To localise cytokinins in <I>V. inaequalis</I> infected apple tissue immuno-fluorescence microscopy was employed and demonstrated that cytokinins localised around the <I>V. inaequalis</I> hyphae. PCR and Southern analysis were used in an attempt to identify the gene(s) involved in cytokinin production by <I>V. inaequalis</I>. Cytokinin production was also confirmed for the light leaf spot pathogen of brassicas.<I> Pyrenopeziza brassicae</I>, using HPLC-ELISA. Another plant pathogen, <I>Leptoxphaeria maculans</I>, appeared not to be producing cytokinins under the conditions tested. Cytokinin-O-glucoside cleaving β-glucosidase activity that released free base zeatin from zeatin-O-glucoside was identified for the first time in plant pathogenic fungi. In <I>V. inaequalis</I> cytokinin-O-glucoside cleaving β-glucosidase activity was found to significantly increase, relative to total β-glucosidase activity was found to significantly increase, relative to total β-glucosidase activity, when the fungus was grown under growth limiting instead of nutrient rich-conditions <I>in vitro</I>. A protocol was developed for the purification of the enzyme that produced this activity and it was purified to apparent homogeneity. Attempts were made to gain a handle on the gene(s) involved in producing this activity using heterologous Southern hybridisation to known cytokinin glucoside cleaving β-glucosidases from plants. In addition cytokinin receptors were sought from apple in order to provide a means to assess fungal cytokinin production <I>in planta</I>. Genes might be involved in the biotrophic phase of <I>V. inaequalis</I> infection were sought by constructing a genomic library of <I>V. inaequalis</I>. The library was differentially screened with 1<SUP>st</SUP> strand cDNAs derived from <I>V. inaequalis</I> grown under growth limiting and nutrient rich conditions to identify putative fungal genes expressed <I>in planta</I>. The findings of this study were related to the modes of nutrition of the plant pathogens studied. It emerged that, in general, cytokinin production and cytokinin-O-glucoside cleaving β-glucosidase activity were a feature of biotrophic and hemibiotrophic fungi but not necrotrophic fungi.

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<I>Rhizoctonia solani </I>is a vigorous soilborne, fungal plant pathogen that is responsible for substantial losses to many agriculturally important crops. The pathogen's destructive nature and wide host range has promoted considerable research into its taxonomy, pathology, and ecology, in an effort to develop effective methods of disease control. The population dynamics of <I>R. solani </I>have received considerable attention in regard to plant infection and disease development. However, few studies have focused on the saprophytic population dynamics of this organism that has been described as a saprophyte in which parasitism is largely incidental to saprophytism. The objectives of the present study were to investigate the effects of abiotic and biotic factors, principally incubation temperature and the presence of the fungal antagonist <I>Trichoderma viride, </I>on the temporal and spatio-temporal dynamics of saprophytic populations of two isolates of <I>R. solani </I>under controlled environment conditions. The saprophytic population dynamics of <I>R. solani </I>were investigated using a combination of fungal quantification techniques and inoculum placement studies. After investigation of the Enzyme Linked Immunosorbent Assay, ELISA, as a tool for quantification of <I>R. solani, </I>in comparison with ATP and chitin assays, ELISA was selected as the most appropriate assay for an investigation of population dynamics. Inoculum placement studies were used to evaluate the effects of <I>T. viride </I>on the growth and ability of <I>R. solani </I>to colonise a substrate from varying distances. The progress of the parasitic phase of <I>R. solani </I>is determined by, among other factors, initial inoculum density, propagule size and isolate. This study has shown that saprophytic populations of <I>R. solani </I>exhibit cycles of fungal activity that are affected by interactions between temperature with initial inoculum components and isolate. These factors determine the magnitude, duration and timing of cycles of saprophytic activity, as measured by ELISA. In no instance was the antagonist, <I>T. viride, </I>able to eliminate <I>R. solani</I> within a microcosm. Placement studies, in which propagules of <I>T. viride </I>were placed at varying distances from propagules of <I>R. solani, </I>concluded that the controlling effects of <I>T. viride </I>were localised and limited due to the slow growth of the fungus from its initial substrate in comparison with the growth of <I>R. solani. </I>

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