Abstract

The secondary metabolism of plants produces allelopathic substances which are able to interfere with germination and growth of other species, when released in the environment. In order to evaluate the allelopathic effects of Luetzelburgia auriculata on the germination and early growth of lettuce (Lactuca sativa), leaf extracts and roots were tested in lettuce seeds sowing. The L. auriculata plant material was collected from adults, subsequently washed, dried, weighed, crushed and thus used to preparing a raw extract. In a completely randomized design, six concentrations (0, 20, 40, 60, 80 and 100%) of the extracts of leaves and roots were tested separately with four replications on lettuce seeds in germitest paper. The experiment was conducted in a germination chamber TE 402 during seven days with photoperiod of 12 h light and a constant temperature of 20°C, to check the germination speed index (GSI), germination percentage (% G) and initial growth lettuce (radicle length and hypocotyl). The data were submitted to a variance analysis applying the F test at 1% probability and using the error bars model. It was observed that the results of the treatments with root extract and leaf extract, when compared to the control test, were negatively affected by the aqueous extracts of L. auriculata. The GSI and %G of seeds treated with roots extract were the parameters that presented most significant responses to the allelopathic effects of L. auriculata extract at 20% concentration, followed by GSI and %G seeds subjected to 20% leaf extract. Both extracts at other concentrations reduced GSI and %G in 85 and 90%, respectively. The length of the radicle and hypocotyl decreased by 32 and 15% respectively when the extract was used at a lower concentration, and 40% (radicle) and 30% (hypocotyl) in other concentrations. The aqueous extracts of leaves and roots L. auriculata caused negative allelopathic interference on the germination and growth of lettuce seedlings.

Key words: Secondary metabolites, Brazilian semiarid region, allelopathy.