Agriculture and Food Systems - Theses

Permanent URI for this collection

Search Results

Now showing 1 - 10 of 427
  • Item
    Thumbnail Image
    Economic analysis of ameliorating subsoil constraints using subsoil manure in a cropping system
    Henty, Sam James ( 2019)
    To date, no studies have accounted for the effects of the yield and/or price risks that will occur over a run of years on the profitability of investing in ameliorating subsoil constraints within a cropping system. While addressing subsoil constraints is likely to increase grain yield, the key economic question for a grower is whether the income from extra grain produced covers the extra costs of ameliorating the subsoil. The focus of this thesis was the likely profit and risk of investing in ameliorating subsoil constraints. Investment costs and annual activity gross margins for a set rotation were used to estimate the economic performance of subsoil amelioration. The marginal change to the gross margin as a result of subsoil amelioration was assessed using partial discounted cashflow budgets. Risk analysis was used to assess the effect of price and yield variability on the mean and variance of outcomes from an investment in ameliorating subsoil constraints in cropping. This study shows an investment in subsoil amelioration was more profitable on average than an alternative investment earning 6% (real). The size of the expected extra yield benefits and longevity of these benefits are the most important factors for a grower to consider when assessing the likely merit (return and risk) of investing in subsoil amelioration in their own situations.
  • Item
    Thumbnail Image
    Formulating curcumin in a biodegradable polymeric composite material: a step towards wound healing applications
    Shahnia, Maryam ( 2017)
    The natural process of wound healing typically consists of four distinct but overlapping phases which include, hemostasis (platelet aggregation and blood clot formation), inflammation (migration of blood cells), proliferation (angiogenesis or blood vessel formation), and remodelling (reorganisation of collagen and scar tissue formation). However, in diabetic patients, this elaborate well-programmed process becomes disrupted, and there is an urgent need for compounds and formulations that can improve wound healing in these cases. A variety of natural components, including curcumin, have been identified as wound-healing agents. Curcumin, is a yellow hydrophobic natural polyphenolic pigment derived from the rhizomes of the herb Carcuma longa, which has been identified as the active principal of turmeric. The inability to efficiently deliver curcumin in a soluble form presents a chief challenge for its clinical use. Here we characterised, and optimised different biodegradable and biocompatible formulations of curcumin encapsulated particles, in order to enhance the efficiency of curcumin wound healing effect. The size of the optimised curcumin particles ranged from 1286 to 1485 nm, with an encapsulation efficiency of 75%. The zeta potential exhibited values in the range of (-7.2) to (-7.96) with the PDI of 0.4. Physical characterisation using TEM imaging ensured the successful fabrication and encapsulation of curcumin in the polymeric matrix, which had been fabricated in rod shape. Release profile occurred in a biphasic manner including an initial burst, followed by a sustained release trend for curcumin particles. In vitro cytotoxicity assays along with microscopic imaging confirmed safety of the applied concentration of curcumin particles below 25 µg/ml. Moreover, the results of cellular uptake study validated the internalisation of curcumin particles. Overall this thesis, elucidated the developed biocompatible and biodegradable formulations for curcumin encapsulation do have the potential to be employed as a drug delivery vehicle for curcumin. Further validation of the potential of this preparation to enhance wound healing is still needed.
  • Item
    Thumbnail Image
    Livestock performance in a varied landscape and climate
    Court, Jane ( 2016)
    The sheep and beef industries are significant contributors to Victoria’s economy. Despite competition for land and water resources and an increasingly variable climate, these industries need to continue to increase productivity to remain profitable. As major contributors of greenhouse gases, particularly methane, reducing emissions is also a challenge for these enterprises when considering alternative food and fibre sources. Financial benchmarking, modelling and emission intensity studies seldom recognise that these enterprises are often grazed on diverse landscapes and in the most variable climates, where options for alternative food production are limited. The co-production of meat and fibre from most sheep breeds is often not well recognised and consistently attributed in greenhouse gas emission allocation. This study aimed to investigate whether the relative profitability of a range of sheep and beef enterprises, change across land class and climate. It also aimed to develop measures of and to provide insight into drivers of flexibility, efficiency and profitability leading to guidance on better placed enterprise choice for environment. Four farm case studies were selected to represent climate and land class variability and modelled in GrassGro™. Each farm had one to three land classes enabling eleven ‘farms’ differing in land class over four locations to be simulated. Diversity of land class in this study represented differences in soil type, depth and fertility, slope of land and pasture species. A range of sheep and beef enterprises were tested across all farms to enable comparisons of profitability, flexibility and enteric methane emissions over a forty year period (1970-2010). Enterprise profitability was estimated as net margin per hectare, to allow for labour requirement differences between the enterprises. Flexibility was explored by considering enterprise profit variability and profit response in the top and bottom 10% of years. Strategies that reduced the effects of poor years (higher profit) and increased or did not reduce profitability in good years were considered to have greater flexibility. Enteric methane emissions were calculated in GrassGro™ and an estimation of total end-product made to address the differences in processing stages of red meat and wool, and provide a measure of emission intensity. To further consider the effects of droughts, studies were conducted to quantify commodity price changes in droughts and early warning indicators. A model using total soil water and the Southern Oscillation Index was tested to investigate the potential for predicting droughts before the onset of spring and so provide opportunity for early decision making to mitigate some of the financial impacts of droughts. Wool contributed most to enterprise profitability when pasture production was lowest, as on unimproved pastures, poor soil types and/or in low rainfall years. As pasture production increased across sites and was more reliable, live weight was a stronger driver of profit and systems that had a high proportion of immature animals, tended to perform the best. The specialist meat sheep enterprises were the most profitable when pasture production was highest, but had the highest sensitivity to climate variability. The spring calving enterprise tested in this study was consistently more profitable than the autumn calving enterprise, although the difference was less when pasture production was lowest. These results support, and help to explain, farm financial analyses that have reported enterprise profitability changes between rainfall or regional zones. Where these results did not reflect modelling studies, it was considered to be due to the range in pasture production at the sites tested in this study, as most of the differences were evident at the extremes in pasture production. Most modelling studies in Victoria use sites with high and reliable rainfall, and/or highly productive pastures. Whilst wool production provided a buffer to the susceptibility to droughts, the ability to increase meat production from the system increased flexibility and enterprise profit. For the prime lamb enterprises, a first cross or self-replacing meat enterprise suited to the climate and land class were equally profitable and able to provide options for increased flexibility by feeding and selling lambs early, joining ewes as lambs and running less ewes. Total pasture production, seasonal pasture supply curves as well as replacement ewe turn over price contributed to the most profitable and flexible strategies. The results help to explain some of the inconsistency in the literature on the contribution of strategies to enterprise profit and add to the discussion on the value of increasing reproduction rates. The method for measuring flexibility in this study provides a more quantifiable measure of the term, and addresses factors other than average profitability, of particular relevance to highly variable climates. As with profitability, relative differences in emissions between enterprises were less and/or changed at the sites with the lowest pasture production. As most modelled studies make estimations on fully improved pastures at high rainfall sites, they may overestimate the relative efficiencies of meat specialist systems over wool or dual purpose systems in poorer pasture and land class environments. Research has identified strategies that contribute to lowering emission intensity, such as increased fecundity, improving the feedbase and/or genotype and systems that have a higher proportion of immature stock associated with higher feed efficiency. Consistent with research, these strategies reduced emission intensity but were also most profitable when flexibility rather than profit maximisation was addressed. Therefore the most efficient systems that were also highly profitable tended to be those that maximised returns in good years and reduced the susceptibility to droughts, compared to those that focused on profitability alone. Strategies to do this were not always the same across sites. Analysis of feed and stock prices in recent droughts indicated that steeper price changes occurred from July onwards, compared to other years. Incorporating proportional price changes in drought years in programs like GrassGro™ would allow more realistic analyses of the potential financial implications of drought. Early warning of droughts could provide the opportunity to mitigate losses by using tactical strategies such as selling surplus stock before prices fall and through early purchasing of feed. An explorative study tested triggers of soil moisture and the Southern Oscillation Index which provided reliable indicators of low decile pasture producing springs, with limited risk of above average springs. Further studies are required to test and validate this across more sites and explore the useability for farmers to make informed decisions. The changes in relative profitability, flexibility and emission intensity across landscapes contribute insight into the variability in performance of farm enterprises, within regions and/or when measured as per unit of rainfall. Hence the ability for some farms to attain enterprise profitability achieved by the top 20% of farms based on profitability per mm of rainfall, may not be realistic or achievable. Whilst the industry is currently pushing to increase reproduction rates in sheep enterprises, this study indicates that strategies to do so may vary across enterprise and land class and may not be the most appropriate strategy or profit driver across all farms. More in depth work is needed to identify profit drivers for sheep meat production across land class and environment, particularly in the less reliable pasture production sites. With predictions of increased climate variability, some areas may need to reconsider the suitability of the enterprise for the location and land capability. Similarly, modelling studies that use only sites with high rainfall and improved pastures may not be able to confidently extrapolate results across the wider Victorian environment and may be underestimating emission efficiencies.
  • Item
    Thumbnail Image
    Physiological and biochemical responses of wheat to combined heat stress and elevated CO2 during grain-filling
    Macabuhay, Allene Andaya ( 2016)
    The increase in atmospheric CO2 concentration primarily drives the increase in global temperatures. While the concentration of CO2 has been stable for a long time, it is now rapidly increasing and is expected to reach ~550 ppm by the middle of this century. Concurrent to this, the global temperature is projected to have a 2ºC increase by 2050, a condition that will bring extreme weather events such as heat stress. The interaction of elevated CO2 and heat stress will have profound impacts on future global food production, particularly that of cereals. Wheat (Triticum aestivum L.) is the most important and commonly utilised cereal, and its growth and production will be potentially at risk of any climate-driven changes. CO2 is vital to plant processes and increases in concentration of CO2 have been reported to generate positive impacts in crop yield through increased biomass and improved water-use efficiency, although at the expense of nutritional quality. Heat stress, on the other hand, causes negative effects on crops through reduced phenology and yield reduction. While responses under each individual exposure are relatively well-understood, the interactions between these two climate change factors under field conditions create substantial complexity that is not currently well understood. This study on wheat was conducted at the Australian Grains Free Air CO2 Enrichment (AGFACE) facility using purpose-built heat chambers, simulating actual field condition of future high temperature and elevated CO2 in order to test whether elevated CO2 can potentially ameliorate or aggravate the effects of heat stress, and whether the responses vary within the plant and among cultivars. The first experiment looked into the remobilisation of nitrogen (N) and water-soluble carbohydrates (WSC) during pre-anthesis and grain-filling. Wheat cultivar Yitpi was used and subjected to three heat stress treatments: 5 days before anthesis (HT1), 15 days after anthesis (HT2) and 30 days after anthesis (HT3) under ambient and elevated CO2. Specific traits investigated were net assimilation rates (Anet), stomatal conductance (gs), chlorophyll content (SPAD), flag leaf N and stem WSC concentration and remobilisation, grain N and weight. The second experiment investigated the potential intraspecific differences on the response mechanisms of two wheat cultivars, Yitpi and Scout, as well as the differences between the mainstem and tiller response. Whole wheat plants were harvested and separated into mainstem and tillers; where, physiological parameters such as Anet, gs, SPAD were measured from the mainstem and biochemical analysis of total N concentration and stem WSC concentration were done on both mainstem and tillers. On a mainstem basis, elevated CO2 ameliorated the reduction caused by heat stress on Anet, present during heat stress treatment at pre-anthesis, but with decreasing stimulation after anthesis due to moisture availability. Contributing factors for amelioration effect were improved water-use efficiency and enhanced temperature tolerance of photosynthesis. Inconsistent effect was found for stomatal conductance and flag leaf N remobilisation. Stem WSC concentration was increased by elevated CO2 but decreased by heat stress under both CO2 levels; and this is associated with heat-induced reduction in net assimilation rates. On the other hand, elevated CO2 exacerbated the reduction in properties such as chlorophyll content, stem WSC remobilisation, and grain N concentration, which may lead to even lower grain nutritional quality. Intraspecific variations on the responses to combined heat stress and elevated CO2 of the two cultivars Yitpi and Scout were found in this study. Generally, prior to anthesis, Yitpi performed better than Scout in terms of higher chlorophyll content, N concentration and stem WSC concentration. Scout’s high transpiration efficiency and early vigour leading to efficient water use under heat stress, as well as its enhanced tillering capacity under eCO2, however, was more beneficial in maintaining high stem WSC under environmental variables, particularly before anthesis. After anthesis, when grain-filling is characterised by decreasing water availability, Yitpi showed higher stem WSC than Scout across all environmental conditions, potentially indicating that Scout has already remobilised most of its stem WSC into the grains. Mainstem showed more interactions of treatments as compared with tillers; but tillers also revealed potential to be a source of remobilised stem WSC for the mainstem when it acts as a sink. Interaction results for Anet substantiated the amelioration effect of elevated CO2 in the reduction caused by heat stress; while SPAD results showed further aggravation in the reduction induced by heat stress. This research study provided insights as to the potential responses of wheat crops under future climate condition.
  • Item
    Thumbnail Image
    The economic viability of automatic milking systems in Australia's pasture-based dairy farm systems: a case study analysis
    Taing, William ( 2016)
    Fluctuations in prices, costs and seasonal conditions, and increasing competition will continue to place pressure on profit margins for operators of all dairy systems. Good management and decision making skills is fundamental to ensuring that introducing new technologies, such as automatic milking systems (Mcwilliams et al.), are integrated into the whole farm system to make the best use of a given set of resources and circumstances, and realise the wide array of benefits technology has to offer some people in dairy. Increasing intensity of dairy farms and rising labour costs have helped to induce wider adoption of AMS technology in Europe and other countries. Similarly, the characteristics that have led to the wide adoption of AMS technology are increasingly evident in Australia’s dairy industry. Adapting the AMS technology to Australia’s pasture-based dairy systems has in the recent past been considered a complex challenge and requiring careful implementation as information remains limited on a national and global level. However, in recent years, the knowledge around the adoption of AMS in Australia’s pasture-based dairy systems has increased markedly with the ‘practical operated experience’ of AMS farms being fine-tuned and operating competitively. The key research question to be investigated in this thesis is if AMS technology adopted in Australia’s pasture based systems with voluntary cow traffic is competitive, in terms of profit, returns to capital, risk and non-pecuniary net benefits, when compared to Australian dairy farmers using conventional milking systems. This proposition will be tested by assessing the biophysical and economic performance of two dairy farm case studies, a Gippsland farm using ‘single box AMS’ and a Tasmanian farm using the ‘automatic milking rotary’. These two dairy farm case studies were chosen because they are deemed to have successfully integrated AMS into their whole farm system and are realising the benefits that are available from AMS. The case studies represent the use of the AMS technology at a steady state. For each case study, its biophysical and economic performance for an individual year was compared with the performance of other farmers in the region using conventional milking systems in the same year, where possible, and also over a hypothetical run of years with ranges of prices and seasonal conditions. Risk and uncertainty is also investigated in detail by running scenarios that represent long term typical prices, costs and rainfall. The major finding of this investigation is that the two AMS farms studied in Gippsland and Tasmania are capable, under the current management, of operating competitively under the seasonal and economic conditions that have occurred in the past and are likely to occur in the future, when compared to farms using conventional milking systems in the same region and under the same conditions. Ultimately, the success of incorporating AMS into Australia’s pasture-based dairy systems will depend almost completely on the human element. Good managers can make almost any system work well and profitability.
  • Item
    Thumbnail Image
    The relationship between social behaviour, feeding behaviour and stress in lambs in intensive finishing systems
    Rice, Maxine ( 2016)
    The production of lamb meat is a large and important agricultural industry in Australia. Variability and seasonality of the climate and the demand for a consistent product (in terms of weight and age) have led to an increase in the use of feedlot systems for finishing lambs. An estimated 5-20% of lambs in feedlots are prone to ‘shy-feeding’ or inappetance. Factors considered to contribute to the condition of shy-feeding include: neophobia (environment and concentrated feeds), acidosis and competition around feeding; however, little is known about the individual characteristics of these animals. The aim of this thesis was to examine the relationships between social behaviour, feeding behaviour and stress in lambs in intensive finishing systems. A preliminary study examined relationships between temperament, feeding behaviour, social interactions and cortisol concentrations in lambs in the first 2 weeks in an intensive finishing system (feedlot). Lambs in two 20-lamb feedlots (with 2 m2 floor space/animal) were studied. Prior to entry to the feedlot the lambs were subjected to a temperament test (Isolation Box Test) in which activity was measured. Weight gain, general activity, lying time, time at the feeder, number of feeding bouts, displacement at the feeder and plasma cortisol concentrations in weeks 1 and 2 in the feedlot were recorded. A parsimonious general linear model was developed to relate the logarithm of cortisol concentration to all other measurements. Cortisol was most elevated if the lamb’s activity in the feedlot (number of steps) was low (P=0.000025) and also for those lambs that fed more frequently (P=0.0010). Higher levels of activity in the temperament test were associated with higher cortisol concentrations in week 1 when the lamb was not displaced from the feeder. However there was an interaction with the number of displacements (P=0.0016), leading to little effect when a displacement occurred. A linear model could not be fitted for cortisol in week 2. A second study investigated some individual characteristics associated with shy-feeding. Forty lambs in a feedlot pen were studied in 3 cohorts (120 lambs total) over 16 months. This study focused on the behaviour of lambs in the first week in the feedlot. Lambs were provided with 2 m2 floor space per animal and 4 cm trough length each. Temperament and weights were recorded before entry to the feedlot and weights were recorded again at the end of the first week. Based on total time spent feeding over a 24-h period in week 1, lambs were categorized into two distinct groups: “Shy-feeders” (<30 min feeding, n=22) and “Feeders” (>1 hour feeding, n=98). Accumulated analysis of variance was used to compare entry weights, temperament, growth (live weight change), and feeding behaviour of each group. Most of the Shy-feeders lost weight in the first week whilst most of the Feeders gained weight, however within each grouping there was no relationship between growth and time at the feed trough despite time at the feed trough varying from 1 to 5 h for Feeders. Shy-feeders were displaced less from the feed trough by other lambs than Feeders (P<0.001), but were twice as likely to visit the feed trough when there were no other lambs there (P=0.022). There was no difference between Shy-feeders and Feeders in entry weight (P=0.64) or in any of the recorded measures of temperament (P>0.50). This thesis demonstrates that relationships exist between temperament, behaviour and stress in lambs early in the feedlot. Shy-feeders could clearly be classified by the time spent feeding over a 24-h period in week 1, although measures of temperament and entry live weight were not related to the condition of shy-feeding. A better understanding of these behavioural and stress relationships early in the feedlot may identify strategies to assist vulnerable animals to adapt to feedlots.
  • Item
    Thumbnail Image
    Change in welfare of elephants at Melbourne Zoo following a transition in management regime
    Ficken, Kristina Lorna Grace ( 2016)
    The management regime of Melbourne Zoo’s elephants recently transitioned from free-contact to protected-contact, predominantly driven by the desire to improve keeper safety. This study investigated the potential effects that this change may have had on elephant welfare. Elephants were monitored using a range of welfare indicators between December 2013 and March 2015. Most data were collected over three Study Periods of approximately 2 months each, allowing for potential changes in elephant behaviour and welfare to be assessed from the time that protected-contact management was implemented. The study revealed some changes in training method, directed towards achieving protected-contact management, with the reduction in ankus use and an overall increase in positive reinforcement. A decline in elephant obedience during training was evident over the course of the study, with an increase in average number of commands required to elicit a particular response and the proportion of commands repeated. However, this did not result in changes that adversely affected management, as the reduction in obedience was typically resolved with a single repeat of command, and no change was observed in compliance to medical treatment, foot condition (due to the dependence of foot condition on foot care), or number of timeouts required during training sessions. Moreover, there was no evidence that protected-contact has resulted in a decline in health. Although elephant body condition increased over time, it remained well within a healthy range – though ongoing monitoring is recommended to allow timely adjustments in management if this trend continues, to ensure that they do not become overweight. Due to the decrease in keeper-lead activity that occurred under protected-contact, there was a potential risk to elephant health through decreased movement. However, changes were not observed in movement by members of the female herd or in foraging rates by members of either the male or female herd, which is important to health, as decreased foraging activity may result in increased abnormal behaviours owing to boredom (e.g. stereotypy) or weight gain. Similarly, no change was observed in foot condition, which also relates to movement. A decrease in movement was found in the male herd, but this was most likely linked to a reduction in stereotypical behaviour (pacing in circles) and thus not necessarily a negative effect to welfare. Rates of habitat manipulation and exploration increased over time for both the female and male herds, which indicates an increase in species-specific natural behaviours and incidentally an increase in movement and exercise. Skin condition may also have improved based on reduced rates of comfort scratching in both males and females, potentially owing to a change in bathing method (from physically scrubbing to pressure washing) and/or an improved mud pool. Lastly, this study found no evidence that protected-contact resulted in increased stress among the elephants. Stereotypical behaviour decreased over time in both the female and male herds (although this was more likely due to changes in herd social structures than the implementation of protected-contact). There was also no overall change over time in faecal cortisol, though males had higher levels than females – most likely owing to natural gender differences. Similarly, no change was observed in aggression within the herds or the social proximity and vocalisations of the herd members – any of which may have indicated change in stress. In summary, and with consideration to all measured welfare indicators, this study found no evidence that the welfare of the elephants at Melbourne Zoo has been negatively affected following implementation of the protected-contact management regime. Instead, there was evidence for some beneficial changes to welfare – although some of these changes were likely to have resulted from changes other than the transition to protected-contact.
  • Item
    Thumbnail Image
    Nitrogen fixation by Casuarina oligodon agroforestry in the Papua New Guinea central highlands
    Wemin, Johnny Minga ( 2006)
    Casuarina oligodon L. Johnson is a multipurpose tree species grown in the highlands of Papua New Guinea (PNG). The integration of C. oligodon into agricultural systems is seen by villagers as means of restoring soil fertility, controlling soil erosion, providing shade for crops and producing fuel wood and building materials. Biological nitrogen fixation by C. oligodon through symbiotic relationships with Frankia (micro-organism) under field conditions in short (5-10 years) and long (11-15 years+) fallows in the PNG central highlands was investigated using the 15N natural abundance technique. Results from the study showed that as much as 70% of N in C. oligodon was derived from the atmosphere. The rate of N2 fixation was relatively low in short fallows of casuarina and increased as the trees aged in the long fallows. A rate of N2 fixation up to a maximum of 36 kg N ha -1 year -1 was estimated based on commonly practiced tree stocking rates and field conditions in the PNG highland areas. Although casuarina fallows tend to accumulate higher total N and C compared with equivalent period of grass fallows, the amounts of N and C in the surface soils of all systems under the study showed no significant difference. The amounts of total N and C under long fallows of casuarina (11-15 years+) were generally greater than short fallows of casuarina (5- 10 years). A significant proportion of the total N was stored in the above ground biomass of trees that were more than 10 years of age. Management of the standing biomass, particularly when the fallow is converted back to the cropping phase, is therefore critical in ensuring that the farmers are able to gain maximum benefit from the fixed N. Whilst the removal of stem wood for use as fuel or building material may be an important product of the agroforestry system, retaining the foliage, small branches and bark on the site is vital in sustaining agricultural productivity.
  • Item
    Thumbnail Image
    Studies of Ascochyta rabiei in Australia
    Pradhan, Prashanti ( 2005)
    Ascochyta rabiei (teleomorph: Didymella rabiei) which causes ascochyta blight is the most serious disease of chickpea (Cicer arietinum) in Australia as it causes significant losses in crop yield and quality. Although A. rabiei is heterothallic and genetically diverse elsewhere in the world, a study carried out on Australian isolates collected between 1995 and 2000 identified only one mating type and a low level of genetic diversity within the Australian A. rabiei population. In 2002, ascospores of Didymella rabiei, the sexual state of A. rabiei, were trapped in a discharge chamber, from chickpea stubble naturally infected with ascochyta blight in Western Australia. Examination of the stubble revealed pseudothecia typical of Didymella rabiei. The reported presence of the teleomorph in Western Australia indicated that the second mating type had been introduced into Australia or that the pathogen was capable of a low level of homothallic compatibility, previously undetected. The aims of this research were, to undertake a new survey of Australian A. rabiei isolates, to test for the presence of the second mating type, to determine if there has been a change in the diversity of the Australian population and to investigate if pathogenic variability was displayed among isolates. Sixty-seven isolates collected from chickpea fields in South Australia, New South Wales, Queensland, Victoria and Western Australia during the 2003 cropping season were single spored and confirmed as A. rabiei using a PCR test. The isolates were typed for mating type using MAT gene specific PCR primers and compared with tester isolates from USA. This test revealed that all the 67 isolates belonged to mating type 2 (MAT 1-2), thus, the presence of mating type 1 (MAT 1-1) in Australia could not be confirmed. Sequence Tagged Micro Satellite (STMS) markers were used to examine the genetic diversity of the A. rabiei isolates. The isolates were assessed for allelic variation at 19 microsatellite loci, each of which amplified a single locus. Seven of the loci were polymorphic across all the 67 isolates, while the remaining twelve were monomorphic. Based on the allele profiles at the seven polymorphic loci, 19 distinct A. rabiei haplotypes were identified with a total of 33 alleles. One haplotype constituted 35.8 % of the population and was found in the collections from South Australia, New South Wales, Queensland and Victoria. Cluster analysis did not show a clear distinction between isolates based on the state from which they were collected. Polymorphism across the 19 microsatellite loci revealed a slight elevation in diversity in the 2003-2004 population (Ht = 0.07; compared to 0.02 in the 1995 to 2000 collection) and an increase in the number of haplotypes compared with that detected in the previous study of Australian isolates. To examine the pathogenic variability of the Australian population of A. rabiei, nine isolates were inoculated on five chickpea differentials, ranging from highly susceptible to resistant, under controlled conditions optimal for A. rabiei growth and infection. Eight of the isolates were virulent on the susceptible and intermediate chickpea cultivars but not the resistant cultivar and one isolate was only virulent on the susceptible cultivar. Based on these results the isolates were classified into two pathotype groups. The results obtained from the study of the population structure and the pathogenic variability of A. rabiei in Australia will enable the Australian chickpea breeders to understand the A. rabiei population better for formulating management and breeding strategies.
  • Item