School of Agriculture, Food and Ecosystem Sciences - Theses

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    Sustainable use of recycled water for irrigating lettuce
    Ph?m, Th? H� (University of Melbourne, 2009)
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    A genetic evaluation of dystocia in Australian Holstein-friesian cattle
    McClintock, Sara Elizabeth Juliette (University of Melbourne, 2004)
    This thesis presents the first large-scale study of the genetic and non-genetic influences on dystocia (calving difficulty) for dairy cows in Australia, and their costs, focusing especially on the Holstein-Friesian breed, but also with some analyses of frequently occurring crossbreeds. Analyses used data collected since 1986, collected by the Holstein-Friesian Association of Australian and the Australian Dairy Herd Improvement Scheme. The calving traits examined were gestation length, calf size, dystocia (measured as any or none, severe or none, and none, slight and severe). I investigated the influence on calving ease of non-genetic variables such as month of calving, cow age or parity, calf sex, and breed of cow and bull. The genetic parameters were estimated: the heritabilities and genetic correlations between traits calculated, separately for primiparous and multiparous, and for sires, maternal grandsires and the maternal effects. Costs associated with dystocia (such as labour costs, loss or fertility, veterinary costs and deaths of cow and or calf) are estimated, and a cost model for dystocia under Australian conditions is proposed. The influence of crossbreeding on calving was investigated, especially with respect to dystocia and calf mortality. Recommendations are made for improving the recording system and the evaluation of bulls, as the sire of calf and as the sire of cow.
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    Host pathogen interactions of Brassica juncea and Brassica napus with blackleg (Leptosphaeria spp.) in south eastern Australia
    Elliott, Vicki Louise (University of Melbourne, 2009)
    Canola quality Brassica juncea (juncea canola) is a new crop developed for Australian low rainfall environments. It will provide areas previously not adapted to canola production with a viable alternative oilseed crop for use in crop rotations. Blackleg, a fungal disease caused by the pathogens Leptosphaeria maculans and Leptosphaeria biglobosa, is considered a significant threat to the developing juncea canola industry, as well as the existing canola industry. In order to provide an indication of the likely impact of blackleg on juncea canola, data on the long term survival of canola culti va rs against blackleg was evaluated. Erosion of polygenic resistance has been thought to occur in many B. napus cultivars, where the level of resistance has appeared to slowly decrease over time.This study has confirmed that erosion of resistance occurs, with erosion occurring faster in some cultivars compared to others and rates varying between canola growing regions. It is possible, therefore, that the same response may be seen in juncea canola over time. An extensive field survey of internal infection severity of blackleg in juncea canola was undertaken throughout south eastern Australia in 2006 and 2007. Blackleg was found at all sites surveyed and in both years some sites showed significantly higher internal infection in the juncea canola lines compared to the conventional canola cultivars. This is the first report that Leptosphaeria isolates virulent on juncea canola are already widespread throughout the Australian canola growing regions. Leptosphaeria isolates collected from B. juncea stubble were screened for their ability to infect and cause disease symptoms on a set of six Brassica differentials. This was the first survey of Leptosphaeria isolates cultured from B. juncea stubble in Australia. Sixty four L. maculans isolates and eighty eight L. biglobosa �canadensis� isolates were collected from B. juncea stubble over two years (2005-06) and screened over three juncea canola lines and three B. napus lines. As expected L biglobosa �canadensis� isolates caused lower disease severity than the L maculans isolates. However, 13 L biglobosa �canadensis� isolates were capable of causing >50% mean internal infection on at least one of the six Brassica differentials. Although these isolates were cultured from B. juncea stubble, disease severity was low when juncea canola lines were inoculated. The same differential lines were also screened in the field by placing pots containing the differential lines of juncea canola and canola onto 6. napus and 6. juncea stubble from commercial paddocks. At one site B. napus stubble caused higher internal infection severity than juncea stubble in all cultivars except B. napus cultivar ATR- Beacon. At the other site, however, inoculum from B. juncea stubble produced more internal infection in one B. juncea line in 2007 and in four in 2008. The numbers of pseudothecia and discharged ascospores were compared between B. juncea and B. napus stubble. Pseudothecial coverage of stubble and ascospore discharge was assessed in both juncea canola and B. napus over two years, 2007 and 2008. No differences in pseudothecial coverage of the stubble were found between the two species, however, seasonal differences over the three years were observed within both B. juncea and B. napus. Greater numbers of ascospores were discharged from the B. napus stubble, demonstrating that there is a potential for increased disease severity due to increased inoculum production. With a view to minimising the damage caused by blackleg in both juncea canola and canola, the use of a biological control was assessed. Artificial inoculation of B. juncea and B. napus with a L. biglobosa isolate, capable of causing only low disease severity, prior to or at the same time as, inoculation with an aggressive L maculans isolate, reduced blackleg disease severity in both species. The reduction in blackleg severity by inoculating plants with a non-aggressive Leptosphaeria isolate consistently occurred for both B. napus and B. juncea cultivars. The only exceptions were the susceptible 6. napus control cultivars, Karoo and Q2. As discussed earlier, this study demonstrated the potential for erosion of resistance in future in B. juncea cultivars. Although current disease levels are low in juncea canola there is the potential for severity to increase, as virulent isolates are already in the canola growing areas of Australia and inoculum production could increase in the future. Also, the use of highly resistant juncea canola cultivars will likely impose selection pressure on the pathogen population. Disease management practices will play an important part in minimising the effect of blackleg on juncea canola, and breeding tools such as blackleg nurseries will be valuable for early notification about any cultivars in which the resistance becomes less effective over time.
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    The late quaternary palaeoecology of Western Tasmania
    Fletcher, Michael-Shawn. (University of Melbourne, 2009)
    This is a summary of the PhD thesis contained in this volume and supervised by Dr Ian Thomas at the University of Melbourne. This thesis uses pollen analysis to explore the Late Quaternary Palaeoecology of western Tasmania, a cool, wet and humid region that is characterised by a vertiginous relief and distinct flora. Firstly, a comprehensive modem pollen analysis was undertaken to address the following: (i) to test whether pollen spectra can be used to predict vegetation type in western Tasmania; (ii) to test for any relationship between modem pollen spectra and the environment; and (iii) to asses the ability of using pollen spectra in western Tasmania for quantitative palaeoenvironmental reconstmctions. This is the first regional modem pollen assay for western Tasmania and one of the few performed in Australia. Relationships between modem pollen representation and individual plant taxa, plant communities and environmental correlates were quantified using various numerical methods. Modem pollen rain was found to be a good indicator of vegetation type in the modem environment and a significant relationship between pollen representation and average annual temperature was identified. The results of the modem pollen analysis were used to aid the interpretation of a number of pollen cores from the region and to review the current published pollen literature for western Tasmania. Pollen core sites were chosen to address the following: (i) to test the relationship between fossil pollen spectra and temperature change in western Tasmania and the magnitude of temperature change through the Late Quaternary recorded in regional proxies; (ii) to ascertain the nature of vegetation change in western Tasmania during the Late Glacial and Holocene and whether vegetation change over this time was diachronous or synchronous. Vegetation change through the Late Quaternary in western Tasmania was found to have occurred in tandem with regional climatic change, with essentially modem lowland plant taxa established at mid to low altitude during interglacial phases and cold climate plant taxa at these altitudes during glacial phases. Temperature curves produced from transfer functions derived from modem pollen - temperature relationships match regional temperature reconstmctions remarkably. The magnitude of terrestrial temperature change through the Late Quaternary, as reconstmcted by the pollen based transfer function, is markedly less than estimates based on intuitive interpretations of pollen data. The degree of Last Glacial Maximum cooling is almost identical to reconstmctions of ocean temperatures offshore from western Tasmania at this time and it is apparent that objective numerical analyses of pollen data are superior to intuitive estimates. Little vegetation change was found to have occurred through the Late Glacial and Holocene in mid to low altitude western Tasmania, contrary to the dominant regional model of vegetation change for the region. It is apparent that fire has been a significant factor in retarding the post Last Glacial Maximum expansion of rainforest in western Tasmania and that the present mix of fire-promoted and fire-sensitive vegetation in the region has persisted since the Late Glacial at least. One possible explanation for this sequence, which is not evident in any previous interglacial, is the advent of human lit fires after the arrival of Aboriginal people in to western Tasmania approximately 35,000 years ago.
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