School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemInvestigations into rhizoctonia root rot resistance in aegilops tauschii and other wild wheat relatives(University of Melbourne, 2005)
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ItemA genetic evaluation of dystocia in Australian Holstein-friesian cattle(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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ItemWeeds in Victorian landscapes(University of Melbourne, 2007)
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ItemModelling spatial variability of wheat yield in the Victorian Southern Mallee(University of Melbourne, 2007)
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ItemNo Preview AvailableDeveloping a reintroduction program for the threatened terrestrial Orchid Diuris fragrantissima(University of Melbourne, 2006)Diuris fragrantissima D. L. Jones et M. A. Clem. is a perennial terrestrial orchid endemic to the state of Victoria, Australia. The species is listed as Critically Endangered in Victoria under the criteria of the International Union for the Conservation of Nature and Natural Resources (IUCN), having suffered a severe population decline since the 1930s. A recovery plan for Diuris fragrantissima has been developed by the Department of Sustainability and Environment (DSE) which includes reintroduction as an important conservation strategy. There is, however, limited research on terrestrial orchid reintroductions, and most of the previous reintroductions reported have been unsuccessful. This study investigated the taxonomic status, genetic diversity, fungal symbiont and ecological requirements for the reintroduction of Diuris fragrantissima. Phylogenetic relationships between D. fragrantissima and some closely related Victorian Diuris species was assessed by direct sequencing of the nuclear ITS and plastid trnT-F regions. Low numbers of maximum parsimonious trees (MPTs), high congruence and strong bootstrap support for clades in both separate and combined analyses indicate that Diuris is monophyletic, with the exception of D. sulphurea, which had uncertain placement. Yellow and purple flowered Diuris species formed well supported monophyletic sister clades. Purple flowered species, including D. fragrantissima were unresolved. Morphological and genetic relationships between species in the D. punctata complex were further investigated at population level using morphometrics and Amplified Fragment Length Polymorphisms. Morphological and genetic datasets were congruent in showing that purple-flowered species formed individual phenetic clusters and that D. fragrantissima was a distinct taxon. D. daltonii clustered within D. punctata, showing that the recent elevation of this variety to species level in 2004 was unwarranted. Levels of genetic variation were comparable between in situ and ex situ D. fragrantissima and its closest relatives. Gene flow was detected among all species (Nm=2.34) and populations (Nm=0.65). Fungi were successfully isolated from ten populations of five Victorian Diuris species. Three fungal isolates (from D. punctata, D. dendrobioides and an ex situ D. fragrantissima plant), germinated seed of D. fragrantissima. Ten fungal isolates were recovered from asymbiotically propagated ex situ D. fragrantissima, nine of which were mycorrhizal, with the ability to induce host seed germination in vitro. Mycorrhizal fungi were also isolated from protocorms and in situ adult D. fragrantissima. Germination percentages were below 55%. Germination was not affected by subculturing. All fungal isolates had ITS regions of at least 94% similarity to Tulasnella calospora. ITS and nLSU sequence data were congruent in showing that all fungi isolated in this study formed a monophyletic clade with high boostrap support. Therefore, although not highly specific for certain isolates, the genus Diuris appears to be specific to a narrow taxonomic group of Tulasnella species in Victoria. Genetic similarity was found between fungi isolated from D. fragrantissima protocorms and adult in situ and ex situ plants. Experimental reintroductions, involving source ex situ D. fragrantissima, showed that plant survival was greater when reintroduced as actively growing seedlings (mean = 49%) rather than dormant tubers (mean = 16%). Tuber size was positively correlated with plant size and health. A combination of support inoculum and soil aeration significantly improved plant growth and survival of spring reintroduced plants but had no significant effect on plants reintroduced in autumn. Fungal inoculum support alone did not improve plant growth or survival in either planting time. Fungi present in plant roots at the time of reintroduction were sufficient to support the transition from nursery to field. Optimum monitoring dates for reintroduced D. fragrantissima were determined to be July, when most plants were emergent, and late October to early November, when stem height and flowering were at their greatest. Fungi were isolated from plants one year after reintroduction, and identified as having ITS regions of >98% identity to isolates from ex situ D. fragrantissima, showing that mycorrhizal relationships persisted in situ. Nine of ten sampled plants in treatments with support inoculum were found to have become associated with the support inoculum, showing that D. fragrantissima was able to form new associations with fungi in situ. This study was successful in developing a reintroduction program for Diuris fragrantissima, by investigating the taxonomic status, morphological and genetic relationships in the Diuris punctata species complex, and their mycorrhizal relationships. The information obtained from this research was used to implement experimental reintroductions of D. fragrantissima, which have survived for over a year, including two dormant seasons.
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ItemMicropropagation and population diversity of the Gymea lily, Doryanthes excelsa(University of Melbourne, 2006)
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ItemNo Preview AvailableSulfur assimilation in Vicia sativa L. : molecular and biochemical characterization of a putative o-acetlyserine (thiol) lyase gene(University of Melbourne, 2006)A putative OAS-TL gene was successfully isolated, cloned, sequenced and characterized from Vicia sativa L. cv. Blanche Fleur. The gene, designated Voas-t15 (GenBank Accession No. DQ456491), was 871 bp long comprising 68 amino acids. The gene was found homologous to Arabidopsis CS26 (GenBank Accession No. NM_111234.3) at the nucleotide level. However, the degree of homology with other plant OAS-TL genes was low and the sequence lacked important protein domains. This was attributed to the high GC regions of the template, which may have led to an incomplete sequence. Phylogenetic analysis clustered the Voas-t15 sequence with other cytosolic OAS-TL genes in the Bsas 5 subgroup. Further evidence that the gene was potentially active and the product localized in the cytosol was gathered through differential centrifugation and OAS-TL enzyme assays. The OAS-TL activity measured in the cytosol accounted for 46% of the total activity. The amount of protein in the chloroplast was 32.2 .tg/mL, which accounted for 76% of the total protein content of the extracted tissue. A 52-kD protein band was detected from the plant cytosolic fraction using native PAGE and OAS-TL enzyme activity staining. Using real-time PCR, differential transcription of Voas-t15 was detected in both leaf and root tissues as a response to sulfur stress. Transcription levels were generally higher in the leaves than roots most probably because the enzymes and reactions of the sulfate assimilation pathway are located in the chloroplasts. The gene copy number of Voas-t15 was determined to be singular using Southern hybridization and digoxigenin labeling. The probable function of the gene was indicated by over-expression of the full length Voas-t15 sequence in the E. coli NK3 mutant strain, lacking the ability to synthesize cysteine. The resultant transformed bacteria were able to grow in minimal media lacking cysteine. Understanding the molecular and biochemical properties of enzymes involved in the plant sulfate assimilation pathway, such as OAS-TL, can be applied to the future development of crops with greater agricultural productivity.
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ItemThe interactive effects of soil water and nitrogen supply on grapevine vigour and juice quality in a cool climate vineyard in North East Victoria(University of Melbourne, 2006)Excess vigour due to abundant N supply is a major problem in cool climate vineyards resulting in poor fruit and wine quality. A study was undertaken to investigate the relationship between grapevine vigour and inherent N-fertility of soil in cool climate vineyards. The study included a laboratory experiment in which the relationship between grapevine vigour and N-mineralization potential of soils from selected cool climate vineyards (Whitlands vineyard in King Valley, Hoddles Creek vineyard in Yana Valley and T' Gallant vineyard in Mornington Peninsula) was determined. The soil at the main site (Whitlands) was a Red Ferrosol. The study showed that the potentially mineralizable-N (No) from soil organic matter (SOM) was high in the selected cool climate regions. Internode length of vines showed reasonable agreement with vine vigour of respective high and low vigour blocks. The positive relationship (R2 = 0.61) observed between No and soil total N indicated the possibility of using No values to interpret mineral-N availability to grapevines in these cool climate regions. Production of mineral-N was highest in the first 10 cm of these deep fertile soils and the correlation between No and soil total N was better in the 0-10 cm layer than the 10-20 cm layer. A field experiment was undertaken to investigate the interactive effects of soil water and soil mineral-N, manipulated through irrigation and inter-row management, on vegetative growth and juice quality of grapevines. There were two main treatments. In one treatment irrigation was applied to keep the surface soil layer close to field capacity (FC) during the growing season. The other treatment was the non-irrigated treatment, where the surface layer was allowed to dry-out during the growing season. There were four inter-row treatments (Control, Ryegrass, Clover and Dead mulch). During the three seasons of the experiment, rainfall, heat degree days and vine water use varied showing the seasonal variability that might occur in a cool climate vineyard. In all three seasons, irrigation resulted in a smaller soil water deficit (SWD) in the irrigated treatment than the non-irrigated treatment during berry development, but the largest difference in SWD between the irrigated and non-irrigated treatments was observed in the last season of the experiment (2003/2004 season). Leaf water potential values (?leaf) observed in vines from irrigated and non-irrigated treatments were well above the stress limit for wine grapes (> -1.5 MPa), which indicated that vines were not stressed even under nonirrigated conditions in this deep clay loam. Seasonal water balance showed that considerable drainage (from 133-148 mm for a comparatively dry year and 302-316 mm in an average year) occurred during winter and early spring when vine water uptake was negligible or very small. This shows the potential for groundwater pollution through leaching of excess NO3- produced during summer months in these viticultural soils. Soil mineral-N contents varied with time due to seasonal changes or due to grapevine or grass uptake and to leaching. High levels were due to increased mineralization and/ or low N uptake by the vines. Even during the period, when the demand for N by grapevines is greatest, there was plenty of soil mineral-N mostly in the form NO3- (250- 294 kg N ha-1). In the comparatively dry year of 2002/2003 there was a significant decline in mineral-N under ryegrass at flowering under both irrigated and non-irrigated treatments. The vigour-inducing effect of irrigation through increased soil water and mineral-N availability was observed as increased internode lengths, summer trimmings and winter prunings. These effects were prominent during the second and third seasons of the experiment. Irrigation increased yield in the first two seasons of the experiment, but the large amount of irrigation applied during the third season had a negative impact on the yield of irrigated vines. Grapevine N status was affected by seasonal variability and irrigation, or as a result of both. Irrigation affected all juice quality parameters in a fairly dry year, when juice from irrigated vines had significantly lower pH, higher titratable acidity (TA) (p < 0.01), lower �Brix and �Baume contents (p < 0.01) than non-irrigated vines. In all three seasons, juice from irrigated vines had lower pH and higher TA than non-irrigated vines indicating that they are the mostly affected juice quality parameters due to increased soil water and mineral-N availability. Use of highly enriched (15NH4)2SO4 (98%15N) as a tracer enabled the depth of mineral- N uptake of vines under irrigated and non-irrigated conditions to be determined. Cumulative mineral-N uptake was four times greater in the irrigated vines than the nonirrigated vines. This may be due to increased N availability and accessibility due to applied irrigation. The differences in SWD (indicating water extraction) in different depth layers suggested that drip irrigation induced more feeder roots in the surface 15 cm of soil. As a result more mineral-N was taken up from 0-15 cm depth layer under irrigation than without irrigation. The results of this experiment confirmed the potential to use irrigation practices as a tool to enhance or lessen N uptake from different soil depths in a deep fertile soil. The 15N natural abundance method was used to assess the contribution of biologically fixed N (BFN) from clover to the vineyard soil. However, the fact that both ryegrass and clover samples from the inter-rows were depleted in 15N and lack of a suitable B value meant that this technique was not effective. The distribution of ?15N values down the soil profile in soil total N and mineral-N fraction indicated that leaching of NO3- was a major mineral-N loss in this highly permeable soil.
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ItemNo Preview AvailableEdaphic and vegetation factors controlling carbon and nitrogen pool sizes and greenhouse gas emissions in south-eastern (sub-alpine) Australia(University of Melbourne, 2005)Climate, vegetation and disturbance regimes in part determine both pools and fluxes of carbon and nitrogen in terrestrial ecosystems. These interactions have not been examined in the Australian Alps. I examined the influence of edaphic and vegetation factors on the size of the pools and fluxes of C and N on the Bogong High Plains (BHP) - a paleoplains formation located at the southern reaches of the mainland alpine formation. Vegetation distribution on the BHP is a function of microclimatic gradients that result from the topography common to the Plains formation. Differences in mean minimum temperatures along the vegetation/topographical gradient were small; usually less than 2 �C separated the different communities. These results might suggest the BHP is at risk of substantial changes in vegetation distribution should there be the predicted 2-4 �C increase in ambient air temperatures in coming decades, and particularly if there is an increase of this magnitude in the minimum temperature or in the diurnal range. Nonetheless there is insufficient data and knowledge to predict if either individual species or communities will acclimate to increasing temperatures or if there will be significant shifts in their distribution. On the other hand, considerable accumulated knowledge suggests soil processes will respond strongly to changes in temperature. Rates of decomposition did not vary amongst communities, however they were strongly correlated with initial litter type (p < 0.001). Such relationships suggest that microclimate exerts control over some elements of the C and N cycles indirectly through its effect on vegetation distribution. Gaseous fluxes of C as CH4 were consistently negative with no effect of vegetation community. Seasonal mean rates of CH4 oxidation ranged from -65 pg m-2 h-1 to -115 ?g m -2 h-1, suggesting that the BHP are a strong sink for atmospheric methane over the entire year. Rates of CO2 flux were generally high with seasonal means ranging from 100 to 700 mg m-2 h-1. Surprisingly, the alpine heathlands were stronger sources of CO2 than the seemingly more productive Alpine Ash forests (p = 0.05) that fringe the BHP. Losses of gaseous N from study plots were strongly stochastic in nature and not correlated with vegetation community. Seasonal mean N2O fluxes ranged from a net uptake of -6 ?g m-2 h-1 to a net flux of 13 ?g M-2 h-1. Fluxes of all three gases displayed general trends with both soil temperature and moisture content in both in situ and in vivo measurements. The greatest moderator of system C and N was undoubtedly fire. Fire stimulated the turnover of soil N through increases in soil inorganic N and pH that remained evident for up to one year following fire, allowing for the possibility of nitrification. Recolonisation of sites following fire further altered C and N dynamics, particularly in the Alpine Ash forest where N-fixing Acacia spp. maintained high levels of soil inorganic N and supported nitrification for up to three years (and possibly longer) after fire. Overall, cycles of C and N in the communities studied here are likely to be only moderately directly affected by changes in climate. On the other hand, there is evidence from this study and others to suggest that increased fire frequency, that may be a result of climate change, has the potential to significantly alter C and N on the BHP.