Plant growth inhibiting flavonoids in exudate of cistus ladanifer and in associated soils

Of the aglycone flavonoids identified in the exudate of cistus ladanifer, t wo, the flavone apigenin-4'-(O)-methyl and the flavonol kaempferol-3,7-di(O )-methyl inhibit development of the seedlings of Rumex crispus at 0.5 and 1 mM. Additive effects were observed between the major flavonols of the exud ate kaempferol-3-(O)-methyl and kaempferol-3,7-di-(O)-methyl in inhibiting the size of the cotyledons and delaying the germination and cotyledon emerg ence. The presence of apigenin-4'-(O)-methyl, kaempferol-3,7-di-(O)-methyl, and kaempferol-3-(O)-methyl was detected in the soils associated with C. l adanifer during the summer and autumn months. That these compounds are pres ent in the soil and are not restricted to the leaves provides support for t he hypothesis that C. ladanifer has allelopathic potential.