Study on allelopathy and its mechanism of watermelon (Citrullus lanatus).

Watermelon, grown with other crops (cucumber, tomato, hot pepper and lettuce), were watered with the aqueous extract of watermelon plant at 0, 0.01, 0.02, 0.03, 0.04 and 0.05 glml. The lower concentration of watermelon aqueous extract inhibited seed germination and root growth of cucumber, watermelon, pepper, lettuce and tomato, but accelerated stem growth of cucumber and watermelon. The inhibitory effects on lettuce increased with the increasing concentration of watermelon extract. The changes of some protective enzymes (superoxide dismutase, peroxidase and catalase) and malondialdehyde levels were closely related to the concentration of watermelon extract.