Allelopathic research of subtropical vegetation in Taiwan. IV : Comparative phytotoxic nature of leachate from four subtropical grasses.

The phytotoxicity of plant leachates was evaluated from four subtropical grasses:Brachiaria mutica, Digitaria decumbens, Imperata cylindrica var. Major, andPanicum repens. The aqueous leachate of each grass was used to water the growth of the four grasses in pots. The leachates exhibited variable inhibition of grass growth as compared to the tap water control. By the 41st day after treatment, the leachate ofD. decumbens significantly suppressed the growth of itself and retarded that ofB. mutica andP. repens. The growth ofB. mutica was inhibited by its own leachate, but that ofI. cylindrica was not affected by any of the grass leachates. In crop growth rate (CGR) analysis, the four grass leachates exhibited a similar inhibition pattern. In laboratory bioassays, the leachates showed a significant phytotoxic effect on the radicle growth of ryegrass and lettuce. Six phytotoxic phenolics were quantitatively compared by high-performance liquid chromatography, and the amount of compounds varied with species. The highest total amount of phytotoxic phenolics occurred inD. decumbens, followed, in decreasing order, byP. repens, B. mutica, andI. cylindrica. These findings show that the leachates of four grasses possess phytotoxic compounds that may play a significant role in grass dominance in the field.