Bioherbicidal activity of drimane sesquiterpenes from Drimys brasiliensis Miers roots

Drimys genus plants are known as source of mono- and sesquiterpenoids compounds with potential roles in plant-insect, plant-pathogen and plant-plant interactions. The aim of this study was to identify secondary metabolites in the Drimys brasiliensis Miers roots with the potential to act as natural herbicides, using wheat coleoptile bioassays. The effects of the most active compound were also assessed on germination and early growth in Barbarea verna (Mill.), Echinochloa crus-galli (L.) and Ipomoea grandifolia (Dammer) O'Donnell. Four drimane sesquiterpenes were isolated from bioactive fractions of D. brasiliensis roots and identified as polygodial, polygodial acetal, dendocarbin L and (+)-fuegin by 1H and 13C NMR analysis. All four of the isolated compounds were phytotoxic to the wheat coleoptiles at the highest concentration tested (1 mM). Polygodial showed the highest levels of activity at low concentrations, with a phytotoxic effect on all of the target species evaluated and exhibiting greater inhibitory activity toward root elongation than shoot early development. This inhibitory effect was observed at the cellular level in I. grandifolia roots, with a significant reduction in the size of metaxylem cells at all of the evaluated concentrations. The phytotoxic effect of polygodial demonstrates the potential of this compound to be used as a bioherbicide.