[Autotoxic effect of ginsenoside extrats on growth of American ginseng in different medium].

Ginsenosides are the abundant secondary metabolites in American ginseng (Panax quinquefolium), it could be released into soil through root exudation and decomposition during plant growth. This study determined ginsenoside contents in American ginseng cultivated soil by HPLC. Three ginsenosides, Rb1, Rb2 and Rd, were detected in the rhizosphere soil of 3-4 years old American ginseng cultivated in Huairou District, Beijing, and their contents were 0.80-3.19 mg x kg(-1). Correspondingly, the contents of the three ginsenosides in soil solution were 4-16 mg x L(-1) at field water-holding capacity of 20%. According to the field soil test data, we designed the concentration of ginsenosides for bioassays (0.2-125 mg x L(-1) in solution or 0.2-125 mg x kg(-1) in soil). The results showed that radicle lengths of American ginseng were reduced by 6%-23% in solution containing 0.2-125 mg x L(-1) ginsenoside extract, and a significant difference was observed at concentration of 125 mg x L(-1) (P < 0.05). The shoot lengths of American ginseng were not significantly inhibited by 0.2-125 mg x L(-1) ginsenosides extractions. After 20 days of growth in nutrient solution amended with 25 mg x L(-1) ginsenosides extraction, plant height of 3-year-old American ginseng seedling was decreased by 28% compared to the control, and the biomass of aerial parts was also reduced by 50% (P < 0.05). However, the growth of newly-grown fibrous root was not significantly inhibited. Comparatively, when American ginseng embryos were cultivated into sterile or non-sterile soil, neither radicle lengths nor shoot lengths were significantly affected by 0.2-125 mg x kg(-1) ginsenoside extracts. In conclusion, ginsenosides showed autotoxic effect on growth of American ginseng radicle and adult seedling, however, this effect was weakened in field soil.