genus. Sections Orobus, Aphaca, and Pratensis form a northern Eurasian-New World clade. Within this clade, the North American and eastern Eurasian species, including both Holarctic species (<i>L. palustris </i>and <i>L. japonicus</i>), form a transberingian clade of relatively recent origin and diversification. In each phylogenetic analysis, the predominantly South American Notolathyrus group is resolved as monophyletic and unrelated to the transberingian clade. This finding refutes the traditional view that the South American species of <i>Lathyrus </i>are derived from the extant North American-East Asian lineage. The South American lineage may be derived from long-distance dispersals directly from Eurasia. This provides support for long-standing morphologically based hypotheses that sect. Notolathyrus is a natural grouping. A synoptic revision provides the first taxonomic treatment to cover all members of sect. Notolathyrus. The treatment recognises 26 species endemic to South America, plus a subspecies of <i>L. pusillus </i>extending to the southeastern USA. One species (<i>L. bolivianus </i>Kenicer) is described as new.

No description available.