ALLELOPATHIC EFFECTS OF Vachellia tortilis, Vachellia nubica, AND Hyphaene compressa ON EARLY GROWTH OF Prosopis juliflora

Abstract

Prosopis juliflora (Sw.) DC is an invasive species negatively impacting plant ecology and livelihoods in introduced areas. Native tree species may produce allelochemicals that inhibits growth of invasive species, resulting in a natural management technique. This study was conducted to evaluate allelopathic effects of selected native tree species (Vachellia tortilis, Vachellia nubica, and Hyphaene compressa) on early growth of P. juliflora. The goal was to identify which of these native tree species could be used to suppress growth of P. juliflora as part of a biological control and management strategy. Allelochemicals and effects of crude leaf and root extracts of studied native tree species on seed germination and seedling growth of P. juliflora were determined. Leaves and roots were randomly collected from the native tree species and used to prepare crude leaf and root extracts of 0%, 1%, 2.5%, 5%, and 10% concentrations. Effects of leaf and root extracts on germination and seedlings growth of P. juliflora were determined in a germination chamber and greenhouse respectively. Both experiments were laid out in a completely randomized design. Tests for presence of allelochemicals were done using standard laboratory procedures. Effects of leaf and root extracts of the native tree species on germination and growth of P. juliflora were summarized into means and tested using three-way ANOVA at 5% significance level and means separated by Tukey test. The study revealed that crude leaf and root extracts of the native tree species had inhibitory effects (p=0.0001) on the germination and growth of P. juliflora as indicated by the reduction in the studied variables. Prosopis juliflora seed coats treated with V. tortilis and V. nubica leaf extracts turned darkish before germination while germinated seeds in 10% leaf extracts of V. nubica aborted. Depending on crude extract concentrations, percent inhibition on germination characteristics were; percent germination (21-74%), wet weight (6-49%), plumule length (10-47%), and radicle length (7-86%) of germinating P. juliflora. Prosopis juliflora seedlings treated with crude leaf extracts of 2.5%, 5%, and 10% of V. nubica, 5%, and 10% of V. tortilis and 10% of H. compressa died during the experiment. Percent inhibition of P. juliflora seedlings growth were; plant height (9-56%), root collar diameter (5-31%), number of leaves (8-42%), root length (29-76%), and dry shoot (6-30%) and root (8-28%) weight. Increase in crude extract concentrations led to an increase in the inhibitory effects. All crude leaf extracts had higher inhibitory effects as compared to all root extracts regardless of extract concentration. Among the leaf extracts, V. nubica had the highest inhibition on germination and seedlings growth of P. juliflora. Tannins, saponins, steroids, glycosides, terpenoids and phenol compounds were all present in crude leaf and root extracts of the studied native trees. Therefore, it was concluded that V. tortilis, V. nubica, and H. compressa exhibited varying allelopathic effects on the germination and seedlings growth of P. juliflora and thus can be promoted to suppress the invasiveness of P. juliflora