School of Botany - Theses
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ItemThe intersection of ecology and evolution: a case study of Eucalyptus in the Grampians Ranges, Australia( 2011)This thesis explores the ecology and evolution of Eucalyptus species in the Grampians ranges, Australia. The Grampians ranges are an ancient isolated collection of three ranges with steep habitat gradients relative to the surrounding homogeneous landscape. This region is a local centre of species diversity and endemism, in which many closely related species interact. I use a range of approaches to understand the ecological and evolutionary history of contemporary patterns of species distribution, traits, and co-occurrence. First, I investigate speciation and gene flow for a clade of Eucalyptus endemic to high elevation rocky outcrops in the Grampians. I document chloroplast DNA structure for the three high elevation species (E. serraensis, E. verrucata, and E. victoriana) and a neighbouring species E. baxteri, which surrounds endemic populations. I found generally high chloroplast diversity, local genetic structuring, and local interspecific gene-sharing. Second, I broaden the scope to include all 20 Eucalyptus species in the region. I am generally interested in relations between species, functional traits, and environments. I model the distribution of species across environmental gradients using a modern niche modelling technique. I incorporate species interaction terms and model groups of species across a taxonomic hierarchy to explore species and clade interactions. Using a subset of variables found to be important in niche models, I then used a hierarchical modelling approach that describes how species responses to environmental variables change as a function of their traits. I used traits from the leaf-height-seed strategy scheme (specific leaf area (SLA), maximum height and seed mass). I found a range of important trait-habitat associations. For example, SLA modified species responses to rock cover such that thicker, denser leaves were found on rocky areas with less soil. Seed mass was associated with edaphic variables such as valley bottom flatness and soil texture. Maximum height of species increased with solar radiation and rainfall. Third, I explored the evolutionary history of these trait-habitat associations with phylogenetically independent contrasts using a phylogeny and niche model estimates. I found a general progression from early divergence of seed mass-edaphic associations to late divergence of height-climatic associations. SLA diverged early with edaphic associations and later with climatic associations. I interpret the early edaphic- late climatic- associations divergences with the paleoclimatic and geologic processes of the Grampians region. Finally, I again explore trait, niches, and phylogenetic relationship, this time in the context of local species assemblages. I address the longstanding observation that within large genera, closely related species do not co-occur in local neighborhoods. I find that habitat drives species assemblages except when species interbreed. I attribute the lack of co-occurrence of reproductively compatible species to reproductive interference via hybridization and introgression. Results from the initial genetics study confirm the importance of geneflow for these species. This approach describes a genetic mechanism underlying an ecological pattern and provides a cohesive story of the ecology and evolution of Eucalyptus in this region.
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ItemThe epidemiology and control of spot form of net blotch of barley in Victoria, Australia( 2011)Spot form of net blotch (SFNB) caused by the fungus Pyrenophora teres f. maculata is a relatively new foliar disease of barley in Victoria. It was first detected during the 1990s and has since become common throughout, due to widespread adoption of stubble retention practices and the cultivation of susceptible varieties. Due to the relatively recent establishment of SFNB, current importance and management strategies have not been investigated. This thesis describes the prevalence of SFNB in Victoria, the associated production loss, effectiveness of chemical fungicides and host plant resistances for future management of this disease. Additionally the genetic and pathogenic diversity of the pathogen population and its ability to develop new virulent pathotypes is reported. The importance of SFNB was investigated during surveys of foliar diseases in barley crops throughout Victoria during 2007, 2008 and 2009. Pyrenophora teres f. maculata was present in more than 90% of crops with severity of up-to 56% on the top three leaves. Severity was typically less than 1% and as a result approximately 25-51% of barley crops grown in Victoria would have experienced grain yield loss, of which the majority was less than 6%. Spot form of net blotch caused significant reductions to grain quality in the Wimmera region of Victoria, with measurements of screenings and retention significantly reduced at two and four out of five trial sites, respectively. This indicates that while SFNB infection was common in barley crops of Victoria, significant production loss was restricted to a low percentage of crops where disease pressure was high. To manage SFNB, a single application of chemical foliar fungicide (propiconazole) was applied at different growth stages of crop development where disease pressure was high. A single application of foliar fungicide at stem elongation (Z31) or flag leaf emergence (Z39) consistently provided the best suppression of SFNB infection, however, these applications did not always maximise grain quality. A range of different fungicides applied to the seed were ineffective in controlling SFNB in the field. Cultivation of barley varieties with host resistance is the best strategy for managing SFNB in Victoria. However, this is reliant on the identification of suitable resistance sources for inclusion into breeding programs. The resistance response of ninety-three barley lines with diverse genetic background was tested toward Australian and North American isolates of P. teres f. maculata as seedlings and as adults. In general, seedling and adult plant resistance was not related with two and fifteen resistant lines identified, respectively. These lines require further investigation to determine the resistance genes involved and to identify suitable molecular markers for their identification in breeding programs. The effectiveness of seedling, adult and complete host resistances in four barley lines was tested. The var. Barque, which possessed complete resistance to SFNB, provided the best control. Varieties with resistance effective at the seedling and adult stages provided control of SFNB in most cases but were generally less effective than Barque, indicating that multiple partial resistances may be required to provide adequate resistance. The population of P. teres f. maculata is genetically and pathogenically diverse and potentially able to overcome host resistances. Analysis of P. teres f. maculata isolates from Victorian barley crops using sequence tagged microsatellite (STMs) primers and mating type primers revealed high genetic diversity and the presence of two-mating types necessary for sexual reproduction. This indicates that the Victorian population of P. teres f. maculata frequently undergoes its sexual cycle and is therefore able to develop new virulent pathotypes. This study has identified several areas of research that can be undertaken in order to better manage this important disease in the future. Further research to determine which of the barley lines identified in this study are suitable for inclusion into barley breeding programs and to monitor the virulences in the P. teres f. maculata population is required. A differential set of barley lines has been proposed for discriminating the effectiveness of resistance sources to P. teres f. maculata.