Phytotoxic activity of dihydrochalcones obtained by bioreduction of chalcones promoted by the endophytic fungus Aspergillus flavus

The aim of this study was to evaluate the phytotoxic effects of dihydrochalcones obtained by biotransformation reactions of the corresponding chalcones, promoted by the endophytic fungus Aspergillus flavus. The compounds 3,4,5-trimethoxydihydrochalcone (1a) and 2,3,4,4'-tetramethoxydihydrochalcone (2a) obtained from their corresponding chalcones (1 and 2) were submitted to the bioassays monitored under controlled temperature of 25 deg C and photoperiod of 12 hours. For bioassays were used as test plants two invasive species, Mimosa pudica L. (malícia) e Senna obtusifolia (L.) Irwin & Barneby (matapasto), belonging to the Fabaceae family. The phytotoxic effects of dihydrochalcones were analyzed at concentrations of 80 and 160 mg L^-1. Substances 1a and 2a, at a concentration of 160 mg L^-1, showed significant inhibitions, respectively, 54% and 65% , against the germination of the species M. pudica. Inhibitions of 61% and 49% of M. pudica radicle growth were observed, respectively, to compounds 1a and 2a at concentration 160 mg L^-1. In the bioassays performed, no significant phytotoxic activity of the tested substances was observed, at concentrations of 80 and 160 mg L^-1 on the weed S. obtusifolia. (author)