The allelopathic potential of pasture weed assa-peixe (Vernonia polyanthes Less.) over the forage grasses Brachiaria humidicola. Brachiaria decumbens e Brachiaria brizantha cv. Marandu was investigated. The effect of aqueous shoot, roots and seeds extracts (in a concentratrion of 10%) on germination (% and speed) and radicle elongation of the grasses were studied. The pH, conductivity and osmotic potential were analysed in each extract. The contribution of the osmotic potential was isolated considering the osmotic potencial of the extracts and the water, and the regression equationss adjusted to each parameter in function of the variation of the osmotic potential in the range from 0,0 to 0,4 MPa. The bioassay were carried out in a BOD chamber, with temperature controlled to 35/15oC (day/night temperature) and photoperiod of 12 hours of ligt (bioassays of germination), and constant temperature of 35oC and photoperiod of 24 hours of light (bioassays of radicle length). It was showed that pH and cations concentration did not contribute to the results obtained. The pasture weed assa-peixe evidenced allelopathic potential that varied in function of receiver species and the part of the donor plant. The speed of germination was the best indicator for the effects of aqueous extracts from assa-peixe.
Allelopathy; grass; forage; weed; pasture