Autotoxicity of phenolic compounds from the soil of American ginseng (Panax quinquefolium L.)

The inhibitory activity of 9 phenolic compounds [p-hydroxybenzoic acid, vanillin, syringic acid, vanillic acid, coumaric acid, ferulic acid, cinnamic acid, salicylic acid, benzoic acid] was investigated in vitro on the radicle and shoot growth of American ginseng (Panax quinquefolium L.) seedlings. These compounds were detected in the soils of commercially cultivated American ginseng. Their test concentrations (0.1 mmol/L to 10.0 mmol/L) were selected based on their content in soils. All phenolic compounds inhibited the radicle and shoot growth of American ginseng in a dose-dependent response and their IC50 values were also calculated. Only 5-compounds caused < 50% inhibition in radicle growth of American ginseng and their autotoxicity followed the order: salicylic acid > cinnamic acid > coumaric acid > vanillic acid > syringic acid. However, p-hydroxybenzoic acid, vanillin, ferulic acid, benzoic acids even at the highest concentration (10.0 mmol/L) did not cause 50% inhibition in radicle elongation. Thus different phenolic compounds displayed variable phytoxicity to American ginseng (Panax quinquefolium L.) and there is a close relationship between the substitutions on the benzene ring of phenolic compounds and their phytotoxicity.