School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemNo Preview AvailablePerformance recording of beef cattle in Victoria and adjacent regions(University of Melbourne, 1968)This thesis comprises four chapters. Chapters 1, 2 and 3 report scientific investigations involving performance recording of beef cattle. Chapter 4 contains conclusions and recommendations based on the investigations described in the first 3 chapters. My responsibilities in the preparation of this thesis included a detailed review of the scientific literature on subject matter pertaining to performance recording of beef cattle. This is presented in chapter 1 and this entire chapter was my complete responsibility. Chapter 2 describes the beef cattle breeding industry and the records which were available for this study. I am responsible for the contents and preparation of this chapter. Chapter 3 includes the analysis and interpretation of the records used in this study. Dr. R. G. Beilharz assisted with the statistical analysis. Chapter 4, which includes conclusions and recommendations resulting from this investigation, was entirely my responsibility.
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ItemStudies on the etiology and control of parsnip canker, caused by itersonilia pastinacae channon( 1968)In Victoria, parsnip canker is caused chiefly by Itersonilia pastinacae Channon and, less frequently by Phoma sp.. Inoculation of both fungi into parsnip roots produced typical symptoms of the disease. The morphology of the local isolates of I. pastinacae was compared with others described and the taxonomy of the genus discussed. The fungus was shown to be seed-borne, the infection being carried in plant debris contaminating the seed and also externally on the seed itself. An aerated-steam heat treatment was developed to eliminate this seed-borne infection. In field studies I. pastinacae in naturally infected roots survived at least 12 months burial in soil. When the root was mutilated by removing the stem apical meristem, to promote rapid decomposition, the fungus survival period was reduced to 6 months. In laboratory studies the fungus, impregnated in fibre glass mesh, survived 6 months burial in unsterile soil, whereas the survival period in sterile soil was at least 12 months. Survival was shown to be due to the presence of chlamydospores; mycelium and ballistospores being rapidly lysed. Chlamydospores germinated directly to form ballistospores. I. pastinacae, also had a low competitive saprophytic ability. Field and laboratory studies demonstrated that ballistospore discharge was influenced chiefly by high relative humidity, the presence of rain being more effective than dew. Spore discharge followed a diurnal periodicity, the maximum discharge occurring between 08.00 and 10.00 hr.. Low temperature, however, reduced spore discharge even at optimum R.H. Ballistospore germination studies demonstrated soil fungistasis an effect destroyed by sterilization of the soil. Germination of ballistospores was also influenced by nutrients, either diffusates from parsnip roots and leaves or by a 2% glucose solution. Strepstomyces sp. and Bacillus subtilis were isolated from soil and antagonism towards I. pastinacae exhibited. Cell-free culture filtrates of both antagonists lysed I. pastinacae while incorporation of the filtrates into media reduced the growth rate of the fungus. Sterile soil inoculated with the antagonists also lysed I. pastinacae. Foliage applications of fungicides, particularly those containing copper, reduced the incidence of parsnip canker in the field. Control was also achieved in the field by keeping the developing crowns covered with soil during the growth of the crop.
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ItemA study of pathogens associated with stunted patches and deadheads in Victorian wheat crops( 1968)Between 1959-1966 seven species of root-rotting fungi and barley yellow dwarf virus were consistently associated with stunted patches and "deadheads" in Victorian wheat crops. The fungi occurring in order of frequency were: Fusarium culmorum (W.G.Sm) Sacc., Curvularia ramosa (Bainier) Boedijn, Helminthoaporium sativum Pammell, King and Bakke, Pythium ultimum Trow var. ultimum, Rhizoctonia solani Kuhn, Ophiobolus graminis Sacc. and Fusarium graminearum Schwabe. Barley yellow dwarf virus was found each season in the higher rainfall areas of the State; in 1961 and 1965 it occurred in epidemic proportions in all districts. These organisms may be divided into three groups based upon their ability to reduce yield of wheat under controlled glasshouse experiments. (1) MAJOR REDUCTION BY: Barley yellow dwarf virus; Ophiobolus graminis; Helminthosporium sativum. (2) MINOR R RUCTION BY: Fusarium graminearum, Fusarium culmorum; Rhizoctonia solani; Pythium ultimum. (3) NO REDUCTION BY: Curvularia ramosa Ophiobolus graminie and barley yellow dwarf virus are the most important of these pathogens in Victoria. Both caused yield losses of approximately 45-60% in the field. Under controlled glasshouse conditions they caused highly significant yield losses. Five other fungi investigated caused some losses, but during the period 1959-66 were not of great economic importance. The incidence of these pathogens could be related to climatic conditions before and during the wheat growing season. (1) Highest incidence after a dry winter and wet spring: Ophiobolus graminis; Pythium ultimum. (2) Highest incidence after a mild winter and dry spring: Barley yellow dwarf virus; Fusarium graminearum; Fusarium culmorum; Helminthosporlua ; Curvularia ramosa. (3) Highest incidence when crop sown under wet conditions: Rhizoctonia solani; Pahiuta ultimum.
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ItemA nutrient culture study on the effect of ammonium and nitrate nitrogen on the growth and development of plants( 1968)Five nutrient culture experiments were designed to study various aspects of ammonium and nitrate nutrition in plants. Test plants were zinnia, Iceland poppy, cabbage and parsnip, and these were selected because of their suspected sensitivity to ammonium nitrogen when grown commercially in sterilized soils. Only in one experiment was any attempt made to stabilize the pH of the nutrient culture with very sparingly soluble calcium salts. In all experiments with unbuffered nutrient cultures, the ammonium fed plants made very poor growth. Nitrate fed plants were the most vigorous, and consistantly outyielded those fed both ammonium and nitrate. The order of decreasing sensitivity to ammonium-nitrogen was Iceland poppy, zinnia, parsnip and cabbage. Symptoms of ammonium damage were stunting, loss of turgidity, leaf chlorosis, tip burn, sap extrudation, epinasty, and a severely restricted root system. It was demonstrated with zinnia that ammonium was equally toxic, at all concentrations studied (14 to 84 p.p.m. N). However with nitrate, and ammonium + nitrate,plant growth increased with increase in substrate nitrogen concentration. The presence of nitrate in a culture containing ammonium, delayed or completely prevented the appearance of ammonium toxicity symptoms. However when nitrate was removed, or substituted by ammonium, symptoms rapidly developed. (Iceland poppy). When the pH of the nutrient cultures was stabilized with CaCO3 or CaHPO4, ammonium toxicity symptoms were prevented. The ammonium fed parsnip plants grew equally well as those fed nitrate, and both were outyielded by those fed ammonium + nitrate. Chemical analysis of plants grown in unstabilized cultures, showed the nitrate fed plants to have the highest calcium, magnesium and lowest nitrogen concentration. The reverse was true for ammonium fed plants. The study with zinnias revealed rapid accumulation of nitrate within the plant before the optimum substrate nitrate concentration for growth had been reached. A trace of nitrate was detected in "ammonium" plants. On stabilizing the solution pH, highest plant nitrogen was found in parsnips fed nitrate, and the lowest in those fed ammonium + nitrate. The calcium content in plant tops was comparable between all nitrogen treatments. The pH of the nutrient cultures fell wherever ammonium was present, irrespective of the nitrate concentration. The pH of the nitrate solutions rose following plant growth. A chromatographic study on free amino acids and amides in young cabbage leaves showed that ammonium fed plants had the highest, and nitrate fed plants the lowest concentration. The amino acid composition was not changed with nitrogen treatment, although with the ammonium nutrition, there was a marked build up of proline, serine, glutamic acid and glutaiaine. The possible mechanisms Involved in the toxicity of the ammonium ion are discussed.
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ItemThe dynamics of growth in even-aged stands of Eucalyptus obliqua (l'herit)( 1968)The genus Eucalyptus contains a large number of species suitable for the commercial production of timber, but the history of their forest management is comparatively recent, being initially founded on traditional European experience. Despite this tradition and the fact that many species have certain silvicultural properties in common distinguishing them from other timber producing genera (Jacobs, 1955), there already exists a diversity in silvicultural systems, even for the one species or species association in a single region. This diversity appears to be associated with the development history of the forest region, because there has been a general tendency to perpetuate the characteristic forest structure of a particular area at the time that planned management was commenced. This structure has varied from extensive areas of even-aged stands of a single species to intimate mixtures of species of all ages and sizes in association. The variation in forest structure appears to have developed largely from a diversity in the history of settlement and early exploitation. Fire history, access history, intensity and frequency of past utilization have all played a prominent role in forming the characteristic forest structure of a particular area. Regardless of whether growing in regular or irregular forests, the determination of tree and stand age for the majority of eucalypts is extremely difficult or even impossible. The identification of annual rings is reasonably reliable only for those species growing in subalpine and alpine climatic zones of Australia. Therefore, in the absence of adequate compartment and stand history records, management planning in the eucalypts must be based on methods which do not require precise knowledge of tree and stand age. While age is not normally required for the management of irregular forests, it has been fundamental to the planned management of even-aged forests. The ability to distinguish sites of differing productive capacities is an important aid in forest management. The most popular method of site classification is the site index, which gives stand height at a particular reference age. If age is unknown this method cannot be used and alternative methods of site quality determination have not yet been developed for the eucalypts. (From Introduction)