Agriculture and Food Systems - Theses
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ItemStudies of Ascochyta rabiei in Australia( 2005)Ascochyta rabiei (teleomorph: Didymella rabiei) which causes ascochyta blight is the most serious disease of chickpea (Cicer arietinum) in Australia as it causes significant losses in crop yield and quality. Although A. rabiei is heterothallic and genetically diverse elsewhere in the world, a study carried out on Australian isolates collected between 1995 and 2000 identified only one mating type and a low level of genetic diversity within the Australian A. rabiei population. In 2002, ascospores of Didymella rabiei, the sexual state of A. rabiei, were trapped in a discharge chamber, from chickpea stubble naturally infected with ascochyta blight in Western Australia. Examination of the stubble revealed pseudothecia typical of Didymella rabiei. The reported presence of the teleomorph in Western Australia indicated that the second mating type had been introduced into Australia or that the pathogen was capable of a low level of homothallic compatibility, previously undetected. The aims of this research were, to undertake a new survey of Australian A. rabiei isolates, to test for the presence of the second mating type, to determine if there has been a change in the diversity of the Australian population and to investigate if pathogenic variability was displayed among isolates. Sixty-seven isolates collected from chickpea fields in South Australia, New South Wales, Queensland, Victoria and Western Australia during the 2003 cropping season were single spored and confirmed as A. rabiei using a PCR test. The isolates were typed for mating type using MAT gene specific PCR primers and compared with tester isolates from USA. This test revealed that all the 67 isolates belonged to mating type 2 (MAT 1-2), thus, the presence of mating type 1 (MAT 1-1) in Australia could not be confirmed. Sequence Tagged Micro Satellite (STMS) markers were used to examine the genetic diversity of the A. rabiei isolates. The isolates were assessed for allelic variation at 19 microsatellite loci, each of which amplified a single locus. Seven of the loci were polymorphic across all the 67 isolates, while the remaining twelve were monomorphic. Based on the allele profiles at the seven polymorphic loci, 19 distinct A. rabiei haplotypes were identified with a total of 33 alleles. One haplotype constituted 35.8 % of the population and was found in the collections from South Australia, New South Wales, Queensland and Victoria. Cluster analysis did not show a clear distinction between isolates based on the state from which they were collected. Polymorphism across the 19 microsatellite loci revealed a slight elevation in diversity in the 2003-2004 population (Ht = 0.07; compared to 0.02 in the 1995 to 2000 collection) and an increase in the number of haplotypes compared with that detected in the previous study of Australian isolates. To examine the pathogenic variability of the Australian population of A. rabiei, nine isolates were inoculated on five chickpea differentials, ranging from highly susceptible to resistant, under controlled conditions optimal for A. rabiei growth and infection. Eight of the isolates were virulent on the susceptible and intermediate chickpea cultivars but not the resistant cultivar and one isolate was only virulent on the susceptible cultivar. Based on these results the isolates were classified into two pathotype groups. The results obtained from the study of the population structure and the pathogenic variability of A. rabiei in Australia will enable the Australian chickpea breeders to understand the A. rabiei population better for formulating management and breeding strategies.
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ItemEffects of organic applicants in a southern Victorian vineyard( 2007)Mulch is a material applied to the surface of the soil to reduce weed growth and reduce soil moisture loss through evaporation from the soil surface. The use of organic mulches will alter the soil environment. This alteration may include reducing soil temperature fluctuations, increasing soil organic matter, increasing soil microflora populations modifying soil chemical properties and increasing soil moisture retention. An experiment was conducted to compare composted green waste mulch and barley straw mulch with herbicide as alternative means of maintaining the undervine strip in a cool climate vineyard. Plant and soil responses to the different undervine treatments were monitored. Grapevine budburst was retarded, however, by the fourth week of vine growth there were no observable differences in grapevine growth stage. Both mulches stimulated grapevine growth and increased yield, with the compost mulch increasing vegetative growth with respect to fruit yield. The fruit quality parameters juice pH and titratable acidity were not significantly altered by the different undervine treatments. In the second year of the experiment the juice soluble solids were lower on the straw mulched grapevines. The compost mulch increased soil pH and carbon levels. The straw mulch improved soil water retention and the mass of soil fungal hyphae. Both mulches increased soil cation exchange capacity. The straw mulch increased soil exchangeable Mg to a greater extent than was predicted from straw nutrient content. The significant variations seen in soil cation content under the mulch treatments were not observed in the tissue analysis. Mulch can be used in a cool climate vineyard to increased yield without deleterious side effects.
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ItemThe effect on some milking characteristics of cows of changing the flow rate thresholds of automatic cluster removers in a seasonally calving dairy herd( 2004)An experiment to investigate the effects of altering the end-of-milking point values of automatic cluster removers (ACRs) from 0.40 kg/min (Control) to 0.70 kg/min (Fixed ACR), or 1.00 kg/min (Rising ACR) over an extended period from the peak until the end of lactation of a seasonally calving pasture based herd has been conducted at the Victorian Department of Primary Industries Ellinbank research dairy. One hundred and ninety two cows. and heifers were used in the experiment (64 animals statistically allocated to each treatment group). A comparative analysis of results for each treatment group is presented for average milk yield, average milking duration, average maximum milking duration, average milk flow rate, average peak milk flow rate and udder health. The Fixed ACR treatment reduced the average daily milking duration by up to 7.6%, but only for a small portion of the treatment period. The Rising ACR treatment reduced the average daily milking duration significantly by up to 15.3%, for the majority of the treatment period. The Fixed ACR treatment did not reduce the average daily maximum milking duration whilst the Rising ACR treatment reduced the average daily maximum milking duration significantly by up to 17.9%, for the more than half of the treatment period. A marginal increase in average milk flow rate was observed for the Rising ACR treatment. Even though the Rising ACR treatment began the experiment with higher average peak flow rate for AM and PM it declined less than the Fixed. ACR or Control treatment throughout lactation, providing a mechanism for the, removal of the same amount of milk in a reduced time when compared with the other treatments. However the difference observed in peak flow rates was not statistically significant. No difference was found amongst the treatment groups when analysed for new cases of sub-clinical or clinical mastitis. The geometric mean of individual cow cell counts was significantly reduced for the Rising ACR treatment in the latter stages of lactation. Flow rate curves have been constructed from real milking data and are presented as examples of the large variation of actual- flow rate from a cows udder. The flow rates curves are used to track individual cows through lactation to observe changes in the cow's milking characteristics. Theoretical consideration is given to how particular types, or brands, of ACR operate under various conditions and it is shown that the results from this experiment could be replicated by using other types of ACR if they are managed correctly. This study has shown that significant labour productivity. benefits could be achieved by, increasing the ACR end-of-milking point settings to 1.00 kg/min without impacting milk yield. However, further work is suggested to ensure that udder health is not compromised. This is to certify that the thesis comprises only my original work except here indicated in the preface; due acknowledgement has been made in the text to all other material used; the thesis is 19400 words in length, inclusive of footnotes, but exclusive of tables, maps, appendices and bibliography.
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ItemThe Welfare of gestating sows housed in conventional stalls and in large groups on deep litter( 2005)Confinement of breeding sows and gilts is one of the most controversial issues in livestock production and there is worldwide interest in finding alternative housing systems for gestating sows and gilts. The present study was conducted to measure aspects of the . welfare of gestating sows housed in either large groups on deep litter (Hoops) or conventional stalls (Stalls). Six hundred and forty sows were studied, with 40 recently mated sows entering each treatment each week over an 8-week period. Large groups were formed by 40 experimental and 45 non-experimental (n = 85) animals per group. Sows in Hoops had a higher (P < 0.001) number of scratches, presumably due to fighting, particularly in the first week of gestation (25 vs. 3.3 scratches/sow). In addition, there was a strong tendency (P = 0.06) for higher salivary cortisol concentrations in week 1 of gestation in the sows in large group housing (6.29 vs. 4.03 nM), which may correspond to increased aggression as reflected by more scratches and a higher (P < 0.01) return rate to oestrus between 19 and 43 days after mating (13.2% vs. 7.4%). Sows in Stalls had a higher (P < 0.01) incidence of lameness at 9 weeks of gestation (7% vs. 0%), and this treatment difference became more pronounced (P < 0.001) later in gestation (13.8% vs 0.8 %.at week 15). There was evidence that the capability of the immune system of the sows in the Stalls treatment, perhaps as a consequence of stress, was reduced late in gestation: sows in the Stalls treatment had a higher (P < 0.05) percentage of neutrophils (46% vs. 41%) and a lower (P < 0.05) number and percentage of lymphocytes (4.59 x 106 vs. 5.16 x 106 c/mI and 41.6% vs. 46.5%) and consequently a higher neutrophil: lymphocyte ratio (1.22 vs. 0.94, P < 0.05) than sows in the large groups on deep litter. There was a strong tendency (P =.0.06) for a higher reproductive failure in the Hoops treatment (27.3% vs. 14.5%). The Stalls treatment had a higher (P < 0.001) farrowing rate (76.8% vs. 66%) and while sows in Stalls weaned less piglets (P < 0.01) per litter (8.31 vs. 8.97), the average weaning weight of these piglets was higher (P < 0.005) than sows in Hoops (8.69kg vs. 8.01 kg). The combination of these reproductive parameters shows that the sows in the Stall treatment weaned the equivalent of 46 more piglets per hundred mated sows. The results of this experiment suggest that sows housed in large groups on deep litter may have faced greater welfare challenges in the early stages of gestation whereas sows in Stalls may have experienced greater welfare challenges later in gestation. However, further more detailed research on the welfare of gestating sows in these two housing systems is clearly required.
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ItemPrice risk management in the Australian cotton industry( 2004)Over 95 per cent of Australian cotton producers have attempted to manage price risk at some time, through a broad range of management strategies. The findings of this study suggest that the cotton industry has to date, embraced the principals of price risk management more so than other agricultural commodity industries in Australia. Nearly 60 per cent of Australian cotton producers stated that price risk management had a positive effect on their farm business. Findings from the study suggest that price risk management is only one of a suite of business management tools, but when implemented strategically, it can lead to positive outcomes in terms of business planning and ultimately through increased profitability. A lack of understanding of price risk management and, more specifically, recent currency exchange losses and high production risks were the key contributing factors for the 21 per cent of producers who stated that price risk management had a negative impact on their business. Approximately 10 per cent of cotton producers operated dryland production systems. These producers often incurred a broader range of production risks, and the resulting production uncertainty inhibited effective use of some price risk management strategies. One in four cotton producers had an agriculture-related tertiary qualification, yet few (around five per cent) had undertaken any form of specialist price risk management training. While some cotton producers are competent managers of price risk, the primary conclusion from the study is that much of the current uptake and effectiveness of price risk management in the Australian cotton industry generally, is somewhat limited by a lack of producer experience, confidence and understanding of price risk management principles and processes.
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