School of Agriculture, Food and Ecosystem Sciences - Theses

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    Control of the black field cricket teleogryllus commodus (walker) (orthoptera: gryllidae) in Victoria
    Murphy, Graeme, 1954- (University of Melbourne, 1985)
    Techniques for improving control of the black field cricket Teleogryllus commodus were studied between 1981 and 1985 in series of laboratory and field trials in the western district of Victoria. In the laboratory, techniques were developed for assessing the palatability of substances to T. commodus. A number of plant extracts, especially water and acetone extracts from grasses, and other substances including sucrose and vegetable oils were shown to stimulate feeding in the cricket. Further laboratory trials showed that feeding stimulants could be used to encourage feeding on a commonly used substrate in cricket baits (wheat). Field trials to assess bait attractiveness revealed oats to be more attractive as a bait than wheat or barley. Efficacy trials conducted over consecutive years however, showed no differences in the level of control achieved with baits using wheat, oats or barley as the substrate. In addition, feeding stimulants added to the bait did not improve control, nor did the use of higher baiting rates. The level of control obtainable with the current recommended bait is between 80% and 95%.
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    Genotype environment studies in Pisum Sativum L. in relation to breeding objectives : ideotypes of pea
    Berry, G. J. (University of Melbourne, 1981)
    The overall objective of this thesis is to provide the information necessary to produce new varieties of pea which are more productive, easier to harvest and better suited to present day markets. This thesis defines ideal plant types (ideotypes) of pea and outlines how a breeding programme could produce and test them. Some effects of genotype and environment on morphology, development, growth, nodulation and yield component interactions are documented. Sets of near-isogenic lines, segregating populations and collection lines were grown in environments varying for photoperiod, temperature, daily radiant flux and soil nutrient levels. The results obtained, and reviews of the literature, provided the knowledge necessary to specify ideotypes. The ideotypes are defined at two levels: 1. Traits which confer benefits in terms of increased general adaptation to cropping systems, and 2. Traits which are specific to particular cropping systems and product uses. Increased general adaptation of pea should result from changes to plant form (e.g., leaflets replaced by tendrils, pods clustered at the top of the plant instead of being spread along the stems) and appropriate manipulation of yield components (e.g., high number of seeds/pod rather than many pods/node). Also, total yield of agricultural products from a crop rotation system will depend, in part, on the nitrogen fixing, ability of the pea crop. The time of flowering is an important trait conferring adaptation to specific cropping systems. The ideotypes have a condensed flowering period compared with current cultivars, so it becomes critical that flowering occurs at the optimum time. Models to predict the time of flowering from climatic data are presented for a range of genotypes. Other traits required in specific situations are determined by aspects such as market preferences and disease and insect problems. The genetic control of most of the ideotype traits is known and is relatively simple, so new plant types could be produced rapidly. A breeding programme based on the ideotype concept could use backcrossing to a recurrent parent to combine the desired traits into one plant type. It would be wise to do this on a range of genetic backgrounds and it would be necessary to test the new plant types for negative gene interactions and detrimental pleiotropy.
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    The soil-root interface of Lupinus Albus L. and its significance in the uptake of manganese, iron, and phosphorus
    Gardner, W. K. (William K.) (University of Melbourne, 1981)
    It has been demonstrated using an agar film technique that L.albus is able to dissolve colloids of iron/silicate, iron/ phosphate, aluminium/silicate and aluminium/phosphate and also suspensions of manganese dioxide, calcium mono-hydrogen phosphate and ferric hydroxide. Dissolution of these compounds was most marked in proteoid root regions of lateral roots (dense clusters of 20 laterals of limited growth) and certain regions of the tap root. Soil associated with these root regions was found to contain more protons, reductants and chelating agents than the bulk soil. The effect of iron and phosphorus nutrition was examined in acid washed sand. The effect of phosphorus nutrition was also examined in three soils (acid, neutral and alkaline) under glasshouse conditions. The response of wheat, L.angustifolius and L.albus to phosphorus was compared at three sites (acid, neutral and alkaline) in field trials. Proteoid root formation was found to be predominantly controlled by the phosphorus status of the plant. Manganese uptake in L.albus was related to proteoid root formation, and inversely related to phosphorus supply in both L.albus and L.anqustifolius. The ability of L.albus to utilise soil and added phosphorus decreased as the pH of the soil increased. The role of micro-organisms in proteoid root formation and function was investigated. Proteoid roots formed under sterile conditions, but more formed under non-sterile conditions. The effect of varying root morphology on exudation characteristics in the rhizosphere was examined by computer simulation. The main exudate from the roots of L.albus has been identified by gas-liquid chromatography and mass spectrometry as citric acid. It is hypothesised that citrate ions react with the soil colloid and form a diffusible polymeric ferric hydroxy phosphate which moves to the root surface where it is broken up by a combination of ferrous ion uptake, proton secretion and reduction. An attempt has been made to examine iron in the roots using electronmicroscopy and X-ray microprobe. The results suggest that iron is mobilised about the root system in large amounts, although this is not reflected in above ground parts. The effect of intercropping wheat and L.albus was examined in both glasshouse and field for effects on the mineral nutrition of both species. Wheat intercropped with lupins appears to have access to a larger pool of available phosphorus, manganese and nitrogen than has wheat grown on its own.
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    Efficiency of nitrogen fertilization of dry-seeded rice in south-east Australia
    Humphreys, Elizabeth ( 1986)
    The efficiency and fate of fertiliser nitrogen applied to combine-sown rice were investigated in field experiments in which fertiliser timing, water regime and soil type were varied. The information gained was used to predict strategies for optimising fertiliser efficiency using current techniques, and to predict and test improved fertilisation technologies. The stage of crop growth, water regime and soil properties all had large and interacting effects on agronomic efficiency. On an infertile alkaline grey clay soil, agronomic efficiency of urea applied at sowing was very low (8 kg kg-1) compared with later applications associated with continuous flooding (up to 56 kg kg-1). The low efficiency was due to nitrification and subsequent de-nitrification during the flushing period. Nitrogen-15 balance studies indicated that 80% of the urea nitrogen was lost from the soil-plant system. The rapid nitrification rate and high loss of nitrogen on the grey soil contrasted with the very low levels of nitrate and low losses of nitrogen (10-25%) from urea applied to rice growing on an infertile acidic red soil under alternating conditions of saturation and aeration (sprinkler-irrigation). Furthermore, on a fertile acidic red soil in the same region, other authors have measured large yield responses to nitrogen applied at sowing. These differences highlight the need to consider soil properties and water management when attempting to predict optimum fertilisation strategies. Yields of sprinkler-irrigated rice (managed to replace water lost by evaporation) were reduced by more than 50% compared with rice grown under continuous flood. However, this was not due to decreased plant uptake or increased loss of fertiliser nitrogen in the sprinkler-irrigated treatments. The low yields appeared to be associated with plant water stress, decreased nitrogen mineralization (by approximately half) and location of the fertiliser nitrogen near the soil surface where root activity was probably restricted due to inadequate moisture. On the grey soil, maximum agronomic efficiencies occurred with application shortly before permanent flood or at early panicle elongation. Efficiency was doubled when urea was applied before permanent flood compared with shortly after permanent flood. The greater efficiency appeared to be associated with the deeper transport of the applied nitrogen into the soil, and consequently lower losses by ammonia volatilisation and/or nitrification/de-nitrification. However, even with the most efficient fertilisation strategies, plant 15N recoveries were less than 40%, while losses exceeded 20%. When the 15N balance data were considered in conjunction with the agronomic data,. it appeared that it would be possible to further increase agronomic efficiency if plant recovery of applied nitrogen could be increased. In particular, minimisation of losses of nitrogen (via nitrification/de-nitrification) from fertiliser applied before permanent flood was a most attractive option. Potential methods identified for increasing agronomic efficiency by minimising losses of nitrogen applied before permanent flood were deep placement and the use of nitrification inhibitors and slow release nitrogen sources. Several experiments were conducted in an attempt to improve fertiliser efficiency by banding urea and modified urea sources 5-7 cm below the soil surface before permanent flood. Plant recovery of 15N was increased by up to 20% with banding compared with surface broadcasting. The best recoveries were from urea super-granules (USG). An experimental fertiliser rig and a commercial seeder fitted with a triple disc assembly were used to band the fertilisers in the main plots. There was no significant yield advantage with banded urea over broadcast urea applied before permanent flood. The fertiliser rig caused considerable plant damage. Using the triple disc applicator, it was possible to band fertiliser below the soil surface with minimal soil disturbance, and plant damage, but only under i ideal conditions of soil moisture. Furthermore, where the soil surface was dry and cracked, penetration with the triple discs was no greater than the depth of the cracks into which surface applied urea prills would be washed upon flooding. The yield test of USG was unsatisfactory because of the excessive plant damage with this method. With current technology, there appears to be little scope for improving the efficiency of urea applied before permanent flood by mechanical placement below the soil surface.
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    Lactation in mice as a model to study genetic improvement of dairy cattle in the tropics
    Westra, Paridjata ( 1989)
    In chapter one of this thesis aspects of reproduction and production, mainly milk production were reviewed. Components of reproductive efficiency such as the fertility components: age at calving, service periods, days open, calving interval and non return rate; were also investigated. The physiological relationship between those traits and milk production and persistency, in both temperate and tropical environments, was also considered, as well as longevity or stayability as other alternatives for evaluating reproduction. Attention was put on first and second lactation performance. With a view towards understanding physiological aspects of reproduction and production in dairy cows, the nature of lactation in mice was reviewed from the relatively few works that have been done. The papers reviewed included the role of pre-natal and post-natal maternal effects and the relationship between littersize and milk-yield. Daily yield and lactation from a number of studies were compared. Theories of genotype-environment interaction (GM) and adaptation, as well as their implications, were reviewed in the subsequent part of. chapter 1. Evidence of GEE in dairy cattle (Friesian, Holstein or Friesian-Holstein, crossbred with Friesian, and native) in both reproductive characters and milk production throughout the tropic regions were examined particularly closely. Mating systems and selection responses in genetic improvement programmes also were reviewed. Constraints and shortcomings for the achievement of genetic progress through natural mating, AI and progeny-testing in the tropics were examined in conjunction with attainment of high milk production in the temperate countries. The use of new technology (MOET) for manipulating reproductive efficiency was also introduced in the hope that it can be used to increase breeding efficiency in the tropics. The milk-yield and reproductive . characters, of two genotypes of mice (one genotype had been selected for high early reproductive and milking performance and the other was a random bred control) were measured in the normal and a hot environment to check if GEI were present. Both genotypes had been developed in the normal temperature. Evidence of interaction was found in the second parity and only in reproductive traits, e.g. fecundity, interval between mating and birth of second parity. These results are supported by many studies of GEI for both milk-yield and reproductive characters in dairy cattle in the tropics. Milk production does not show GEI, if the environment is defined merely as temperature. The previous selection of the improved genotype had resulted in positive correlated responses in: litter size and litter weight at birth in the first parity, production characters (growth characters and preweaning weight of the litters) in both parities, and on milk production but not on persistency. The selected line did maintain its superiority across environments. However females from the improved genotype performed worse in almost all characters in the hot environment compared to the normal environment. In an analogy with dairy cattle, the high production capacity of the selected line was not exhibited in the adverse environment. Problems of genetic improvement in the tropics were discussed. They included the use of appropriate selection criteria based on . more knowledge of both physiological and genetical relationships between milk-yield and other-characters, with the aim of increasing adaptability and productivity in the target environment. Other possibilities for genetic improvement of dairy cattle in the tropics and the use of synthetic breeds for overcoming the problems in the long term were also discussed.
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    Studies of the preovulatory LH surge and ovulation in the ewe
    Phillips, David James ( 1989)
    The studies presented in this thesis addressed the hypothesis that the induction of the preovulatory LH surge and ovulation in the ewe involves changes in the pattern of GnRH and gonadotrophin secretion, which can be compromised by the effects of glucocorticoids from the adrenal gland. A series of experiments tested the hypothesis that administration of exogenous GnRH or gonadotrophins could induce the growth of follicles to the point of ovulation in ewes deficient in endogenous gonadotrophins. A number of regimes were tested in hypophysectomized ewes where the timing, dose and type of exogenous gonadotrophin varied, but none of these could elicit ovulations consistently. When one of these regimes was administered to hypothalamic-pituitary disconnected (HPD) ewes, a greater response was obtained (33% of ewes ovulating versus 4% in hypophysectomized ewes). Administration of exogenous pulses of GnRH was able to elicit ovulations in HPD ewes consistently (88% of ewes ovulated). These findings imply that a pituitary factor besides the gonadotrophins may be important for the normal growth and ovulation of follicles. In another group of experiments, exogenous regimes of GnRH were administered to ovariectomized HPD ewes to test whether modifications in GnRH input could effect changes in LH secretion during an oestrogeninduced LH surge. It was found that `signal' pulses of GnRH, as either a single large pulse or a rapid series of smaller pulses, were required to initiate an LH surge in the presence of oestrogen. These `signal' pulses of GnRH were unable to cause a similar surge of LH in the absence of oestrogen. A continuous infusion of 250 ng/hour GnRH decreased the magnitude of the oestrogen-induced LH surge compared to 250 ng pulses of GnRH, but elicited a significantly greater response than if GnRH input was abolished, suggesting that the basal secretion of GnRH as well as the pulsatile format was important in eliciting an LH surge. When the continuous infusion was doubled to 500 ng/hour, this treatment was as effective as the 250 ng pulses of GnRH, whereas decreasing the GnRH pulse amplitude from 250 ng to 125 ng had no effect. These findings suggest that an increased baseline level of GnRH secretion can overcome the lack of pulsatile input, and that within the range tested, the amplitude of the GnRH pulses is not critical during the oestrogeninduced LH surge. Removal of GnRH inputs following the initiation of the oestrogen-induced LH surge significantly decreased in the amount of LH secreted compared to when GnRH pulses were maintained, showing that GnRH input to the pituitary gland is still required once the LH surge has begun. To investigate the hypothesis that gonadotrophin subunit mRNA levels are dynamic during an oestrogen-induced LH surge, ovariectomized and ovariectomized HPD ewes were treated with oestrogen and sacrificed at various times during the short-term negative and positive feedback events. In the ovariectomized ewes, all gonadotrophin mRNA levels decreased progressively, with LH/3 mRNA levels being significantly less than control values by the onset of the LH surge, whereas FSH/3 and a subunit mRNA levels declined significantly during the LH surge. These findings are at variance with those reported for ovary-intact ewes, suggesting that the mechanisms responsible for the LH surge in ovariectomized ewes treated with oestrogen may be different from those involved in the preovulatory LH surge. In the ovariectomized HPD ewes, the levels of a subunit mRNA levels diminished after treatment with oestrogen, whereas the levels of LHJ3 and FSH/3 mRNA levels were unchanged, implying that the a and f3 gonadotrophin subunits may be differentially regulated. Another series of experiments investigated the hypothesis that the synthetic glucocorticoid, dexamethasone, modified reproductive function. Chronic administration of dexamethasone at rates of up to 2 mg/day had little or no effect on gonadotrophin secretion, the incidence of behavioural oestrus or ovulation rate in either the breeding or non-breeding seasons. Based on these findings, it was revealed that in the ewe, the induction of the preovulatory LH surge involves changes in the pattern of GnRH and gonadotrophin secretion, but that glucocorticoids from the adrenal gland have, at most, only a minor role in modulating these processes.
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    Growth of Pinus radiata (D.Don) stands in relation to intra- and inter-specific competition
    Bi, Huiquan ( 1989)
    This study investigated the growth of even-aged Pinus radiata stands in relation to intra-specific and inter-specific competition. The first part of the thesis used a data set of 30 year experiments together with a glasshouse experiment. A maximum stand biomass-density line was estimated for the P. radiata stands undergoing self-thinning. This line constrained the stand biomass-density trajectories of the individual stands. Growing along the trajectories, most stands increased the skewness of tree size distribution and the size hierarchy of the population. This was closely related to competitive status-dependent growth and death of trees in the stands. Height/diameter ratio decreased with competitive status. The relationship between them did not change significantly during stand growth. The experiment with P. radiata seedlings implied that competition for light was relatively important in affecting the growth, allocation and allometry of P. radiata during intra-specific competition. The second part of the thesis studied a 10 year old P. radiata plantation invaded by Eucalyptus obliqua. The study was done in conjunction with a replacement experiment with P. radiata and Eucalyptus regnans seedlings. The experiment revealed that P. radiata was more aggressive towards Eucalyptus regnans at the seedling stage. In P. radiata stands invaded by E. obliqua, the size and stem form of P. radiata was closely related to the polygon area defined by its by' E. obliqua neighbours. As the density of E. obliqua increased, its rooting density also increased. This related closely to the decrease in (1) rooting density, (2) aboveground tree size, (3) total projected leaf area, (4) total stem volume and to the increase in the skewness of size distribution and the size hierarchy of the P. radiata populations. The results suggested that competition for water and nutrients was relatively important for P. radiata in competition with E. obliqua in these stands.
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    Effects of urea and superphosphate fertilizers and soil moisture and temperature on forest soil respiration in a radiata pine plantation
    Ba Than ( 1987)
    The effect of urea and superphosphate fertilizers and the influence of temperature and soil moisture on forest soil respiration were investigated over a 9- month period. The investigation was conducted in an 18- year-old Pinus radiata D.Don. plantation in southeastern Australia. The fertilizers were applied to the forest floor at two rates (200 and 400 kg N ha-1, and 100 and 200 kg P ha-1) in a 3 x 3 factorial design. Soil respiration was measured as CO2 evolution using a soda lime absorption technique. Measurements were conducted at 14-day intervals from the 18th November, 1985 to the 6th August, 1986. The influence of temperature and soil moisture on soil respiration was more marked than fertilizer application, rates being highest when soil moisture was non-limiting. When soil moisture was under 12.5% (oven-dry weight basis), CO2 evolution was strongly moisture-dependent and 31% to 90% of the variability in CO2 evolution was explained by soil moisture. At soil moisture levels above 12.5%, soil maximum temperature was the best predictor of soil respiration, showing a significant positive correlation. This correlation explained 35% to 88% of the variation in CO2 evolution. The influence of moisture and temperature could be accurately predicted by a model which incorporated a moisture dependent Q10. The same model and model parameters successfully estimated soil respiration in the majority of fertilizer treatments. The addition of superphosphate fertilizer resulted in a significant stimulation of respiration rates, while the effect of urea addition was less marked. In treatments which received urea alone, CO2 evolution was depressed, although not significantly. However, in the presence of superphosphate, urea addition increased CO2 evolution with rates being highest in treatments which received the highest urea application rate. This result was attributed to an increased availability of phosphorus since microbial and faunal activity in this ecosystem appeared to be limited by P availability. An attempt was made to estimate the contribution of the forest floor, roots and soil to total forest soil respiration. Measurements were taken on two sampling occasions. On the first occasion, the forest floor plus mineral soil and roots contributed 85.0% and 15% to total soil respiration, respectively. On the second contribution was 68.7% and 31.3% respectively. In the field experiment, inorganic nitrogen concentrations in the soil and forest floor were measured on 60, 90, 240, 270 and 300 days after fertilization. Ammonium-N was the dominant N form. Inorganic-N concentrations were consistently highest in the treatments which received urea alone. Nitrate concentrations were highest in the treatments which received the highest urea application rate. A 30-day incubation experiment was conducted in the laboratory using the forest floor and soil collected from the experimental site one year after fertilization. Initial water-soluble phosphate (W-S P) concentrations were considerably higher in superphosphate treatments in the forest floor, while no appreciable concentrations were detected in any of the soil samples or in the forest floor of the control and treatments which received urea alone. During incubation, W-S P concentrations increased in all treatments with the highest rates being found in the treatments which had received phosphorus. Nitrate production and net N mineralization rates were highest in treatments which received urea alone, both in the soil and the forest floor samples. Superphosphate addition increased net N mineralization in soil samples. However, it only increased net N mineralization in the forest floor in the presence of added N. Urea elevated pH while superphosphate depressed it. No clear influence of pH changes on CO2 evolution were evident.