Effect of Inoculation with Rhizobia on the Gum-Arabic Production of 10-Year-Old Acacia senegal Trees

Abstract

ABSTRACT The aim of our study was to assess if the inoculation of Rhizobium on mature Acacia senegal trees would have an effect on the gum-arabic yield. A plantation located in Rotto (Department of Linguere Senegal) containing 80 similar 10-year-old trees was identified. The distance between each tree planted was about 5 m. Soil analysis showed soil characteristics were not different within the plantation. The plantation was divided into two parts: one part where the 10-year-old trees were inoculated at the beginning of the rainy season (August 2002 and August 2003) with 1 L of a liquid inoculum prepared with dried alginate beads containing a mixture of selected rhizobial strains (CIRADF 300, CIRADF 301 and CIRADF 302). The taping was done at the same intensity on each tree and when the leaves started to fall. The gum-arabic production was measured for every tree during two years (December 2002/April 2003 and December 2003/April 2004). The rainfall the first year was low, about 250 mm. The effect of the inoculation was assessed in terms of percentage of trees producing gum and amount of gum-arabic produced. Results were not significantly different (P ≤ 0.05). Before the second rainy season, mature trees from the inoculated plot were reinoculated and tree taping accomplished. The annual rainfall the second year was around 440 mm. Data suggested that gum-arabic yield of inoculated trees was significantly higher compared to the noninoculated tree gum-arabic yields. We can assume that the inoculation of 10-year old-trees will enhance the gum-arabic yield under natural conditions.