Browsing by Subject "Trockenstress"

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    Identifizierung und Quantifizierung von Trockenstressreaktionen an ausgewählten Zierpflanzenkulturen
    (2013) Krato, Theresa; Wünsche, Jens Norbert
    The present thesis gives attention to the development of a practicable screening process for the identification of drought-stress tolerant ornamental plants. Requirements are to be created in terms of reduced water use, market expansion to warmer regions and increased ability of transportation. The studies were included into a cooperative research project involving 4 plant breeding companies, research centre Jülich, research institute Geisenheim and the GFP. Scope of the thesis was the deployment and evaluation of an assessment scheme to quantify drought-stress reactions, the development of dehydration experiments under stationary climatic conditions and to search for physiological markers of drought-stress tolerance. The experiments were mainly conducted on Petunia Cultivars and Impatiens Neu Guinea Grp. Genotypes. Main results of the investigation are listed below: 1. The species specific assessment schemes are based on an accurate visual characterization of the wilting process. The wilting is rated using ranks from 1 ? 9. Assessed parameters were the phyllotaxy, surface texture and leaf color. The assessment schemes were proved to be acceptably objective and precise during the experiments and the genotypes were evaluated accordingly. 2. The plants were dried out under standardized conditions in climate chambers. The decrease of water as well as the occurrence of wilting was recorded. Climatic conditions (temperature, humidity and radiation) in dehydration experiments were set up to reach a rank of 9 in 5 to 9 days according to drought-stress tolerance and pretreatment of genotypes. For this reason, an adequate differentiation between genotypes was ensured even with a single assessment per day. However, the system weight (substrate and plant), which was used to characterize the stress intensity has to be corrected about the fresh weight of plants. The investigated genotypes of Impatiens behaved similarly regarding to their drought-stress tolerance in many replications and consequently allowed for a ranking. In contrast, the ranking order of investigated genotypes of Petunia was vague in experimental replications. However, an influence of water supply on the wilting behavior of plants was detected in this context. 3. In order to search for physiological markers of drought-stress tolerance, studies on water potential, gas exchange and thermal imaging were conducted in line with the dehydrogenation experiments. A tendency was shown, that drought-stress tolerant genotypes reacted later and less distinctive on drying of the substrate compared to susceptible plants. But a correlation between water potential of shoots and water supply in the substrate as well as a differentiation between genotypes was certainly week. This was mainly due to high variation of data. The transpiration rate of investigated plants reacted more on water supply though. The ranking, which was based on the parameter transpiration rate correlated well with the ranking of the wilting behavior from the dehydrogenation experiments. Consequently, the stomata management appears to be a promising indicator of drought-stress tolerance. Thermal imaging showed an increase of leaf temperature with decreasing moisture content of the substrate. Accordingly, the leaf temperature of Impatiens can serve as an indicator for the opening rate of stomata. 4. Currently, the dehydrogenation experiments can be considered as the easiest and most practicable approach to identify drought-stress tolerant genotypes of Impatiens and Petunia due to the results of the present thesis. Physiological measurements supported the ranking of genotypes, which was developed according to the dehydrogenation experiments. Especially, data on the opening rate of stomata illustrated differences between the tested genotypes. However, the dehydrogenation experiment does not provide information of the dependence of vegetative and generative performance of plants on water supply, which is very important for producers of ornamentals. 5. The ranking of drought-stress tolerance from climatic chambers corresponds only partly with results of experiments under field conditions. Therefore, a screening concept has to be developed in a subsequent project to investigate the complex context of climate-stress tolerance.
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    Optimizing selection efficiency in maize for the drought prone eastern and southern African environments
    (2013) Kebede, Aida; Melchinger, Albrecht E.
    Breeding for stress tolerance is the most cost effective way of avoiding drought-induced yield reduction in the tropics. Optimizing breeding for drought tolerance at CIMMYT could enhance the effectiveness of this multi-national breeding program and warrant fast delivery of drought tolerant materials to the farmers. Thus, the overall aim of my study was to improve the efficiency of drought tolerance breeding of maize at CIMMYT for the rapid and cost effective advancement of drought tolerant materials for the drought prone regions of the ESA (Eastern and Southern African countries). We screened a diverse source of tropical germplasm for their haploid induction rate (HIR) and the seasonal variation of this trait. We then compared various managed drought and well watered experiments conducted as line per se performance trials (LP) and testcross performance trials (TP) in Kenya and Mexico. Further, we estimated the relative selection efficiency of the principal breeding regions of CIMMYT for the tropics in ESA and Mexico with unselected and selected breeding materials. The specific objectives of my study were to (1) monitor the variation for HIR among diverse source germplasm in tropical maize, (2) determine the relative importance of general (GCA) and specific (SCA) combining abilities of the source germplasm for HIR, (3) investigate the influence of tropical summer and winter seasons and genotype × season interactions on this trait, (4) determine if LP is predictive of TP for yield under drought in sets of lines under development by the CIMMYT maize breeding program in Kenya and Mexico, (5) determine the genetic correlation between performance of lines per se under drought and testcrosses under optimal conditions and assessing its effect on yield potential, (6) examine the correlation between TP under well-watered and drought stress conditions for potential indirect selection efficiency of well-watered conditions in comparison with drought stress, (7) determine the relative importance of regional adaptation of maize hybrids to Mexico and ESA by subdividing the genotype × environment interactions and determining genotypic correlations between both regions, (8) calculate the indirect selection efficiency for selecting materials based on test results from one region on the selection gain in the other region, and (9) identify the most suitable stage for exchanging breeding materials between Mexico and ESA. Source germplasm and induction season affected HIR and MCR (mis-classification rate) considerably in tropical maize. Source germplam with high HIR and low MCR could be used in the initial stage of implementing the DH technology in the tropics. GCA effect was more important than SCA or genotype × season interaction effects for HIR in tropical maize. Thus, enhancing HIR in source germplasm can be achieved through cyclical breeding or recurrent selection. Winter season was considered the best season for induction because it provides suitable environmental conditions for higher HIR and lower MCR. Overall HIR was high enough to apply the in vivo DH technology in the routine breeding activities in tropical maize. There were moderate genotypic correlation and ISE (Indirect Selection Efficiency) values between LP and TP under drought that increased with an increase in stress level. Hence, LP trials were predictive of TP trials particularly under severe drought stress. Furthermore, screening of lines for LP under drought stress did not compromise yield potential. TP under well-watered conditions were not predictive of TP under drought stress emphasizing the need of managed drought trials to identify drought tolerant materials. With the current shift of inbred development to large scale DH line production, LP evaluations can reduce the cost of making large numbers of testcrosses and optimize breeding for drought tolerant hybrids in the tropics. The exchange of breeding materials between ESA and Mexico can be done with early and late generation materials. This is because there was negligible genotype by region interactions as compared to genotype by location interactions within each region and high genotypic correlations between the two regions. Further, ISE estimates for trials conducted in Mexico and in ESA were high. Adaptive diseases for each location might hamper the exchange of materials, however, with current molecular marker tools like marker assisted selection and genomic selection, the problem of selecting for disease resistance in the region where the disease is not prevalent seems promising. In conclusion, there are ample opportunities in the CIMMYT maize breeding program to optimize breeding for drought tolerance in the tropics through rapid and large scale production of DH lines and evaluation of these lines for LP in managed drought trials. Moreover, breeders from ESA and Mexico could benefit from each other?s materials and test results by regular exchange of breeding materials at both the early and late stages of testing.
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    Quality impact of nitrogen in wheat grain properties and protein development for higher baking quality
    (2022) Rekowski, Azin; Zörb, Christian
    Storage protein concentration and composition influence the baking quality of wheat. Traditionally, baking quality is correlated with the total protein concentration in flour. However, despite similar protein concentrations, the baking qualities of different cultivars can vary, and the variances may be related to differences in the storage protein composition (Zörb et al., 2018). Though both protein concentration and composition are affected by fertilization management (especially nitrogen) and water availability, it is not certain whether compositional changes will suffice to enhance the quality of final products. Additionally, there is a high risk for the environment, associated with nitrogen losses in wheat production. To increase nitrogen efficiency, minimize nitrogen losses and optimize the baking quality, it is crucial to improve nitrogen fertilizer management. To address the question whether nitrogen and water management induce changes in protein composition which result in altered baking qualities, several investigations were conducted in the present work. Total protein was extracted from wheat flour and SDS-PAGE (Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis) was used to detect proteins sub-fractions. To assess baking quality, the specific volume, freshness retention as well as the hardness of the bread were evaluated. In chapter two, as part of a pot experiment, two different levels of late nitrogen fertilizer were tested using two winter wheat cultivars of different quality classes (Discus and Rumor). Both cultivars produced more grain yield and total protein concentration as a result of late nitrogen supply. However, bread volume was only increased in Discus, possibly related to the greater changes in total gluten concentration and protein composition including HMW-GS and ω-gliadins. However, an increase of late nitrogen level did not further improve baking quality. Compared to Discus, an addition of late nitrogen did not result in significant changes in the protein composition of Rumor. Collectively these results indicate that late nitrogen management strategies are practical but need to be adjusted depending on the cultivar used. Chapter three describes a field experiment where three different nitrogen forms were used ((i)ammonium nitrate, (ii) urea with 46% total N, (iii) urea as before amended with urease inhibitor N-(2-nitro-phenyl) phosphoric triamide (2-NPT) and (iv) control (no nitrogen addition)). While no significant/only a slight effect was observed for urea alone, ammonium nitrate and urea plus urease inhibitor similarly increased total grain protein concentrations. Although both fertilizers boosted the levels of ω-gliadins and HMW-GS among the storage protein fractions, the influence was more pronounced in the ammonium nitrate application. In comparison to the urea treatment, the combination of urea plus urease inhibitor significantly influenced protein composition and generated higher specific baking volumes and the best fresh-keeping characteristics. Due to the strong enhancement in NUE and baking quality obtained with the urea plus urease inhibitor application, accompanied by reduced nitrogen losses and easy handling, this treatment could be considered as a substitute for urea alone or ammonium nitrate. Chapter four describes a field study conducted in Iran with different German (Impression, Discus, Rumor, Hybery) and Iranian (Alvand, Mihan) genotypes representing diverse quality classes and grain protein levels. Two different levels of water stress were applied during anthesis and grain filling period. Overall, no significant changes in total protein concentrations were recorded. In addition, the concentrations of different protein fractions were unchanged in five out of the six genotypes. However, German genotypes exhibited an increase in HMW-GS under severe drought conditions, and an increased severity of drought stress amplified the percentage of ω-gliadins in all genotypes. Even though drought stress did not alter the concentrations of the HMW-GS sub-fraction in Iranian genotypes, a high specific bread volume was still observed, most likely related to an increase in ω-gliadins. All in all, the protein composition should be considered in addition to yield and total grain protein concentration when developing new wheat varieties for challenging climatic conditions. In summary, late nitrogen and urea application, along with the addition of urease inhibitors, can enhance the gliadin and glutenin content and improve the baking quality. In addition, it may be possible to develop wheat genotypes with optimal baking properties by paying attention to the protein composition when drought stress exists. Although genetically determined subunits of the gluten fractions are known to be associated with bread-making quality, the studies presented here indicate that additional factors, such as the levels of nitrogen supply or water limitation, affect the composition of grain protein fractions and can be positively correlated with baking quality. Therefore, total grain protein concentration alone is not a reliable indicator of grain quality. Additionally, several individual proteins were altered by different management practices. Consequently, these proteins can have great effects on the quality of breads, so further studies should evaluate whether those individual proteins directly correlate with bread baking quality.
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    Rye (Secale cereale L.) : agronomic performance under drought and methods of crop physiology to determine the drought tolerance of winter rye
    (2015) Kottmann, Lorenz; Fangmeier, Andreas
    Winter rye (Secale cereale L.) is predominantly cultivated on light and sandy soils with a low water holding capacity and will therefore be especially affected by drought induced yield losses in Central and Eastern Europe in the future. Drought adaption through breeding is therefore an important task in order to adapt this crop to future climate conditions. In this context, the crop physiology methods canopy temperature depression (CTD = Tair - Tcanopy) and carbon isotope discrimination (delta) were examined for their suitability as selection criterion under drought on a small number of genotypes. Two sets of each 16 genotypes were therefore grown under different drought conditions in rain-out shelters and under well-watered conditions in the years 2011, 2012, and 2013. The CTD was determined several times during the growth period using two infrared (IR) thermometers and an IR camera. delta-analyses were performed on mature flag leaves (delta_leaf) and grains (delta_grains). Furthermore, ash content in mature flag leaves and grains, as well as mineral concentrations in mature flag leaves (Ca, K, Mg, and Si) were examined for their use as surrogates for the expensive and time-consuming delta-analyses. In addition to the evaluation of possible selection criterions, the agronomic performance of rye in the different drought regimes was assessed: Grain-, straw-, and total aboveground biomass yields, the grain yield components spikes m-2, kernels spike-1, and thousand kernel weight (TKW), leaf area index (LAI), and phenological characteristics were examined. Drought induced grain yield reductions ranged from 14 to 57%, whereas straw yield was generally lesser affected. The growth period was shortened by up to 12 days under drought conditions compared to optimal water supply. Grain yield was positively associated to straw yield, LAI, spikes m-2, and kernels spike-1 under water deficit. High number of grains per area land seemed to be especially important for high grain yields under drought. Furthermore, the results suggest a strong importance of pre-anthesis reserves for the reallocation of assimilates for grain filling under drought in rye. Regarding the suitability of possible selection criterions, CTD was significantly positively related to grain yield under drought. Significant correlations between CTD and grain yield were, however, only observed when the measurements were carried out on days with optimal weather conditions. Optimal conditions turned out to be days with a clear sky, a solar irradiation >700 W m-2, an air temperature of at least 20°C, as well as wind speeds <3 m s-1. Furthermore, the results showed that also rather inexpensive IR instruments are suitable to assess the CTD. Regarding the carbon isotope discrimination, delta_leaf was significantly positively related to grain yield under water deficit, but the correlation was weaker than between CTD and grain yield. Delta_grains was not related to grain yield at all. Ash content and mineral concentrations were significantly related to grain yield under drought, but the correlations were quite inconsistent between the two experimental years. Because of the weak or missing relationship with grain yield, carbon isotope discrimination and its potential surrogates ash content and mineral concentration cannot be recommended for their use as selection criterions under German climate conditions at present. A general limitation of the preset work was, however, the low genetic variability of the genotypes, which may have reduced the significance of the results. The results should therefore be validated with a more diverse set of genotypes. However, especially the CTD seemed to be a promising selection criterion which may help to develop drought tolerant rye genotypes, if this method can be successfully integrated into the breeding process.