Thesis (doctoral)--University of Tartu, 2004.

Thesis (M.S.)--Oregon State University, 2000. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 1996. / Typescript (photocopy). Includes bibliographical references. Also available online.

Thesis (M.S.)--University of Kentucky, 2008. / Title from document title page (viewed on December 10, 2008). Document formatted into pages; contains: vii, 56 p. : ill. (some col.). Includes abstract and vita. Includes bibliographical references (p. 47-55).

Thesis (Ph.D.) - University of Queensland, 2004. / Includes bibliography.

Thesis (Ph. D.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains vii, 97 p. : ill. Includes abstract. Includes bibliographical references.

Arbuscular mycorrhizal fungi (AMF) are obligate plant symbionts that colonize the roots of the majority of vascular land plants. These fungi have a unique nuclear organization, in which thousands of nuclei co-exist among an unsegmented fungal body. In individual strains these nuclei can all be genetically similar (homokaryotic) or be derived from two distinct parents (dikaryotic). In other fungal groups the presence of two distinct nuclei in one cell (fungal dikaryons) can change their fitness, function, and symbiotic relationship; begging the question, what impact does the presence of two parental genotypes have on the arbuscular mycorrhizal symbiosis? I am investigating this by measuring the mycorrhizal response (MR) of potato cultivars with different degrees of domestication using representative AMF homokaryons (4) and AMF dikaryons (4). I found that the genetic organization (dikaryotic vs homokaryotic) and domestication status of the host (modern vs old) are both significant factors in the mycorrhizal response of host plants. Specifically, biomass is significantly greater when inoculated with homokaryotic AMF compared to dikaryotic AMF. Dikaryotic strains have low arbuscule colonization in modern cultivars and higher in old, although there are not significant differences in other fungal responses between homokaryotic and dikaryotic AMF. Furthermore, nutrient uptake (N and P) is greater in old cultivars than modern cultivars, although the root:shoot ratio is lower in old cultivars. Analyses of single spores using digital droplet PCR (ddPCR) confirm that nucleotype ratio of dikaryotic spores shifts depending on the host identity. This research provides novel insights into the role of AMF genetic organization in the mycorrhizal symbiosis in greenhouse conditions. In particular, this work shows that the presence of two distinct nucleotypes results in the fungi being more readily adaptable to the host leading to a more stable MR and a potentially selfish strategy, when in symbiosis with potato cultivars.

Arbuscular mycorrhizal (AM) fungi are a group of fungi that are able to establish a symbiotic relationship with the root system of many land plants. This symbiosis improves plant fitness by increasing the uptake of crucial mineral nutrients, particularly phosphorus and nitrogen. In return, the fungi receive organic carbon from the plant host in the form of sugars and lipids. The objective of my research is to assess whether the Nitrate and Peptide Transporter Family (NPF) of transport proteins play a role in mediating AM symbiosis. Firstly, we explored the involvement of NPF genes NPF1B and NPF4.12 by examining the phenotype of Medicago truncatula mutants. Secondly, we employed a modified yeast two-hybrid system to determine the phytohormone import capabilities of these NPF transport systems. Lastly, we employed reporter gene fusions to assess the spatial and temporal expression profiles of these NPF genes. The results of our research do not support our hypothesis that these NPF genes play a role in mediating AMF symbiosis. The results of the modified yeast-two hybrid tests revealed abscisic acid (ABA) and gibberellic acid (GA3) import capabilities of the transport system encoded by the gene NPF4.12. Future study of the diverse mechanisms that underpin AM symbiosis will nonetheless be useful to the agricultural industry by reducing farmer's reliance on chemical fertilizers.

Please read the abstract in the section, 00front, of this document / Thesis (PhD)--University of Pretoria, 2008. / Plant Science / unrestricted

published_or_final_version / Botany / Doctoral / Doctor of Philosophy