The aim of this work was to study the allelopathic effect of leaf aqueous extract of A. annua on seed germination and seedling development in lettuce (Lactuca sativa L.) and wild poinsettia (Euphorbia heterophylla L.). Crude aqueous extract was prepared from 250 g fresh leaves extracted in 1 L distilled water. This first extract was filtered and centrifuged and the supernatant was used. The following concentrations were employed of 100% (filtered and centrifuged extract), 75%, 50%, 25% (dilutions of the 100% extract) and 0% (distilled water). Seeds of the tested species were distributed in Petri dishes and placed into germination chambers. The analyzed variables were: germinability (G), germination mean velocity (V), germination mean time (t), radicle length (RL) and seedling dry matter. The increase in the concentration of A. annua aqueous extract reduced lettuce germinability and, from 50% concentration, germination was completely inhibited. For wild poinsettia, germination was completely inhibited from 75% concentration. There was a significant reduction in lettuce germination mean velocity with increasing extract concentrations, which was not observed for wild poinsettia. Radicle length in wild poinsettia significantly reduced at the concentrations 25 and 50% and was totally inhibited at 75 and 100%. As regards lettuce, 25% concentration significantly reduced radicle length, and the concentrations 50, 75 and 100% completely inhibited root formation, indicating this species is more sensitive than wild poinsettia. A. annua aqueous extracts presented inhibitory allelopathic action on seed germination and seedling development in lettuce and wild poinsettia.
allelopathy; germinability; germination mean velocity; germination mean time
