Potential allelopathy of aqueous extracts from rubber leaves on three vegetables

In order to better understand the allelopathy of rubber tree, potential allelopathy of aqueous extracts from rubber tree(Hevea brasiliensis) leaves under different concentrations on tomato(Solanum lycopersicum L.), lettuce(Lactuca sativa L.) and radish(Raphanus sativus L.) was examined through a petri dish assay with imbibed seeds. The results showed that aqueous extracts of rubber leaves at lower concentrations(≤50 g/L) exhibited stimulatory or even weak inhibitory effects on the germination potential, final germination percentage, germination index, vigor index of three vegetable seeds. With the concentration increasing, the positive effect tended to be weakened, while, inhibition effect continuously enhanced. In particular, aqueous extracts of rubber leaves at high concentration of 200 g/L showed strong allelopathic inhibitory effect on the germination potential, final germination percentage, germination index, vigor index of three vegetable seeds. With the increases of concentration of aqueous extracts from rubber leaves, mean germination time of tomato and lettuce seeds continuously prolonged, whereas mean germination time of radish seeds shortened firstly, and then prolonged. With the increases of concentration, aqueous extracts from rubber leaves had increasing inhibitory effects on root length of tomato, lettuce and radish seedlings. Aqueous extracts of rubber leaves at concentration of 0~100 g/L had increasing stimulative effects on shoot height of tomato, lettuce and radish seedlings,but at concentration of 200 g/L, the promoting effects on shoot height of tomato, lettuce seedlings significantly weakened, whereas the inhibitory effects on shoot height of radish seedlings were found. At concentration of 200 g/L of aqueous extracts, comprehensive allelopathic indices of tomato, lettuce and radish were-0.125, 0.081 and-0.304,respectivel y. It was concluded that the allelopathic sensitivity of three vegetables to aqueous extracts from rubber leaves was in the order of radish tomato lettuce.