Agriculture and Food Systems - Theses
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ItemThe effect of oxygen and carbon dioxide atmospheres on the quality of packaged fresh-cut lettuce( 1999)The present study investigated the potential of using alternative storage atmospheres to maintain microbial and storage quality of fresh-cut lettuce salad mix for longer periods than those currently obtained in air and traditional low oxygen (O2): high carbon dioxide (CO2) modified atmosphere packaging (MAP). The outcome of this research was to assist the freshcut industry through improved shelf life and safe food supply. The effects of modified atmospheres containing air or 100% oxygen at pH 5.0, 6.0 and 7.0, on the growth and survival of two strains of Pseudomonas fluorescens (FSAW 3107 and ATCC 13525) were determined on an agar surface at 5C for 10 days. The aim of this preliminary study was to determine the response of this spoilage organism in a model system where the surfaces of packaged chilled fresh-cut vegetable and MAP conditions were simulated. The results demonstrated the ability of two different strains of Ps. fluorescens to survive and grow in storage atmospheres of up to 100% O2 tested at any of the pH levels, except pH 5.0. The reduction in the pH of the medium to 5.0 was sufficient to inhibit the growth of the bacteria regardless of storage atmospheres. Further studies compared the impact of 100% O2, 80% O2 : 20% CO2, passive MAP and air atmospheres on the microbial growth and storage quality of fresh-cut lettuce mix stored at 5C for 10 days, using four packaging films of differing gas permeabilities. The study also compared and evaluated the suitability of barrier, experimental, and commercial packaging films for using the 80% O2 : 20% CO2 gas mixture. A 100% O2 storage atmosphere maintained with the barrier packaging film inhibited enzymatic browning in lettuce tissue, as determined by visual assessment and colour measurements. On visual examination, the product was still acceptable for consumption after 10 days of storage at 5C, compared to all other film and atmosphere treatments. Polyphenol oxidase activity declined in lettuce stored under 80% O2 : 20% CO2 and passive MAP storage atmospheres, and was the lowest at 100% O2 treatment compared with that of air, and the atmosphere conditions that developed where high permeability experimental films were used. Accumulation of CO2 to levels above 20% in the barrier and commercial packaging films initially flushed with 80% 02 : 20% CO2 gas composition resulted in several disorders in lettuce, such as severe tissue softening and development of off-odours. The same gas mixture used with a high permeability experimental film stabilised at 20.0% O2 and 5.2 % CO2, and the product quality was poorer than in all other treatments except for lettuce stored under air. Fresh-cut lettuce stored in commercial MAP bags had a passively modified atmosphere comprising 0.9% O2 : 17.1% CO2 after 10 days at 5C. The quality of this product was not acceptable after 8 days, due to discolouration of lettuce and off-odours. In conclusion, of the modified atmospheres tested, 100% O2 retained an acceptable visual quality of fresh-cut lettuce salad mix at 5C, without a marked effect on the growth of pseudomonads, Enterobacteriaceae and the total viable count. The choice of film permeability was also demonstrated to be an important factor when using the alternative storage atmospheres. Film permeabilities that would allow development of storage atmospheres containing CO2 above 20% with high oxygen levels, should not be used since this was shown to promote physiological damage of the fresh-cut lettuce.
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ItemSeed dormancy in vetch (Vicia species)( 1999)The aims of this study were to develop appropriate methods for screening Vicia species for dormancy and dormancy mechanisms and determine factors responsible for the development of seed impermeability and how impermeability can be overcome. The materials recommended by the International Seed Testing Association (ISTA 1993 and 1996) for the germination of seeds were evaluated. Loamy sand, paper towel and Petri dishes were all suitable for germination of Vicia seeds. The three types of material have their advantages and disadvantages but the advantages outweighed the disadvantages in the different type of media. The towel method was chosen for this study because it was easier to germinate many seeds (100 seeds per towel) at a time and the towels could be reused until the end of the study. Also, there was no need for regular watering during the tests because towels held enough water for two weeks. The optimum temperature for Vicia seed germination was identified to be between constant 15 and 20C. These results agree with recommendations by ISTA of germinating most Vicia seeds at 20C. A fluctuating temperature of 22/11C also had good germination but the germination rate was reduced. Ten Vicia species and subspecies were assessed for dormancy. Vicia sativa, V. benghalensis, V. ervilia and V. articulata had no impermeable seeds. Almost all the V. villosa accessions had a high level of impermeable seeds ranging from as low as 10% to a high of 60%. Breeding against this trait has been successfully achieved by SEEDCO, a seed company based in South Australia and cultivars with reduced levels of impermeable seeds have been released. The remaining species; V. sativa ssp nigra, V. sativa ssp sativa, V. serratifolia, V. amphicarpa and V. lutea all had higher levels of impermeable seeds ranging from 50 to 95%. These studies concentrated on overcoming impermeable seed coat by mechanical and chemical scarification. Scratching the seed coat with a pin was enough to enhance germination. Commercial scarifier was not as effective as scratching the seed coat with a pin. This could partly explain the need to penetrate the seed coat as achieved by a pin as compared to rubbing off part of the seed coat with sand-paper. The use of sulphuric acid was effective in enhancing germination in Vicia seeds with high proportion of impermeable seeds. Exposure of the seeds to the acid for 30 minutes was effective. Low temperature storage (5C) reduced the level of impermeable seeds in most species. The seed moisture was increased under low temperature storage and this resulted in higher germination. This type of storage is not suitable for long term storage but can be used if the relative humidity is reduced to about 0%. High temperature storage reduced seed moisture and encouraged seed impermeability. Fluctuating temperature of 22/11C reduced the proportion of impermeable seeds. Storage environment also played an important role in the development of impermeable seeds in Vicia. Dry conditions imitated by desiccator reduced seed moisture and resulted in higher levels of impermeable seeds. Seed storage under laboratory conditions had no effect on the proportion of impermeable seed.
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ItemDNA fingerprinting of Ascochyta blight of chickpea caused by Ascochyta rabiei( 1999)Chickpea (Cicer ariatium L.) is an important legume crop in Australia and all over the world. A major limiting factor of chickpea production is ascochyta blight, a devastating disease, caused by the fungal pathogen Ascochyta rabiei (Pass.) Labrousse. Molecular marker methods, including RAPD and ITS analysis, were applied to 33 fungal isolates collected from different regions in Australia. These methods, combined with pathogenicity tests, were able to distinguish true A. rabiei isolates from other nonpathogenic fungal isolates of similar morphology. Molecular markers specific to A. rabiei were detected which can be developed into probe(s) for future A. rabiei identification. A study of the genetic diversity among 33 A. rabiei isolates, sampled from the five chickpea-growing states in Australia, revealed a relatively low level of genetic diversity among the isolates. Two other isolates were shown to be relatively dissimilar at the 105 loci assessed, most likely due to their more recent introduction into Australia. The heterothallic nature of the mating system of A. rabiei is largely responsible for the increases in genetic diversity of this pathogen. Preliminary studies of the mating type distribution in Australia failed to detect mating type 2 (Mat-2) and hence provided evidence of only a single mating type in Australia (Mat-1). The genetic inheritance of the mating type character was investigated using an F I population developed from a single pseudothecium, from a sexual cross between a known Mat-1 isolate from Rosebery, Victoria, Australia and a Mat-2 tester isolate, supplied from the USA. Of the total 74 F1 progeny randomly assessed, 56 isolates were shown to be Mat-1, four isolates were able to mate with both tester isolates (Mat-1 and Mat-2) and the remaining 12 isolates did not mate with either. Due to the possibility of multiple nuclei within single ascospores, the Mendelian nature of the gene(s) involved in mating type was not determined. However, this study represents a first essential step towards elucidating the genetic mechanism controlling the mating type character of Ascochyta rabiei.
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ItemFormulation of a national institutional framework for sustainable irrigation development in the Lao People's Democratic Republic( 1999)The primary objective of the thesis is to develop recommendations for institutional arrangements within various levels of government agencies concerned with irrigation for improved development and management of small scale irrigation in Lao PDR. Secondary objectives of the thesis are the identification of a legal framework to protect the rights of investors, developers and beneficiaries; and the identification of financial arrangements to ensure the availability of funds for construction and development, as well as the generation of funds for effective operation and maintenance. Using experience from studies in other Association of Southeast Asian Nations countries and within Lao PDR, the thesis reviews existing organisational arrangements for the irrigation sub-sector in Lao PDR and makes recommendations for change. It is acknowledged that some of existing arrangements, although not ideal, are unlikely to be changed within the next few years. Funding arrangements for irrigation are set out on the basis that the water users will contribute substantially to costs. Government funding flows are detailed and again it is noted that change is unlikely. The organisation of the National level Department of Irrigation is considered in some detail with recommended roles and responsibilities recommended for five operational divisions. These are the Survey, Study and Design Division; the Technical Management Division; the Operations and Maintenance Division; the Administrative Division; and the Planning and Cooperation Division. Operational units of each of these divisions are also detailed. Staff numbers for each unit have been estimated and the recommended minimum number of staff required to effectively operate the Department of Irrigation is specified. Detailed job descriptions determined from an analysis of the capabilities and needs of the Government and experiences of the literature review, sub-sectoral review and case studies have been published separately. These recommendations are considered to adequately meet the objectives of the thesis.