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 extractsfrom 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. Theresults showed that aqueous extracts of rubber leaves at lower concentrations (50 g/L) exhibited stimulatory or evenweak inhibitory effects on the germination potential, final germination percentage, germination index, vigor index ofthree vegetable seeds. With the concentration increasing, the positive effect tended to be weakened, while, inhibitioneffect continuously enhanced. In particular, aqueous extracts of rubber leaves at high concentration of 200 g/L showedstrong allelopathic inhibitory effect on the germination potential, final germination percentage, germination index, vigorindex of three vegetable seeds. With the increases of concentration of aqueous extracts from rubber leaves, meangermination time of tomato and lettuce seeds continuously prolonged, whereas mean germination time of radish seedsshortened firstly, and then prolonged. With the increases of concentration, aqueous extracts from rubber leaves hadincreasing inhibitory effects on root length of tomato, lettuce and radish seedlings. Aqueous extracts of rubber leaves atconcentration 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 significantlyweakened, whereas the inhibitory effects on shoot height of radish seedlings were found. At concentration of 200 g/L ofaqueous extracts, comprehensive allelopathic indices of tomato, lettuce and radish were -0.125, 0.081 and -0.304,respectivel y. It was concluded that the allelopathicsensitivity of three vegetables to aqueous extracts fromrubberleaveswasintheorderofradish>tomato>lettuce.