Browsing by Subject "Dehydration"

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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.