The goal of this study was to evaluate the effect of controlled burns, drought and the presence of arbuscular mycorrhizal fungi (AMF) on a dry coastal grassland in Hawai'i Volcanoes National Park. Two introduced African grasses, Hyparrhenia rufa thatching grass, and Melinis repens - Natal redtop, along with one indigenous grass Heteropogon contortus - pili grass composed most of the cover at the study sites. The response of the grasses to fire, AMF infection potential of the soil, and in situ seedling AMF infection were monitored in the field for three years from 1997 to 2000 at Keauhou, Ka'aha, and Kealakomo in Hawai'i Volcanoes National Park. A greenhouse experiment compared the competitive ability of the three grasses with or without AMP inoculation or water stress. The population dynamics of the three grasses were modeled based on their responses to fire, AMF infection, competition and water. At low fire intensities Heteropogon and Hyparrhenia had similar high survival rates while Melinis had a low survival rate. At higher fire intensities all species had low survival rates. The fire decreased the AMF infection potential of the soil at Kaaha, but in situ seedlings AMF infection levels remained high and not statically between the burned and unburned Kaaha sites. In the greenhouse portion of this study Heteropogon biomass increased in response to AMF infection while the other two species did not respond positively to infection. These results suggest that AM fungi increase the growth of the native species, thereby decreasing the impact of competition from two co-occurring alien grasses. When population dynamics were modeled to include the effects of fire, drought and AMF, Melinis and Hyparrhenia produced more biomass in the simulations than the native grass Heteropogon. Drought and AMF decreased the difference in biomass production between the species but did not reverse the competitive ranking of the species.

Thesis (M.S.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references (leaves 56-61). / x, 61 leaves, bound ill. 29 cm

Serratia entomophila, the causative agent of amber disease, is an endemic bacterium used for the biocontrol of New Zealand grass grub larvae. Although the available biopesticide is effective, its use is limited to areas where sub-surface application is feasible, and is also impacted by soil conditions such as moisture levels and osmolarity. The aim of this study was to elucidate the responses of S. entomophila to osmotic and desiccation stresses in relation to challenges encountered during production, storage and soil application, with the goal of developing a more robust and versatile biocontrol agent. RpoS is a key factor in the stress response of many enteric bacteria. In order to dissociate the effect of RpoS from subsequent cellular stress studies, an rpoS mutant was constructed by site-directed mutagenesis. Assessment of the rpoS mutant showed that RpoS was not implicated in NaC1 or desiccation tolerance of S. entomophila. The rpoS mutant was instead found to have enhanced salt tolerance and could be distinguished from the wild-type by the ability to ferment arabinose, a phenotype that was confirmed through complementation. Complete abolition of the amber disease process was observed using an rpoS strain also missing the Sep virulence genes, suggesting that RpoS is a regulator of the S. entomophila anti-feeding prophage (Afp). These findings indicate a subtle interplay between NaC1 tolerance, virulence and RpoS-mediated regulation of amber disease in S. entomophila. A transposon mutagenesis screen was carried out to identify genes associated with NaC1 tolerance in S. entomophila. Fourteen mutants displaying NaC1 sensitivity were identified, two of which had mutations in genes with potential implications for the formulation of the bacterium as a biocontrol agent. The gene leuO that encodes a LysR-family transcriptional regulator was found to be essential for S. entomophila NaC1 tolerance. The toxicity of increased cellular LeuO from an over-expression vector led to the investigation of the effects of leuO mutation on the proteome. Multiple protein changes observed by two-dimensional gel analysis suggested that LeuO may be a global regulator in S. entomophila, as has been hypothesised for Salmonella species. A second NaC1-sensitive mutant contained an insertion in afp15, the product of which is thought to be involved in assembly of the Afp. As well as being sensitive to NaC1, the afp15 mutant was unable to induce the anti-feeding component of amber disease, again highlighting the link between stress tolerance and virulence in S. entomophila. This study also determined that pre-exposure to NaC1 in conjunction with the provision of exogenous glycine betaine significantly enhanced the survival of S. entomophila either in a desiccated state or after application to soil, regardless of the soil moisture content. The implication of this finding on the future formulation of S. entomophila led to investigation of the underlying genetic mechanisms involved in glycine betaine synthesis and NaC1 tolerance. The genes involved in glycine betaine biosynthesis from choline were identified through genomic comparison, degenerate PCR and primer walking. A 6.5 kb region was sequenced and found to contain four genes with homology and similar chromosomal arrangement to the E. coli bet genes (betTIBA). The S. entomophila betIBA genes comprised an operon, flanked by the divergently-transcribed betT gene whose product is responsible for choline transport. To ascertain the relative transcription levels of components of the bet operon, quantitative RT-PCR was performed. Results of qRT-PCR showed that choline in conjunction with NaC1 induced the greatest levels of bet gene transcription, and that levels of the betA transcript were significantly lower than those of the other bet genes. Examination of the betA 5� non-coding region identified a previously undetected hairpin region, possibly accounting for the observed decrease in betA transcript levels. The findings of this study have significantly advanced our understanding of how S. entomophiia responds to stress, and will contribute to the development of formulation strategies for the production of a robust product capable of application to pasture by a range of teclmiques. In addition, there is significant potential to utilise these findings in the development of other bacterial inocula for a range of biotechnological applications.

Thesis (M.S.)--University of Kentucky, 2008. / Title from document title page (viewed on March 18, 2008). Document formatted into pages; contains: viii, 73 p. : ill. (some col.). Includes abstract and vita. Includes bibliographical references (p. 67-72).

Thesis (M. Ag. Sc.)--University of Adelaide, Dept. of Plant Pathology, 1986. / Includes bibliographical references (leaves 179-185).

Thesis (M. Sc.) (Hons.) -- University of Western Sydney, Hawkesbury, 2000. / Includes bibliographical references (leaves 136-152).

Thesis (M.S.)--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references.

Texte remanié de: Diss.--Technische Universität Berlin, 1981. / Bibliogr. p. 212-219.

Zugl.: Münster (Westfalen), Univ., Diss., 2008

Thesis (doctoral)--Friedrich-Alexander-Universität zu Erlangen-Nürnberg. / Includes bibliographical references (p. 203-214).