School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemEfficiency of nitrogen fertilization of dry-seeded rice in south-east Australia( 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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ItemAgroforestry : a study of agroforestry extension and a model of light interception in agroforestrry( 1986)This thesis examines two important aspects of agroforestry in Australia: agroforestry as an agricultural innovation and light interception by the tree crop. (1) Agroforestry as an innovation The ideas and opinions of farmers and professionals involved in agroforestry in Australia were studied by mail-return questionnaires. Questionnaires were sent to all farmers and professionals known to be actively involved in agroforestry. - The study is not a statistical survey of a population. The potential of agroforestry as an agricultural innovation is discussed with reference to the response to the survey and the literature. The need for a universally accepted classification of agroforestry practices is demonstrated and a system suitable for agroforestry in Australia and New Zealand developed. The classification is an adaption of agroforestry classifications developed for use in less industrially developed countries. The adopters of agroforestry involved in the study are shown to be more educated, of-higher social status, and more innovative than farmers in general. Most show opinion leader status within their local community and have a positive attitude towards agroforestry, as do the professionals involved in the research and extension of agroforestry. It is argued that agroforestry adoption is following the general trend of innovation adoption and can be expected to be adopted at an increasing rate in the near future. Factors that may limit the extent or rate of adoption are identified and a strategy developed to ensure good two-way communication between researchers and potential adopters so as to encourage successful adoption of agroforestry by interested farmers. (2) Light interception Light is shown to be a major limiting factor affecting agricultural production in agroforestry. Light interception by the tree crop reduces light availability at ground level and therefore growth of agricultural crops. Past models of light interception by discontinuous tree canopies are reviewed and a new computer based model developed. The model, TREE-SHADE, allows estimates to be made of the light interception by a stand of widely spaced trees at any time on any date. Input variables include the nature of the site, the mean size and shape of the tree crop, the spatial arrangement of the trees and the times and dates of interest. The model is tested against field results collected in a seven year old agroforest of Pinus radiata near Canberra. The model was shown to slightly underestimate solar radiation availability at ground level beneath the trees. The difference was partly explained by variability in spacing and was not considered significant enough to detract from the value of the model.
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ItemCytology and fertility of wheat-rye (Secale) hybrids with induced pairing between homoeologous chromosomes( 1986)Studies were made of the influence of individual rye chromosomes and their arms on crossability, chromosome pairing and pollen and spikelet fertility in hybrids of hexaploid wheat cv. 'Chinese Spring' and its two homoeologous pairing mutants, ph2a and phIb , each with six wheat (cv. 'Holdfast') rye ('King II') chromosome addition lines and their telocentrics. Crosses were also made of the three 'Chinese Spring' parents each with seven rye (Secale) accessions, including different species. Studies were made of crossability, hybrid viability, pollen and spikelet fertility, and chromosome pairing in both the amphihaploids and amphidiploids from these crosses. Studies were also made of crossability, chromosome pairing and pollen and spikelet fertility in the F1 of crosses of the three 'Chinese Spring' wheats with both an octoploid and a hexaploid triticale. In these studies new information was being sought, both on genetic and evolutionary affinities between rye and hexaploid wheat and on approaches for the more efficient exploitation of genetic variation in the rye gene pool for wheat improvement.
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ItemAntagonistic interactions between Colletotrichum graminicola and yeasts on maize leaves( 1986)During the last two decades it has been demonstrated many times that populations of leaf surface micro-organisms are capable of reducing the levels of disease caused by various fungal pathogens. The various mechanisms by which this may be achieved have been studied and reported. In many cases, the disease depressing interactions are effective in depressing germination of spores of pathogens, in causing lysis of germtubes or in hyperparasitising the pathogen. This work is reviewed. The objective of the present study was to determine how the leaf-colonising yeasts, Cryptococcus laurentii var. flavescens and Sporobolomyces roseus reduced the infection of maize by the anthracnose fungus, Colletotrichum graminicola. Initial experiments did not support the hypothesis that the yeasts suppressed germination, nor did they demonstrate an effect of the yeasts on appressorium production. Experiments on attached leaves, however, provided data which showed that maize leaves inoculated with equal inocula in the presence and absence of the yeasts produced many more infection courts than with yeasts. This suggested, since there were equal numbers of appressorium on each set of leaves, that appressorium behaviour was different in the presence of yeasts from in their absence. In further experiments, using different techniques, it was found that in the presence of the yeasts, the proportion of appressoria which germinated was reduced. It is suggested that the effect of the yeasts on appressorium behaviour is similar to fungistasis. It was also found that in the presence of yeasts fewer acervuli developed, and individual acervuli produced fewer setae and conidia. The manner in which the cohabiting yeasts influence the behaviour of C. graminicola during its post-penetration phase was not investigated here, but offers another challenging research topic. The implications of the present findings are discussed in relation to the natural and manipulated control of plant pathogens by biological agents.
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ItemIntake and digestion of cereal straws by sheep( 1986)This thesis reports on a series of experiments which examined the utilization of cereal straws by sheep. Cereal straws are considered low quality feeds as their intake and digestibility are low. The intake and digestibility of cereal Straws can be influenced by many characteristics of the straws themselves, by genotype/species of animal consuming the straw and by the physiological state of these animals. The effects of these factors on straw utilization are reviewed in Chapter 1. It is apparent that the intake and digestibility of straws can be increased by various pretreatments or by supplementation. The experiments conducted were intended to provide new and useful information on the effects of calcium hydroxide [Ca(OH)2] or urea pretreatments on the intake and digestion of cereal straws by sheep. The objectives of the first study were to investigate the effects of Ca(OH)2 treatment of a wheat straw on : (i) its intake and digestibility in sheep and the effect of restricting the intake of the treated material on its digestibility (Chapter 2) (ii) the effects of high calcium levels in the treated straw on the utilization of other macro-minerals (Chapter 2) and (iii) the effects of this treatment on digestive processes within the reticulo-rumen (ReRu) and on the sites of fibre digestion (Chapter 3). Pretreatment of the straw with Ca(OH)2 increased organic matter intake (WI) (685 vs 398 g/day) and digestibility (OMD) (62 vs 54%) resulting in an increase in digestible organic matter intake (DOMI) of 98%. Restricting the intake of the treated straw, which was intended to increase retention time in the ReRu, resulted in only small ( 2% units) increases in OM or neutral detergent fibre (NDF) digestibility. Although the treated straw diet contained high levels of calcium (21 g/kg DM), most of this was excreted in faeces and there were no adverse effects on phosphorus or sulphur balance. As the experiment was of 49 days duration and the ad libitum intake of the treated straw diet was maintained throughout this period, it was apparent that no serious mineral imbalances were imposed. Further, the sheep consuming the Ca(OH)2-treated straw diet lost less weight (40 vs 140 g/day) than the control animals. As regards the measurements of the amount and composition of digesta in the ReRu and the rates of digestion and passage from that organ, there was large variability between sheep within treatments. Consequently, comparisons of the dietary treatment effects were not significant due to the small number of animals used and the fact that these treatments were imposed on different animals. However, there were significant positive relationships between dry matter intake (DMI) and DM load in the ReRu and between DMI and DM flow through the abomasum. The apparent mean retention times (MELT) of DM in the ReRu for the treated straw diet fed at near ad libitum intake was 22 h and this tended to be less than that of 27 h in sheep given the untreated straw. There was also a tendency for increased fractional digestion and passage rates of the NDF of the alkali-treated compared to untreated straw. Hence, the increase in intake of the Ca(OH)2-treated straw was associated with apparent increases in ReRu DM load (40% increase) , and with non-significant increases in fractional digestion (110% increase) and passage (40% increase) rates. The amount of non-ammonia-nitrogen (NAN) apparently digested in the intestines was greater (4.8 vs 2.9 g/day) for the treated compared to untreated straw, but there were no differences when considered as the amount of crude protein apparently digested (DCPi) per 100 g DWI (7.8 vs 9.1 g DCPi/100 g DOMI). Urea pretreatment, which involves spraying straws with a urea solution followed by a period of air-tight storage, is known to increase the intake and digestibility of these feeds. However, the extent to which these improvements are due to the effects of the added nitrogen or to an alkali effect per se are not clear. An experiment was carried out in two periods in which a rice straw was fed to sheep untreated or treated with urea. In the first period both diets were supplemented with urea and sodium sulphate, while these supplements were not given in the second period. The effects of pretreatment and/or supplementation on straw intake and digestibility are reported in Chapter 4, while the processes of digestion in the ReRu and the sites at which digestion occurred in sheep given the two supplemented diets are presented in Chapter 5. Urea and sulphate supplementation of the untreated rice straw increased OMI (803 vs 576 g/day) and (MD (54 vs 48%). While the intake of urea-treated straw, which was airdried prior to feeding, was similar to that of urea-supplemented-untreated straw (779 vs 803 g/day), the OND (61 vs 54%) and NDF digestibility (60 vs 49%) were increased. The nitrogen intake on these two diets was similar and the increase in digestibility was presumably due to an alkali effect during storage. Supplementation of the treated straw with urea and sulphate further increased intake to 932 g OM/day, but had no additional effect on digestibility. Thus, while urea supplementation reduced the rate of liveweight loss of sheep from 138 to 20 g/day, sheep fed the treated and supplemented straw maintained weight (+ 38 g/day). For this particular straw, it is concluded that 50% of the improvement in nutritive value gained by pretreatment was due to the additional nitrogen added. These results are discussed in relation to the likely effects of treating or supplementing straws of higher or lower nutritive value than the one used in the present work. There were no differences in the quantity or composition of digesta in the ReRu of sheep fed untreated straw supplemented with urea and sulphate or urea-treated straw given with similar supplements (Chapter 5). The MRT of DM in the ReRu was less (18 vs 21 h) in sheep given the treated rice straw. In addition, treatment increased fractional digestion rate (3.4 vs 1.9 %/h), but did not affect fractional passage rate (2.7 vs 2.9 %/h) of NDF. While the higher intake of the treated and supplemented straw was associated with increased amounts of NAN reaching (17.6 vs 12.6 g/day) the small intestines, there were no differences in the amounts of NAN apparently digested in the intestines (9.3 vs 8.0 g/day or 9.8 vs 11.2 g DCPi/100 d DCtII). These results are discussed in relation to current theories on the regulation of intake in sheep. In the final experiment (Chapter 6), the effect of body condition of sheep on the intake and digestion of the urea-treated rice straw used in the previous experiments was examined. The sheep used were those involved in previous experiments and they were allocated to two groups. Prior to the experiment, one group was fed a forage (grass hay + urea-treated rice straw in the proportion 0.75 : 0.25) and lupin grain diet (0.84 forage : 0.16 grain, DM basis) ad libitum, while the other group was given the same diet at a restricted level. At the commencement of the experiment the sheep weighed 57.7 versus 42.6 kg fleece-free liveweight and had 15.8 versus 9.7 kg total body fat. At this point the sheep in both groups wire offered the treated straw ad libitum and were given infusions of urea and sodium sulphate into the rumen. Feed intake was measured continously for 51 days, while the quantity and composition of digesta in the ReRu and flowing through the abomasum were measured on four occasions (about days 10, 18, 32 and 50). The thin sheep consumed consistently more (1170 vs 1040 g/day) feed throughout the experiment, but there were no differences in digestibility. Associated with the increased intake were larger ReRu fills (8.59 vs 7.67 kg) and DM loads (1040 vs 960 g) in the thin animals. However, the fractional digestion (3.3 vs 3.4 %/h) and passage (2.0 vs 2.0 %/h) rates of NDF were not different in the two groups of sheep. These results are discussed in relation to the likely effects of body condition on the intake of less digestible straws where nutrient limitations might exist. In the concluding chapter (Chapter 7) the implications of these findings are discussed in relation to other information on the utilization of cereal straws.
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ItemThe rate of fibre digestion in ruminants( 1986)This thesis presents a study of some aspects of the rate of fibre digestion in ruminants. There is a continued need for simple, reliable laboratory techniques for estimating the in vivo digestibilty of a range of forages. Tjandraatmadja (1981), a former postgraduate student in this school, developed a method for measuring in vitro methane production, but recognised that although his preliminary results were satisfactory, further evaluation of the technique was required before it could be used as a predictor of the in vivo digestibility of forages. This series of experiments was conducted to assess the reliability of this technique for routine laboratory determinations of forage digestibility. The first chapter consists of a literature review of some aspects of fibre digestion. A knowledge of the digestive process is required to detect the limitations in any laboratory assessment technique. The second chapter describes the utilisation of the developed method. Twenty forages were used in an attempt to establish the suitability of the method for a range of forages with varying anatomical structures. The rates of methane production and organic matter disappearance were assessed. The third chapter describes an in vivo experiment to determine the change in extent and rate of digestibility of wheat straw, due to its treatment with calcium hydroxide. The diets used in this experiment were assessed in vitro in the following chapter. This experiment was conducted in collaboration with two other postgraduate students in this school, Ir. Andi Djajanegara and B.T. Molina, who were studying different aspects of fibre digestion. The fourth chapter returns to the experimental technique described in chapter 2 to assess fermentation rates from a limited range of forages which. had been used in vivo experiments. The comparative in vitro and in vivo rates were established and the value of total gas or methane production as an estimate of these rates was investigated. This evaluation of a new technique has shown some possibilities for its use in forage evaluation, but there are still many limitations which must be quantified before it will become a routine laboratory technique.
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ItemStudies on the rehabilitation of manganese tailings at Groote Eylandt, Northern Territory( 1986)The thesis briefly-describes the location where the work was conducted ie Groote Eylandt, Northern Territory, its climate, biophysical environment, mining operation, ore beneficiation process, tailings dams and rehabilitation research programmes. A review of tailings disposal methods used throughout the world, including land and marine based systems, alternative uses, and reprocessing are discussed. The potential for air and water pollution from tailings, including the local examples of Captains Flat and Rum Jungle are described. Examples of the various means of surface stabilization ie vegetative, physical, and chemical and a brief outline of tailings stabilization work conducted at most major metalliferous mining and ore processing operations in Australia is given. An overview of the major aspects of soil manganese chemistry is presented in Chapter 2. Subjects discussed include manganese mineralogy, heating, storage and drying effects, the influence of lime, organic matter, and compaction and the interactions between manganese and other ions, in particular Calcium, Iron, Phosphorus, Aluminium and Cobalt. The research work was conducted in the period 1987-83 and had the primary objective of "finding a long term, self sustaining vegetative cover to stabilize tailings and prevent them from becoming sources of air and water pollution, while enhancing the aesthetics of the area". Detailed chemical and physical characterization of tailings from a 2 hectare study area was conducted. The study area was located within a major group of earthen walled tailings dams, some of which were being actively used for tailings disposal. The analyses found that the black coloured tailings were variable in physical properties with textures ranging from sands to clays, with corresponding variations in bulk density and water holding capacity. No extreme pH, soluble salt, or exchangeable aluminium levels were recorded, although total nitrogen and available phosphorus levels were found to be low. A series of sequential extractions were used to determine water soluble, exchangeable, easily reducible and dithionite soluble manganese fractions. The results obtained indicated that the exchangeable, easily reducible and total manganese levels would be above the critical levels for plant growth to occur. Characterization of the temperature regime on the tailings dams during starrier was undertaken using mercury in glass thermometers over the summer months. Comparisons obtained between the tailings study area, undisturbed open forest and a backfilled area rehabilitated with pasture, indicated that the tailings were not hotter than the other sites studied. Although the results indicated that no adverse microclimate exists in the tailings in terms of temperature regime, measurements with thermocouple needles at all three sites to confirm this finding would be useful. Because some local plants were growing on the dams, a series of agronomic trials were initiated using nine tropical pasture grasses and five tropical legumes, without the addition of any soils. Vigorous growth of the grasses occurred and despite many different treatment combinations, no successful growth of legumes occurred. The main fertilizer response from the grasses was dependent upon phosphorus with the addition of nitrogen, and various trace elements in the absence of phosphorus not resulting in any significant growth. Analysis of the results led to the conclusion that the key factor in determining the growth of the grasses in the tailings was the level of water soluble manganese. Following the success of the agronomic trials, work was then directed towards utilizing local plant species in the tailings rehabilitation work. Botanical surveys identified G1 plant species comprising 19 families growing on the dams. These were found to be nearly twice the number of plants identified by Langkamp, Ashton and Balling (1981) as growing on a manganese ore outcrop on Groote Eylandt. Comparisons between the tailings and ore outcrop, suggest that physical impedence to plant establishment and growth on the ore outcrop, rather than the manganese levels is the reason for the many differences between the two plant communities. The use of seed traps and a surface roughness and phosphorus trial, showed that a large number of grass seeds were being blown across the dams. It was shown that if a rough surface was provided, together with a phosphate fertilizer, colonization of abandoned dams would occur at a much faster rate than currently occurs. To complete the study programme, a large trial using the seed of 26 local trees and shrubs and four provenences of Eucalyptus cemadulensis was conducted. Treatments applied to the seeds included combinations of phosphorus, mulch and Rhodes grass. The trial determined that there are some local species which do not grow and survive in the tailings, yet many other common local species had impressive germination, survival and growth rates. The application of surface mulch resulted in higher germination percentages and the application of the cover crop appeared to be beneficial to the young seedlings. Overall, the regeneration trial established that the tailings dams can be rehabilitated by similar methods to the forest regeneration programme for mined out and backfilled quarry areas and that the broad objective of the research programme was achieved.
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ItemStudy toward the effective inoculation and growth of Leucaena leucocephala with vesicular arbuscular mycorrhiza( 1986)The dependence of plants on vesicular-arbuscular (VA) mycorrhiza for growth is influenced by factors in addition to the compatibility of the symbiont. Important among these are edaphic factors. This thesis describes the effect of VA mycorrhiza on the early growth of Leucaena leucocephala (Lam) De Wit in soils containing different levels of phosphorus. The objective of the first experiment was to estimate the number of infective propagules of the most common VA mycorrhizal fungi in natural and cultivated soils in the Melbourne region using the most probable number (MPN) and wet sieving methods. The natural soils collected from disturbed and undisturbed Cranbourne heath soils contained 49 spores and 8 spores per 100 g air dried of soil respectively. These were considerably fewer than spores obtained from agricultural soils which yielded 174 spores per 100 g air dried of soil. Under glasshouse condition there was considerable variation in the infectivity of the indigenous VA mycorrhizal fungi present in the soils. Infection of leucaena seedlings grown in the Cranbourne heath soils developed in 9 - 11% of the root system by 6 weeks after inoculation. This represented a lower proportion of mycorrhizal roots than developed in the same plants grown in agricultural soil (22%). Similarly it represented a much lower infection rate than that occurred in subterranean clover in all soils tested (30-78%). The effect of VA mycorrhizal fungi on the growth of leucaena seedling in soils containing different levels of phosphorus was established in a pot experiment. Inoculation increased the seedling growth significantly when no or only low levels of phosphate (20-60 mg phosphate/pot) were applied. This growth stimulation was reflected in the increased of apical growth (37 - 100%), shoot dry matter ( 222 - 234%), root dry weight (113 - 139%) and phosphorus uptake (250 - 370%) of infected seedlings relative to the controls. Glomus fasciculatum showed its superiority in stimulating leucaena seedling growth relative over the other VA mycorrhizal fungi tested. In pot cultures used for producing inoculum, it was obvious that Glomus fasciculatum was the most rapid infecting and best universal symbiont, as it infected all replicates of each host much faster than the other fungi tested. It is evident from the study that the selection of and inoculation of leucaena with an effective VA mycorrhizal fungus provides substantial benefit when preparing plants for growth in low phosphorus forestry situations.
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ItemA study on damping-off in a regeneration mixed eucalypt forest( 1986)Although damping-off is known to cause considerable loss before and after emergence of seedlings in forest nurseries, little is known of its role in seedling mortality after direct seeding in artificial regeneration of mixed eucalypt forests. Findings reported in this thesis are the result of a survey for the presence of damping-off fungi in soils and dying seedlings, and tests of their pathogenicity to a range of eucalypts found in the Wombat State Forest of Victoria. This study was carried out in conjunction with a research programme established by the Victorian Department of Conservation, Forests and Lands to determine which factors govern the successful establishment of E. obliqua and E. radiata in three seed-bed types under five levels of overwood. Propagule counts for Pythiaceous fungi in burnt and unburnt soils from field experiment, plots prior to sowing indicated that the inoculum level was low and differed with levels of overwood retained following site preparation in summer (Chapter 2). Baiting the soils with E. sieberi cotyledons, apples or directly sowing E. sieberi seed in samples of the field soil showed that both burnt and unburnt soils were variably infested with Pythium spp., Fusarium spp., and Cylindrocarpon destructans. A small portion of the seed to be sawn in the field plots without any fungicidal pre-treatment was found to harbour a range of fungi, sane of which had the potential to inhibit germination of the eucalypts sown on the plots (Chapter 3). The fungi having this ability were however not isolated from damped off seedlings in the experimental plots. Field studies showed that the proportion of germinated seedlings killed as a result of damping-off was lower than that attributable to frost heave, droughting following freezing and insect damage (Chapter 4). Damping-off was found to be widespread over the entire study site and the rate of damping-off to differ with seed-bed type. Overwood density did not affect the disease level. Although Pythium spp. were responsible for most deaths, Cylindrocarpon destructans and Fusarium spp. also caused some mortality. Pathogenicity tests (Chapter 5) confirmed that the fungi associated with seedling mortality in the field can cause significant pre- and post-emergence damping-off in a range of eucalypts found at the study site. The fungi differed in their pathogenicity to the eucalypts and sane induced feeder root necrosis after the two leaf stage of seedling development. No differences in susceptibility to post-emergence damping-off were found between the tree species sown on the plots and others of economic importance in the forest. The overall findings and their implications for direct sowing as a management option in future field regenerations are discussed in Chapter 6.
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