The bioactivity of semipurified fractions (hexane, ethyl acetate and ethanol-water) obtained from S. occidentalis aerial-part ethanol extract was evaluated by germination and growth bioassays using Lactuca sativa (lettuce), Lycopersicon esculentum (tomato), Allium cepa (onion) and Triticum aestivum (wheat), in the laboratory. Three concentrations of each fraction (250, 500, 1000 mg L-1) and untreated control were used, on four replicates of 50 seeds each. Germination bioassays revealed that lettuce, tomato and onion germination were delayed by all tested semipurified fractions, and tomato and onion germination were inhibited by the hexane and ethyl acetate fractions. In growth bioassays, the hexane fraction stimulated root growth and inhibited hypocotyl growth in the eudicots. The same fraction inhibited root and coleoptile growth of the assayed monocots. The ethyl acetate fraction inhibited seedling roots and hypocotyl/coleoptile growth, of tomato and onion. The ethanol-water fraction stimulated tomato root growth and lettuce hypocotyl growth, and inhibited onion and wheat root and onion coleoptile development at 1000 mg L-1. Bioassays performed with commercial herbicides presented similar results to those observed in germination to the semipurified fractions in the growth by hexane and ethyl acetate fractions. The layer chromatography revealed that the tested hexane fraction contains terpenes, and the ethyl acetate fraction has phenolic compounds and alkaloids. The spectrophotometric analysis revealed greater yields of phenolic compounds and flavonoids in the ethyl acetate fraction.
allelochemicals; natural herbicides; weeds
