Increased gum arabic production after infestation of Acacia senegal with Aspergillus flavus and Pseudomonas pseudoalcaligenes transmitted by Agrilus nubeculosus

Abstract

The aim of this study was to investigate the correlation between the beetle Agrilus nubeculosus and gum arabic production by Acacia senegal. Some trees were tapped and left open to facilitate infestation by A. nubeculosus and others were covered with wire mesh as control. Gum yield, physical and chemical properties of gum were determined for infested and control trees. A. senegal infested by A. nubeculosus produced significantly more gum than control trees. Infestation also caused significant changes in some physical properties of gum (colour, shape, size, moisture content and optical rotation) and chemical properties (ferrous, calcium, magnesium and nitrogen contents), whereas, no significant difference was recorded in phosphorus and manganese contents. Aspergillus flavus Link. and Pseudomonas pseudoalcaligenes Monias were isolated from the mouth parts of A. nubeculosus. Inoculation of the tapped branches of A. senegal with a suspension of A. flavus alone or in combination with P. pseudoalcaligenes, resulted in highly significant gum yield as compared to the control. It seems that A. flavus and P. pseudoalcaligenes acted as elicitors that have stimulated the synthesis of gum arabic. A. nubeculosus transmitted A. flavus and P. pseudoalcaligenes to the tapped areas. Hence, the beetle was significantly associated with gum production.

Key words: Acacia Senegal, gum arabic, Aspergillus flavus, Pseudomonas pseudoalcaligenes, Agrilus nubeculosus, inoculation elicitors.