Thesis (Ph.D.)--McMaster University, 2006. / Supervisor: G.D. Wright. Includes bibliographical references.

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 170-204). Also available in print.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1963. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 91-95).

No description available.

This investigation includes a morphological and cultural study of four rather common pathogenic fungi one of which attacks Zinnia elegans, one Lagerstroemia indica, one Ligustrum lodense and one Euonymus japonica. The problem includes, first, a determination of the genera of these four fungi as revealed by their morphology in natural habitat; second, a determination of the growth and cultural characteristics of these on Cornmeal, Potato, Bean, Prune and Carrot agars; third, a comparison of the growth and cultural characteristics of these in natural habitat with the same on the various agars used; and fourth, an evaluation of the five artificial culture media in so far as their usage is concerned in the growth and cultivation of these four species of fungi.

Call number: LD2668 .T4 1978 A43 / Master of Science

No description available.

Under storage conditions of ambient temperature and relative humidity in South Africa, seed-associated mycoflora proliferates. Fusarium moniliforme is ubiquitous in newly-harvested maize, persisting for variable periods in storage, while Aspergillus flavus may represent the final group of species in the succession of aspergilli after grain storage under high temperature and/or high humidity. Many strains of these fungi produce toxigenic secondary metabolites (mycotoxins) under local storage conditions. Since pathogenic fungi may be present within the tissues of stored seeds, these contaminants will not be eradicated by external fungicide treatment, therefore a possible alternative is biological control. The aim of the present investigation was to ascertain whether certain strains and/or species of Trichoderma have potential as biocontrol agents against the seed-associated pathogenic fungi, Aspergillus flavus and Fusarium moniliforme. A study of the fungal growth in dual cultures revealed that from nine isolates of Trichoderma spp. (T harzianum and T viride), four had a noticeable inhibitory effect on the growth of the pathogenic fungi. Scanning electron microscopical investigation of fungal interaction demonstrated no obvious hyphal penetration by - Trichoderma spp. In addition, significant alteration of Fusarium hyphae, with pronounced collapse and loss of turgor, and production of aberrant conidial heads and microheads by A. flavus were observed. Evidence derived from some biochemical studies revealed that antibiosis (by production of extracellular enzymes, volatile compounds and possible antibiotics) is probably the mechanism involved in the antagonistic effect of the four aggressive Trichoderma spp. The in vitro studies demonstrated that the use of Trichoderma spp. as biocontrol agents against A. flavus and F. moniliforme appears promising. / Thesis (M.Sc.)-University of Natal, 1995.

The genus Bacillus is comprised of Gram-positive, rod-shaped, spore-forming bacteria which are well known for their ability to produce a diverse array of antimicrobial compounds. Ofparticular interest is the ability of certain strains to produce antifungal compounds. Such organisms have the potential for application in agriculture where they can be used as biocontrol agents against selected plant pathogenic fungi. A study was undertaken to further characterize selected Bacillus isolates that exhibit broad spectrum antifungal activity. Dual culture bioassays were used to screen seven selected Bacillus isolates for activity against four plant pathogenic fungi in vitro. All isolates were able to inhibit the pathogens to varying degrees. Two isolates, R29 and B81, were selected for further testing and characterization. Further bioassays were performed on five complex nutrient media which were adjusted to pH S.S and 7, and both incubated at 2SoC and 30°C" respectively. It was found that pH and media composition showed significant influences on the antifungal activities of the isolates tested, but that a SoC temperature difference in incubation temperature did not. Tryptone soy agar was found to give rise to the largest inhibition zones. Both isolates were tentatively identified using standard biochemical and morphological tests. Based on its phenotypic characteristics, R29 was identified as a strain of B. subtilis. B81 proved to be more difficult to assign to a specific group or species of Bacillus, though B. subtilis and B. licheniformis were considered to be the nearest candidates. Genomic DNA was extracted from both isolates and a portion of each of their 16s rDNA genes were amplified and sequenced for homology testing against the GeneBank database. Homology testing confirmed that both isolates were members of the genus Bacillus and most probably strains of B. subtilis. The DNA fragment used for sequencing proved to be too small to give conclusive identification of the isolates. Isolate R29 was selected for further characterization of its antifungal compound/so Growth curve studies using a defined synthetic medium showed that antifungal activity arose during the stationary phase and appeared to be closely linked to sporulation. The antifungal component of cell free culture supematant was extracted using various methods including thin layer chromatography, acid precipitation, hydrophobic interaction chromatography and methanol extractions. High performance liquid chromatography (HPLC) analysis of extracts from acid precipitation and hydrophobic interaction chromatography revealed two active peaks indicating that at least two antifungal compounds were produced. Methanol extracted samples produced the cleanest sample extract but only revealed one active peak from the HPLC fraction . Nuclear magnetic resonance analysis of purified samples indicated that the antifungal compound/s have aromatic complex and peptide structures. The extracted antifungal compounds were Protease K resistant and found to be thermostable at temperatures ranging 80-121oC, and, were active at pH ranges of 3-13. The antifungal compounds were found to exhibit similar properties to known antifungallipopeptides i.e. iturin A and fengycin A and B. Further characterization and identification of the active compounds is recommended usmg methods such as liquid chromatography mass spectrometer and matrix-assisted laser desorption ionisation time-of- flight. The results presented in this dissertation provide a basis from which antifungal compounds produced by strains ofBacillus can be further characterized. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2004.

Thesis (Ph. D.)--University of Adelaide, Dept. of Plant Science, 1996? / Includes bibliographical references (leaves 307-329).