Abstract: To optimize the combination and inoculum density for co-culture system of Echinacea adventitious roots(ARs),three species:Echinacea purpurea (Epu) , Echinacea pallida (Epa) and Echinacea angustifolia (Ean),the adventitious roots of which as experiment materials were inoculated into 500 mL flasks containing 200 mL of half strength Murashige and Skoog (MS) medium supplemented with 1 mg·L^-1 of indole-3-butyric acid (IBA).The effects of species combinations and inoculum densities 5 g/L,7 g/L and 10 g/L were evaluated via the biomass of Echinacea ARs,content of secondary metabolites in the ARs and the antioxidant activity of the ARs extract.The results show that the maximum yield of ARs dry weight（6.75 g/L）was the combination of Epa+Epu with inoculum density of 7 g/L,in which both the content and productivity of total phenolics (40.31 mg/g DW and 272.09 mg/L) and flavonoids (34.29 mg/g DW and 231.46 mg/L) maximized.Only in ARs of Epa+Epu combination could all six caffeic acid derivatives be detected simultaneously among combinations.Furthermore,the caffeic acid,which could not be examined out in ARs of Epa or Epu in single culture was generated by the stimulation of co-culture system.The total content of caffeic acid derivatives in ARs of Epa+Epu combination achieved a maximum with 7 g/L inoculum density,productivity of which 136.22 mg/L was respectively 1.35 times and 1.73 times of that in Epu and Epu in single culture.The strongest reducing power and DPPH radical scavenging ability was also from the ARs extract of Epa+Epu combination with 7 g/L inoculum density.Such optimization of culture conditions will beneficial for the large-scale production of Echinacea biomass and bioactive compounds for antitumor and antioxidant biomedical materials.

Key words: Echinacea, adventitious root, co-culture, secondary metabolites, antioxidant activity