School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemEpidemiological and physiological studies of the effects of peach rosette and decline disease on the peach, prunus persicae L. Batsch( 1975)The incidence in the field of the disease peach rosette and decline (PRD), which is of considerable economic importance in the Goulburn Valley, causing fruit loss and tree death, was shown to increase from 0.9 to 91.3% in an orchard of cv. Golden Queen in 10 years. Similar results were found with the cv. Pullars Cling, in which infection increased from 1.5 to 29.7% over five years. The pattern of spread was mainly from infected trees to contiguous uninfected trees. This is consistent with the view that the main causal agent, prune dwarf virus (PDV), is transmitted only via the transfer of infected pollen : a previous finding in cherries which was confirmed in peaches. Prunus necrotic ringspot virus (PNRV) is the other virus always present in the field in PRD-infected trees. The mode of spread of PNRV is also by pollen. Within the tree, PDV moved erratically from the first infected limb, via phloem but not xylem, into the other limbs well in advance of the appearance of symptoms. Three months after flowering, PDV was detected in 65% of main limbs adjacent to the first infected limbs but in only 30% of limbs more remotely positioned on the tree. However, removing infected limbs within four weeks of flowering, when the initial infection was presumed to have occurred, did not prevent the movement of PDV into the rest of the tree. Laterals from peach trees infected with PRD were tested for the presence of PDV, using woody virus indicators (cvs Golden Queen, Italian Prune and Elberta seedling). Golden Queen was found to be a more reliable indicator for detecting PDV than Italian prune, as the presence of PNRV with PDV killed 71% of the Italian prune buds compared to only 34% of the Golden Queen buds. Golden Queen also developed more obvious foliage symptoms of PDV infection than Elberta seedlings. The probability of failing to detect PDV in infected field trees, using all three indicator plants, was higher in the first year of infection. The rate of spread of PRD was reduced in the orchard by preventing infected trees from flowering, either by removing obviously infected trees or by deblossoming. Removing infected trees resulted in a three-fold reduction in the spread of the disease in two seasons. Removing the flowers from infected trees before pollination reduced the spread of the disease by about half. This, only partial, control of the spread of PRD by tree removal or deblossoming was attributed to the presence of up to 14.3% of trees without symptoms being latently infected with PDV. It was observed that deliberate infection with PDV by pollen also resulted in a slow expression of the symptoms of PRD. The effects of PRD on the growth of young peach trees was obvious in the first three months of growth. There were considerable varietal differences in the severity of this effect. Those varieties based on cvs. Golden Queen or Levis Cling were more severely affected than the variety Elberta. The results from shoot elongation measurements agreed with those obtained from conventional growth analysis methods. These latter experiments showed that, after three months, the dry weight and leaf area of infected Golden Queen plants were reduced by 94%. The fruit yield from mature PRD-free trees was three times that of trees infected for the first season, even though symptoms were apparent only on one limb; and six times that from chronically affected trees infected for two seasons. The effect of virus infection on the photosynthetic ability of single, attached peach leaves was studied under laboratory conditions using infra red gas analysis. The constants derived from the equations describing the relationship between net photosynthesis (Pn) and both irradiance and CO2 concentration were used to analyse the effects of infection by PRD on photosynthetic characteristics of the leaf. The asymptotic value of Pn (Pmax) in young leaves was reduced 15% by PRD-infection, mainly through an increase in the "residual resistance" to 002 diffusion and a decrease of 23% in the parameter indicating photochemical efficiency. There was also evidence that the gas phase resistance was higher in infected leaves at low levels of irradiance. Dark respiration was 51% higher in infected leaves, but this difference was not significant. PRD did not reduce Pn in 60-day-old leaves, normal leaf senescence having a predominant and greater effect. It was concluded that PRD infection had its large effects on growth via a reduction in leaf area; the effects on the photosynthetic capacity per unit leaf area being minor. An effect of PRD infection on the translocation of 14C-assimilatesout of leaves was also observed. Infected leaves retained twice the assimilates than did uninfected leaves. It is concluded that the most promising methods of control of PRD include removal of infected trees, deblossoming suspected infected trees until diagnosis is confirmed, use of virus-tested plants, the gradual destruction of infected orchards and protecting young, healthy orchards from infection either by barrier crops or deblossoming the young plants until they reach an economic bearing age.
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ItemThe codling moth in Williams pears : a report of an investigation into the problem in the Goulburn Valley, 1936-19( 1944)The codling moth (Cydia pomonella,L.) is the most serious pest of pears in the Goulburn Valley irrigation area. In the Shepparton, Kyabram, and Ardmona districts, there are approximately 3500 acres of Williams Pon Chretien pears grown principally for canning purposes. For some years past, the losses of pears due to the codling moth have been considerable. In 1936 it was estimated, by executives of the Northern Victoria Fruitgrowers' Association, that codling moth losses accounted for as much as 20% of the total pear crop from the area, that is, a loss of at least �20,000 per annum was being experienced by the industry. No investigation of the codling moth had ever been conducted in the Goulburn Valley; and, although a considerable amount of research had been done elsewhere on the control of the pest in apples, little information was available on combatting the codling moth in pears. Ward (1936) conducted a survey of the pear-growing districts of the Goulburn Valley and found that there was a complete lack of uniformity among growers as to the control measures being used against the codling moth. Having no precise information on the seasonal activity of the pest, growers were not In a position to apply their sprays at the correct time, nor was there an efficient spray schedule in general use. In response to a request from the Northern Victoria Fruitgrowers' Association, and with funds made available from a Commonwealth grant for research and advisory work in relation to the apple and pear industry, an investigation of the problem of codling moth in 'NEC pears was commenced in 1936 by the Victorian Department of Agriculture. For the first two years of the investigation, portion of the Oriental Peach Moth Laboratory at the Ardmona Cannery was kindly made available by the Council for Scientific and Industrial Research, and so facilitated a study of the bionomics of the codling moth under Goulburn Valley conditions.
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ItemAn investigation of potato gangrene in Victoria : including the identification and comprehensive study of the causal organism, Phoma foveata Foister and a comparison of the Scottish and Victorian isolates with P. eupyrena Sacc., P. solanicola Prill et Del. and Phomopsis tuberivora Guss et Fost( 1957?)In October 1963 attention was drawn to the possibility of an hitherto unknown storage disease of potatoes in Victoria. Diseased tubers if the variety ton ware brought to the Plant Research Laboratory, Burnley, from a property at Clarke's Hill, via Ballarat, and a pycnidial-forming fungus was isolated consistently from lesions by Anderson (1953). Later that month, apparently identical isolates were obtained from diseased tubers of two other varieties which were received from the same property. In consequence, an investigation of dry rots in storage was commenced in September, 1954. One of the original objectives was to determine whether this pycnidial-forming fungus was a causal organism of tuber rot. As the investigation proceeded, it became evident that the fungus in question was responsible for a particular type of rot. In other countries similar types of tuber disease have been attributed to species of the Phomaceae. In the detailed study that followed, attempts were made to identify Victorian isolates with, or to distinguish them from, some of these other storage pathogens. As a result of the investigation, the pycnidial forming fungus has been identified as Phoma foveats Foister.. This fungus is responsible for the disease known as Gangrene of tubers in the British Isles. It has not been recorded previously outside that area. Although most of the work described in this report is laboratory in nature, one of the main aims has been to collect information which may may assist in determining an approach to the control of the disease.
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ItemStudies on the cereal cyst nematode (Heterodera avenae Woll.) in Victoria( 1973)Ten populations of the cereal cyst nematode (Heterodera avenge Will.) from the Victorian Mallee and Wimmera districts, were tested for their variation in pathogenicity, using a selected range of cereal species and cultivars as.indicators. The tests were made in a glasshouse between 1967 and 1969. Of the oats used, Avena sterilis and A.strigosa were resistant, but all other cultivars and species were susceptible to each of the populations. Two barley cultivars, Morocco, and Marocaine 079 were resistant to all populations, but all other barleys used were susceptible. None of the cultivars of wheat was resistant; the spring wheat cv. Loris was very susceptible. Rye cv. South Australian was resistant to all populations. The results indicate that a single biotype of H. avenge is present in Victoria. It appears to be more "aggressive" than any of the biotypes known in Europe. Two hundred and forty cereal species and cultivars (wheat, barley, oats, rye and Triticales) were field . tested for resistance to H. avenge at Sea Lake in the Victorian Mallee between 1966 and 1969. All wheats tested were susceptible to very susceptible, and all Triticales were susceptible. Two barley cultivars Morocco, and Marocaine 079 were resistant and two others moderately resistant. Avena sterilis and A. strigosa were resistant and fifteen cultivars of A. sativa were moderately resistant. Rye cv. South . Australian, posseses a high degree of resistance in contrast to European ryes. The systemic nematicides "Temik" and "Lannate", and the fumigant nematicides ethylene dibromide and dibromochloropropane, were tested for control of H. avenge in a field experiment with Wheat at Sea Lake in the 1968-69 season. All chemical treatments reduced white cyst production, and four of the treatments increased grain yield, and reduced nematode carryover. "Temik" (11 kg/ha broadcast), gave the best nematode control and more than trebled grain yield. "Lannate" (13'kg/ha broadcast) was almost as effective. Dibromochloropropane was an effective nematicide, but was phytotoxic at 56 1/ha. The systemic nematicides "Temik", "Lannate", "Nemafos", "Vydate", "Nemac ur P", and the contact nematicide "Mocap" were tested for control of H. avenge in field experiments with wheat; at Greenland Dam in the Wimmera (1969-70), and at Sea Lake in the Mallee (1969-70 to 1971-72). In one series of experiments all the nematicides were compared on a broadcast basis. All chemical treatments reduced white cyst production and nematode carryover. Plants from plots treated with "Temik" (9 kg/ha) were always cyst-free. "Mocap" when used at the same rate was severely phytotoxic. Grain from plots treated with "Temik" and "Lannate" at the higher rate (9 kg/ha) were analysed for the presence of chemical residues. No "Lannate" residues were detected, and "Temik" residues were less than 0.1 ppm. In a second series of experiments, a comparison was made of methods and rates of application of "Temik" and "Lannate". All broadcast nematicide applications, except those at Sea Lake in 1969-70, reduced white cyst production and nematode carryover. All nematicide applications with superphosphate in the drill row, except for "Lannate" 0.3 kg/ha at Sea Lake in 1971-72, also reduced white cyst production and nematode carryover. Significant grain yield increases were obtained in each experiment. "Temik" (9 kg/ha broadcast, and 2.2 kg/ha in the drill row) consistently gave the best control of H. avenge. Plants from plots receiving these treatments were always cyst-free. In all experiments "Lannate" dusted wheat seed provided little, if any, control of H. avenge. When used at comparable rates of application, "Temik" was a more effective nematicide than "Lannate".
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ItemThe occurrence of brittleheart in Eucalyptus regnans and its effect on various wood properties( 1990)This project is mainly concerned with a description of anatomical and ultrastructural characteristics of cell wall deformations in brittleheart of E. regnans, development of methodology for quantification of percentage of broken fibre pieces (PBFP) in E. regnans, and physical and anatomical properties of E. regnans in relation to the occurrence of brittleheart. Two 1939 regrowth E. regnans butt logs and one mature growth E. regnans butt log removed from a tree approximately 120 years old were used in the study. The anatomical and ultrastructural characteristics of cell wall deformations were examined with bright field, polarized light, and scanning electron microscopy. The microscopic compression lines were found to consist of slip planes, minute compression failures, corrugations, and buckles. The width of microscopic compression lines along the longitudinal fibre axis ranged from one single fold in the cell wall up to 7 times the average fibre width. The length of the microscopic compression lines ranged from ones which only crossed a few fibres to ones which crossed up to 200 fibres. The severity of microscopic compression lines appeared to be dependent on the type of cell wall deformations and degree of compaction in the deformed zone. In the methodology studies it was found that for a pulp sample prepared from a 2 mm by 2 mm by 15 mm wood chip approximately 400 cellular elements in 8 out of 16 areas on a slide needed to be counted in order to obtain PBFP with less than 10% error. For macerated thin sections, all the cellular elements on 2 slides each carrying about 600 fibres and fibre pieces needed to be counted. A highly significant correlation was found between the length of microscopic compression lines per unit area and the microscopically determined PBFP. A highly significant correlation was found between the theoretical PBFP and the microscopically determined PBFP. These findings confirm that maceration of wood containing cell wall deformations results in broken fibres and verifies the validity of the maceration technique for quantifying the amount of microscopic compression lines. PBFP was found to increase with macerating time. A maceration time around 10 hours appears sufficient to cause fibres having cell wall deformations to break but longer times cause fibres without cell wall deformations to also break due to overmaceration. A significant relationship was found between PBFP determined after 5 hours and after 10 hours of maceration at the same temperature. It was found that parameters extracted or derived from cell length distributions produced by the Kajaani FS-200 may be used to determine the amount of fibre fragments in pulp samples. These parameters were the high peak, the length weighted average, and the mass weighted average of the cell length distributions for pulps which had PBFP greater than 10. Based on the maceration technique, brittleheart was detected in both the mature and the 1939 regrowth logs. Brittleheart was more severe and occupied a larger area in the mature growth than in the regrowth wood. The PBFP was found to be mostly below 5 in the regrowth wood although relatively high PBFP values of 21 and 30 were observed. PBFP values as high as 85 was found in the mature growth wood. In general, PBFP was found to be higher nearer the pith, decreasing toward the bark, and dropping to zero before reaching the two-thirds theoretical point where the stress is assumed to be 0. A large circumferential variation in PBFP was observed in four adjacent growth rings of the mature log. A large variation in PBFP was also found within a volume of 1000 mm^3 for both the mature and the 1939 regrowth wood. The earlywood PBFP was found to be significantly higher than the latewood PBFP for the mature and regrowth logs. A total of 72 green and 132 12% MC Izod specimens were prepared from the two 1939 regrowth logs and tested for impact strength. The mean Izod value was found to be 9.9 ft.lb for the 132 12% MC Izod specimens and 9.2 ft.lb for the 72 green Izod specimens. For side-matched Izod specimens, the mean Izod value was found to be 9.2 ft.lb at green and 9.7 ft.lb at 12% MC and the mean for the 12% MC specimens did not reflect the expected increase in strength with moisture loss. Excessively low Izod values (eg. 1.8 ft.Ib) were found in the 12% MC Izod specimens located near the pith. For 76 12% MC Izod specimens, their PBFP, fibre length, and specific gravity were also measured. Significant relationships (p=0.01) were found between Izod values and specific gravity, PBFP, and fibre length for these 76 12% MC Izod specimens. Specific gravity and fibre length positively contribute to the impact strength whereas PBFP negatively affects the impact strength. Brash-break specimens showed a low mean Izod value, a low mean specific gravity, the presence of brittleheart, and a short mean fibre length.
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ItemStudies of barley yellow dwarf virus infection in ryegrass (Lolium spp.)( 1989)Measurements were made of the effect of barley yellow dwarf virus (BYDV) infection on the early growth of four commercial cultivars of ryegrass (Lolium spp.) under two different temperatures (24C and 16C). At 24C, BYDV infection was associated with reduced root dry weight (30-40%) in all cultivars; the effect of infection on shoot dry weight and leaf area was variable. At 16C, the effect of BYDV infection was variable, being associated with increases in both leaf area and root and shoot dry weight in one cultivar (Grasslands Arild) and decreases in another (Victorian). In two other cultivars, both leaf area and root and shoot dry weight were not significantly affected (p > 0.05) by infection with BYDV. There was no evidence of visible symptoms associated with BYDV infection. At 240C, reductions in root dry weight associated with BYDV infection were not reflected in reductions in the relative growth rates of the roots. Up to at least 28 days after inoculation (46-50 days after germination) reductions in root dry weight were associated with both aphid-feeding damage and virus infection. Experiments with the cultivar Victorian showed that shoot dry weight was not significantly affected (p > 0.05) by feeding with either viruliferous (BYDV) or non-viruliferous aphids (Rhopalosiphum padi L.). At 16C, changes in root and shoot dry weight were associated with changes in the respective relative growth rates. Both visual scoring and changes in plant dry weight were found to be unreliable criteria for assessing disease severity. Two assay systems, an enzyme-linked immunosorbent assay (ELISA) and a nucleic acid, or complementary DNA (cDNA) probe, were developed for the detection of BYDV in ryegrass. The conditions for detecting BYDV with the ELISA (the "double sandwich" variant) were optimized. Exposure of the virus to extracts of ryegrass leaf tissue for 30 min or more resulted in reductions in absorbance, with the amount of the reduction dependent on the antigen (virus) incubation temperature. The optimization of conditions for the immunoglobulin (IgG) used for coating microtitre plates (coat IgG), the IgG - alkaline phosphatase conjugate (conjugate IgG) and the antigen (virus), in conjunction with the use of polyethylene glycol - 6 000 in the preparation of the conjugate buffer, gave a rapid and reliable ELISA procedure for the consistent detection of BYDV at levels of 2 ng/ml. Both ELISA and cDNA probe techniques were used to study the incidence of BYDV isolates in perennial ryegrass at three sites (Balmoral, Mininera and Hamilton) in south-western Victoria. BYDV was detected in perennial ryegrass cultivars from the three sites, with different levels of incidence of BYDV isolates between cultivars. While the PAV-related isolate was prevalent at the three sites, the incidence of the MAV- and RPVrelated isolates varied with the site and the cultivar. One difficulty with the ELISA was that absorbance values did not fall in to distinct infected and uninfected groups within the cultivars, and at Mininera, the incidence of BYDV varied significantly between the various positive - negative ELISA thresholds that were used. At Balmoral, the incidence of BYDV determined with each threshold was compared with that determined by cDNA probing using a Spearman correlation test. A threshold of double the mean negative (uninfected ryegrass) control showed the highest correlation with the cDNA probe for a number of replicate plots at the site. The incidence of the PAV-related isolate was compared for the two cultivars Ellett and Victorian, and significant (p < 0.01) reductions in its incidence in cv. Ellett compared with cv. Victorian at the three sites, suggested that cv. Ellett is resistant to the PAVrelated isolate of BYDV. The comparative resistance of cv. Ellett to at least this isolate of BYDV indicated the feasibility of breeding and selecting for resistance to other isolates of BYDV in perennial ryegrass. In attempts to quantify resistance in perennial ryegrass, the ELISA was further developed to allow measurement of BYDV titre in ryegrass shoot tissue. In twenty selections of cv. Victorian, the performance, as measured by changes in both root and shoot dry weights, of individual selections to infection with BYDV, did not significantly (p < 0.05) correlate with virus titre measurements. Experiments with twenty selections of cv. Ellett indicated that its resistance to BYDV that was e' ident at the three field sites was not associated with resistance to aphid (Rhopalosiphum path) feeding, and consequently, transmission of the virus. Attempts to inoculate cv. Ellett with either the PAV- or RPVrelated isolates were of limited success, and it was speculated that its resistance to the virus may be due to reductions in the level of virus replication.
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ItemDecline of river red gum (Eucalyptus camaldulensis Dehnh.) on grazing lands in Western Victoria( 1988)River Red Gum (Eucalyptus camaldulensis Dehnh.) is a common and extensively distributed tree in western Victoria. Widely-spaced stands of this species are a prominent feature of pastoral landscapes in that area. Many of these remnant stands are in a state of decline, with individuals being lost through deliberate clearing, senescence or the effect of rural dieback disease syndromes. This thesis reports on a study of the decline of one stand of E.camaldulensis trees growing on part of a grazing property near Buangor, in west-central Victoria. The rate of tree loss from agricultural land in the Buangor district was assessed from aerial photographs taken in 1947 and 1980. The average compounding rate of tree loss over that period was 1.1% p.a.. Rates of tree loss were greater from the remnant box-stringybark stands (1.9% p.a.) occurring in the district than from remnant River Red Gum stands (0.8% p.a.). The size and crown condition of all trees in the stand under investigation were assessed. Dieback-affected trees had relatively small and open crowns, that often had many dead branchlets and branches. The crowns of dieback-affected trees were largely of secondary or epicormic origin. Tree height and stem girth were not affected by contemporary crown health. The age of one tree was estimated by radiocarbon dating to be 440. ± 110 y B.P.. Detailed investigations of trees classified as either "healthy", "average" or "unhealthy" were undertaken. The amount of organic matter in soil declined as the quality of tree cover changed from "healthy" to "unhealthy" tree to open pasture. This change was probably linked with reduced additions of organic material through litterfall as tree crown cover deteriorated. The possible consequences of reduced litterfall and declining soil organic matter levels were that; (i) it may have disrupted biogeochemical nutrient cycling; and (ii) it may have increased the susceptibility of trees to root damage and other problems associated with animal traffic. Measurements of soil strength and bulk density indicated that soil under open pasture had been compacted, presumably by animal traffic. Soil under trees was harder during winter than soil under open pasture and was therefore less susceptible to puddling. Soil under trees was not as strong as soil under open pasture during spring and hence provided more favourable conditions for root growth. Investigations into the mineral nutrition of study trees found that "unhealthy" trees did not appear able to mobilize some macronutrient elements (N,P, K, Mg) to the same extent as "healthy" trees. The apparent nutrient deficiency may have been due to disruptions to the biogeochemical nutrient cycle as dieback progressed. The nutrient deficiency may exacerbate this disruption, since it was associated and possibly linked with delayed new foliage production in "unhealthy" trees and reduced area growth in that foliage. Measurements of leaf water potential, diffusive conductance and transpiration showed that atmospheric, rather than soil water deficits had the greatest influence on water relations in the study trees. The measurements showed that "unhealthy" and "average" trees did not greatly restrict transpiration during periods of high evaporative demand. "Healthy" and "average" trees transpired more water and assimilated more carbon than did "unhealthy" trees. Differences in gas exchange were due only to large differences in leaf area. Soil under "healthy" and "average" trees remained drier than soil under "unhealthy" trees and open pasture throughout the study period. However, there was little difference in soil water depletion during the summer, even though the annual pasture had died off. Measurements provide evidence of deep infiltration of water beyond plant root zones, particularly under open pasture and "unhealthy" trees. The healthier trees appeared to have a beneficial impact on the local water balance. Continued rural dieback and/or tree loss is likely to exacerbate disruptions to the local water balance that commenced with clearing for agriculture.
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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.