Effects of Inorganic Mulches on Achillea millefolium L. Sesquiterpene Lactones

Abstract

Aims: Sesquiterpene lactones are one of the most important groups of bioactive substances in Achillea millefolium, a perennial herb cultivated because of its medicinal interest. We sought to determine if the use of inorganic mulches for weed control in A. millefolium crops could lead to differences in their sesquiterpene lactones (SLs) content. Study Design:  A field experiment using a randomized complete block design with three replications was conducted to determine the effect of black polypropylene, black polyethylene of 100 µm and black polyethylene of 175 µm on A. millefolium SLs content. Place and Duration of Study: Department of Crop Production, University of Santiago de Compostela, between September 2004 and August 2005. Methodology: LC/MS analysis of A. millefolium flower heads grown over the three different inorganic mulches and in control plots was carried out in order to determine SLs. Results: Chromatographic analysis of A. millefolium flower heads grown over polypropylene and in control plots revealed the highest diversity of SLs, whereas those developed over black polyethylene showed the least. Polypropylene mulches were shown to be the most efficient with a 2-3 fold increase of total SLs (P < 0.001). The effects of inorganic mulches on individual SLs were of limited relevance. However, the use of black polyethylene (100 µm) resulted in an increase of   8-desacetylmatricarin (P = 0.005), a SL of biological and pharmacological interest. In contrast, concentrations of three unidentified SLs decreased in yarrow plants grown over black polyethylene. Conclusion: Weed density did not show as a major factor influencing the total amount of SLs but growth parameters such as yarrow dry matter were inversely related.