Allelopathic potential in lettuce (Lactuca sativa L.) plants.

Lettuce (Lactuca sativa) is known' to contain water-soluble substances that are allelopathic. Aqueous or methanol extracts and residues from leaves of lettuce cv. Cheong, which showed the most inhibitory effects, were assayed to determine their allelopathic effects on seed germination and early seedling growth of several plant species. The aqueous extracts applied to filter paper significantly inhibited seed germination of lucerne with increasing of extract concentration. Methanol extracts from hexane fraction of lettuce plants showed the most inhibition on lucerne root growth and 1,9-l, lowed by ethylacetate, butanol and water fiactions. Incorporation with leaf residues of 100 g kg⁻¹ into soil significantly inhibited shoot and root fresh weights of barnyard grass (Echinochloa colonum [E. colona]) by 79 and 88%, respectively. These results suggest that extracts or residues fiom lettuce plants had potent allelopathic activity and that the activity differed depending on cultivar, extract or fiaction.