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Lycoris radiata Herb., a common medicinal plant of Far East Asia, was examined for its potential use in paddy weed control. The preliminary screening in greenhouse conditions indicated growth inhibitory activities. The emergence, root and shoot growth, and root dry weight of the bioassay species were reduced when grown in soil mixed with the leaves of L. radiata. Aqueous extracts of the fresh leaves at various concentrations inhibited the root and shoot growth of all tested plant species. To identify the active components, L. radiata ethanolic extract was subjected to bioassay-guided fractionation, purification, and spectroscopic analysis. This process led to the isolation of lycorine as a potential allelochemical. The concentration of lycorine in the dry leaves of L. radiata is estimated to be 0.08%. It is possible that lycorine is exuded from the roots or leaches from the living or decomposing leaves, along with other numerous inhibitors, and inhibits the growth of neighboring or successional plants. These results suggest that L. radiata has the potential to inhibit plant growth and lycorine acts as one of the most important plant growth inhibitors. This plant can be grown as a ground cover plant and its dead leaves could be applied as cover mulch. [ABSTRACT FROM AUTHOR]

Spiraea thunbergii Sieb. was found to contain 1-O-cis-cinnamoyl-β-d-glucopyranose and 6-O-(4′-hydroxy-2′-methylene-butyroyl)-1-O-cis-cinnamoyl-β-d-glucopyranose as major plant growth inhibitory constituents along with related compounds of lower phytotoxicity including 6-O-(trans-cinnamoyl)-1-O-(4″-hydroxy-3″-methyl-furan-2″-one)-β-d-glucopyranose, 6-O-(4′-hydroxy-2′-methylene-butyroyl)-1-O-trans-cinnamoyl-β-d-glucopyranose, and 1-O-trans-cinnamoyl-β-d-glucopyranose. The former three compounds were cinnamoyl glucosides. [Copyright &y& Elsevier]

In order to elucidate the allelopathic effect of leaf litter leachates under laboratory conditions, a modified ‘sandwich method’, which places leaves between two layers of agar, was used. Fifty mg of leaves was used per 10 cm2 cell. Agar concentrations at 0.5–1.0% were the best for gel support in determining radicle and hypocotyl elongation of lettuce. The optimum incubation time for bioassay was three days after imbibition onset. Among 20 typical tree species in Asia, Cymbopogon citratus and Derris scandens showed the strongest inhibitory activity determined by the sandwich method, followed by Piper betle, Tamarindus indica, and Gliricidia sepium. This bioassay seems to be a reliable method for screening allelopathic activity from leaf litter leachates. [ABSTRACT FROM AUTHOR]