Herbicides
are a key element in agriculture but they do cause environmental
problems and natural alternatives are being sought. In this context,
invasive plants could provide an as yet unexplored source for the
development of future herbicides. Urochloa humidicola has great invasive potential in Brazilian environments as it hampers
the establishment of other plants. The phytotoxicity of U.
humidicola root extracts has been evaluated, and the major
components have been identified. The phytotoxicity of the extract
was assessed in the wheat coleoptile assay on seeds of troublesome
weeds and on Anadenanthera colubrina, a tree species
used in ecological restoration programs. The ethyl acetate extract
showed the highest activity, and the most affected weeds were E. crus-galli, M. maximus, and A. viridis with the latter weed more affected by the extract
than by the herbicide Logran. Microscopic ultrastructural analysis
of A. colubrina roots indicated possible signals
of cell death. Seven compounds were identified in the ethyl acetate
extract of which one diterpene and four saponins are new. Six of these
compounds were tested in the wheat coleoptile bioassay. The most active
were diterpene 1 and saponins 2, 3, and 6. The phytotoxic activity of U. humidicola explains the issues observed in ecological restoration with A. colubrina in the presence of Urochloa species, and its effect on weeds reinforces its potential use in
agriculture.