PhD Dissertation

The social and economic importance of the baobab (Adansonia digitata L.) and a study of its ecological, morphological, genetic, and biochemical variability

ASSOGBADJO Achille (2006)
PhD, Ghent University, Belgium

The present study has been performed in the three climatic zones of Benin (West Africa): the Guinean zone (6°25 N – 7°30 N), the Sudano-Guinean zone (7°30’ N et 9°45’ N) and the Sudan zone (9°45 N et 12°25 N). It uses a transdisciplinary approach to design a better conservation and management strategies for the baobab’s genetic resources within the traditional agroforestry systems for the benefit of its users. The ethnobotanical surveys have been performed among 11 ethnic groups in the whole country and have mainly focused on the uses of baobab products, its socio-economic importance and on the endogenous criteria used by rural people for the species characterization. The ecological and intra specific genetic diversity in the baobab populations have been assessed according to the climatic gradients and the conservation and restoration strategies have been proposed accordingly. To help for the valorization of baobab products in the diet and nutrition, biochemical analyses of the organs (leave, pulp, kernel) have been performed according to their provenance. Also, propagation tests have been done to assess the aptitude of the species for domestication. The study showed that A. digitata is a multipurpose tree species used by rural communities for food, medicinal, cultural, cultural and economic purposes. Rural populations use several criteria to differentiate baobab individuals in traditional agroforestry systems: the characteristics of the fruits (color and seed size, precocity in maturity, tree productivity, capsule shape, taste of the pulp); of the bark (color, structure) and of the leaves (color, taste and shape). The use of differentiation criteria of baobab individuals in rural area shows that the species has high cultural value. From that the “Plus Trees” having a high value for rural communities have been identified and can then be used for the conservation and valorization of the species’ genetic resources for the benefit of the users. A five months market investigation in Malanville district (north of Benin), showed that 200 tons of baobab seeds coated with pulp, 10 tons of baobab pulp and 1 ton of baobab leave powder were commercialised and generated up to 15 millions FCFA (US$ 30,000), 400000 FCFA (US $ 800) and 200000FCFA (US $400) for 139 rural populations involved in that business. Based on these results, it can be concluded that baobab has a socio-economic importance and can be used as fonctional food for the wellbeing of rural communities. The study also revealed that the density and productivity of baobab vary according to the climatic zones. In the ecological point of view, the correlation between environmental and biotic characteristics (production and dendrometric variables) showed that the zones with high values of potential evapotranspiration, rainfall, relative humidity, temperature, percentage of clay and fine silt are associated with a low seed and fruit pulp production. In contrast, high values of C/N (Carbon / Nitrogen) ratio were shown to be negatively associated with pulp and kernel production as well as with the development (morphological traits) of baobab individuals. Therefore, the development of baobab depends on the environmental conditions. Moreover, genetic analyses using AFLP fingerprinting showed a clustering of all genotypes sampled into six gene pools. Generally, samples collected in the same climatic zone belong to the same gene pools indicating that the genetic structuring of the sampled individuals is correlated with their geographic origin. As it is, the in situ conservation strategy of baobab genetic resources should consist in define the conservation units in each climatic zone. The biochemical studies showed that the baobab’ organs are rich in minerals and vitamins (pulp and leave) and in proteins (seed). The biochemical composition of the organs does not vary according to the provenance of the trees, except for the vitamin C content. On the other hand, it was shown that the physico-chemical characteristics of the soil have an influence on the nutritive value of baobab organs. Highly basic soils (high pH value), rich in carbon, clay, fine silt and organic matter positively affect the organs contents in iron, potassium, vitamin C, carbohydrates, zinc, proteins and lipids and negatively affect their contents in magnesium, calcium, vitamin A and fibers. In contrast, soils rich in crude silt and sand have an opposite effect on these same biochemical parameters of the organs. Finally, propagation tests showed that the best mean percentage of seed germination was obtained with the seeds scarified before sowing. Moreover, it was shown that storage duration of more than 3 months negatively affects seed germination whatever their provenance. Based on the found results, valorization, domestication and conservation strategies for the baobab’s genetic resources have been analyzed for the wellbeing of its users. 

Keywords: Adansonia digitata, genetic diversity, ethnobotany, conservation, domestication, valorisation.