Allelopathic potential of Acacia pennata (L.) Willd. leaf extracts against the seedling growth of six test plants

Acacia pennata (Willd (Mimosaceae), a woody climbing plant, is used as a traditional medicinal plant in the South and Southeast Asia regions and has been documented to have various pharmacological effects. However, the allelopathy of this plant still remains unclear. Thus, the allelopathic potential of A. pennata leaf extracts was examined against the seedling growth of dicot plants [alfalfa (Medicago sativa L.), cress (Lepidium sativum L.), and lettuce (Lactuca sativa L.)] and monocot plants [barnyard grass (Echinochloa crus- galli (L.) Beauv.), Italian ryegrass (Lolium multiflorum Lam.), and timothy (Phleum pratense L.)] at six different concentrations. The results showed that the A. pennata leaf extracts inhibited the seedling growth of all the test plant species at concentrations >= 3 mg dry weight (D.W.) equivalent extract mL-1. The inhibitory activity of the extracts against both shoot and root growth varied with concentration and tested plants. The concentrations required for 50% inhibition of the test plant shoots and roots were 1.5-16.1 and 1.4-8.6 mg D.W. equivalent extract mL-1, respectively. The root growth of all the test plant species was more sensitive to the extracts than their shoot growth, except alfalfa. The results of the present study indicate that the A. pennata leaf extracts may have allelopathic potential and may contain allelopathic substances. Therefore, further studies are required for isolation and identification of the growth inhibitory substances which are responsible for the allelopathic effect of A. pennata.