World agriculture is challenged by the increasing demand on diminishing resources of fresh water. Climate change and salinity are both issues, resulting in a major international research effort to breed more resistant crops. The aim of this thesis is to contribute to this effort by determining how wheat varieties respond to salt stress. This study describes an analysis of three wheat varieties (Gamina and Bohoth 105, from Libya and of reported salt tolerance, and Hereward) representing different palis of a salt tolerance spectrum. The effect of induced salt stress on leaf growth rate and final length was investigated by analysing water and solute relations at single cell resolution, using Single Cell Sampling and Analysis (SiCSA). The parameters for the wheat were compared with those of the halophyte (salt tolerant plant) Sea Blight (Suaeda maritima), in order to determine which wheat variety showed the most similar response. All four plants showed rapid cell osmotic adjustment (leaf and root) under salt stress, and leaf turgor pressure was at control levels by 48 hours after salt stress in all wheat varieties. However, varietal differences were evident in terms of cation activity, cortical cell osmotic adjustment, and root turgor regulation, with Bohoth 105 most resembling Suaeda in each. An unexpected observation for wheat leaf cells was a continued increase in turgor pressure after control values had been reached at 48 h post stress, which was not accompanied by an increase in osmotic pressure.

Climate change models predict an increase in the amount and intensity of winter rainfall in the UK. A series of experiments using both container grown plants and field trials was undertaken, to investigate the effect of winter waterlogging on the growth, development and yield of current varieties of winter wheat. The interaction of waterlogging with other factors such as summer drought, seed rate, and sowing date was also investigated. In the field, waterlogging decreased plant population, and uptake of nitrogen over winter from 50 kg/ha to 25 kg/ha. Plants formed new porous nodal roots, which were able to penetrate below the water level. All the varieties tested had a good ability to recover from damage by waterlogging. Plant dry weights per area of waterlogged plots were 50% of controls at the end of treatment in March, 75% at anthesis and 85-90% at harvest. In all varieties except Xi-19, recovery was due to increased number of tillers per plant, a higher proportion of which survived to form an ear. Xi-19 increased the number of grains per ear and the weight of individual grains. Waterlogging early in the season (autumn and early winter) killed more plants, but allowed longer for surviving plants to recover and compensate. Spring waterlogging caused the greatest decrease in grain yield. Sowing in September allowed autumn and spring tillering, thus two chances for compensatory growth. November sown plants did not tiller until spring, and if waterlogging occurred at this time yields were especially poor. Waterlogging did not make crops more vulnerable to subsequent drought or lodging, but the incidence of take-all and stem-base disease did appear to increase. Despite the lack of disparity in tolerance, varieties did appear to have different responses to waterlogging. Varieties with a higher growth rate and demand on resources due to weaker winter dormancy (Xi- 19) appeared to suffer more leaf chlorosis than those with a stronger dormancy (Claire). Deben had good ability to recover due to its high tillering rate in spring, and had the largest yield. Hereward showed the smallest decrease in yield, but had the lowest yield under control and waterlogged conditions. It was hoped that it would be possible to find a simple screening method to identify tolerant varieties at an early stage. Unfortunately plant appearance during waterlogging was not predictive of final yield. Research into stress tolerance has tended to concentrate on identifying `stress genes' but in this case it appears that multi-gene traits are more important in determining crop yield.

The effect of waterlogging on concentrations of dissolved gases and various solutes in soil were investigated in the laboratory, to determine whether early symptoms of-waterlogging damage in wheat (Triticum aestivum L. ) were associated with specific changes in the soil. Waterlogging restricted fresh weight and nutrient accumulation by the shoot, and the growth of the seminal roots. Shoot dry weight accumulation was initially increased above that of the non-waterlogged controls, and thus was a poor measure Of damage when used alone. Symptoms of damage were associated with the fall in soil oxygen concentrations, rather than any changes in soil nutrient concentrations, or the production of toxins: the symptoms of waterlogging damage could be reproduced by deoxygenating solution cultures. The extent to which damage was due to the inability of roots to absorb nutrients from anaerobic media, and whether this could be attributed to low oxygen concentrations alone were investigated and discussed. \pplications of nitrogen compounds during the waterlogging period delayed the onset of premature leaf senescence, but did not assist shoot or root growth. However , shoot growth during the anaerobic period was associated with the shoot nutrient content at the start of that period, and high nitrate concentrations in the rooting medium were beneficial, if supplied before the onset of the anaerobic period. Experiments carried out at different soil temperatures showed that providing there was no abrupt change in temperature at the start of the waterlogging period, the soil temperature had little effect on the growth of the waterlogged plants when expressed as a percentage of the non-waterlogged controls.

The growth and yield of winter wheat was studied after waterlogging at different stages of growth under outdoor conditions, using lysimeters (80 cm diameter, 135 cm deep) containing undisturbed monoliths of sandy loam and clay soils, and cylinders (20 cm diameter, 100 cm deep) filled with sandy loam. Soil oxygen concentration fell from 20% to 3% or less after waterlogging to the soil surface for five days at 12°C, but after up to 21 days at less than 5°C. Winter wheat was most sensitive to waterlogging before emergence, when sixteen days of waterlogging killed all seedlings. Six days of waterlogging depressed plant populations by 88% (clay) and 61% (sandy loam) but compensatory growth limited yield losses to around 18%. After emergence, wheat survived surface waterlogging for up to 120 days. In several experiments on the sandy soil, grain yields were depressed by around 8% after waterlogging for seven weeks during seedling growth, six weeks during tillering, and three weeks during stem elongation. Losses of grain from one experiment on the clay were 16% and 12% respectively at the latter two stages of growth. On both soils, yield losses were largest when yields were high (10 t ha-1), and small when yields were low (4 t ha- and influenced by disease, late frosts and high summer temperatures. Waterlogging increased leaf chlorosis, and depressed tillering, although ear numbers were less affected. Tiller survival appeared related to soil nitrogen availability; waterlogging increased nitrous oxide concentrations, and decreased the nitrate loss in drainage, indicating average denitrification losses of around 12 kg N ha-1. Additional nitrogen fertilizer after winter waterlogging increased ear numbers and grain yield, and a higher proportion of the nitrogen in a winter waterlogged crop was obtained from fertilizer nitrogen than in the freely drained crop.

Wheat (Triticum aestivum L.) is the most widely grown of any crop and provides one-fifth of the total calories of the world's population. Since the 1960s, increases in productivity have been achieved as a result of wide-scale adoption of Green Revolution technologies. However, in spite of growing demand, the challenges of increasing production to feed an estimated world population of 9 billion in 2050 are still considerable. Due to the increased demand, it is estimated that food production must be increased by about 50% by the year of 2050. Improving wheat productivity through developing cultivars with high yield potential and with high adaptability to specific environments is the key objective in the wheat breeding programs worldwide to fill the gap between the production and the demand. The overall aims of the present study were to: (i) investigate the physiological basis of yield potential progress from 1966 to 2009 in spring bread wheats released at the International Center for Maize and Wheat Improvement (CIMMYT) in the irrigated high potential environment of NW Mexico, (ii) investigate the physiological basis of effects of the tiller inhibition Tin1A gene on ear-fertility traits and yield potential and interactions with plant density in NW Mexico and UK environments in lines of a doubled-haploid (DH) population segregating for Tin1A/non-Tin1A alleles and (iii) identify breeding targets for new cultivars with higher yield potential. Four experiments were conducted in NW Mexico at the CIMMYT research station at Ciudad Obregon. Two of these experiments studied a set of 12 historic CIMMYT spring wheat cultivars released from 1966 to 2009 in 2008/9 and 2009/10. The other two experiments examined selected lines from a doubled-haploid (DH) population derived from a cross between CIMMYT spring wheat L14 and UK winter wheat Rialto contrasting for the presence/absence of the TinlA allele for tiller inhibition and their interaction with seed rate in 2008/9 and 2009/10. In addition, two other field experiments were conducted in the UK, one in 2008/09 at KWS UK Ltd in Thriplow, Hertfordshire and one in 2009110 at the University of Nottingham Farm, Sutton Bonington campus, Leicestershire. The plant material for both of these experiments was selected lines from the CIMMYT spring wheat advanced line Ll4 (+Tin1A allele) x UK winter wheat Rialto (-TinlA allele) DH population and the Rialto parent. In the experiment at Thriplow in 2008/09 the DH lines were examined at one seed rate and in the experiment at Sutton Bonington in 2009/10 at two seed rates. At the CIMMYT site in 2008/9 and 2009/10, a randomized complete block design was implemented with four replications for the experiments examining the CIMMYT wheat historic releases and a split-plot randomised complete block design with three replications was implemented for the experiments examining the +/- Tin1A DH lines, with three seed densities (50, 150 and 450 seeds per square metre); seed rates were randomized on main plots and eight genotypes randomized on sub-plots. At the UK site, in the KWS experiment, 24 DH lines (12+Tin1A allele) and (12-TinlA allele) from the L14 x Rialto population were used. There was only one seed rate (300 seeds m-2) and a completely randomised design in three replicates was implemented. The same 24 DH lines were examined in the experiment at the SB site, at two seed rates (40 and 320 seeds m-2) in a split plot randomised complete block design in three replicates. Seed rate was randomized on main plots and DH lines were randomized on sub-plots. In all experiments examining the DH lines of the Ll4 x Rialto population, lines were selected in pairs so that the two groups of +Tin1A and -Tin lA lines were approximately balanced for flowering time and plant height, i.e. every +TinlA line has a non-Tin1A pair with similar height and flowering date. Plots were sampled for destructive measurements of dry weight and DM partitioning and ear-fertility traits at four stages in the historic experiments at (GS3l, GS39, GS61+7d and at maturity) and at two stages in the DH population experiments (GS61+7d and at maturity). The water soluble carbohydrate (WSC) content of the stems plus attached leaf sheaths was also measured at GS61+7d and at maturity. In the historic experiments, at GS 61+14 days, a degraining treatment was implemented by removing all spikelets from one side of the ear (i.e. ca. 50% of the spikletes) in the histories experiment. Non-destructive measurements were taken for stomatal conductance, canopy temperature, fractional photosynthetically active radiation (PAR) interception and normalized difference vegetative index at various dates both pre- and post-anthesis in the historic experiments. In the experiments examining the set of 12 historic CIMMYT spring wheat releases, results showed that from 1966 to 2009 the linear rate of genetic gain in yield potential was 32 ha-1 yr-1 (0.59 % yr-1) (r = 0.76. P = 0.01). Yield progress was primarily associated with harvest index (percentage above-ground DM as grain DM) in the period from 1966 until about 1990 increasing from 43% to 49%, but deceased with year of release thereafter. A non-linear genetic gain in AGDM was evident over the 43-yr period with AGDM increasing from about 1990 from which point it increased rapidly to 2009. There was no association between genetic progress in grain yield and grain number per m2 in this set of 1 cultivars; a small increase in ears per m2 was counteracted by a decrease in grains per ear. However, grain weight tracked the improvement in yield potential over the 43-year period with a linear increase of 0.23 mg yr-1. No change was found in rachis length with plant breeding; however, number of fertile spikelets per ear decreased since about 1990 and was associated with the decrease in grains per ear. There were statistically significant differences in above-ground DM production at all growth stages and a tendency to produce more biomass during the GS31 to GS61+7d phase with year of release. No differences amongst cultivars were found in the amount of radiation intercepted by the whole canopy from GS3l to GS6l+7 days. Although not conclusive, since Bacanora was an exception to the trend and radiation-use efficiency (above-ground biomass per unit PAR interception; RUE), there was a tendency for RUE to increase with year of release which was consistent with a positive association with crop growth rate (above-ground DM per m2 per day; CGR) and the trend for an increase in biomass accumulation during the stem-elongation phase with plant breeding. Although there was a trend for an increase in biomass accumulation from GS31 GS61+7d this was counteracted by a decrease in ear DM partitioning so that ear DM per m2 at GS61+7d and grains per m2 did not change with plant breeding. Results showed that the improvement in the individual grain weight from 1966 to 2009 in this set of cultivars was associated with improvements in the grain filling rate from 1966 to ca. 1990 and in the duration of grain filling from ca. 1992 to 2009. Averaging across years, there was a significant positive association between post-flowering canopy-temperature depression and grain yield. Fractional PAR interception by the canopy layers of the ear, flag leaf and the penultimate leaf was increased with year of release since about 1990. This increase in the fractional interception of PAR correlated significantly with the grain weight and grain yield amongst the 12 cultivars. Grain growth of the cultivars in this historic set was generally sink limited rather than source limited. There was no change in source-sink balance as indicted by grain growth responses to the degraining treatment with year of release.

Wheat grain yield is strongly related to nitrogen (N) fertiliser input, a major cost factor and potential environmental pollutant. Much of the grain N requirement is met by N remobilisation from the canopy. Unfortunately, a consequence is canopy senescence and decreased photosynthetic capacity, reducing carbon available for grain-filling. One approach to achieve both higher N use efficiency and grain yield would be to extend the duration of photosynthesis using delayed leaf senescence “stay-green” phenotypes. Three stay-green and two fast-senescing EMS mutants of wheat (cv. Paragon) were characterised. A fast-senescing line, a stay-green line and the wild-type were grown to characterise the interaction between senescence and N availability. Stay-green line SG3 was able to allocate similar proportions of N to the grain under N-limiting and N-sufficient conditions. The accelerated senescence of line FS2 reduced grain yield and N allocation to the grain. Candidate regulatory genes of leaf senescence genes were characterised by correlating their expression with leaf senescence by screening wheat genotypes with varied senescence characteristics in the field. Among the genes were members of the WRKY and NAC transcription factor families that have been related to senescence. Overexpression of the NAC gene resulted in a stay-green phenotype and increased grain N concentrations, but had no effects on shoot biomass or grain yield. Expression of a WRKY-RNAi construct did not reduce WRKY mRNA levels, but led to accelerated leaf senescence and increases in plant height, the number of fertile tillers and grain yield. These results show that the relationships between senescence, nitrogen remobilisation and grain yield are complex and not easily manipulated. The phenotypes and genes identified could contribute to wheat improvement.

Winter wheat (Triticum aestivum L.) is the most extensive arable crop in the UK grown on about 2M ha p.a. There is a need to identify traits to ameliorate yield losses to drought which are on average about 15% per year. These losses will be exacerbated with predicted climate change. The overall objectives of the present study were to investigate the physiological and genetic bases of water-use efficiency (ratio of above-ground dry matter production to evapotranspiration; WUE) in winter wheat grown in UK conditions and to quantify relationships between WUE and yield performance under drought. The present study used a doubled haploid (DH) population of 33 lines derived from a cross between Beaver and Soissons, known from previous work to contrast for WUE. Two glasshouse experiments (2002/3 and 2003/4) and two field experiments (one at ADAS Gleadthorpe, Nottinghamshire in 2002/3 and the other at Sutton Bonington, University of Nottingham in 2004/5) were conducted. In the glasshouse experiments, two irrigation treatments (with and without irrigation) were applied to four genotypes (two parents and two DH lines), and in the field two irrigation treatments (rainfed and fully irrigated) were applied to the two parents and the 33 DH lines. A range of physiological traits was measured, including developmental stages, carbon isotope discrimination (Δ13C), leaf gas-exchange variables, green areas and biomass at sequential samplings, and these traits were related to grain yield. Transpiration efficiency (ratio of above-ground dry matter production to transpiration; TE) was assessed using the established inverse relationship between TE and Δ13c. In the glasshouse, WUE measured as the regression slope of dry matter on water use, did not differ amongst genotypes in 2003, but did in 2004. Soissons showed higher WUE than other genotypes under irrigation, and also higher WUE than Beaver under drought. For measurements of TE according to Δ13. Soissons and line 134G showed lower Δ13C values (higher TE) than line 134E and Beaver (P<0.05) in 2004 under both irrigation and drought. Soissons and line 134G showed consistently higher TE on account of lower stomatal conductance (gs ) and sub-stomatal C02 concentration (C) values. The early developing Soissons and line 134G exhibited greater flag-leaf green area persistence under drought than the late developing Beaver. Beaver tended to use more water than Soissons under both irrigation and drought, but reductions in water use under drought were similar amongst genotypes. Lower seasonal water use for Soissons than Beaver was associated with a smaller root system. There was a tendency for dry matter of Beaver to be more depressed under drought than Soissons in both the years. Overall, it was not possible to detect significant differences in biomass responses to drought amongst the genotypes, but there were consistent genetic differences in WUE and TE observed under both irrigated and droughted conditions. In the field experiments, the onset of drought coincided broadly with anthesis. The average grain yield losses under drought were 0.5 t ha-1 in 2003 and L6 t ha-1 in 2005. Averaging across site/seasons, Δ13C correlated positively with grain yield amongst the 35 genotypes under irrigation (r--0.35; P<0.05) and under drought (r--0.54; P<0.01), indicating a negative trade off between TE and yield. A 13C decreased under drought and a higher TE was associated with a reduction in average flag-leaf gs, measured from flag leaf emergence to anthesis + 4weeks. Stomatal conductance was measured for eight of the 33 DH lines including the parents, and there was a trend for lower Δ13C (higher TE) to be associated with lower gs, The genetic differences in gs, were generally associated with corresponding decreases in Ci and net photosynthetic rate (A). Therefore results suggested that the negative relationship between TE, as indicated by Δ13C and yield was associated with corresponding reductions in seasonal water use. There was a nonsignificant irrigation x genotype interaction at Gleadthorpe in 2003 and Sutton Bonington in 2005 for Δ13C indicating that this trait was of high heritability. There was an irrigation x genotype interaction for grain yield (P<0.05). A small number of genotypes showed higher yield associated with low Δ13C and these outlier lines could potentially be identified for breaking the negative linkage between yield and delta. In summary, WUE was negatively correlated with yield under drought in this population; and season-long water use appeared to be the most important component affecting yield levels under drought. It is suggested that selecting genotypes indirectly for high Δ13C (low WUE) may be a strategy to improve grain yield under drought. In the quantitative genetic analysis, the putative QTLs identified for target physiological traits were generally different at Gleadthorpe in 2003 and Sutton Bonington in 2005. The most confident putative QTLs for Δ13C were mapped on chromosomes 3B (LOD=2.32) and 2D (LOD=1.43). The identification of QTLs as potential candidate genes on these chromosomes may be associated directly with WUE in the Beaver x Soissons DH mapping population. The Δ13C QTL on chromosome 3B was detected commonly in both the irrigation environments and the direction of allelic effects was consistent with the parental differences in Δ13C. This QTL may therefore represent a novel gene for optimising WUE. It is suggested that breeders could optimise TE by selection according to a marker for this gene involving further fine-mapping to identify a marker tightly linked to the gene. Such a marker would also provide a target for gene discovery in future work. The results suggest that water use is the most important component of Passioura's yield model for yield improvement under UK conditions. Nevertheless, WUE and harvest index and their responses under drought will also likely play a role in yield improvement through breeding in the UK targeted at drought-prone environments in future years.

Bibliography: leaves 174-210 / 210 leaves, [5] 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, 1987

Errata slip inserted. / Bibliography: leaves 68-93. / viii, 93, [42] leaves, [15] leaves of plates : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Rye chromosome 6R in triticale contains a gene useful for resistance to cereal cyst nematode. This study shows that the complex structure of this chromosome may prevent render its use impracticle in introgression of this resistance into wheat. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1998

Die Veröffentlichung informiert über Untersuchungen zur Sicherung der sächsischen Qualitätsweizenproduktion bei konservierender Bodenbearbeitung nach Mais und unter Beachtung der Wasserrahmenrichtlinie sowie des Nationalen Aktionsplans zur Reduzierung des Pflanzenschutzmitteleinsatzes. Der aus Gründen des Erosionsschutzes praktizierte Verzicht auf die wendende Bodenbearbeitung hat ein höheres Anbau- und Vermarktungsrisiko für den Landwirt zufolge. Grund sind mögliche höhere Belastungen mit Mykotoxinen und Probleme bei der Einhaltung von Grenzwerten. Forderungen nach einer generellen Reduktion des chemischen Pflanzenschutzes sind insbesondere in Fusariumbefallsjahren in der Praxis schwer zu realisieren. Ebenso ist der Anbau wenig anfälliger Sorten in Verbindung mit der halbkrumentiefen Einmischung gemulchter Maisreste unerlässlich. Aus den Projektergebnissen wurden Handlungsempfehlungen für Landwirte und Berater abgeleitet.