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University of Copenhagen (2014)

Adaptive properties of Adansonia digitata L. (Baobab) & Parkia biglobosa (Jacq.) R.Br. (African Locust Bean) to drought stress

Zoéwindé Henri-Noël Bouda

Titre : Adaptive properties of Adansonia digitata L. (Baobab) & Parkia biglobosa (Jacq.) R.Br. (African Locust Bean) to drought stress

Auteur : Zoéwindé Henri-Noël Bouda

Université de soutenance : University of Copenhagen

Grade : Doctor of Philosophy (PhD) 2014

Résumé
For arid zones such as the Sahel, drought is one of the most important constraints to the survival and development of plants playing a key role in the livelihoods of human populations. The domestication of fruit trees such as Adansonia digitata and Parkia biglobosa for the Sub-Saharan region has been suggested as a strategy to improve local population livelihoods. To promote domestication and define a strategy for conservation of tree species, it is important to improve our knowledge of their biology, genetics, physiology, and potential adaptation to different climatic conditions. In the present thesis I studied the adaptive properties to drought stress of A. digitata and P. biglobosa at nursery level. The two species are native to African savannas. So far, many studies have been made on the two species, but very few were focused on their adaptive properties to drought stress at nursery level. For the current studies, nursery trials were established with seeds from seven provenances of P. biglobosa (Kantchari, Monkin, Peni and Saponé in Burkina Faso, Bakaribougou, Tabakoro and Zangasso in Mali) and seven provenances of A. digitata (Kolangal, Liptougou and Nobéré in Burkina Faso, Komodiguili, Koumadiobo and Samé in Mali, Mkundi in Tanzania). Three different water regimes were applied : soil high, medium and low water content (HWC, MWC and LWC) corresponding respectively to 100%, 75% and 50% of field capacity. A split-plot experimental design was used with the provenance as main plot and the water regime as sub-plot, replicated three times. Each provenance was represented by 30 seedlings in each replication, corresponding to three lifespans with ten seedlings each (six, twelve and eighteen months after water stress started) . For both species I investigated the effects of drought stress on the seedling survival, growth and dry matter partitioning. For A. digitata I also investigated the effects of drought stress on seedling morphology and physiology.
Subjected to water stress at the same age and approximately the same period, A. digitata had a much higher survival rate than P. biglobosa. However, both species showed a strong reduction of the relative growth rate (diameter and height) and the total dry weight under the effect of applied water stress. Despite differences between provenances of P. biglobosa, it was not possible to link their geographical position or climatic parameters to growth performance, fresh to dry weight or shoot to root ratios. For A. digitata, although some morphological parameters (number of branches, number of leaflets and leaf length) were correlated with the rainfall, the latitude and the average temperature), none of the physiological differences between provenances were correlated to environmental parameters of the site of origin. However, the provenance from East Africa was in several aspects (germination and survival rates, growth, morphology and physiology) different from the West African provenances.
For none of the species, there was correlation between the studied parameters and the performance under stress. It follows that I am reluctant to give any provenance recommendations for planting based on the results, other than to use extreme caution if provenances from East Africa are introduced to West Africa, in the case of A. digitata. Until a better understanding of the two species morphology and physiology under drought stress has been achieved, there seems to be no alternative to field testing. Therefore, longterm investigations are needed before reliable recommendations can be made for the end users. In addition to biological and physiological aspects, ethnobotanical knowledge should be taken into account in determining the criteria for selection of the best plant material, in order to find a compromise between adaptation to environmental conditions (especially drought) and the acceptability by the populations who have been exploiting the two species for millennia.

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Page publiée le 14 janvier 2015, mise à jour le 17 juillet 2017