Bibliography: leaves 220-247. / x, 247 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 2001

"June 2001." / Includes bibliographical references (leaves 217-248). / vi, 248 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The effects of a sustained period of moderately high temperature on physiological and biochemical aspects of grain development were investigated in wheat cultivars grown under controlled environment conditions. The effect of variation in plant nutrition on the responses of cultivars to high temperature was also studied. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 2001?

There is consensus that high CO2 results in enhanced growth and yield for most crop plants. However, most of these studies were carried out in the presence of adequate nutrients, which is also the case in agricultural systems (managed ecosystems). About 20% of the earth’s land mass have sufficiently low levels of nutrients to cause some kind of stress to plants. On the other hand, elevated [CO2] decreases foliar nutrient elements in plants and as a result partitioning of certain nutrient elements in plants is altered. Little data is available on the partitioning of most nutrient elements in plants, and this will definitely impact on growth and yield. To investigate this, wheat (Triticum aestivum L. c.v. Gamtoos) was grown in controlled environment cabinets at 360 and 700 µmol mol -1 CO2. The full Long-Ashton nutrient solution comprising of three-nitrogen concentrations ([N]) viz. (4,6 and 12 mM) was used to water plants everyday. The measurement of net assimilation rate (NAR), stomatal conductance (gs), transpiration rate (E), water use efficiency (WUE), foliar [N], nitrogen use efficiency (NUE) and growth parameters (total plant biomass (TPB), total plant height (TPH), leaf area (LA), shoot and root dry weight) were made 7 days after germination (7 DAG) till the onset of flowering. The increase in nitrogen supply in the order of 4, 6 and 12mM resulted in an increase in NAR, g_s_ , WUE and a decline in E under elevated [CO2]. Under elevated [CO2] NAR was observed to increase during the first two weeks reaching its maximum at 14 DAG, thereafter followed by a decline reaching its maximum at 28 DAG. This was later followed by an increase at 35 DAG onwards. Under elevated [CO2], NAR was increased significantly between the nitrogen regimes during the first (7-14 DAG) and the last two (35-42 DAG) weeks. The response of assimilation as a function of internal [CO2] (Ci), showed a decrease with age at ages 14, 28 and 35 DAG. This negatively affected the initial slope and the CO2 saturated photosynthetic rates under all treatments. This suggest that acclimation may have been as a result of both stomatal and biochemical limitations. All the photosynthetic pigment levels (chl_a_, chl_b_, chl_(a+b)_, and C_(x+c)_ ) increased with an increase in nitrogen supply from 4 to 6mM [N]. A 12mM [N] resulted in a significant decline in the photosynthetic pigment levels compared to a 6mM [N]. Chla remained higher than chlb under all treatments. Also, NAR was seen to increase and decrease concomitantly with the photosynthetic pigment levels. Foliar [N] was seen to decrease with an increase in nitrogen supply from 4 to 6 mM [N] under elevated [CO2] and the effects were adverse under the 4mM [N]. Under the 6mM N regime foliar [N] was positively correlated to NAR for elevated [CO2] grown plants. Similarly, E was positively correlated to foliar [N] under the same conditions. Elevated CO2 and increase in nitrogen supply had a pronounced effect on total plant height (TPH), total plant biomass (TPB), leaf area (LA), shoot and root dry weight and nitrogen use efficiency (NUE). The effects were more pronounced under a 6mM [N] as a result of high NUE. However, under 12mM [N] growth was not as expected as a result of lower NUE. Under all treatments shoot dry weight (SDW) was positively correlated to NUE. Anatomical studies revealed that total leaf and midrib thickness was significantly increased with an increase in nitrogen supply under elevated CO2 to support the larger leaf areas. There were no significant changes in the chloroplast ultrastructure as a result of the increase in nitrogen supply and CO2 enrichment. Starch grain surface area was seen to decline with an increase in nitrogen under both ambient and elevated CO2. Elevated CO2 and increase in nitrogen supply significantly increased total grain dry weight per plant by 47 and 46% respectively under 6 and 12mM [N]. In contrast, the increase was by about 21, 61 and 67% respectively under 4, 6 and 12mM [N] between the CO2 regimes.

Call number: LD2668 .T4 1985 K87 / Master of Science / Agronomy

Thesis (MScAgric (Agronomy))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: See full text for the abstract / AFRIKAANSE OPSOMMING: Sien volteks vir opsomming

Bibliography: leaves 216-237 / vii, 327 leaves, [31] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Physiology, 1985

This study comprised three major parts: a comparative physiological study of drought responses under controlled conditions; a genetic study to construct the skeleton map of a doubled haploid (DH) population; and a quantitative trait loci (QTL) analysis to identify QTLs associated with drought tolerance traits in the field. In the first part (Chapter 3), three cultivars of wheat (Triticum aestivum L.) adapted to South Australian conditions were tested for drought tolerance under cyclic drought in growth rooms and glasshouse. Extensive physiological traits, including stomatal conductance, chlorophyll content and fluorescence, ABA content, water status traits (e.g. osmotic adjustment, RWC and leaf water potential), water soluble carbohydrates (WSC) and carbon isotope discrimination (Δ¹ ³C) were measured during experiments. Through these experiments, the drought responses of the three cultivars were physiologically dissected and the likely processes contributing most to drought tolerance were identified. In the South Australian wheatbelt, cyclic drought is a frequent event, represented by intermittent periods of rainfall which can occur around anthesis and post-anthesis in wheat. Three South Australian bread wheat cultivars, Excalibur, Kukri and RAC875, were evaluated in two growth room experiments under cyclic water-limiting conditions. In the first experiment, where plants were subjected to severe water stress, RAC875 and Excalibur (drought tolerant) showed significantly (P < 0.05) higher grain yield under cyclic water availability compared to Kukri (drought susceptible), producing 44% and 18% more grain yield compared to Kukri, respectively. In the second growth room experiment, where plants were subjected to a milder drought stress, the differences between cultivars were less pronounced, with only RAC875 showing significantly higher grain yield under the cyclic water treatment. Grain number per spike and the percentage of aborted tillers were the major yield components that affected yield under cyclic water stress. Excalibur and RAC875 adopted different morpho-physiological traits and mechanisms to reduce water stress. Excalibur was most responsive to cyclic water availability and showed the highest level of osmotic adjustment (OA), highest stomatal conductance, lowest ABA content and most rapid recovery from stress under cyclic water stress. RAC875 was more ‘conservative’ in its responses, with moderate OA, high leaf waxiness, high chlorophyll content and slower recovery from stress. Within this germplasm, the capacity for osmotic adjustment was the main physiological attribute associated with tolerance under cyclic water stress, which enabled plants to recover from water deficit. In the second part (Chapter 4), the genetic linkage map of a DH population including 368 lines, which was developed from a cross between ‘RAC875’ and ‘Kukri’, was constructed. The genetic linkage map consisted of about 500 molecular markers including ~300 DArT (Diversity array technology) and ~200 SSR (Microsattelite markers). In the third part (Chapter 5), Quantitative Trait Loci (QTLs) linked to plant phenology and production traits under irrigated and drought stress conditions were mapped by means of a DH population. To phenotype the population, 368 DH lines were cultivated in two replicates in five environments (three sites across South Australian wheatbelt in collaboration with Australian Grain Technology (AGT) in 2006, and two trials in Mexico in collaboration with CYMMIT, 2007). Data of grain yield, yield components, maturity related traits and some morpho-physiological traits such as leaf chlorophyll content, leaf waxiness, plant height, peduncle length, flag leaf and spike length were measured. Raw data were then analysed for spatial variation for each single trial using the REML procedure in GenStat (version 6). The DH lines showed significant variation for plant phenology, grain yield and yield components under irrigated and drought stress conditions. QTL analyses were performed using QTLCartographer and QTLNetwork for each trait in each site. Two major QTL for maturity traits were identified on chromosomes 2BS and 2DS corresponding to Ppd-B1 and Ppd-D1, respectively. A region was identified on chromosome 7A that harbored major QTL for grain yield, number of grains per square meter, number of grain per spike and spike fertility under drought stress. For yield data in the irrigated trial, two major QTL were identified on chromosome 3B which were not detected in drought stress environments. By using different datasets in the QTL analysis (splitting the population into two subpopulation based on heading time and also adjusting the phenotypic data for heading time to eliminate heading time effect), a QTL for grain yield was consistently detected on chromosome 7A in drought-affected environments. The coincidence of a drought response index QTL on this chromosome indicated that it might be a QTL for yield response under drought. This study demonstrated that the region on the long arm of chromosome 7A identified for grain yield and yield components is a drought response QTL which is closely linked to, but separate from, a heading time QTL. This QTL cluster on chromosome 7A could be used as a good target for positional cloning and gene isolation. However further work would be required to confirm and validate the identified QTLs in this preliminary QTL analysis. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1340056 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2008

This study comprised three major parts: a comparative physiological study of drought responses under controlled conditions; a genetic study to construct the skeleton map of a doubled haploid (DH) population; and a quantitative trait loci (QTL) analysis to identify QTLs associated with drought tolerance traits in the field. In the first part (Chapter 3), three cultivars of wheat (Triticum aestivum L.) adapted to South Australian conditions were tested for drought tolerance under cyclic drought in growth rooms and glasshouse. Extensive physiological traits, including stomatal conductance, chlorophyll content and fluorescence, ABA content, water status traits (e.g. osmotic adjustment, RWC and leaf water potential), water soluble carbohydrates (WSC) and carbon isotope discrimination (Δ¹ ³C) were measured during experiments. Through these experiments, the drought responses of the three cultivars were physiologically dissected and the likely processes contributing most to drought tolerance were identified. In the South Australian wheatbelt, cyclic drought is a frequent event, represented by intermittent periods of rainfall which can occur around anthesis and post-anthesis in wheat. Three South Australian bread wheat cultivars, Excalibur, Kukri and RAC875, were evaluated in two growth room experiments under cyclic water-limiting conditions. In the first experiment, where plants were subjected to severe water stress, RAC875 and Excalibur (drought tolerant) showed significantly (P < 0.05) higher grain yield under cyclic water availability compared to Kukri (drought susceptible), producing 44% and 18% more grain yield compared to Kukri, respectively. In the second growth room experiment, where plants were subjected to a milder drought stress, the differences between cultivars were less pronounced, with only RAC875 showing significantly higher grain yield under the cyclic water treatment. Grain number per spike and the percentage of aborted tillers were the major yield components that affected yield under cyclic water stress. Excalibur and RAC875 adopted different morpho-physiological traits and mechanisms to reduce water stress. Excalibur was most responsive to cyclic water availability and showed the highest level of osmotic adjustment (OA), highest stomatal conductance, lowest ABA content and most rapid recovery from stress under cyclic water stress. RAC875 was more ‘conservative’ in its responses, with moderate OA, high leaf waxiness, high chlorophyll content and slower recovery from stress. Within this germplasm, the capacity for osmotic adjustment was the main physiological attribute associated with tolerance under cyclic water stress, which enabled plants to recover from water deficit. In the second part (Chapter 4), the genetic linkage map of a DH population including 368 lines, which was developed from a cross between ‘RAC875’ and ‘Kukri’, was constructed. The genetic linkage map consisted of about 500 molecular markers including ~300 DArT (Diversity array technology) and ~200 SSR (Microsattelite markers). In the third part (Chapter 5), Quantitative Trait Loci (QTLs) linked to plant phenology and production traits under irrigated and drought stress conditions were mapped by means of a DH population. To phenotype the population, 368 DH lines were cultivated in two replicates in five environments (three sites across South Australian wheatbelt in collaboration with Australian Grain Technology (AGT) in 2006, and two trials in Mexico in collaboration with CYMMIT, 2007). Data of grain yield, yield components, maturity related traits and some morpho-physiological traits such as leaf chlorophyll content, leaf waxiness, plant height, peduncle length, flag leaf and spike length were measured. Raw data were then analysed for spatial variation for each single trial using the REML procedure in GenStat (version 6). The DH lines showed significant variation for plant phenology, grain yield and yield components under irrigated and drought stress conditions. QTL analyses were performed using QTLCartographer and QTLNetwork for each trait in each site. Two major QTL for maturity traits were identified on chromosomes 2BS and 2DS corresponding to Ppd-B1 and Ppd-D1, respectively. A region was identified on chromosome 7A that harbored major QTL for grain yield, number of grains per square meter, number of grain per spike and spike fertility under drought stress. For yield data in the irrigated trial, two major QTL were identified on chromosome 3B which were not detected in drought stress environments. By using different datasets in the QTL analysis (splitting the population into two subpopulation based on heading time and also adjusting the phenotypic data for heading time to eliminate heading time effect), a QTL for grain yield was consistently detected on chromosome 7A in drought-affected environments. The coincidence of a drought response index QTL on this chromosome indicated that it might be a QTL for yield response under drought. This study demonstrated that the region on the long arm of chromosome 7A identified for grain yield and yield components is a drought response QTL which is closely linked to, but separate from, a heading time QTL. This QTL cluster on chromosome 7A could be used as a good target for positional cloning and gene isolation. However further work would be required to confirm and validate the identified QTLs in this preliminary QTL analysis. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1340056 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2008

This study comprised three major parts: a comparative physiological study of drought responses under controlled conditions; a genetic study to construct the skeleton map of a doubled haploid (DH) population; and a quantitative trait loci (QTL) analysis to identify QTLs associated with drought tolerance traits in the field. In the first part (Chapter 3), three cultivars of wheat (Triticum aestivum L.) adapted to South Australian conditions were tested for drought tolerance under cyclic drought in growth rooms and glasshouse. Extensive physiological traits, including stomatal conductance, chlorophyll content and fluorescence, ABA content, water status traits (e.g. osmotic adjustment, RWC and leaf water potential), water soluble carbohydrates (WSC) and carbon isotope discrimination (Δ¹ ³C) were measured during experiments. Through these experiments, the drought responses of the three cultivars were physiologically dissected and the likely processes contributing most to drought tolerance were identified. In the South Australian wheatbelt, cyclic drought is a frequent event, represented by intermittent periods of rainfall which can occur around anthesis and post-anthesis in wheat. Three South Australian bread wheat cultivars, Excalibur, Kukri and RAC875, were evaluated in two growth room experiments under cyclic water-limiting conditions. In the first experiment, where plants were subjected to severe water stress, RAC875 and Excalibur (drought tolerant) showed significantly (P < 0.05) higher grain yield under cyclic water availability compared to Kukri (drought susceptible), producing 44% and 18% more grain yield compared to Kukri, respectively. In the second growth room experiment, where plants were subjected to a milder drought stress, the differences between cultivars were less pronounced, with only RAC875 showing significantly higher grain yield under the cyclic water treatment. Grain number per spike and the percentage of aborted tillers were the major yield components that affected yield under cyclic water stress. Excalibur and RAC875 adopted different morpho-physiological traits and mechanisms to reduce water stress. Excalibur was most responsive to cyclic water availability and showed the highest level of osmotic adjustment (OA), highest stomatal conductance, lowest ABA content and most rapid recovery from stress under cyclic water stress. RAC875 was more ‘conservative’ in its responses, with moderate OA, high leaf waxiness, high chlorophyll content and slower recovery from stress. Within this germplasm, the capacity for osmotic adjustment was the main physiological attribute associated with tolerance under cyclic water stress, which enabled plants to recover from water deficit. In the second part (Chapter 4), the genetic linkage map of a DH population including 368 lines, which was developed from a cross between ‘RAC875’ and ‘Kukri’, was constructed. The genetic linkage map consisted of about 500 molecular markers including ~300 DArT (Diversity array technology) and ~200 SSR (Microsattelite markers). In the third part (Chapter 5), Quantitative Trait Loci (QTLs) linked to plant phenology and production traits under irrigated and drought stress conditions were mapped by means of a DH population. To phenotype the population, 368 DH lines were cultivated in two replicates in five environments (three sites across South Australian wheatbelt in collaboration with Australian Grain Technology (AGT) in 2006, and two trials in Mexico in collaboration with CYMMIT, 2007). Data of grain yield, yield components, maturity related traits and some morpho-physiological traits such as leaf chlorophyll content, leaf waxiness, plant height, peduncle length, flag leaf and spike length were measured. Raw data were then analysed for spatial variation for each single trial using the REML procedure in GenStat (version 6). The DH lines showed significant variation for plant phenology, grain yield and yield components under irrigated and drought stress conditions. QTL analyses were performed using QTLCartographer and QTLNetwork for each trait in each site. Two major QTL for maturity traits were identified on chromosomes 2BS and 2DS corresponding to Ppd-B1 and Ppd-D1, respectively. A region was identified on chromosome 7A that harbored major QTL for grain yield, number of grains per square meter, number of grain per spike and spike fertility under drought stress. For yield data in the irrigated trial, two major QTL were identified on chromosome 3B which were not detected in drought stress environments. By using different datasets in the QTL analysis (splitting the population into two subpopulation based on heading time and also adjusting the phenotypic data for heading time to eliminate heading time effect), a QTL for grain yield was consistently detected on chromosome 7A in drought-affected environments. The coincidence of a drought response index QTL on this chromosome indicated that it might be a QTL for yield response under drought. This study demonstrated that the region on the long arm of chromosome 7A identified for grain yield and yield components is a drought response QTL which is closely linked to, but separate from, a heading time QTL. This QTL cluster on chromosome 7A could be used as a good target for positional cloning and gene isolation. However further work would be required to confirm and validate the identified QTLs in this preliminary QTL analysis. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1340056 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2008

Understanding the effects of water stress on wheat growth, yield and quality is essential for good irrigation management. In South Africa most of the wheat production areas are vulnerable to drought stress during crop development. That causes substantial reduction in grain yield, depending on the developmental stage at which water stress occurred. Supplemental irrigation is the main strategy for adaptation and stabilisation of yield under water stress. However, agriculture is the leading single water-use sector locally, consuming about 60% of total available water. Therefore, the need to improve water use efficiency (WUE) in crop production is clear, since South Africa is classified as a water-scarce country. Experiments were conducted under a rain shelter at Hatfield Experimental Farm, University of Pretoria, in the 2010 and 2011 seasons. The main objective of the study was to evaluate the effects of water stress at different stages on growth, yield, and quality of three wheat cultivars, namely Duzi, Steenbras and SST 843. Water stress was imposed by withholding water at either of three growing stages. The first treatment was stressed during tillering stages to flag leaf (stem elongation (SNN)), followed by water stress from flag leaf to the end of flowering (flowering stage (NSN)), and lastly water stress from grain filling to physiological maturing (grain-filling stage (NNS)), whereas optimal supply of water was maintained throughout the season by weekly irrigating to field capacity for the control treatment (NNN). Irrigation treatments and cultivars influenced growth, yield and quality, depending on the developmental stage at which irrigation was withheld. The control treatment (NNN) and the treatment stressed in the flowering stage (NSN) had highest and lowest grain yield respectively in both seasons. Water stressed treatment NSN reduced grain yield by 33% and 35% in the 2010 and 2011 seasons respectively, when compared with the control treatment (NNN). Reduction of grain yield due to stress in the flowering stage (NSN) was ascribed to reduction in the number of seeds per ear, number of ears per unit area, ear length, and flag-leaf photosynthesis rate (Pn). In the flowering stage (NSN) water stress reduced Pn by 59% which was due to increased leaf temperature because of lower transpiration (E) and stomatal conductance (gs). The water stress treatment NSN reduced transpiration by 72% and stomatal conductance by 84% in the flowering stage. Plant height was reduced by 23% because of water stress imposed in the flowering stage (NSN), which consequently decreased biomass yield by 29% in the 2011 season. Growth and yield parameters showed dramatic recovery when stress was terminated during the flag-leaf stage (SNN). The cultivar Steenbras had lower yield reduction under stress, whereas Duzi and SST 843 had higher yield potential under the well-watered conditions (NNN). In the 2011 season SST 843 had higher WUE of 14.2 kg ha-1 mm, which corresponded to higher grain yield of 7210 kg ha-1 and higher ET of 509 mm. Water-stress treatment SNN gave the highest WUE of 14.9 kg ha-1 mm, which corresponded to a total water use (ET) of 451 mm and grain yield of 6738 kg ha-1. Water stress treatments SNN and NNS reduced ET by 27% and 17%, respectively, which translated to 173 mm and 105 mm water saved by each treatment correspondingly. Grain protein content (GPC) was reduced most by the treatment exposed to stress in the stem elongation stage (SNN). However, the GPC was acceptable (>12%) in all treatments in both seasons. Hectolitre mass was reduced most by water stress imposed during grain filling (NNS). Water stress treatment NNS lowered the hectolitre mass by 3% and 4% in the 2010 and 2011 seasons respectively. Generally all quality parameters in the present study were acceptable for all irrigation treatment and cultivars. The hypothesis that water stress in the stem elongation and grain-filling stages will have little effect on yield and improve WUE was accepted. Therefore it can be recommended that supplemental irrigation should be applied from flag leaf to end of flowering (NSN) stages of wheat in order to minimise grain yield losses in the absence of rainfall. Further research should focus on extrapolation of these results to other production regions using crop models. / Dissertation (MInstAgrar)--University of Pretoria, 2013. / Plant Production and Soil Science / unrestricted