Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

"June 2002" / Bibliography: leaves 179-194. / 194 leaves : ill. (col.), plates (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The overall aim of the research presented in this thesis was to determine if the growth and function of external hyphae of Arbuscular Mycorrhizal (AM) fungi is affected by changes in soil pore size. / Thesis (Ph.D.)--University of Adelaide, Dept. of Soil and Water, 2002

Thesis (Ph.D.) -- University of Adelaide, Dept. of Soil and Water, 2001. / Bibliography: leaves 106-132.

Thesis (M.Sc.)--University of Western Australia, 2003.

Thesis (Ph. D.)--West Virginia University, 2000. / Title from document title page. Document formatted into pages; contains vii, 146 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 126-145).

Thesis (M.S.)--West Virginia University, 1999. / Title from document title page. Document formatted into pages; contains viii, 85 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.

Arbuscular mycorrhizal (AM) fungi are naturally occurring in roots of terrestrial plants. AM fungi are capable of benefiting the host plant through various mechanisms such as enhanced nutrient supply, alleviation of environmental stress and inhibition of plant fungal pathogens. AM fungal spore-associated bacteria have been previously isolated and shown to have plant growthpromoting (PGP) abilities by several authors. Some bacterial isolates are able to promote AM fungal colonisation of host plants and are known to be mycorrhizal helper bacteria (MHB). This study focused on the isolation of AM fungal spore-associated bacteria, characterization of the isolates according to plant growth promoting abilities and evaluation of their potential to enhance plant growth and mycorrhizal colonisation. AM fungi were extracted from soils sampled from natural indigenous forest sources, raspberry (Rubus idaeus cv. Heritage) and strawberry (Fragaria ananassa) farms in South Africa and from a raspberry (Rubus idaeus cv. Autumn Bliss) plantation in Argentina. A total of 52 sporeassociated bacteria were isolated from the external and internal surfaces of AM fungal spore morphotypes from the two countries. The bacterial isolates were evaluated for their PGP abilities such as phosphate solubilisation, indole-3-acetic acid production, ammonia production and inhibition of the fungal pathogens Fusarium oxysporum and Phythophthora nicotianae through mechanisms such as siderophore and/ or hydrolytic enzyme production. A total of 23 bacterial isolates from both South Africa and Argentina showing the most potential to be PGP, were identified molecularly as belonging to the genera Acinetobacter, Alcaligenes, Bacillus, Microbacterium, Micrococcus, Serratia and Staphylococcus. The ability of ten selected bacterial isolates showing multiple PGP capacity were evaluated for their plant growth promotion and mycorrhizal colonisation enhancement ability on raspberry (Rubus idaeus cv. Meeker). Significant differences in increased shoot and root dry weights were shown by the treatments compared to the uninoculated control. The highest increase in shoot and root dry weights were shown by South African (Bacillus mycoides) and Argentinean (Alcaligenes faecalis) isolates. AM fungal colonisation was significantly enhanced by the South African (Bacillus mycoides) and Argentinean (Micrococcus luteus) isolates compared to the AM fungal singly inoculated control.

Wheat crops are known to be devastated by infections of soil-borne pathogens, especially the fungus <i>Gaeumannomyces graminis </i>var. <i>tritici</i> (Ggt) that causes ‘take-all’. Plant growth promoting rhizobacteria (PGPR) such as <i>Pseudomonas fluorescens</i> have received much attention as biocontrol agents against Ggt, mainly due to their ability to produce antibiotics. The polycetide secondary antimicrobial metabolite 2,4-diacetylphloroglucinol (DAPG) is produced by a number of fluorescent pseudomonad strains and is known to suppress Ggt. Another soil microbial group which have been under investigation for their biocontrol potential against Ggt, are arbuscular mycorrhizal (AM) fungi which have the potential to out-compete Ggt and improve host plant nutrition and vigour. In this thesis, I report results from experiments that investigate interactions among AM fungi, Ggt, and DAPG-producing bacteria. A central hypothesis is that carbon flow from plants and AM fungi stimulates DAPG production. I therefore focus on interactions among AM fungi, Ggt and bacteria <i>in vivo</i> with wheat plants and <i>in vitro</i> with only fungal exudates. The synergistic co-operation of pseudomonads and AM fungi against Ggt was demonstrated and the fungal exudates (from AM and Ggt) produced both <i>in vitro</i> and <i>in vivo</i> increased DAPG production by <i>P. fluorescens</i>. The ecology and functioning of beneficial AM fungi was found not to be influenced by the presence of either Ggt or DAPG, highlighting the potential sustainable suppression of “take all” in wheat rhizosphere.

No description available.

Bibliography: leaves 106-132. This project investigated the role of VAM fungi in the growth and nutrition of Linum usitatissimum L. in agricultural soils in southern Australia. It had two general aims: (1) to examine the role of indigenous VAM fungi in the growth and nutrition of linseed in field soil collected near Clare, South Australia; and (2) to examine the effect of VAM fungi on the Zn nutrition of Linola.