Phytotoxic activity and phytochemical characterization of Lotus ornithopodioides L., a spontaneous species of Mediterranean area.

The search of new bioactive compounds produced by plants represented an eco-friendly and alternative strategy in sustainable agriculture. In this context, the aerial parts of Lotus ornithopodioides L. (Fabaceae), annual herbaceous plant of Mediterranean area, were collected in Calabria (Southern Italy). Leaves and stems of L. ornithopodioides were extracted with methanol and subsequently bio-fractionated with n-hexane, chloroform and ethyl acetate. In vitro assays on germination and root growth of lettuce (Lactuca sativa L.) were performed to evaluate the phytotoxicity of the methanolic extract and its fractions, by a dose-response curve, comparing the ED50 values. Then, the most bioactive fractions were characterized through GC-MS. The crude methanolic extract strongly inhibited both processes showing, after 48 h of treatment, ED50 values equal to 9.01 and 1.16 mg/ml for germination and root growth, respectively. The bioguided-fractionation showed the following hierarchy of phytotoxicity for both processes: ethyl acetate > chloroform >= n-hexane. A large amount of phenolic compounds were found in the ethyl acetate fraction (522 mg/g of dry fraction) and some of them have been characterized through HPLC analysis. On the other hand, the n-hexane and chloroform fractions showed the presence of many semiochemicals, such as phytone, methyl hexadecanoate, ethyl hexadecanoate, methyl octadecanoate and 4-methyl-2-heptanone. These results make L. ornithopodioides L. a suitable source of natural compounds potentially usable as natural herbicides. Further studies will be necessary to understand the phytotoxic mechanisms of these molecules, alone or in combination and their effects on green-house and field experiments.