Agriculture and Food Systems - Theses
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ItemFrom Cruelty to Care: informing human behaviour change interventions to improve dog welfare( 2022)From cruelty and neglect to mismanagement and suboptimal care, the primary cause of most dog welfare problems is owner behaviour. Consequently, owner behaviour change is likely the most promising avenue for improving the lives of companion dogs. Behaviour change as a scientific discipline is well-established in other fields such as health psychology, but has had limited systematic work in animal welfare settings. Previous animal-related interventions have largely lacked appropriate foundational research to understand the nature of the chosen problem and appropriate targets for interventions, including target audiences and target antecedents of the relevant behaviours. Consequently, the aim of this thesis was to contribute to the evidence base regarding dog welfare problems and owner behaviour to inform future intervention development. The thesis examines both ends of the ‘dog welfare spectrum’, from animal cruelty and neglect, through to appropriate care and management, to present a broader understanding of the topic. The first study provides novel insights about the prevalence and nature of cruelty and neglect at the community level. Using a representative telephone survey it demonstrated that mistreatment is common, underreported, and mostly neglect. Additionally, it showed that rates of community reports made to authorities are not accurate indicators of mistreatment prevalence within a given region and should not be relied upon for selecting intervention target audiences. Finally, a higher prevalence of mistreatment was identified in the regional cities surveyed compared to the metropolitan and interface regions. This was likely attributable to socioeconomic challenges. The second study built upon the first by evaluating community attitudes towards animals and their treatment as potential targets for interventions. Specifically, it examined whether the prevalence and reporting trends found in the first study were reflected in community attitudes. While small differences were found that reflected these trends, overarchingly the study demonstrated the complexity of community attitudes. This complexity highlights the need for clear identification and understanding of an intervention’s target audience. Moving from the community level to the individual level, the third study investigated antecedents to dog owner care-related behaviour, specifically the concept of ‘duty of care’ as a motivational construct. It used a mixed methods approach to better understand the potential dimensions of duty of care, their interrelationships, and develop psychometrically valid tools to measure them in companion dog owners. One key finding was that many dog welfare problems may not be the result of lacking duty beliefs, but rather weaknesses in other ‘activation’ factors such as problem awareness. This then informed the final study. The final study further explored the concept of problem awareness and owner perceptions of dog welfare as potential targets for behaviour change interventions. This involved a 2 week field-study to examine relationships between owner perceptions of their dog’s welfare and animal-based indicators of dog welfare. This study also served as a pilot to trial the use of PetPace ‘smart collars’ as a practical approach to collecting dog welfare data in the home environment. Overall, there were few relationships between owner perceptions of welfare and animal-based indicators. These results provide preliminary evidence to support the development of a dog owner behaviour change intervention which targets owner perceptions of dog welfare and problem awareness. In all, this multi-disciplinary research has produced a significant contribution to the emerging field of human behaviour change for animal welfare. Throughout, this research has highlighted the complexities of owner behaviour, demonstrating the need for further research and development to ultimately improve the lives of companion dogs.
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ItemAssessment of thermotolerance in sheep based on changes in phenotypic and genotypic markers( 2022)Heat stress (HS) is one of the most significant single stressors affecting the global animal production by influencing physiology, development, growth, and reproduction, and the impact is likely to increase as global temperature rise. Given that the total magnitude of the stress experienced by an animal also depends upon the inherent individual genetic potential of the animal, identification of genetic traits for greater adaptability to extreme environmental conditions (high temperature, feed scarcity, water scarcity) is important to develop an effective strategy for climate change adaptation. Similarly, assessing the relative adaptive capacity of different sheep breeds to adverse climates could help the sheep industry to be resilient and adapt to climate change. In Australia, majority sheep population is comprised of Merino or Merino crosses, while some other breeds such as Dorper are gaining popularity due to their hardiness, low labor requirements, and high production efficiency. Dorper sheep are single-purpose hair sheep, tolerant of harsh environments. While 2nd cross Merino lambs are known for faster growth rates and superior carcass and meat quality traits, their ability for adaptation to higher temperatures is relatively unknown. Furthermore, there is lack of some simple and no invasive heat tolerant phenotypes, and molecular markers that could be utilized for the selection of heat tolerant sheep. This thesis investigated the potential phenotypes and biomarkers to assess thermotolerance, comparative thermotolerance of different sheep breeds, and optimized a non-invasive measure of HS in sheep using infrared thermography and machine learning. The first study compared the thermotolerance of Dorper and second cross (SC; Poll Dorset x Merino/Border Leicester) lambs based on changes in their phenotypes and molecular responses. Thermotolerance in these two genotypes were evaluated by exposing lambs to either thermoneutral (TN) or cyclic HS for two weeks and measuring physiological, metabolic factors, prolactin concentrations as well as difference in expressions of important genes related to production and adaptation, which are markers of HS response. Overall, two weeks of HS significantly altered their physiology, blood biochemical profile, prolactin concentration and gene expression patterns in both the sheep breeds. However, significant differences between genotype were evident in a series of parameters including water intake, feed intake, respiration rate (RR), rectal temperature (RT), skin temperature (ST), blood urea nitrogen (BUN), creatinine, non-esterified fatty acid concentrations (NEFA), prolactin concentrations, as well as heat shock protein A1A (HSPA1A), interleukin 2 (IL2) and prolactin receptor (PRLR) mRNA expressions. Comparatively lower influence of HS on several parameters indicated superior thermotolerance of Dorper, however further research involving a large population under natural grazing conditions is required. Dorper is a broad term that is frequently used to refer to both black-headed (Dorper) and white-headed (White Dorper) variants and any differences in their heat tolerance are unknown. A preliminary study was conducted to compare the thermotolerance of these two genotypes. This study was conducted on a commercial farm and twenty lambs of each (10 ewes and 10 rams; 3-4 months old) Dorper and White Dorper variants were selected. Based on the proposed weather forecast two collection days were selected: TN day and HS Day. Physiological responses [RR, RT and heart rate (HR)] and prolactin concentrations were measured on both the days. Genotype variations were observed only for RT and prolactin concentrations. Lower RT and prolactin concentrations were observed in White Dorper on both the days suggesting better thermotolerance of White Dorper to HS challenges. Given that the duration of heatwaves (acute vs chronic) influences effects on individual animals, the third animal experiment investigated the effects of different duration of HS on productive and adaptive traits of Merinos. Twenty-four (4-5 months old) healthy Merino sheep were selected and were randomly allocated to TN or cyclic HS treatments in a climatic chamber for four weeks. Overall findings indicated that Merino sheep can adapt to HS exposure for up to three weeks by enacting behavioral and physiological changes, without adversely affecting production metrics like growth. However, if heat exposure is prolonged beyond three weeks, sheep find it extremely difficult to maintain homeothermy, as evidenced by an increasing trend of physiological responses and a negative impact on growth rate. It is suggested that Merino sheep appear to be well adapted to short duration HS periods; however, HS mitigation measures would be needed where sheep are more likely to be exposed to long-duration heat waves. Identification of heat stressed animals under farm conditions is challenging due to the complexity of HS response and large population. From the perspective of the implementation of early interventions to mitigate HS, identification of heat stressed animals is crucial, subsequently measures that can be collected easily under farm conditions at a low cost are needed. A combination of computer vision algorithms and infrared thermal imaging (IRT) techniques were tested as a promising strategy to assess HS in sheep based on body temperature recorded from third animal study. This study aimed to test whether a combination of IRT and machine learning techniques can be applied to predict sheep RT when subjected to HS. In general, forehead and eye IRT temperatures had the strongest correlation with temperature-humidity index (THI) and RT. Furthermore, Bayesian Regularization with one hidden layer containing ten neurons with tangent sigmoid transfer functions demonstrated the highest correlation and performance. The model developed could be a quick and low-cost method for monitoring real-time body temperatures in sheep and detecting HS with minimal restraint. In absence of strategies for mitigating the effects of HS, sheep are likely to suffer HS over the hot summer months which are likely to be hotter and stay longer due to climate change and global warming. Therefore, there is continued need to improve knowledge around negative impact of HS and revisit husbandry practices to mitigate these effects. Therefore, the final sheep study, investigated the effects of provision of shade on behavior, physiological responses, and growth performance of Merino lambs exposed to natural southern Australian summer conditions. Sixty Merinos were randomly allocated to either pasture with shade (n=30; paddock with trees) or a pasture without shade (n=30; paddock without any trees). Sheep were grazing in the pastures as per the standard protocols followed on the farm with ad libitum access to water. The exposure to natural summer negatively influenced the behavior, physiology, and productive potential in grazing sheep. Further, access to adequate shade could be adopted as an effective ameliorative strategy to mitigate HS effects during natural summer, as evidenced by higher lying frequency, and lower RR, RT, seeking water troughs frequency, faecal and wool cortisol concentrations and prolactin concentrations, and improved average daily gain in sheep with access to shade. Overall, it can be inferred from a series of experiments that HS compromise thermoregulation in sheep leading to negative impact on their behaviour and production, though the degree of this influence may vary among different breeds. Comparatively, Dorper breed show superior adaptability to HS challenges compared to SC Merinos. Further, the results also indicate that chronic HS (>3 weeks) compromise both adaptive and production potential of Merino sheep and suitable strategies are required to ameliorate these effects. Combination of infrared thermography and machine learning techniques could be used to predict RT in sheep non-invasively. Finally, this research further confirms that providing access to shade is an effective ameliorative strategy to mitigate HS and improve growth rate in sheep during summer.
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ItemMetal-Phenolic Networks: From Fundamental to Agricultural Applications( 2022)Urea, as a nitrogen-rich fertilizer, plays a vital role in increasing and maintaining soil fertility, and crop yield. The efficiency of urea as a fertilizer reduces through ammonia volatilization, nitrification, denitrification, nitrate leaching to groundwater, and runoff. Nitrogen loss can be reduced through controlled-release ureas (CRUs), which can control the physicochemical release of urea in soil. Materials used for the fabrication of CRUs are mostly non-biodegradable polymers, which further spread pollutants into the environment. In an effort to reduce environmental impact, this thesis investigated the possibility of using metal-phenolic networks (MPNs) as a means of coating urea such that the MPN coating provides a physical barrier against water, controlling urea dissolution and release into soils. Self-assembly of MPNs in a non-aqueous solvent (acetonitrile) on urea granules was first conducted to engineer thickness-tunable coatings. Tannic acid and iron ions were chosen as model compounds for the assembly of MPNs. Varying operational conditions were assessed to determine the underlying mechanism for which MPNs were formed. Specifically, parameters, including the MPN self-assembly method, solution aging time, metal-to-ligand molar ratio, precursor concentration, and processing temperature all influenced the formation kinetics, thickness, and surface roughness of the films. Upon placement of coated urea granules in water the complete dissolution of urea occurred within 3-5 hours. The release rate of urea in water was controlled via the pH-dependent behavior of the self-assembled MPNs. Although urea coated with MPNs could control the dissolution of urea, the fabrication of CRU involved the use of solvent, which makes it not ideal for large-scale manufacturing processes where the volume of liquid media required makes handling difficult. Thus, in the second effort, a one-step mechanochemical grinding approach was utilized to synthesize MPNs in the absence of solvent. After an investigation of the mechanism of MPN formation in solvent-free conditions, the fabricated material demonstrates tunable mechanical resistance and stiffness that adjust with aging and thermal post-treatments. It is demonstrated that the encapsulated urea within MPNs can prolong the release period of nitrogen in the soil by up to 9 days depending on the type of post-treatment applied. This work provides a systematic understanding of the possible formation of MPNs using the self-assembly coating technique in non-aqueous media on urea granules (chapter 3) and encapsulation of urea in the MPN matrix (chapter 4). These simple fabrication methods open new chapters for utilizing environmentally friendly materials to control-the release of urea. The implementation of environmentally friendly materials is a key consideration in addressing the challenge of more sustainable and socially responsible agricultural production.
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ItemImpact of gestational heat stress on the fetus and neonatal piglet( 2022)High ambient temperatures adversely affect the welfare and reproductive performances of sows over the summer months. Gestating sows are particularly sensitive to heat loads with implications on both dams and their progeny. There is evidence that pig progeny born to sows that experience heat stress during gestation had altered phenotypes, such as increased carcass fatness and compromised lean tissue deposition. However, the cause for the phenotypic change remains largely unknown. Evidence from human epidemiological and animal experiments suggests that the postnatal growth of the progeny might be programmed by prenatal life. To better understand the aetiology, this PhD thesis aimed to investigate the effect of sow heat stress during critical stages of gestation (early to mid-gestation and late-gestation, respectively) on sow physiology and the development of fetuses, with a specific focus on the placental nutrition and oxygen transport function, fetal skeletal muscle development and perinatal survival of newborn piglets. The aims were achieved through climate-controlled studies using primiparous gestating sows (gilts). It is hypothesised that gestational heat stress caused placental insufficiency that would have a subsequent impact on fetal development and piglet survival. The thesis first aimed to investigate the changes in placental and fetal morphology in response to sow heat stress during early to mid-gestation. This time window was investigated because it is coincident with rapid placental functional development and fetal primary muscle fibre myogenesis. These experiments showed that gestational heat stress during this critical stage caused compensatory growth of the pig placenta and reduced fetal muscle fibre number density without affecting the body mass of the developing fetus at mid-gestation. Further transcriptome analyses of the placenta demonstrated that gestational heat stress altered the expression of genes and proteins that impaired placental major nutrient transport, including the glucose, amino acids and cation ions. These studies provided the molecular evidence underpinning the placental adaptation to gestational heat stress. In fetal skeletal muscle, gestational heat stress inhibited the muscle capacity for muscle-specific gene transcription and angiogenesis, and upregulated the pro-inflammatory responses, adipogenesis and fibrogenesis in a sexually dimorphic manner such that the differentially expressed genes were only detected in female fetuses. Collectively, the change in molecular pathways suggests a cross-link between sow gestational heat stress, placental insufficiency and compromised skeletal muscle development, possibly explaining the altered carcass phenotype of the progeny born to heat-stressed dams. Finally, the effect of heat stress during late-gestation was investigated on sow farrowing physiology, umbilical oxygen concentration and survival of newborn piglets. These studies demonstrated that, for the first time, gestational heat stress reduced umbilical oxygen supply from the placenta to the piglet at parturition, contributing to increased risks of piglet hypoxic stress, stillbirth, and liveborn mortality during the neonatal stage. Taken together, findings from the current thesis indicate that gestating sows are sensitive to high ambient temperatures with a particular vulnerability over the late-gestational phase. Placental insufficiency seems to be the primary consequence of sow gestational heat stress, which causes a carry-over effect on fetal development and perinatal piglet survival. Sow heat stress during early to mid-gestation adversely affected placental major nutrient transporter abundance and fetal skeletal muscle myogenesis. On the other hand, sow heat stress during late gestation and farrowing had a detrimental impact on piglet perinatal survival, possibly associated with umbilical oxygen insufficiency. Collectively, findings from the current thesis address the knowledge gaps on impacts of gestational heat stress on the sow, fetus and neonatal piglet, by adding that placental insufficiency, impaired fetal development and increased perinatal piglet mortality could be all associated with sow heat exposure during gestation. Furthermore, these findings suggest that intervention strategies are warranted to mitigate against the heat stress impact on pig production efficiency.
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ItemThe contribution of grape- and wine-derived volatile compounds to the perception of flavour in wine( 2022)Wine quality is determined by the local terroir, nature of grapevines, viticultural practices and vinification processes. Scientists have identified chemical compounds, typically volatiles, that can give desirable sensational attributes during wine tasting and potentially become chemical markers of high-quality wine. However, there is a lack of convincing statistical models using grape volatile composition to predict the resulting wine quality. Besides, there are still volatiles and other factors such as variations in biological factors of consumers to be revealed. Overall, this PhD thesis examines the influences of grape and wine volatiles on wine quality classification and perception during wine tasting.
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ItemTHE DEVELOPMENT OF NITROGEN ISOTOPIC DISCRIMINATION TO ESTIMATE URINARY NITROGEN EXCRETION AND MANURE AMMONIA EMISSION FROM SHEEP( 2022)A series of PhD studies was developed to investigate use of the nitrogen (N) isotopic fractionation or discrimination (known as delta15N) technique in sheep with two main objectives. Firstly, to investigate the relationship between N partitioning, particularly focused on the relationship of urinary N excretion (UN) and UN/N intake (NI; UN/NI), with plasma-feed N isotopic discrimination (plasma Delta15N; plasma delta15N – feed delta15N) in non-lactating sheep. Secondly, to explore the relationship between manure delta15N and NH3 emission from sheep manure. Treatment effects were assessed using ANOVA; the relationships between tested variables were analysed by regression analysis. The first N balance (NB) study (Chapter 3) was conducted to assess the effect of genetic merit (G) and feed allowance (F) and their interactive effects on N partitioning and plasma Delta15N in non-lactating sheep, whilst the second NB study (Chapter 4) explored the relationship of plasma Delta15N with UN and UN/NI of non-lactating sheep, offered three levels of dietary non-protein N. For Chapter 5, two 10-day in vitro studies were conducted to investigate: 1) the relationship between manure delta15N and NH3 emissions when incubating different manures (mixing manure with lignite and including grape marc (GM) in sheep diets to alter manure NH3 losses); and 2) the relationship between manure delta15N and manure NH3 emission of sheep, with manures comprising three different ratios of urine and faeces. Feed allowance had a more pronounced effect on N partitioning and isotopic discrimination than the Genetic effect (Chapter 3). Lower N use efficiency (NUE) and higher UN/NI were observed with lower F (P < 0.01). Evaluating treatment means alongside sheep literature data showed positive and negative linear relationships between UN/NI and plasma Delta15N, and NUE and plasma Delta15N, respectively (P < 0.01). In Chapter 4, positive and negative linear relationships between UN/NI and NUE with plasma Delta15N, respectively (P < 0.01), were observed. The two in vitro studies (Chapter 5) confirmed that manure-N content and urine to faeces ratio in the manure were the main factors to determine manure NH3 emission. Application of lignite directly to manure reduced NH3 emission significantly (P < 0.001). The observations from this PhD project indicated that plasma Delta15N can estimate UN/NI from sheep and the relationship between plasma Delta15N and UN/NI was linearly significant (Chapter 3 and 4). Additionally, a significant non-linear relationship was observed between manure delta15N and cumulative manure NH3 emissions (Chapter 5). These studies showed that delta15N may be developed as biomarkers for estimation of UN/NI and cumulative manure NH3 of non-lactating sheep
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ItemComparative sensory and textural assessment of plant-based and traditional yoghurts( 2022)The rising global population has exerted pressure on the existing food systems and there is a need to look for alternative plant sources to fulfil the growing protein demand. The prevalence of flexitarian diets and lactose intolerance are other reasons for the growing interest in plant-based foods. The present study focused on understanding the consumer acceptance of yoghurt products using both dairy-based and alternative plant-based alternatives. A specific aim of this study was to identify the properties of dairy and non-dairy yoghurts that can be acceptable to consumers. This was done by measuring the sensory, perception, and textural attributes of dairy and non-dairy products and developing interrelationships between their attributes. Furthermore, non-dairy yoghurts were formulated with the knowledge of texture, structure and flavor aspects acquired in previous sections of this research. As a summary of the experimental parts of this dissertation, chapter 3 focused on using qualitative techniques for understanding the consumer preferences of yoghurts in the market. This chapter also showed the discussion regarding the use of traditional hedonic techniques and the relationships of sensory outputs with the textural and structural aspects of yoghurt products. It was shown that dairy and plant-based yoghurts can be similarly liked by consumers if they have similar textural and structural properties. The findings of this study can have important implications for the formulation of plant-based yoghurt products. Chapter 4 focused on understanding the emotions elicited by consumers towards yoghurts selected by quantitative testing from the previous chapter. This also included understanding the variations across the cultural groups, Westerns and Asians, that could not be differentiated using traditional sensory methods. The emojis, emotion terms and facial expression recognition were used as the three methods for emotion comparison. All the methods displayed similarities in predicting the liking of yoghurt samples. However, the use of emojis was shown to best predict the variations and differences across cultural groups. The results from this chapter helped to understand the emotions beyond the liking of yoghurt products, which is an important consideration during product development. In chapter 5, physiological responses related to liking were measured, using heart rate and facial expressions. These physiological measurements were then correlated to the physicochemical properties of yoghurts. Measurement of near-infrared (NIR) wavelengths of these samples were used to develop predictive models of sensory liking. Until now, plant-based yoghurt alternatives showed to be promising in terms of sensory liking, and textural/structural attributes. This indicates that the reason for the negative perception of these yoghurt types can be attributed to the consumers’ mindset. Hence, in the next chapter 6, consumer perceptions toward dairy and plant-based yoghurt products were compared using an online survey technique. This study found that dairy was ranked higher as compared to the plant-based and was the preferred choice among consumers, as they perceived it to be better in terms of affective and cognitive responses. Social responses in terms of the environmental benefits were rated higher for the plant-based products but these were the least relevant factors for consumer perceptions. The affective and cognitive benefits were the major deciding factors for liking. Finally, the last experimental chapter 7 utilized the understanding developed in the previous chapters and further demonstrates the formulation of non-dairy yoghurts with microalgae-soy combinations, using Chlorella and Spirulina as raw materials. A mechanical technique of high-pressure homogenization (HPH) was used for milk formation due to the advantages of this being a green technique and offering the benefits of better-structured milk. Fermentation improved the texture and aroma attributes of these vegan yoghurts. Spirulina in combination with soy showed to be a promising candidate for forming yoghurts, with firm texture and structure. The outcomes of this research have opened up avenues for the utilization of microalgae in non-dairy yoghurts. Plant-based yoghurts have shown a huge growth potential, but consumers need to be made more aware about their attributes and environmental standing. The major gap in popularity of plant-based yoghurt alternatives is due to consumer perceptions, which need to be focused upon in product development. The findings of this thesis can help to develop better plant-based yoghurt products more acceptable to consumers.
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ItemImpact of Silicon on tolerance mechanisms of wheat (Triticum aestivum L.) under drought and heat stress environments( 2022)Bread wheat (Triticum aestivum L.) is widely cultivated and amongst the major staple food crops of the world. With a total grain production of around 760 million tonnes in 2020, the crop provides ~ 20 percent of the total dietary calories and protein to the human population around the world. However, global wheat productivity faces challenges due to climatic adversities, which are becoming more acute in most of the world's established agricultural regions, raising concerns for future food security. Abiotic stress factors such as drought and heat are the primary causes of crop grain yield reduction worldwide, and the frequency of their concomitant effects has increased in the semi-arid wheat belts of the world. Plant available silicon (Si) has been widely reported for its beneficial effects on plant development, productivity and attenuating physiological and biochemical impairments caused by various abiotic stresses. This research work investigated the impact of Si application on the morphological, physiological, and biochemical mechanisms in contrasting bread wheat cultivars at critical growth stages under individual and combined drought and heat stress. Firstly, a preliminary screening experiment was conducted to categorize 46 wheat genotypes, mostly from Australia, for terminal drought and heat stress tolerance. The stress tolerance level of each genotype was determined on the basis of morphological and physiological traits, including rapid, non-destructive infrared thermal imaging for computational water stress indices (Tc, CTD, Ig, Tdry, Twet, and CWSI). Multivariate data analysis on significant traits was performed to group drought and heat stress-tolerant and susceptible genotypes. Based on their overall performance, this study identified the top ten best and five lowest-performing genotypes for drought and heat stress tolerance. After identifying the drought and heat tolerance level of wheat cultivars, a series of experiments were conducted to evaluate the role of Si on drought and heat stress susceptible and tolerant wheat cultivars at critical growth stages. In this series, to evaluate the role of Si on the wheat root system and canopy physiology under drought stress, an experiment was conducted with two contrasting bread wheat cultivars (RAC875, drought tolerant; Kukri, drought susceptible) in the glasshouse. Results showed that compared with control (drought and no Si), Kukri had a significant increase in primary root length (PRL, 44 percent) and lateral root length (LRL, 28.1 percent) with Si treatment under drought stress compared with RAC875 having a significant increase in PRL (35.2 percent), but a non-significant increase in LRL. An increase in the wheat root system positively impacted the canopy physiology (photosynthesis, stomatal conductance, and transpiration) and computational water stress indices (Tc, CWSI, CTD, Ig) in Kukri and RAC875 under drought stress. These results showed that Si has the potential to influence below-ground traits, which regulate the moisture uptake ability of roots for a cooler canopy in tolerant and susceptible wheat cultivars under drought stress. Subsequently, a comparative study of drought tolerant (RAC875) and drought susceptible (Kukri) wheat cultivars investigated the impacts of pre-sowing Si treatment in attenuating the physiological and biochemical disruptions caused by pre-anthesis drought stress. The results showed, compared to the controls (drought and no Si), Si application significantly improved the relative water content (RAC875, 10.8 percent; Kukri, 18.1 percent), chlorophyll content (RAC875, 8.7 percent; Kukri, 12.7 percent), and chlorophyll fluorescence (RAC875, 10.1 percent; Kukri, 22.3 percent) in Si treated plants under drought stress. Similarly, the concentrations of various osmolytes and antioxidants increased with Si treatment in drought tolerant and susceptible cultivars under drought stress. Results showed that the impact of a Si-induced percent increase in physiological and biochemical traits was higher in Kukri (susceptible wheat cultivar) than tolerant wheat cultivar (RAC875) under pre-anthesis drought stress. Overall, these results showed that Si has the potential to enhance plant morphological, physiological, and biochemical traits and alleviate oxidative damage by improving antioxidant defense mechanisms, both in tolerant and susceptible wheat cultivars, during pre-anthesis drought stress conditions. Following this, another experiment was conducted to study the impact of pre-sowing Si treatment on the individual and the cumulative effects of drought and heat stress during later growth stages of contrasting wheat cultivars (drought and heat stress-tolerant, RAC875, Excalibur, ECH957, RAC622; drought and heat stress-susceptible, Kukri, CM59443). Results showed that Si treatment significantly improved various stress-affected morphological, physiological, and biochemical traits, including grain yield (tolerant wheat cultivars, > 40 percent; susceptible wheat cultivars, > 31 percent) and yield components. The highest averaged Si-induced increase in thousand-grain weight across all the stress treatments was observed in Excalibur (8.6 percent), followed by Kukri (6.9 percent) and CM59443 (4.9 percent). With Si treatment, osmolytes concentrations increased significantly by > 50 percent in tolerant and susceptible wheat cultivars. Similarly, computational water stress indices also improved with Si treatment under drought, heat and drought-heat combined stress in susceptible and tolerant wheat cultivars. The study concludes that Si treatment has the potential to mitigate the detrimental effects of individual and combined stress of drought, heat, and drought-heat combined stress at early grain-filling stages in susceptible and tolerant wheat cultivars in a controlled environment. Finally, to fully understand the role of Si under natural drought and heat-stressed field conditions, a field experiment was conducted at International Maize and Wheat Improvement Center (CIMMYT), Mexico. The study aimed to determine the effects of Si application on the performance of contrasting wheat cultivars (five checks, eight tolerant, and three susceptible to drought stress) in response to terminal drought and heat stress under field conditions. Results showed a significant (p < 0.05) Si effect on most of the measured agronomic and physiological traits, including improved grain yield (p < 0.01) under drought and heat-stressed environments. Relative grain yield gain with Si application among susceptible cultivars ranged from 7.8 percent to 61.4 percent, compared with 4 to 44 percent among the tolerant cultivars under drought and heat-stressed conditions. A significantly (p < 0.05) lower mean canopy temperature was observed in Si-treated plots compared with the control for both tolerant and susceptible cultivars. The stay-green phenotype at the mid-grain-filling stage, which was estimated using relative NDVI decay and relative rate of flag leaf greenness decay (based on SPAD measurements), was significantly (p < 0.01) enhanced in tolerant (9.7 percent) and susceptible cultivars (6.3 percent). Based on these findings, it can be concluded that Si application under field conditions significantly improved various agronomical and physiological traits both under drought and heat stress. Overall, the findings from the thesis revealed that Si has the potential to mitigate critical growth stage individual and combined effects of drought and heat stress in wheat cultivars through improved morphological, physiological, and biochemical attributes. The findings also revealed that Si application has the potential to enhance the tolerance level of susceptible wheat cultivars under critical growth stage drought and heat stress. This study suggests that Si addition as a nutritional element can potentially be a sustainable management strategy to mitigate individual and combined effects of drought and heat stress on susceptible and tolerant wheat cultivars in the rainfed cropping system.
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ItemInvestigation of the interaction of sugarcane phenolics and fiber and the effects on gut microbiota( 2022)During the last two decades, there has been an increasing interest in the role of gut microbiota in human health. The gut microbiota is the dynamic and complex microbial community that resides along the human gastrointestinal tract. Diet is one of the crucial factors in the establishment and regulation of the gut microbiota because various dietary compounds can interact with it in a different way and can cause significant impacts on the microbial activity and composition. Polyphenols and fiber that are commonly found in plant-based diets may contribute to the beneficial effects of the diets on gut microbiota enterotypes associated with good health. Sugarcane bagasse, a waste product from the processing of sugarcane, is known to be rich in fiber that could be beneficial to human health through the production of short chain fatty acids from bacteria fermentation. Sugarcane polyphenols have been shown to inhibit digestion of sucrose and starch and to inhibit absorption of glucose from the gut, modulating postprandial hyperglycaemia. Moreover, these polyphenols may have the ability to selectively stimulate the growth and activity of beneficial gut bacteria and simultaneously inhibit pathogenic bacteria likewise. Therefore, there is a possibility for sugarcane fiber and polyphenols to act in concert or synergistically in mitigating gut dysbiosis and altering the gut microbiota. One of the major difficulties in presenting extracted or purified polyphenols to the colonic environment from oral route is to escape modification, degradation and absorption in the stomach and small intestine. Using carriers such as dietary fiber might overcome such restrictions. Thus, the aim of my PhD research is to study whether sugarcane fiber (SCFiber) can behave as a carrier of sugarcane polyphenols to the colon and whether they can then selectively modify pig gut microbiota studied in an in vitro system. I begin by investigating the bio-accessibility of phenolic compounds to the colon after in vitro sequential gastric-intestinal digestion, using SCFiber in combination with a sugarcane crude extract (Phytolin) and a polyphenol rich sugarcane fraction (Polynol). The combinations of SCFiber with either Phytolin or Polynol showed a substantial increase in phenolic materials available for colonic fermentation after the digestions. I then move on to examine the effects of Phytolin, Polynol, SCFiber and their respective combinations on the gut microbiota profile and on short-chain fatty acid (SCFA) production in an in vitro pig fecal fermentation system. These samples are found to have modulatory impacts on the gut bacterial community to different extents, including alterations on the alpha-diversity and beta-diversity. Furthermore, they regulated the gut microbiota composition by affecting the relative abundances of bacterial genera throughout the fermentation process. Synergistic effects were showed by the Phytolin+SCFiber and Polynol+SCFiber combinations on specific bacterial genera, which included the increases of beneficial bacteria and inhibitions of potential pathogenic bacteria. While SCFiber was effective in increasing total SCFA produced during fermentation, its combination with sugarcane polyphenols from Phytolin and Polynol affected the production dependent on the phenolic contents. These changes in SCFA production were postulated to be associated with specific metabolic pathways that are predicted to be possessed by different abundant bacteria present within the gut microbiota community. I further investigate the effects of the major flavones in sugarcane, luteolin, tricin, diosmetin and diosmin, to define the polyphenol-fiber interactions more clearly, particularly in providing firm evidence of synergistic action on the gut microbiota between the two components using the in vitro pig fecal fermentation system. In their respective combinations with SCFiber, these flavones caused unique gut microbiota profile by changing the operational taxonomic units counts and alpha- and beta-diversities and leading to synergistic modulatory effects on the relative abundances of specific bacterial genera throughout the in vitro fermentation. In addition, associations of different bacterial taxa were found within different treatments as compared to the baseline bacterial community. Depending on the flavone, their combinations with SCFiber also synergistically improve the productions of specific SCFA. Overall, this thesis described my research in elucidating the potential of using SCFiber as a natural carrier for the delivery of bioactive sugarcane polyphenols to the colon, with a view to improving colon health by the modulation of the gut microbiota towards a better profile and increasing SCFA production. It also provides the fundamental perspectives to the study of potential synergistic interaction between fiber and polyphenols with the gut microbiota.
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ItemNo Preview AvailablePhenotypic investigation of Saccharomyces cerevisiae morphogenesis and the effects of sourdough yeast-bacteria interactions on colony morphology( 2022)The yeast Saccharomyces cerevisiae is a prominent model organism and instrumental in several industrial and food fermentations. The morphological state of the yeast has significant impacts on how it operates within these applications. Thus, greater understanding of how S. cerevisiae regulates its morphology is critical in maintaining and improving the yeasts functions. Particularly, within the field of sourdough fermentation, understanding how S. cerevisiae behaviour is affected by the presence of different microbial species allows better prediction of the effects of this mixed culture on bread quality. Therefore, this thesis aims to investigate the control of morphogenesis in S. cerevisiae and how colony morphology is impacted by sourdough yeast-bacteria interactions. The morphological switch to filamentous growth in S. cerevisiae is claimed to occur through the intercellular signalling mechanism of quorum sensing. However, the vague definitions surrounding quorum sensing makes the presence of this mechanism uncertain in the yeast. In this thesis, I begin by proposing more precise definitions for intercellular signalling and quorum sensing. I, then, use these criteria to critically analyse prior research in the area. A lack of evidence was found to support a critical signal concentration triggering morphogenesis and failure to use physiological concentrations of putative signal molecules. A novel methodology to address these research gaps was developed, which used polarised budding as a proxy for filamentous growth. This allowed the identification of the critical cell density and physiological metabolite concentration present when cells switched to more polarized growth. Results indicated that only non-physiological concentrations of the putative quorum sensing molecule, 2-phenylethanol, induced this morphological switch. Therefore, a quorum sensing mechanism was not supported, and a toxicity mechanism to induce polarised budding was proposed. Sourdough fermentation to produce bread is still a relatively new research area. To date, no studies have characterised the morphological phenotypes of sourdough S. cerevisiae isolates. Therefore, I investigated a range of phenotypes in previously uncharacterised sourdough isolates and compared them to laboratory isolates. Established assays were applied to investigate the phenotypes of colony and mat morphology, mat formation, agar invasion, pseudohyphal growth, polarized budding and metabolite production. The lack of correlation found between the phenotypes highlights their matrix- and strain-dependency. Differences in metabolite production between sourdough and laboratory yeast isolates suggests that sourdough isolates are more likely to produce better quality bread. Sourdough interkingdom interactions were investigated by analysing the effect of co-culturing sourdough S. cerevisiae and bacteria on colony morphology. The presence of bacteria caused growth inhibition and filamentous growth in the yeast. Limosilactobacillus fermentum also underwent morphogenesis when grown in the presence of yeast. While preliminary, these results reveal novel effects of yeast-bacteria interactions that should be explored in further studies. Overall, the results presented here further fundamental knowledge of the control of morphogenesis in laboratory and sourdough strains of S. cerevisiae. This can be applied to understand similar processes in higher organisms and is relevant to improving fermented food and beverage quality and bio-ethanol production.