The overall objective of the work presented in this thesis was to investigate roles of arbuscular mycorrhizal ( AM ) fungi in growth and phosphorus ( P ) nutrition of wheat ( Triticum aestivum L. ) in a highly calcareous soil from the Eyre Peninsula, South Australia. The soil used for this study is one of the main soil types used for wheat production in South Australia. It is severely P - deficient, but plant responses to conventional fertiliser application are poor. Although the total P and Colwell - extractable P contents of the soil are high, the resin - extractable P content is very low. Resin - extractable P is better able to predict P availability for plant growth than Colwell - extractable P. The soil is also strongly P - fixing. Moderate levels ( about 20 mg kg [superscript minus 1] ) of resin - extractable P for wheat could only be achieved by adding high rates ( up to 100 mg kg [superscript minus 1] ) of CaHPO4 in this soil. A bioassay with wheat showed that it can be highly colonised by AM fungi in the soil. AM fungi have been shown to improve P nutrition of plants, particularly in nutrient poor soils. They may thus be important for wheat grown in the soil with low amounts of plant - available P such as the one used. The first part of the work involved conventional pot experiments. Effects of AM fungi on wheat were compared between sterilised soil and non - sterile soil, sterilised soil inoculated with non - sterile soil or with Glomus intraradices or noninoculated, with different soil / sand mixes. Colonisation of wheat at 8 weeks was high, with about 75 % of root length colonised for indigenous fungi and 55 % for Glomus intraradices, regardless of the soil treatments. Growth and P uptake of wheat were significantly increased by both indigenous fungi and G. intraradices, irrespective of soil / sand mixes. Effects of indigenous fungi on plant growth were larger in sterilised and inoculated soil than in non - sterile soil. In sterilised soil, increases of plant growth by AM fungi were higher with G. intraradices than with indigenous fungi. Dilution of the soil by mixing with sand reduced plant growth and P uptake of both AM and non-mycorrhizal ( NM ) plants. In another experiment, responses of wheat to AM fungi and P supply were compared with those of clover. Plants were inoculated with four different AM fungi. Colonisation of wheat was lower than clover. Although suffering from P deficiency, NM wheat ( 6 weeks ) grew relatively well with no added P ( P0 ) and application of P at 100 mg kg [superscript minus 1] ( P100 ) increased the dry weight ( DW ). Shoot P concentrations increased with P application and there were positive effects of all AM fungi at P100. In contrast, NM clover ( 8 weeks ) grew very poorly at P0 and did not respond to P application. Clover responded positively to all AM fungi at both P levels, associated with increases in P uptake. The results showed that responses of wheat to AM inoculation and P supply were quite different from those of clover, and emphasized the different abilities of the two species to access P in the very high P - fixing soil used. Responses of two wheat cultivars ( Brookton and Krichauff ) to AM fungus ( G. intraradices ) were also evaluated with different P supplies at two developmental stages ( vegetative and maturity ). Colonisation by G. intraradices of both cultivars was well established at 6 weeks ( ~ 50 % in P0 plants ) and continued to increase up to maturity ( ~ 70 % ), but decreased greatly at both harvests as P supply was increased ( up to 150 mg P kg [superscript minus 1] ). Addition of P significantly increased plant growth, grain yield and P uptake irrespective of cultivar and harvest time, and the optimum soil P for grain yield was 100 mg kg [superscript minus 1]. In both cultivars, a growth depression in AM plants occurred at 6 weeks at all P levels, but this disappeared at 19 weeks with added P. At P0, AM plants produced lower grain yield per plant, but with higher P supply, AM plants produced higher grain yields than NM plants. There was a significant positive effect of AM on grain P concentration at P0, but not at other P levels. Brookton was somewhat more P efficient than Krichauff, and the latter responded more to AM fungi. The results showed that responses of wheat to AM fungi and P supply changed during development. Growth depression induced by AM fungi in low P soil was overcome by addition of moderate amounts of P, resulting in significant increases in grain yield in AM plants. Additional approaches were used to help determine the roles of AM fungi in wheat growth and nutrition. The effects of plant density were tested, as it was expected that increasing density might decrease the negative effects of AM fungi on wheat growth. Large growth depressions were induced by both G. intraradices and Gigaspora margarita in wheat grown at low density, although % colonisation by G. intraradices was higher than by Gi. margarita. With increasing plant density, the growth depressions were smaller, indicating that competition modulates growth responses. Although there may be effects due to competition for soil P, it is clear that with increasing plant biomass per unit soil volume, the AM fungal biomass did not increase in proportion ; in fact, hyphal length density decreased. Accordingly, costs of AM in terms of organic carbon loss per plant decreased with increasing plant density, thus mitigating the growth depression. The results add to the increasing body of evidence that mycorrhizal growth responses of plants grown singly may not apply at the population or community level as in crops. Two compartmented pot systems were used to examine whether the fungal hyphae deliver the P into the plants even in the absence of positive growth responses. An experiment in which plants were constricted in a mesh bag, but hyphae of AM fungi could explore a large soil volume was carried out. Results suggested that AM fungi helped the plants acquire P, although mesh bags did not remove AM growth depression. The experiments in which AM fungi were supplied with [superscript 32]P in a small soil compartment to which only hyphae had access showed that a considerable amount of P was delivered to wheat plants via AM fungi. The original aim was to calculate the percentage of total P entering the plants via the AM pathway. However, realistic values were not obtained probably because of difficulties of determining plant-available P and uneven distribution of hyphae in the soil. It is also possible that plants and AM fungi access different P pools. This study demonstrated the potential roles of AM fungi in growth and P nutrition of wheat grown in the highly calcareous soil from the Eyre Peninsula, South Australia. Further studies on the effects of the interactions between AM fungi and wheat in the field are needed to assess the contribution of AM fungi to plant nutrition. / Thesis (Ph.D.)--School of Earth and Environmental Sciences, 2005.

Thesis (MSc)--University of Stellenbosch, 2006. / Bibliography. Also available via the Internet.

Twelve F(,1) families of alfalfa (Medicago sativa L.) plants having different potential for nitrogenase activity, and the two parental populations were tested for response to mycorrhizal inoculation in a low-phosphate soil mixture in the greenhouse. The purpose of this study was to: (a) determine the effects of vesicular-arbuscular mycorrhizae on growth, nutrition and nodulation of these 14 populations, (b) determine if differences existed between the populations with regard to several morphological characteristics, and (c) determine if certain characteristics can be transmitted across generations. The 14 populations were evaluated under four treatments: control no Myorrhizae, no Rhizobium; Rhizobium alone; Mycorrhizae alone; and the combination of Mycorrhizae and Rhizobium. The growth parameters measured differed significantly among the treatments and among the 14 populations studied, and no significant interaction between the populations and the treatments were found. The dual Mycorrhizae and Rhizobium treatment significantly increased plant height at 30 days and 60 days after planting, leaf area per plant, and plant top-dry-weight at two harvest dates. Mycorrhizal inoculation, however, decreased specific-leaf-weight significantly. Nitrogen fixation parameters such as nodule mass score, fibrous root score, and nitrogenase activity were increased significantly by the dual inoculation of mycorrhizae and rhizobium. The 14 populations differed significantly in nodule mass score, fibrous root score, and nitrogenase activity. Mycorrhizal inoculation increased nitrogen fixation more than plant growth. Correlation coefficients indicated that increased Nitrogenase activity is positively correlated with increased nodule mass, increased fibrous root mass, greater top-dry-weight, and leaf area. A step wise multiple regression showed that 49% of the variation in nitrogenase activity can be explained by the variation due to nodule mass, fibrous root mass, top-dry-weight, and leaf area. Several morphological characters showed a heritable response. Plants selected for high nitrogenase activity and high top dry weight transmitted these characteristics to their progenies.

Ericoid mycorrhizal fungi form mycorrhizal associations with Ericaceae plants and are regarded as essential to the ecological fitness of the plants in extremely nutrition-poor soils world-wide. The culturable fungible assemblages associated with hair roots of Epacris pulchella and Rhododendron lochiae (Ericaceae) from different forest habitats in eastern Australia were investigated using rDNA internal transcribed spacer (ITS) restriction fragment length polymorphisms (RFLPs) and sequence analysis, and the abilities of the fungi to form ericoid mycorrhizas were tested. The functional significance of members of the H. ericae complex, Sebacinaceae and the ectomycorrhizal basidiomycetes are discussed particularly in regard to the possibility of symbiont sharing between Ericaceae and ectomycorrhizal hosts. / Doctor of Philosophy (PhD)

"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 (doctoral)--Oulun yliopisto, 2003. / Includes bibliographical references. Also available in electronic format.

Inoculation of Parthenium argentatum (guayule) with an endomycorrhizal fungus (Glomus intraradices) increased the growth of guayule in saline and non-saline soils low in available phosphorus. Addition of 100 ug/g of P as Ca(H2PO4)2 to soils low in available phosphorus was as efficient as G. intraradices in stimulating the growth of guayule. The concentrations and total plant accumulations of minerals within guayule shoots varied depending on growth of the plants and the minerals assayed. In most cases, the concentrations of Cu, Zn, Mn, Na and Cl increased in the shoot tissues of guayule grown in soils which contained added NaCl. Generally, addition of phosphorus to the soil resulted in decreased concentrations of Cu and Zn and increased concentrations of PO4 in guayule shoots. The total accumulations of minerals by guayule was directly influenced by the biomass of plants. Increased biomass of plants generally resulted in increased total accumulations of the minerals assayed. The influence of mycorrhizae on the accumulations of minerals by guayule grown in a saline soil was evaluated by comparing nonmycorrhizal plants with the same biomass and phosphorus nutrition as mycorrhizal plants. Mycorrhizae increased the concentrations and total plant accumulations of Zn and decreased the content of Cl within guayule shoots. Colonization of guayule roots by G. intraradices was not affected by addition of P to the soil. Addition of NaCl to the soil decreased the formation of arbuscules and vesicles within roots and increased the incidence in which no fungal structures were seen. The combination of P and NaCl added to soil had a synergistic effect on the mycorrhizae of guayule. Addition of both P and NaCl to soil reduced the occurrence of hyphae, arbuscules and vesicles within roots and decreased the overall infection of guayule roots by G. intraradices.

"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 (B. Sc. Hons)--University of Adelaide, 1984. / Mounted photographs. Includes bibliographical references (leaves [62-73]).

Thesis (Ph. D.)--University of Adelaide, 1994. / Includes bibliographical references.