Bibliography: leaves 169-185.

" August 2002." / Bibliography: leaves 218-235. / viii, 235 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The pathogenicity of Phomopsis taxon 1 is examined in relation to symptom expression and bud loss on grapevines. Phomopsis taxon 1-specific DNA probe, pT1P180, and taxon 2-specific probe, pT1P25, were used to detect Phomopsis taxon 1 and Phomopsis taxon 2 in infected buds, canes and shoots in glasshouse and field experiments. Experiments confirm the isolates of taxon 1 examined did not cause leaf or shoot symptoms associated with Phomopsis cane and leaf spot, and that taxon 2 is more virulent than taxon 1. Suggests that taxon 1 (Diaporthe) is an endophyte which does not cause harm to the grapevine and that chemical control is not warranted for control of taxon 1 on grapevine. / Thesis (Ph.D.)--University of Adelaide, Dept. of Applied and Molecular Ecology, 2002

Tan spot of wheat is an economically significant disease caused by the fungal pathogen, Pyrenophora tritici-repentis. Certain races of the fungus secrete Ptr ToxA (ToxA), a 13.2 kDa proteinaceous host-selective toxin that is responsible and sufficient to cause disease in susceptible wheat varieties. Disease symptoms develop only when the ToxA gene in the fungus and a single gene in the wheat host are expressed. The understanding of this gene-for-gene interaction could be instrumental towards control of the disease and is also being developed as a model system for understanding host-pathogen interactions. Here, this effort is given a solid structural foundation through crystallographic analysis of the ToxA structure. The ToxA structure was solved at 1.65 Å resolution using the anomalous signal from inherently present sulfur atoms. The monomeric toxin adopts a β-sandwich fold of two anti-parallel β-sheets composed of four strands each. The mapping of existing mutation data onto the structure reveals that a sequence of Arg- Gly-Asp(RGD) and surrounding residues required for activity are present on a solvent-exposed loop thereby making them potential candidates for recognition events that are required for ToxA activity. Unexpectedly, after a simple circular permutation, the ToxA structure is topologically identical to the classic mammalian RGD containing fibronectin type III (FnIII) domain, and furthermore the RGD residues are topologically equivalent. These results support the hypothesis that ToxA, like FnIII, interacts with an integrin-like receptor on the host plant cell surface. There has been a renewed interest in the method of using the anomalous signal from sulfur atoms to solve protein structures. As a spin-off of the structure solution work, the data were systematically analyzed to study the effects of crystal decay, resolution and data redundancy on the ability to locate the sulfur positions and subsequent phasing of the protein. The analyses show that the choices made about data redundancy and resolution limits may be crucial for the structure determination and that anomalous correlation coefficients are helpful indicators in making these choices. / Graduation date: 2006

Thesis (M.Sc.)(Microbiology)--University of Pretoria, 2005. / Includes summary. Includes bibliographical references. Available on the Internet via the World Wide Web.

Thesis (M.Sc.(Biochemistry))--University of Pretoria, 2003. / Includes summary. Also available online.

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The fungus Botrytis cinerea is an opportunistic pathogen on a wide variety of crops, causing disease known as grey mould through infections via wounds or dead plant parts. Synthetic fungicides for controlling this disease are fast becoming ineffective due to the development of resistance. This, coupled with consumers world wide becomng increasingly conscious of potential environment and health problems associated with the build up of toxic chemicals, (particularly in food products), have resulted in pressure to reduce the use of chemical pesticide volumes as well as its residues. An emerging alternative to random synthesis is the study and exploitation of naturally occurring products with fungicidal properties. There have been reports on the uses of synthetic fungicides for the control of plant pathogenic fungi. When utilized in two-way mixtures, such fungicides may maintain or enhance the level of control of a pathogen at reduced rates for both components utilized in combinations, or alone at normal rates. For this study it was hypothesize that the addition of plant extracts may enhance the antifungal efficacy of the synthetic strobilurin fungicide, kresoxim-methyl against Botrytis cinerea.

" August 2002." / Bibliography: leaves 218-235. / viii, 235 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The pathogenicity of Phomopsis taxon 1 is examined in relation to symptom expression and bud loss on grapevines. Phomopsis taxon 1-specific DNA probe, pT1P180, and taxon 2-specific probe, pT1P25, were used to detect Phomopsis taxon 1 and Phomopsis taxon 2 in infected buds, canes and shoots in glasshouse and field experiments. Experiments confirm the isolates of taxon 1 examined did not cause leaf or shoot symptoms associated with Phomopsis cane and leaf spot, and that taxon 2 is more virulent than taxon 1. Suggests that taxon 1 (Diaporthe) is an endophyte which does not cause harm to the grapevine and that chemical control is not warranted for control of taxon 1 on grapevine. / Thesis (Ph.D.)--University of Adelaide, Dept. of Applied and Molecular Ecology, 2002