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"April 22, 2003" / Bibliography: leaves 131-147. / 147 leaves : ill., 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Studies the establishment of tree seedlings in Mediterranean-type oldfields in South Australia to test for a correlation between habitat fertility and the intensity of competition. Also investigates whether resource competition and invertebrate herbivory are confounded with each other. Testing for correlation was carried out using a quantitative literature review in combination with field and glasshouse experiments. Results suggest that direct effects,and indirect effects may be heavily confounded, and that a positive correlation between fertility and the intensity of competition is most probable when a phenomenological definition of competition is used. / Thesis (Ph.D.)--University of Adelaide, School of Environmental Engineering, 2003

The response of Canada milkvetch (Astragalus canadensis var. mortonii) to range and forest improvement practices was studied on a stand of mixed-coniferous forest which was clear -cut and burned in 1963 and 1964, respectively. The field studies were conducted on the Hall Ranch of the Eastern Oregon Experiment Station during the summers of 1968, 1969, and 1970. Canada milkvetch, which was virtually absent at the time of treatment, became one of the most important herbaceous species. The cover, frequency, and density of this species rapidly increased from 1965 to 1967; thereafter, these parameters have decreased, even to the levels of 1965 in some cases. The influence of forest canopy and physical site factor s, viz., soil moisture, soil temperature, and hydrogen ion concentration of the soil were studied. Phenology of seedling, root systems, shoot and flower development, seed production and germination were investigated. Studies were also made on the effects of grazing as they influence flowering, plant height, yield and number s of plants. The population parameters which were studied included cover, frequency, and density. The effects of calcium, copper, and cobalt each alone and in all combinations were studied by growing plants in the greenhouse. In addition, nitrogen fixation and the effect of nitrogen upon root nodulation were examined. The environmental parameters that influence Canada milkvetch are soil moisture and temperature for root nodulation and soil moisture for pod ripening. Soil from areas dominated by Canada milkvetch has higher pH values than soils in the forest and lower values than soils dominated by introduced grass species. In the experimental area, the amount of organic materials on the soil can be correlated with the intensity of grazing. Canada milkvetch begins growth shortly after snow melts, flowers in late June and July, and pods ripen in August. Flowering may begin in early June and continue to September, but the ovaries of the flowers produced early or late abort, because pollination occur s only when a medium sized bumble bee (Bombus sp. ) is the most active. This is the only species which trips the flowers of Canada milkvetch.The greatest amount of damage to the reproductive potential of Canada milkvetch is done by a weevil (Apion sp. ) which lives within the developing pod. At least 50 percent of the pods were destroyed by this insect during the summers of 1968 and 1969. Untreated seeds germinate and produce seedlings at the rate of approximately five percent per month. The rate of germination can be greatly increased by moist heat, but the amount of hard seeds remaining decreases and the amount decayed seed increases. The effects of grazing on this species can be evaluated by plant height, dry weight yield per plant, total yield per unit area, and the number of blossoms per flower stalk. Cattle prefer the inflorescences, but graze the leaves and stems along with the associated species at approximately the same intensity of use. On the other hand, big cattle preferentially graze this species from the time it begins growth in early spring until the animals leave the area. Canada milkvetch was always more productive under a grazing regime of cattle only than under a regime of domestic plus wild animals. Because the vegetation of the experimental area is rather low in the successional hierarchy, rapid changes in the values of cover, frequency, and density have occurred. The importance of Canada milkvetch has steadily decreased since 1967 and the relative importance of grasses has increased. Calcium seems to be required for nutrition and nodulation rather than as an amendment to alter the pH of the soil. Low levels of copper and cobalt also increase growth. Further research is required to adequately define the effects of these elements alone and in combination. Perhaps the successional role of Canada milkvetch can be prolonged by adequate fertility. This research provides an example demonstrating that range and forestry improvement must be coordinated and management intensified in order to maximize the biological potential of a given area. / Graduation date: 1971

In the eastern U. S. and other wheat growing areas of the world, powdery mildew is a major constraint to the production of wheat. Currently, the most effective and economical means of control is to use resistant cultivars. Unfortunately, the diversity of the pathogen population enables the pathogen to overcome new resistance genes, often within several seasons of commercial deployment. Surveys to determine the virulence of the population to a set of resistance genes have been performed in many areas of the world. Often, differential frequencies of virulence at varying geographic areas are extended to infer a putative population structure. Due to selective pressure, virulence frequencies are poorly suited to high-resolution analysis of population structure and results may reflect regional cultivar choices and not underlying population phylogeny. A collection of 206 single-ascospore derived powdery mildew isoaltes were utilized to determine virulence frequencies at varying locations in the eastern U. S. Primers were developed to amplify coding sequences in order to assess single nucleotide polymorphisms within this population, which allowed allowed analyses of the distribution of presumably neutral genetic variation. Dendrograms based on Nei?s standard genetic distance (Gst) indicated clustering of virulence frequencies into northern and southern subpopulations, with North Carolina as the putative boundary between groups. DNA sequence based AMOVA analysis using groups derived from Hudson?s sequence based subdivision test (Snn) support this conclusion. Tests for population richness indicate greater haplotype diversity in Virginia and Delaware; a result with several possible explanations based on the known history of North American wheat cultivation.

Three root-colonizing fungi, binucleate Rhizoctonia (BNR) isolate BNR621, BNR isolate P9023, and Trichoderma hamatum 382 (T382) were studied for suppression of Botrytis blight in geranium and demonstration of induced systemic resistance (ISR) as a mechanism of biocontrol. Root isolations of the BNR fungi confirmed that BNR621 and P9023 colonized the geranium root system. Root colonization is considered a requirement for biocontrol. Induction of resistance to Botrytis blight was observed in geraniums transplanted into potting mix amended with formulations of P9023 and T382 2 weeks prior to inoculation with B. cinerea when grown under environments either highly or less conducive to disease development. In the less disease-conducive environment, P9023 and T382 provided protection equivalent (P<0.0001) to a weekly rotation of fenhexamid and chlorothalonil fungicides. The effects of cellular and biochemical changes of ISR on germination of conidia of B. cinerea and Botrytis blight lesion area and expansion rates were tested in vitro. No differences in conidia germination were observed between treatments at any sampling time, with a mean germination rate of 80% across all treatments. The size of the leaf lesion area was dependent upon the length of time between topdressing of the geranium plants with the biocontrol agents and detachment of the leaves for inoculation. In geranium leaves detached and inoculated 7 days after topdressing with a Pesta formulation of either BNR621 or P9023, AUDPC calculated from lesion area was reduced (P<0.0001). In contrast, leaves detached and inoculated 14 days after topdressing with a formulation of T382 had a smaller (P<0.0001) AUDPC from lesion area than plants treated with a Pesta formulation of BNR621. Based on the overall suppression of Botrytis blight in geranium and the reduction in lesion size observed in the detached leaf assays, a role for restriction of lesion development is suspected in the control of B. cinerea in geranium. In a comparison study, induction of resistance to Rhizoctonia stem rot in geranium cuttings taken from stock plants treated with formulations of BNR621, P9023, or T382 was evaluated. No consistent control of Rhizoctonia stem rot in geranium cuttings by a biocontrol treatment was observed. However, cuttings taken from geraniums topdressed with a Pesta formulation of BNR621 14 days prior to propagation and inoculation had a greater probability (P=0.03) of rooting and growing out to healthy plants as compared to inoculated cuttings taken from untreated stock plants.

Peronospora tabacina Adam. is the causal agent of blue mold or downy mildew of tobacco. The pathogen is a fungus-like organism and is a member of the Oomycota. P. tabacina is an obligate parasite restricted to the genus Nicotiana spp. Identification of the pathogen is difficult since symptoms and signs generally occur 6-12 days post inoculation. The spread of the pathogen occurs through aerial long distance dispersal of inoculum and severe epidemics occur yearly in tobacco growing areas of the world. One objective of this work was to develop a real-time Taq Man assay for the detection and quantification of P. tabacina. Optimization of the assay was established at a final concentration of 450nM of primers and 125nM of probe. The assay was useful for detection of the pathogen down to a lower limit of 1fg of DNA. The pathogen could be detected after 4 days post inoculation. The real-time PCR assay was useful for the specific detection of P. tabacina in field samples, artificially inoculated leaves, roots, and systemically infected tobacco seedlings and could be used as a tool for regulatory agencies interested in the detection of the pathogen. A second objective was to examine the genetic structure of the pathogen in North America, Central America, the Caribbean and Europe and determine the direction of migration of the pathogen. The intergenic spacer Igs2 region of the nuclear ribosomal DNA (rDNA) and the Ras-related protein (Ypt1) gene, and the mitochondrial cytochrome c oxidase subunit 2 (cox2 gene) were used. Populations of P. tabacina were characterized by high nuclear diversity, low population division and a possible mixed sexual and asexual reproductive system. Large population size, the mechanism of dispersal, mutation rate and genetic diversity indicate that this pathogen is a high evolutionary risk plant pathogen. An isolation with migration (IM) model was used to study genetic diversity in the U.S./Central America and the Caribbean (CCAM) and the European subpopulations. Results support migration from the CCAM region, Florida and Texas into the northern part of the U.S. including North Carolina. These data validate previous migration reports of the pathogen by the North American Plant Disease Forecasting Center at NCSU. In Europe estimates for the migration of the pathogen from North Central to Western Europe and both these regions to Lebanon support migration reports for the first introductions of the pathogen into Europe. Mitochondrial sequences of P tabacina and Hyaloperonspora parasitica genome were generated using bioinforrmatics approaches and PCR methodology. One quarter of the mitochondrial genome of P. tabacina has been annotated and compared with that of Phytophthora infestans and Hyaloperonospora parasitica. Similarities in direction, arrangement and number of genes and regions have been found. Results from this research will be useful in understanding the evolutionary history of the Oomycetes as well as future population genetics research to investigate how these organisms adapt, survive and attack plants in a changing environment.

Cyst nematodes in the genus Heterodera are sedentary endoparasites that induce elaborate feeding cells within host roots by secreting proteins produced within nematode esophageal glands into plant cells. Functional analyses of selected cyst nematode parasitism genes that encode such secreted proteins was the objective of this dissertation. Homologs of four parasitism genes initially isolated from Heterodera glycines, including Hg4F01 (annexin-like protein), HgSYV46 (CLAVATA3-like plant peptide mimic), Hg4E02 and Hg5D08 (novel proteins with putative host nuclear localization) were isolated from Heterodera schachtii, which can infect Arabidopsis thaliana. Greater than 90% nucleotide and predicted amino acid identity existed between the four parasitism genes homologs of H. glycines and H. schachtii. mRNA in situ hybridization and immunolocalization confirmed the expression of each gene product exclusively within the nematode esophageal gland cells. Since eukaryotic annexins affect many cellular processes involving calcium-dependent membrane association, the potential function of the Hs4F01 secreted into plant cells was analyzed. Similar to annexin mutants in Arabidopsis, transgenic Arabidopsis expressing Hs4F01 produced no observable plant phenotype, but were more susceptible to nematode infection. Hypersensitivity to osmotic stress in an Arabidopsis annAt1 annexin mutant was reduced (complemented) in mutants that expressed Hs4F01, suggesting a functional similarity of nematode and plant annexins within plant cells. Host derived RNA interference (RNAi) to silence Hs4F01 transcripts significantly reduced the number of H. schachtii females developing on roots that express dsRNA to Hs4F01. Expression of Hs4E02 and Hs5D08 in Arabidopsis produced no observable plant phenotype and susceptibility to H. schachtii was not altered in plants that expressed Hs4E02. Silencing of HsSYV46 using host-derived RNAi demonstrated a significant reduction in the development of nematode females on Arabidopsis roots that expressed double-stranded RNA to HsSYV46. Expression of dsRNA to Hs4E02 and Hs5D08 in Arabidopsis roots did not affect nematode susceptibility. In summary, parasitism gene products confirmed to have cellular functions similar to their plant homologs, including Hs4F01 (annexin-like protein) and HsSYV46 (CLAVATA/ESR-like peptide) were demonstrated by RNAi to have a significant biological role in cyst nematode parasitism of host plant roots.