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Boschniakia hookeri Walpers has been found to parasitize the roots of Gaultheria shallon Pursh, Arctostaphylos uva-ursi (l.) Spreng, and Vaccinium ovatum Pursh, all members of the Ericaceae. This is the first documented report of the parasitism of Vaccinium ovatum. The subterranean shoot of B. hookeri originates endogenously from the perennial tubercle of the parasite. The shoot has an eustele, composed of collateral vascular bundles, arranged in four composite fronts and separated by four wide 'leaf gaps.' Pits on metaHylem vessels range from nearly circular to laterally elongated. Rll vessel members have simple perforations. Ouerall, the Hylem of subterranean shoots contained relatively few tracheary elements. Phloem is abundant, with radial series of sieve tube members that have simple sieve plates. Brachysclereids forming large clusters are positioned to both the inside and outside of the vascular bundles. Abundant stomata are present and frequently raised above the shoot surface. RHillary buds along subterranean shoots are capable of producing flowers or branch shoots. Considerable secondary growth occurs in maintained shoots below developing branch shoots. This manifested by the additional production of secondary Hylem and phloem, and the formation of a protective cuticular epithelium. This study of B. hookeri supports the view that the short and fleshy character of the subterranean shoot, increased presence of phloem, reduction of leaves to scales, and a perennial nature are specializations associated with the holoparasitic mode of life.

Thesis (MSc)--Stellenbosch University, 1968. / Please refer to full text for abstract

South Africa has the highest species diversity of ericaceous plants belonging to the Erica genus. There are over 850 identified species in the Cape Floral Region. The Albany Centre of Endemism (ACOE) is located within this region and is a hotspot of diversity consisting of various plant genera. The success of Erica plants is ubiquitously attributed to mycorrhizal relationships they engage in with a diverse group of fungi. This symbiosis is known as the ericoid mycorrhizal (ERM) association. The overall aim of this study was to establish the diversity of root fungi associated with Erica plants using morphological, molecular and 454 pyrosequencing techniques. Six Erica species were identified using leaf and flower morphology according to taxonomic keys. The identified plants were Erica cerinthoides, Erica demissa, Erica chamissonis, Erica glumiflora, Erica caffra and Erica nemorosa. Roots from sampled plants were stained and examined microscopically to determine their mycorrhizal status. Ericoid mycorrhizal associations together with dark septate endophyte (DSE) structures and hyphae that did not form any specific structure were observed in all the roots. In addition arbuscular mycorrhizal (AM) structures in the form of vesicles were detected in E. glumiflora and E. cerinthoides. In order to identify the culturable fungi associated with the respective hosts, sterilised roots were placed on various culture media for cultivation. Thereafter isolated fungi were morphologically classified into 67 morphotypes. These were mostly sterile and darkly pigmented. Non-sporulating mycelia of variable colouration such as white, cream-yellowish, beige, green and brown were also observed. Further identification was carried out using molecular techniques. DNA was extracted separately from pure cultures and amplified using ITS1 and ITS4 primers in a polymerase chain reaction (PCR). Thereafter sequencing and Basic Local Alignment Search Tool (BLAST) were used to identify the isolates to generic level. The fungi were taxonomically classified into 54 operational taxonomic units and 94 percent were Ascomycetes and Helotiales was the dominant order. Unclassified Helotiales with affinities to fungi currently identified as Epacrid root fungus was common in all hosts. Other isolates that were identified included Oidiodendron, Meliniomyces, Phialocephala, Cadophora, Lachnum, Leohumicola Cryptosporiopsis, Chaetomium, Acremonium and Epicoccum species. Basidiomycetes were represented by two OTUs belonging to the genus Mycena. Four OTUs comprised fungi that had no significant alignments in the reference databases. Direct root DNA extraction together with 454 pyrosequencing was used to detect the diversity of culturable and unculturable fungi associated with the identified hosts. The ITS2 region was targeted for sequencing. Although Ascomycetes remained the dominant phyla, Basidiomycetes were also detected in all host plants. Glomeromycota was present in E. caffra and E. cerinthoides. Helotiales was dominant in all Erica plants with the exception of E. cerinthoides and E. chamissonis which were dominated by the order Chaetothyriales. The OTUs identified to genus level included Epacris pulchella root fungus, Oidiodendron cf. maius, Acremonium implicatum, Leohumicola, Lachnum, Capronia and Mycena species. Culture-based techniques and pyrosequencing detected similar fungal composition comprising Ascomycetes, while, pyrosequencing was able to detect Glomeromycetes and Basidiomycetes.

Thesis (MScAgric)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: Characterizing the genetic structure of a pest population can provide an understanding of the factors influencing its evolution and assist in its ultimate control. The aim of the present study was to characterize the genetic structure of woolly apple aphid Eriosoma lanigerum (Hausmann) populations in the Western Cape Province in South Africa. Since this economically important apple pest has not previously been characterized at molecular level, it was necessary to evaluate methods for determining the genetic structure of E. lanigerum populations. Two different molecular techniques were evaluated viz. random amplification of polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP). This study represents the first application of the latter technique to members of the Aphididae. Aphids were sampled from four regions in the Western Cape in South Africa viz. Elgin, Ceres, Vyeboom and Villiersdorp. A spatially nested sampling design was used to establish the distribution of the genetic variance of aphids. A total of 192 individuals from 13 farms were analysed. Ten RAPD primers were chosen for analysis from an initial assay of 25 after fragment reproducibility had been confirmed. For AFLP analysis three different rare-cutting restriction enzymes were evaluated for AFLP analysis, viz. EcoRI, SseI and MluI. The latter yielded the best results in combination with the frequent-cutting enzyme MseI. Twenty-five AFLP selective primer pairs were evaluated, out of which five were chosen for analysis of the total population. Two hundred and fifty AFLP fragments and 47 RAPD fragments were scored for analysis. Both analyses indicated that a low level of genetic variation was apparent in E. lanigerum populations and that no differentiation resulted from geographic isolation. From RAPD analyses it was deduced that all variation could be attributed to differences between individuals. AFLP analysis indicated that, whereas genetic differences in E. lanigerum populations between orchards were negligible, a significant portion of genetic variation could be attributed to differences between farms and individuals within farms. Therefore, AFLP analysis allowed for finer discrimination of the genetic structure of E. lanigerum populations than RAPD analysis and is recommended for studies of other aphid species. The fact that most of the genetic variation present in E. lanigerum populations could be found on small spatial scales indicated that sampling individuals over a wide geographic area was an ineffective way of detecting the genetic diversity present in E. lanigerum populations. The low level of variation in populations is most likely due to the exclusive occurrence of parthenogenetic reproduction, founder effects (including distribution of infested plant material from a limited source) and selective factors such as the use of resistant rootstocks or pesticides. Furthermore, the low level of variation found indicated that the possibility of controlling E. lanigerum in the Western Cape using host plant resistance is favourable. Thus, plant breeders developing resistance to E. lanigerum can expect plant entries to be exposed to most of the genetic diversity present in Western Cape populations, regardless of location. / AFRIKAANSE OPSOMMING: Die bepaling van die genetiese struktuur van 'n landboukundige plaagpopulasie kan lei tot begrip van die faktore wat die populasie beïnvloed en kan uiteindelike beheer vergemaklik. Die doel van die huidige studie was om die genetiese struktuur van die appelbloedluis Eriosoma lanigerum (Hausmann) in die Wes-Kaap Provinsie van Suid-Afrika te bepaal. Aangesien hierdie belangrike appelplaag nie van tevore op molekulêre vlak bestudeer is nie, was dit nodig om metodes vir die bepaling van die genetiese struktuur van E. lanigerum populasies te evalueer. Twee molekulêre tegnieke is geëvalueer, nl. lukraak geamplifiseerde polimorfiese ONS (RAPD) en geamplifiseerde fragment-lengte polimorfismes (AFLP). Hierdie studie is die eerste om laasgenoemde tegniek te gebruik om lede van die Aphididae te bestudeer. Plantluise is verkry van vier verskillende gebiede in die Wes-Kaap Provinsie van Suid-Afrika nl. Elgin, Ceres, Vyeboom en Villiersdorp. 'n Hierargiese sisteem is gebruik om die verspreiding van die genetiese variasie van plantluise te bepaal. In totaal is 192 individue van 13 plase geanaliseer. Tien RAPD inleiers is gekies uit 'n analise van 25 verskillende inleiers nadat fragment reproduseerbaarheid bevestig is. Drie verskillende restriksie ensieme is geëvalueer vir AFLP analise nl. EcoRI, SseI en Mlul. Die beste resultate is verkry toe MluI saam met MseI gebruik is. Vyf-en-twintig AFLP selektiewe inleier pare is geëvalueer waarvan vyf gekies is vir analise van die totale populasie. Twee-honderd-en-vyftig AFLP fragmente en 47 RAPD fragmente is gedokumenteer vir analise. Beide RAPD en AFLP analises het getoon dat daar 'n lae vlak van genetiese variasie in E. lanigerum populasies is en dat geen differensiasie as gevolg van geografiese isolasie ontstaan het nie. Uit RAPD analise is daar afgelei dat al die variasie toegeskryf kon word aan verskille tussen individue. AFLP het aangetoon dat alhoewel verskille in E. lanigerum populasies tussen boorde laag was, kon 'n hoë persentasie van die variasie toegeskryf word aan verskille tussen plase en individue binne plase. AFLP analise het meer insig in die genetiese struktuur van E. lanigerum populasies verskaf, en word dus aanbeveel vir studies van ander plantluise. Omdat meeste van die genetiese variasie oor klein geografiese afstande verkry word, is steekproefueming oor groot gebiede 'n ondoeltreffende manier om die genetiese variasie binne 'n monster te meet. Die lae vlak van genetiese variasie is waarskynlik te wyte aan partenogenetiese vermeerdering, stigter gevolge (insluitend verspreiding van geïnfesteerde plantmateriaal vanaf 'n beperkte bron), sowel as selektiewe faktore soos die gebruik van bestande onderstokke en insekdoders. Verder dui die lae vlak van variasie aan dat die moontlikheid vir beheer deur gasheerplantbestandheid goed is in die Wes-Kaap. Planttelers kan verseker wees dat hulle plante blootgestel sal wees aan meeste van die genetiese variasie in die Wes-Kaap appelbloedluis populasies ongeag hulle ligging.

Bibliography: leaves 172-197.

Bibliography: leaves 172-197. / xvii, 197 leaves : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Soil and Water, 2002?

Commercial AM fungi isolates, Rhizophagus clarus, Gigaspora gigantea, Funneliformis mosseae, Claroideoglomus etunicatum and Paraglomus occulum were tested on four seasonal ornamentals, Dianthus chinensis x barbatus, Impatiens wallerana, Petunia x hybrid and Viola x wittrockiana planted in peat-base medium. The experiment was conducted in a glasshouse with three replicates in a completely randomised design. Various vegetative (height, width, length, number of leaves, leaf area and dry biomass) and reproductive (number of flowers and buds) plant parts were measured in the course of three months. AM fungi was found to increase seedling growth and reduced seedling mortality rate of all the plants studied. Inoculated plants produced more leaves (16-33%) and grew taller (12-28%). Dry biomass of inoculated Dianthus, Impatiens and Viola plants were significantly increased by 25-53%. All plants under low colonisation rates displayed mycotrophic qualities and net growth output thereof were found to be similar to plants with equal or higher colonisation rate. Mortality were less frequent in inoculated plants and they were also less susceptible to transplant shock. / Agriculture, Animal Health and Human Ecology / M. Sc. (Ornamental Horticulture)