Artificial light at night (ALAN), or ecological light pollution, is increasingly prevalent worldwide. Exposure to ALAN tends to negatively impact animals—particularly, nocturnal animals—but life-history strategies may mitigate these costs. Animals in many regions are also increasingly exposed to climate-related stressors, such as heat and drought. Yet, interactions among ALAN, life-history strategy, and stress tolerance are unknown. Therefore, I determined if developmental ALAN exposure (1) affects development, (2) affects adult phenotype, including heat and desiccation tolerance, and (3) affects and/or interacts with life-history strategy. To address my aims, I used the variable field cricket (Gryllus lineaticeps) because its geographic range is increasingly exposed to ALAN, heat, and drought conditions; it exhibits different life-history strategies (flight-capability vs. flight-incapability); and it is mainly nocturnal. Although developmental duration and success were not impacted by ALAN exposure, ALAN affected adult phenotype, with a positive effect on body mass, body size, and reproductive investment, and a negative effect on heat tolerance. Life-history strategy also affected stress tolerance—flight-incapable females had greater heat tolerance, and their desiccation tolerance was improved by ALAN exposure. Thus, key features of environmental change (i.e., exposure to ALAN, heat, and drought) may favor some life-history strategies over others.

Doctor of Philosophy (PhD) / The Australian cotton industry has developed high yielding and high quality fibre production systems and attributes a significant contribution of this achievement to highly innovative breeding programs, specifically focused on the production of premium quality lint for the export market. Breeding programs have recently shifted attention to the development of new germplasm with superior stress tolerance to minimise yield losses attributed to adverse environmental conditions and inputs such as irrigation, fertilisers and pesticides. Various contributors to yield, such as physiology, biochemistry and gene expression have been implemented as screening tools for tolerance to high temperatures under growth cabinet and laboratory conditions but there has been little extension of these mechanisms to field based systems. This study evaluates tools for the identification of specific genotypic thermotolerance under field conditions using a multi-level ‘top down’ approach from crop to gene level. Field experiments were conducted in seasons 1 (2006) and 3 (2007) at Narrabri (Australia) and season 2 (2006) in Texas (The United States of America) and were supplemented by growth cabinet experiments to quantify cultivar differences in yield, physiology, biochemical function and gene expression under high temperatures. Whole plants were subjected to high temperatures in the field through the construction of Solarweave® tents and in the growth cabinet at a temperature of 42 oC. The effectiveness of these methods was then evaluated to establish a rapid and reliable screening tool for genotype specific thermotolerance that could potentially improve the efficiency of breeding programs and aid the development to high yielding cultivars for hot growing regions. Cotton cultivars Sicot 53 and Sicala 45 were evaluated for thermotolerance using crop level measurements (yield and fibre quality) and whole plant measurements (fruit retention) to determine the efficacy of these measurements as screening tools for thermotolerance under field conditions. Sicot 53 was selected as a relatively thermotolerant cultivar whereas Sicala 45 was selected as a cultivar with a lower relative thermotolerance and this assumption was made on the basis of yield in hot and cool environments under the CSIRO Australian cotton breeding program. Yield and fruit retention were lower under tents compared with ambient conditions in all 3 seasons. Yield and fruit retention were highly correlated in season 1 and were higher for Sicot 53 compared to Sicala 45 suggesting that fruit retention is a primary limitation to yield in a hot season. Thus yield and fruit retention are good indicators of thermotolerance in a hot season. Temperature treatment and cultivar differences were determined for fibre quality in seasons 1 and 3; however, quality exceeded the industry minimum thereby indicating that fibre quality is not a good determinant of thermotolerance. Physiological determinants of plant functionality such as photosynthesis, electron transport rate, stomatal conductance and transpiration rate were determined for cultivars Sicot 53 and Sicala 45 under the tents and an index of these parameters was also analysed to determine overall plant physiological capacity in the field. Physiological capacity was also determined under high temperatures in the growth cabinet using a light response curve at various levels of photosynthetically active radiation (PAR). Photosynthesis and electron transport rate decreased, whilst stomatal conductance and transpiration rate increased under the tents as well as under high temperatures in the growth cabinet. Photosynthesis and electron transport rate were higher for Sicot 53 but stomatal conductance and transpiration rate were higher for Sicala 45 under the tents. No cultivar differentiation was evident for plants grown under high temperatures in the growth cabinet. Temperature treatment and cultivar differences in physiological function were greater in a hot year (season 1), thereby indicating the importance of cultivar selection for thermotolerance in the presence of stress. Electron transport rate was correlated with yield in season 1, thus suggesting the suitability of this method for broad genotypic screening for thermotolerance under field conditions. Biochemical processes such as membrane integrity and enzyme viability were used to determine cultivar specific thermotolerance under high temperature stress in the laboratory, field and growth cabinet. Electrolyte leakage is an indicator of decreased membrane integrity and may be estimated by the relative electrical conductivity or relative cellular injury assays. The heat sensitivity of dehydrogenase activity, a proxy for cytochrome functionality and capacity for mitochondrial electron transport, may be quantified spectrophotometrically. Cellular membrane integrity and enzyme viability decreased sigmoidally with exposure to increasing temperatures in a water bath. Membrane integrity was higher for Sicot 53 compared with Sicala 45 under the tents and under high temperatures in the growth cabinet. No temperature treatment or cultivar differences were found for enzyme viability under the tents; however, enzyme viability for Sicala 45 was higher in the growth cabinet compared with Sicot 53. Relative electrical conductivity was strongly correlated with yield under ambient field conditions and under the tents, suggesting impairment of electron flow through photosynthetic and/or respiratory pathways, thus contributing to lower potential for ATP production and energy generation for yield contribution. Thus, the membrane integrity assay was considered to be a rapid and reliable tool for thermotolerance screening in cotton cultivars. Gene expression was examined for cultivars Sicot 53 and Sicala 45 grown under high (42 oC) temperatures in the growth cabinet. Rubisco activase expression was quantified using quantitative real-time polymerase chain reaction analysis and was decreased under high temperatures and was lower for Sicala 45 than Sicot 53. Maximum cultivar differentiation was found after 1.0 h exposure to high temperatures and hence, leaf tissue sampled from this time point was further analysed for global gene profiling using cDNA microarrays. Genes involved in metabolism, heat shock protein generation, electron flow and ATP generation were down-regulated under high temperatures in the growth cabinet and a greater number of genes were differentially expressed for Sicala 45, thereby indicating a higher level of heat stress and a greater requirement for mobilisation of protective and compensatory mechanisms compared with Sicot 53. Cultivar specific thermotolerance determination using gene profiling may be a useful tool for understanding the underlying basis of physiological and biochemical responses to high temperature stress in the growth cabinet. There is future opportunity for profiling genes associated with heat stress and heat tolerance for identification of key genes associated with superior cultivar performance under high temperature stress and characterisation of these genes under field conditions. This research has identified cultivar differences in yield under field conditions and has identified multiple physiological and biochemical pathways that may contribute to these differences. Future characterisation of genes associated with heat stress and heat tolerance under growth cabinet conditions may be extended to field conditions, thus providing the underlying basis of the response of cotton to high temperature stress. Electron transport rate and relative electrical conductivity were found to be rapid and reliable determinants of cultivar specific thermotolerance and hence may be extended to broad-spectrum screening of a range of cotton cultivars and species and under a range of abiotic stress. This will enable the identification of superior cotton cultivars for incorporation into local breeding programs for Australian and American cotton production systems.

Doctor of Philosophy (PhD) / The Australian cotton industry has developed high yielding and high quality fibre production systems and attributes a significant contribution of this achievement to highly innovative breeding programs, specifically focused on the production of premium quality lint for the export market. Breeding programs have recently shifted attention to the development of new germplasm with superior stress tolerance to minimise yield losses attributed to adverse environmental conditions and inputs such as irrigation, fertilisers and pesticides. Various contributors to yield, such as physiology, biochemistry and gene expression have been implemented as screening tools for tolerance to high temperatures under growth cabinet and laboratory conditions but there has been little extension of these mechanisms to field based systems. This study evaluates tools for the identification of specific genotypic thermotolerance under field conditions using a multi-level ‘top down’ approach from crop to gene level. Field experiments were conducted in seasons 1 (2006) and 3 (2007) at Narrabri (Australia) and season 2 (2006) in Texas (The United States of America) and were supplemented by growth cabinet experiments to quantify cultivar differences in yield, physiology, biochemical function and gene expression under high temperatures. Whole plants were subjected to high temperatures in the field through the construction of Solarweave® tents and in the growth cabinet at a temperature of 42 oC. The effectiveness of these methods was then evaluated to establish a rapid and reliable screening tool for genotype specific thermotolerance that could potentially improve the efficiency of breeding programs and aid the development to high yielding cultivars for hot growing regions. Cotton cultivars Sicot 53 and Sicala 45 were evaluated for thermotolerance using crop level measurements (yield and fibre quality) and whole plant measurements (fruit retention) to determine the efficacy of these measurements as screening tools for thermotolerance under field conditions. Sicot 53 was selected as a relatively thermotolerant cultivar whereas Sicala 45 was selected as a cultivar with a lower relative thermotolerance and this assumption was made on the basis of yield in hot and cool environments under the CSIRO Australian cotton breeding program. Yield and fruit retention were lower under tents compared with ambient conditions in all 3 seasons. Yield and fruit retention were highly correlated in season 1 and were higher for Sicot 53 compared to Sicala 45 suggesting that fruit retention is a primary limitation to yield in a hot season. Thus yield and fruit retention are good indicators of thermotolerance in a hot season. Temperature treatment and cultivar differences were determined for fibre quality in seasons 1 and 3; however, quality exceeded the industry minimum thereby indicating that fibre quality is not a good determinant of thermotolerance. Physiological determinants of plant functionality such as photosynthesis, electron transport rate, stomatal conductance and transpiration rate were determined for cultivars Sicot 53 and Sicala 45 under the tents and an index of these parameters was also analysed to determine overall plant physiological capacity in the field. Physiological capacity was also determined under high temperatures in the growth cabinet using a light response curve at various levels of photosynthetically active radiation (PAR). Photosynthesis and electron transport rate decreased, whilst stomatal conductance and transpiration rate increased under the tents as well as under high temperatures in the growth cabinet. Photosynthesis and electron transport rate were higher for Sicot 53 but stomatal conductance and transpiration rate were higher for Sicala 45 under the tents. No cultivar differentiation was evident for plants grown under high temperatures in the growth cabinet. Temperature treatment and cultivar differences in physiological function were greater in a hot year (season 1), thereby indicating the importance of cultivar selection for thermotolerance in the presence of stress. Electron transport rate was correlated with yield in season 1, thus suggesting the suitability of this method for broad genotypic screening for thermotolerance under field conditions. Biochemical processes such as membrane integrity and enzyme viability were used to determine cultivar specific thermotolerance under high temperature stress in the laboratory, field and growth cabinet. Electrolyte leakage is an indicator of decreased membrane integrity and may be estimated by the relative electrical conductivity or relative cellular injury assays. The heat sensitivity of dehydrogenase activity, a proxy for cytochrome functionality and capacity for mitochondrial electron transport, may be quantified spectrophotometrically. Cellular membrane integrity and enzyme viability decreased sigmoidally with exposure to increasing temperatures in a water bath. Membrane integrity was higher for Sicot 53 compared with Sicala 45 under the tents and under high temperatures in the growth cabinet. No temperature treatment or cultivar differences were found for enzyme viability under the tents; however, enzyme viability for Sicala 45 was higher in the growth cabinet compared with Sicot 53. Relative electrical conductivity was strongly correlated with yield under ambient field conditions and under the tents, suggesting impairment of electron flow through photosynthetic and/or respiratory pathways, thus contributing to lower potential for ATP production and energy generation for yield contribution. Thus, the membrane integrity assay was considered to be a rapid and reliable tool for thermotolerance screening in cotton cultivars. Gene expression was examined for cultivars Sicot 53 and Sicala 45 grown under high (42 oC) temperatures in the growth cabinet. Rubisco activase expression was quantified using quantitative real-time polymerase chain reaction analysis and was decreased under high temperatures and was lower for Sicala 45 than Sicot 53. Maximum cultivar differentiation was found after 1.0 h exposure to high temperatures and hence, leaf tissue sampled from this time point was further analysed for global gene profiling using cDNA microarrays. Genes involved in metabolism, heat shock protein generation, electron flow and ATP generation were down-regulated under high temperatures in the growth cabinet and a greater number of genes were differentially expressed for Sicala 45, thereby indicating a higher level of heat stress and a greater requirement for mobilisation of protective and compensatory mechanisms compared with Sicot 53. Cultivar specific thermotolerance determination using gene profiling may be a useful tool for understanding the underlying basis of physiological and biochemical responses to high temperature stress in the growth cabinet. There is future opportunity for profiling genes associated with heat stress and heat tolerance for identification of key genes associated with superior cultivar performance under high temperature stress and characterisation of these genes under field conditions. This research has identified cultivar differences in yield under field conditions and has identified multiple physiological and biochemical pathways that may contribute to these differences. Future characterisation of genes associated with heat stress and heat tolerance under growth cabinet conditions may be extended to field conditions, thus providing the underlying basis of the response of cotton to high temperature stress. Electron transport rate and relative electrical conductivity were found to be rapid and reliable determinants of cultivar specific thermotolerance and hence may be extended to broad-spectrum screening of a range of cotton cultivars and species and under a range of abiotic stress. This will enable the identification of superior cotton cultivars for incorporation into local breeding programs for Australian and American cotton production systems.

Doctor of Philosophy / Agronomy / Allan K. Fritz / Bikram S. Gill / Gary M. Paulsen / Post-anthesis high temperature stress in wheat (Triticum aestivum L.) is a major cause of yield reduction. This process results in the loss of viable leaf area and a decrease in green leaf duration ultimately causing a yield loss. The objectives of this study were to (i) phenotype a recombinant inbred line population for heat tolerance traits, (ii) understand the genetic basis of heat tolerance by mapping quantitative trait loci (QTL) linked to yield-related traits under high temperature, (iii) model stay-green under high temperature stress and map the QTL linked to stay-green parameters, and (iv) validate the markers linked to QTL under field conditions. A filial6:7 (F6:7) recombinant inbred line (RIL) population was developed by crossing Ventnor, a heat-tolerant white winter wheat with Karl 92, a relatively heat susceptible hard red winter wheat. From 10 DAA to maturity, the treatments of optimum temperature or high temperature stress (30/25°C) were imposed on the RILs. The traits measured included grain filling duration (GFD), kernels per spike, thousand kernel weight (TKW), and grain filling rate (GFR). The stay-green traits calculated were: i) time between 75% and 25% green, ii) maximum rate of senescence, iii) time to maximum rate of senescence, and v) percent green at maximum senescence. Genetic characterization was performed using microsatellite (SSR), amplified fragment length polymorphism (AFLP) and a sequence tag site (STS) markers. GFD was positively correlated with TKW and negatively with GFR and maximum rate of senescence. Principle component analysis (PCA) showed kernels per spike, maximum rate of senescence, and TKW accounted for 98% of total variability among the genotypes for heat tolerance. The most significant QTL for yield traits co-localized with marker Xgwm296 for TKW, Xgwm356 for kernels per spike, and Xksum61 for GFR. The QTL for stay-green traits co-localized with markers P41/M62-107 on Chromosome 2A, Xbarc136 on Chromosome 2D, P58/MC84-146 on Chromosome 3B, P58/M77-343 on Chromosome 6A, and. P58/MC84-406 on Chromosome 6B. These results indicate that increased green leaf area duration has a positive effect on the grain yield under high temperature. Once the kernels per spike are established, GFD and TKW can be used as selection criteria for post-anthesis heat-tolerance.