Beining, Alice Marie: Ecophysiological diversity of wild Coffea arabica populations in Ethiopia : Drought adaptation mechanisms. - Bonn, 2007. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
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author = {{Alice Marie Beining}},
title = {Ecophysiological diversity of wild Coffea arabica populations in Ethiopia : Drought adaptation mechanisms},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2007,
note = {Drought is a wide-spread limiting factor in coffee (Coffea arabica L.) production, but the development of adapted cultivars is hampered by a limited understanding of the physiological resistance mechanism and the extreme narrow genetic base of plant material used in breeding. Therefore, the objective of this study was to evaluate the ecophysiological diversity of coffees wild progenitors and their potential for the improvement of drought resistance at its primary gene pool and center of genetic diversity, in Ethiopia.
Complementary field and common-garden studies of populations native to habitats spanning a wide range of climatic conditions were examined by combining seasonal measurements in naturally regenerated stands of wild coffee (in-situ) with an artificial drought stress experiment (ex-situ), where seedlings of these populations were raised under controlled environmental conditions and subjected to different watering and light intensity regimes. Plant ecophysiological behavior was assessed in terms of gas exchange activity, leaf water status determined by water potential and osmotic potential measurements, chlorophyll fluorescence and carbon isotope discrimination.
The results of both experiments revealed that the ecophysiology of wild C. arabica populations was strongly influenced by conditions of water deficit, heat and high irradiance, which had combined effects on the plants during drought periods.
However, the coffee plants were able to adapt to the natural and experimental drought conditions; thereby their resistance mechanism was mainly based on the capability to avoid tissue desiccation. In particular, physiological responses were attributed to fine control of stomatal conductance reducing water loss, high rates of photosynthesis and improved water-use efficiency. Overnight re-saturation of tissue water status with no active osmotic adjustment ability was another important characteristic in drought adaptation of the plants.
In addition, the in-situ ecophysiological behavior of populations from different habitats revealed contrasting strategies in response to drought stress, thereby this habitat-specific variability was also found under common-garden conditions. Thus, the results of this study provide evidence that there is a genetic basis of the marked ecophysiological diversity in wild Coffea arabica and that the contrasting habitat conditions result into different selection pressures for traits related to water-use and promote regional differentiation in adaptation to drought stress.
Furthermore, the coffee plants exhibited substantial phenotypic plasticity for all ecophysiological traits in response to varying soil moisture conditions; thereby the magnitude of plasticity differed markedly among the populations. In particular, plants originating from drier, variable climates showed the highest amount of plasticity suggesting fast adaptation to changing environmental conditions. A high correlation of plastic responses in most characters was an indicator for a high degree of phenotypic integration demonstrating the need for integrative approaches for the evaluation of drought adaptation in this species.
Overall, the profound amount of ecophysiological diversity in the primary gene pool of C. arabica found in this study emphasizes its importance as a unique and valuable genetic resource. The specific adaptations to drought stress suggest a high potential for breeding of improved cultivars and stresses the need for conservation of the profound ecophysiological diversity. In particular, the findings suggest an approach of in-situ conservation within the evolutionary dynamic ecosystems of the natural habitat of Coffea arabica in order to allow the preservation of genes for stress resistance as they co-evolve with their changing environment.},

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