CAN ALLELOPATHIC GRASSES LIMIT SEED GERMINATION AND SEEDLING GROWTH OF MUTAMBO? A TEST WITH TWO SPECIES OF Brachiaria GRASSES

Tree establishment in pasture areas can be inhibited, at least in part, by exotic grasses allelopathy and this can represent an important limitation by changing the patterns of both germination and seedling growth of tree species. This study aims to evaluate the allelopathic potential of Urochloa brizantha and U. decumbens on germination, growth and metabolism of Guazuma ulmifolia seedlings. We performed bioassays evaluating the effect of the crude ethanol extract and semipurified fractions (hexane fraction, ethyl acetate fraction and ethanol-water fraction) of U. brizantha and U. decumbens using completely randomized design, with four concentrations (0, 250, 500, 1,000 mg L-1) and four replications. The variables analyzed were germination percentage, mean germination time, shoot and root growth, catalase and peroxidase activity, chlorophyll content and root respiration. The results showed that both grasses have an inhibitory effect on G. ulmifolia metabolism, affecting both germination and seedlings growth and inducting metabolic defense. Thus, these results show that the grass species evaluated have the potential to restrict the re-introduction of G. ulmifolia in pasture areas due to interference competition.