Identification and Bioassay of Allelopathic Substances from Plant and Rhizosphere Soil Extracts of Adzuki Bean (Vigna angularis [Willd.] Ohwi & H. Ohashi.)

The soil sickness of Adzuki bean [Vigna angularis (Willd.) Ohwi & H. Ohashi] have been getting attention seriously under a continuously mono-cropping management-system in China. To investigate the allelopathy of rhizosphere soil and plant of Adzuki bean, culture dish and pot experiments were conducted. The compounds in the products were identified by High Performance Liquid Chromatography (HPLC).The aqueous extracts from rhizospheric soil and whole plant inhibited seed index (seed germination and seed potential) and plant growth under different degrees, and it showed concentration gradient effect on the inhibition of seed germination. Inhibition was stronger with increasment in extract concentration with the highest effect at 0.16 parts aqueous extract to 1 parts deionized water (0.16g·mL-1). The impact on growth varied among aqueous extracts from rhizospheric soil and the whole plant. Five phenolic compounds, cinnamic, phthalic, p-hydroxybenzoic, and isobutyricand glutaric acids, were detected from the rhizosphere soil and plant extract of Adzuki bean by HPLC method. Cinnamic, phthalic, and p-hydroxybenzoicacids were higher than that of the other phenolic acids. This result suggests that autotoxicity effects of phenolics on Adzuki bean probably happen in continuous mono-cropping systems.