Innovative Microbial Approaches to the Management of Acacia senegal Trees to Improve and Sustain Gum-Arabic Production in Sub-Saharan Africa

A potential solution to land degradation is to promote the utilization, regeneration, and planting of the native legume tree, Acacia senegal, which is the main species in the world producing the internationally traded gum-arabic. This tree species is very important for the livelihoods of many rural populations and has potential for wider use. Sarr et al. (2005a) assessed the rhizobial populations in soils from natural A. senegal forests in Mauritania and the Senegal River Valley. They showed that soils from Mauritania were less rich in native rhizobia than the soils from Senegal. In some cases, no native rhizobia were detected. The low numbers of native rhizobia in the soils of A. senegal forests may have a negative implication on the growth of the trees in very poor soils. In this case, we need to inoculate with selected rhizobial strains to improve the growth of the trees/seedlings. Sarr et al. (2005b) determined the most efficient methods of inoculation to improve nodulation and growth of A. senegal under greenhouse conditions. Their results showed that inoculation, using dissolved alginated beads containing rhizobia, significantly improved the growth of A. senegal and was better than the growth of plants in other treatments, such as liquid inoculum. The same authors demonstrated an interaction between tree provenances and the effect of inoculation with rhizobia. Their results suggest that: (1) it may be possible to improve growth and yield of A. senegal by careful selection of the symbiotic partner; and (2) nursery-grown seedlings of A. senegal should be inoculated, just after sowing, with dissolved alginate beads containing the selected rhizobia. Sarr et al. (2003c) assessed the efficiency of this inoculum in the field and recorded a significant positive impact of rhizobial inoculation on total biomass production by A. senegal trees under irrigation.