ALLELOPATHY OF YELLOW FIELDCRESS (RORIPPA-SYLVESTRIS) - IDENTIFICATION AND CHARACTERIZATION OF PHYTOTOXIC CONSTITUENTS

Both the neutral and acidic fractions of the acetone extract of yellow fieldcress (Kireha-inugarashi, Rorippa sylvestris Besser) inhibited lettuce seed germination. Salicylic, p-hydroxybenzoic, vanillic, and syringic acid were identified in the acidic fraction. In the neutral fraction, hirsutin (8-methylsulfinyloctyl isothiocyanate), 4-methoxyindole-3-acetonitrile, and pyrocatechol were identified. Bioassay using a root exudate recirculating system showed R. sylvestris during flowering inhibited the lettuce seedling growth. Hirsutin (13-mu-g/plant/day) and pyrocatechol (9.3-mu-g/plant/day) were the major compounds released into the rhizosphere. Several combinations of pyrocatechol, p-hydroxybenzoic acid, vanillic acid, and hirsutin reduced lettuce seedling growth. These compounds seemed to be allelochemicals.