Variation in the allelopathic effect of rice with water soluble extracts

The allelopathic effect of rice (Oryza sativa L,) on lettuce (Lactuca saliva L,) and ducksalad [Heteranthera limosa (Sw,) Willd,] was investigated with water soluble extracts. Ducksalad is a major weed in southern USA rice Gelds, 'PI312777' and 'Rexmont', which are suppressive and nonsuppressive to ducksalad in the Geld, were used to establish the bioassay of allelopathic activity in rice. Water soluble compounds, which were extracted from rice seedlings and adult plants, were applied to lettuce seeds, Leaf extract of PI312777 inhibited the root growth of lettuce more strongly than those of Rexmont. Extracts from the leaves of rice seedlings at the six-leaf stage inhibited the growth of ducksalad and lettuce, and a close relationship existed between the inhibitory effect and the two test plants. A wide range of variation in allelopathic activity among rice cultivars was assessed using water soluble extracts from their leaves and lettuce as a test plant.