Thesis (Ph.D.)--Murdoch University, 1999. / Thesis submitted to the Division of Science. Bibliography: leaves 190-217.

Thesis (doctoral)--Swedish University of Agricultural Sciences, 2001. / Includes bibliographical references.

The research presented in this dissertation involves the study of two systems in order to analyze and develop resistance in plants to pathogens. The first study considered the interaction between lettuce (Lactuca sativa L.) and Plasmopara lactucae-radicis, a recently described casual agent of downy mildew. This unique fungus is the only known casual agent of downy mildew that is restricted to the roots of its host. Thirty-eight lettuce cultivars were screened for resistance to P. lactucae-radicis. Two-wk-old lettuce plants grown hydroponically were challenged with this fungus and evaluated 2 and 3 wk after inoculation for resistance. Root necrosis and production of sporangia on roots was considered a susceptible reaction. Five cultivars were determined to be resistant to this fungus. Resistant cultivars, however, were colonized by the fungus but did not support the production of sporangia on roots. Data from F2 and F3 progenies demonstrated that resistance was conferred by a single recessive allele (plr). Fungal infection of susceptible plants resulted in significant decreases in fresh root and shoot weights and leaf number compared to decreases associated with infection of resistant plants. RFLP probes have been identified for mapping the plr gene. The second topic of this dissertation dealt with the development of transgenic tobacco plants that express a chimeric gene that consisted of the 35-S promoter and the coat protein gene of Beet Curly Top Virus, a member of the geminivirus group. Expression of viral coat protein genes in plants has resulted in resistance to the virus from which the coat protein gene was obtained. This type of "coat protein-mediated" resistance has not been demonstrated for any geminivirus. Tobacco leaf discs were inoculated with an Agrobacterium tumefaciens line that contained the chimeric gene. Three transgenic lines were determined by Southern and Northern analysis, and ELISA, to express the chimeric gene and produce coat protein. Trials to determine the resistance of these plant lines to BCTV are pending federal approval.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 115-138).

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

The aim of this PhD was to investigate major gaps in our understanding of how mycorrhizal fungi and aphids interact via their effects on plants, and how these interactions regulate emission of plant volatiles and consequently aphid and parasitoid host location. A series of experiments was designed using broad bean (Vicia faba L.), pea aphids (Acyrthosiphon pisum) and their parasitoid wasp, Aphidius ervi and mixed or single spore cultures of AM fungi as a model system. This PhD has determined that arbuscular mycorrhizal fungi are more important drivers of above-ground ecological interactions than ever considered before. They have key roles in specialist aphid host location and in influencing their development. The antagonistic effect of aphids on functioning of mycorrhizal association suggests that the interactions operate in both directions. However, if plants were supplied with phosphorus the aphids did not affect mycorrhizal colonisation suggesting that at sufficient phosphorus availability plants can tolerate the effect of aphids on mycorrhizal colonisation. This demonstrates how dynamic the multi-trophic systems are and that their outcomes are also influenced by soil nutrient availability, with implications for agricultural practices. This PhD has discovered that underground signals carried through common mycelial networks warn neighbouring plants of aphid attack. This signalling allows plants that receive the signal to initiate their defence system by changing their profiles of volatiles emissions and repel aphids and attract their parasitoids so that they may prevent the attack. Because the signal transfer is rapid it incurs the greatest fitness benefit for the receiving plant and potentially also for the donor of the signal and for the fungi. We now need to determine the wider ecosystem implications of this phenomenon, how the signalling is regulated in nature and in agroecosystems and what the fitness consequences are for each component organism.

Pathogens are one of the prevalent stresses to plants. Resistance mediated by the resistance genes is efficient mechanism for evading the pathogens. To understand the influence of various biotic and abiotic factors on resistance gene promoters, plants having N gene promoter fused with reporter genes were developed. Experiments with tobacco plants revealed that on tobacco mosaic virus infection, the N protein may increase in the cells. Also, extreme temperature may result in decrease in the N protein. The salicylic acid produced during the development of systemic acquired resistance does not hinder the N promoter function. Hence, it can be concluded that the promoter region of resistance genes can be influenced by many biotic and abiotic factors. In the tobacco plants lacking the N gene, infection with tobacco mosaic virus leads to generation of systemic recombination signal. Experiments suggest that this signal can lead to better tolerance of the pathogen in next generation. Also, in the plants which received systemic recombination signal, the resistance gene loci are hypermethylated and the frequency of rearrangement in these loci increases. Hence, the signal results in higher tolerance to pathogen and increased genetic variability in resistance genes. / xvi, 147 leaves : ill. (some col.) ; 29 cm.

This thesis examines a broad spectrum of physiological and silvicultural features of the highly valued woody angiosperm hemi-parasite Santalurn album L. (Indian sandalwood) in relation to its culture in plantations in northern Western Australia. Topics covered include allometry of host and Santalum when grown as single plant pairings in both field and pot culture, nutritional interactions between Santalum and beneficial and non-beneficial hosts, deleterious influences of parasitism on plantation productivity and heartwood induction in young trees. In Western Australia sandalwood is grown in the nursery for 8 months before establishment in the field and during this time a pot host is introduced. Survival of Santalurn after field establishment and its subsequent growth were significantly affected by the time of introduction of the pot host, Alternanthera nana. Increasing the period of the Santalum : Alternanthera association in the nursery to 109 days prior to field establishment markedly increased early growth of Salztalum plantations. Introduction at 134 days prior to field establishment was detrimental to the parasite as the Alternanthera was too vigorous for the small Santalum seedlings. Santalurn plants had a lower root : shoot ratio lower when cultured with Alternanthera in the nursery prior to field establishment compared with seedlings grown without Alternanthera. Alterrzantlzera survival in the field was high when it had been grown with Santalum for 12 weeks or more in the nursery prior to field establishment. After 1 1 weeks in the field a strong negative linear relationship was shown between Santalunz root : shoot ratio and Alternarzthera dry weight, and a positive linear relationship between Salztalum DW and Alternanthera DW. In Western Australia Santalu~n is established in the field with an intermediate host which nourishes the parasite for 3-5 years before Santalum becomes dependent on its long-term host and the intermediate host dies. The relationship between Santalum and several species tested as intermediate hosts was examined by pairing Santalum seedlings with intermediate host seedlings in 25 litre pots over a 10 month period. Growth of Santalum in pot culture with three N2-fixing woody intermediate hosts (Sesbania forrnosa, Acacia traclzycarpa and A. ampliceps), the woody non N2-fixing Eucalyptus camaldulensis or without a host varied considerably between host treatments. Santalum growth was greater and root : shoot ratio lower for seedlings grown with N2-fixing hosts compared with seedlings grown with E. carnaldulensis or with no host. The root : shoot ratio of unattached Santalum increased exponentially over time, whereas for all other treatments it remained relatively constant. An assessment of the value of the hosts, termed host use efficiency, was computed as Santalum shoot DW / host shoot DW. The host use efficiency of A. trachycalpa was greater than that of the other hosts. The xylem sap of hosts and Sarztalum, and ethanolic extracts of endophytic tissue of haustoria of Santalzkm were analysed for amino acids, organic acids and sugars to determine which solutes were available in the host and which were extracted by the Santalum haustoria from different hosts. There were similarities between Santalum and legume hosts in concentration and composition of xylem sap amino acids, and in the amino acid spectra of the corresponding Santalum endophytic tissue, whereas there were low N levels in xylem sap of E. camaldulensis and dissimilarities between its amino acid composition and that of Santalum. This indicated substantial direct intake of xylem N by Santalum from legume hosts but little N from the xylem sap of E. canzaldulensis. There were high concentrations of asparagine, glutamate, aspartate and y-amino glutamate in the xylem sap of the legume hosts, while in the non-legume the most common amino acids were glutamate, aspartate, glutamine and arginine. Proline, the predominant amino acid in the xylem sap of Santalum acurninatum growing in natural vegetation (Tennakoon et al. 1997) was not detected or present in very low concentrations in Santalurn album under these conditions. in the non-legume. Xylem sap of hosts contained variable amounts of sugars (sucrose, glucose and fructose) and organic acids (fumaric, citric and malic acid), whereas that of the parasitic Santalum was dominated by fructose and malic acid. Dissimilarities in the proportional amounts of xylem-borne sugars and organic acids were particularly evident for the E. camaldulensis : Santalum partnership. Diurnal profiles of photosynthesis and transpiration of Santalum were closely similar to those for corresponding hosts, whereas the midday leaf water potential of Santalum was consistently more negative than that of corresponding hosts. Net photosynthesis and water use efficiency was lower, but transpiration rates were similar to that of corresponding hosts. Nitrogen concentrations of foliage of Santalum were higher than their hosts, and higher when on legume hosts than on E. camaldulensis, or without a host. Nitrogen concentrations of Santalum foliage was strongly correlated with net photosynthesis and water use efficiency of Santalum. 813C values of shoot dry matter of Santalum were poorly correlated with instantaneous water use efficiency of Santalum. Tissue water relations of Santalum were similar to that of water-stress tolerant species. S. formosa proved the best host followed by Acacia ampliceps and A. traclzycarpa based on dry matter gains of Santalum. Estimates of heterotrophic gain of C of Santalum when grown in association with the legume hosts over a nine week period indicate 57.9% of C was derived from A. ampliceps, 45.5% from A. trachycarpa and 34.6% fiom S. fomosa. Abundance of haustorial attachments on roots of hosts was poorly correlated to Santalum shoot DW. Root nodules of legume hosts were parasitised by a small proportion of Santalum haustoria. Sodium and phosphorus concentrations of foliage of Santalum were generally higher than that of corresponding hosts. Net gains of calcium, potassium, phosphorus and sodium in Santalum was greatest when grown in association with hosts richest in the corresponding element. Net losses or only small gains of calcium, potassium, phosphorus and sodium were recorded when Santalum was grown with E. camaldulensis or without a host suggesting that Santalum has limited ability for uptake of those minerals through its own root system. To understand the effect of hosts on the productivity of a Santalum plantation a young plantation of Santalum with three host species Cathormion umbellatum, Sesbania formosa and Acacia anuera was selected to study the relationship between host quality and distance of hosts from Santalunz on Santalum health. The selected plantation showed marked decline in health and vigour of both Santalum and hosts between years 3 and 5. Parameters of the host plants were assessed to select the best predictor of Santalunz crown health. The height and diameter growth increment of Santalum between years 3 and 5 was strongly correlated to Santalum crown health. Santaluin crown health and growth increased as host quality increased, and the distance of host fiom Santalum decreased. An index, which combined host quality and the distance of the host from that of Santalum, was a better predictor of Santalum crown health than host distance or quality alone. The age at which heartwood is initiated in Santalum album under plantation conditions in Western Australia in unknown, but in natural stands in India it occurs between 10-13 years of age (Rai 1990). A field experiment was conducted to determine the efficacy of stem injections of paraquat andlor ethrel in initiating heartwood formation in five year old Santalum trees in a plantation. Trees injected with paraquat alone had a significantly greater extension of induced heartwood, both radially and vertically, than those trees injected with ethrel alone or distilled water. Eight months after treatment with paraquat or ethrel or a combination of these chemicals induced heartwood was formed, which had high lipid, and low starch and polysaccharide concentrations compared to the sapwood. Induced heartwood from both chemical treatments and their combinations contained total volatile oil and santalol oil (alpha and beta santalol) concentrations that were equal to or greater than that of naturally formed heartwood and greater than that of sapwood. Moisture content, and concentrations of K and Mg, and in some treatments Ca of induced heartwood were significantly lower than that of sapwood. The thesis concludes with a synthesis of the findings and suggestions for future research, with special reference to mid-rotation aspects of Santaltrm plantation silviculture.

Thesis (Ph. D.)--University of Melbourne, 1994. / Typescript (photocopy). Includes bibliographical references (leaves 235-246).

Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xvii, 232 p.; also includes graphics (some col.). Includes bibliographical references (p. 206-232).