Potential allelopathic interference of Melilotus neapolitana metabolites on three coexisting species of Mediterranean herbaceous plant community

This study is focused on the allelopathic interference of Melilotus neapolitana, an annual stenomediterranean species frequently occurring in the herbaceous plant community of the Mediterranean macchia, on three coexisting species of the Mediterranean herbaceous plant community. The ethereal and methanol extracts of the plant led to the isolation of 11 allelochemicals: coumarin, cis- and trans-melilotoside, the dihydromelilotoside, seven flavone glycosides, as well as the inactive beta-sitosterol, a C13-norterpene glucoside and a polyphenol. All the structures have been elucidated on the basis of their spectroscopic features. The organic extracts and all the pure compounds have been assayed for their allelopathic activity on three coexisting species, Petrorhagia velutina, Dactylis hispanica, and Phleum subulatum. The cluster analysis has shown a clear structure-activity relationship, by evidencing four main groups of compounds witha specific effect patterns. Coumarin, the most abundant compound both in the plant extracts and soil, is found to be highly phytotoxic on all the tested species. As for the flavone glycosides, it is shown that aglycones play an important role due to their bioactivity.