INHIBITORY EFFECTS OF MELIA AZEDARACH L. LEAF EXTRACTS ON SEED GERMINATION AND SEEDLING GROWTH OF TWO WEED SPECIES

Aqueous extracts from three leaf stages (young leaves, mature leaves and old leaves) of M. azedarach were assayed at 12.5, 25, 50 and 100 mg/mL concentrations for their effects on seed germination and seedling growth of barnyardgrass [Echinochloa crus-galli (L.) Beauv.] and wild pea (Phaseolus lathyroides L.). Results revealed that aqueous extracts of M. azedarach at all concentrations had significantly inhibited seed germination and seedling growth of both tested species compared with control. The degree of inhibition had increased with incremental extract concentration. However, degree of inhibition was significantly different between the two bioassay indicator species. All aqueous extracts have more strongly inhibited seed germination and seedling growth of P. lathyroides than E. crus-galli. Extracts from the young leaves had higher inhibitory potential compared to the extracts from the old leaves. Thus, aqueous extract from young leaves was selected to further evaluate some physiological processes inhibited during the seed germination. Aqueous extracts of young leaves (12.5 to 100 mg/mL) were used to determine their impacts upon water uptake and α-amylase activity of E. crus-galli. It was found that both water uptake and α-amylase activity of E. crus-galli were inhibited. It was concluded that young leaves of M. azedarach contained water soluble allelochemicals and caused inhibition of both water uptake and α-amylase activity of E. crus-galli during germination process.