Black cohosh rhizome and phytochemical production in response to shading, spacing, and age

Black cohosh (Actaea racemosa; Cimicifuga racemosa) is a perennial woodland herb native to eastern North America. Its common use as a dietary supplement to treat menopausal symptoms has increased interest in its cultivation. Two studies were conducted in a shadehouse in southwest Missouri, USA. The first study quantified rhizome and root yield, and concentration of four phytochemicals across three harvest seasons and in response to three shading treatments. The second study evaluated rhizome yield and concentration of two phytochemicals in mature plants in response to two plant spacings and three shading treatments. Biomass increased with age but was not significantly affected by horticultural treatments. In the first study, rhizome and root yields were not affected by shading treatments, but rhizome yields did increase over time. Content of cimiracemoside A in rhizomes was higher in those grown in full sun (641 mg/kg) compared with those under 80% shade (492 mg/kg), and content of 23-epi-26-deoxyactein was higher under 40% shade (3,109 mg/kg) than under 0 or 80% shade (2,421 and 2,324 mg/kg, respectively). Shading did not significantly affect concentration of 26 (S) actein in rhizomes, or of any compound in roots. Two-year-old plants had higher content of cimiracemoside A and 23-epi-26-deoxyactein in rhizomes and roots than did one- or three-year-old plants. In the second study, neither shade nor spacing treatments affected long-term plant survival or rhizome yields. Cimiracemoside A content was not affected by shading, but was significantly greater with 0.5 m spacing than with 1 m spacing (427 vs. 187 mg/kg); 23-epi-26-deoxyactein content was significantly higher under 0 and 40% shade (2,842 and 2,779 mg/kg respectively), compared with 80% shade (2,224 mg/kg). The variable responses of phytochemicals to the treatments in these studies suggest that horticultural, temporal, and other influences on phytochemical production are complex. Harvest of two-year-old material might be economically advantageous under certain conditions, although further research into this alternative is required.