Efeitos alelopáticos de extratos aquosos de folhas de Amburana cearensis e Plectranthus barbatus na germinação de Amaranthus deflexus

The objective was to verify possible allelopathic effects exerted by aqueous extracts of leaves of Amburana cearensis and Plectranthus barbatus on the seed germination of the weed Amaranthus deflexus. A. deflexus seeds were put to germinate in Petri plates containing aqueous plant extracts obtained from A. cearensis and P. barbatus leaves under two tillage methods – aqueous extract from fresh leaves and aqueous extract by infusion of dried leaves – and two dosages – 50 and 100 g L-1. We used a completely randomized design with 4 replications and a detached witness composing a factorial 2 x 2 x 2 + 1. It was determined the final percentage and germination speed index. Data analysis revealed differences between treatments and the witness, conditioning different allelopathy levels for the extracts used, dramatically affecting the germination of A. deflexus. The A. cearensis fresh leaves extracts has a high level of allelopathy since they prevent almost completely the germination of the weed A. deflexus. The most damaging dosage for germination of A. deflexus was 100 g L-1.