Phytotoxicities of the invasive species Plantago major and non-invasive species Plantago asiatica

Although Plantago major and Plantago asiatica have similar life-history characteristics, P. major populations expand much more rapidly than P. asiatica in habitats where both species occur. One potential factor contributing to this disparity is the production of phytotoxic compounds. However, the phytotoxic characteristics of P. major and P. asiatica have not yet reported. Therefore, we conducted an investigation of possible phytotoxic compounds with allelopathic activity in both species. Aqueous methanol extracts of both plant species inhibited root and hypocotyl growth of garden cress (Lepidium sativum) in a concentration dependent manner. However, the inhibitory effect of P. major was greater than that of P. asiatica. The extracts were further purified by several chromatographic runs and two main phytotoxic compounds were isolated and identified through spectral analysis as (-)-3-hydroxy-beta-ionone and blumenol A. (-)-3-Hydroxy-beta- ionone and blumenol A inhibited the growth and germination of garden cress at concentrations greater than 1 and 30 mu M, respectively. The level of (-)-3-hydroxy-beta-ionone in P. major was 7.2-fold greater than that in P. asiatica, while the level of blumenol A was equal in both plant species. Although these Plantago species produce two main phytotoxic compounds with allelopathic activity, the higher level of (-)-3-hydroxy-beta-ionone in P. major may result in it contributing the primary inhibitory effects of the extract of P. major. (-)-3-hydroxy-beta-ionone may also serve to distinguish the invasive habit of two species and may be involved in the expansion in habitats of P. major.