Allelopathic effect of Azadirachta indica fresh leaves on the germination of native plants in the Seasonally Dry Tropical Forest

Abstract

Allelopathic potential, which is characterized by harmful or beneficial effects on a species, is a hypothesis that could explain the success of a vegetable species in process of invasion. For that reason, this study aims to investigate the allelopathic effect of the fresh leaf extract from Azadirachta indica on the germination and early growth of native species (Mimosa caesalpiniifolia, Pityrocarpa moniliformis, Astronium urundeuva, Cenostigma pyramidale, and Libidibia ferrea) in the seasonally dry tropical forest (caatinga). The raw extract was prepared with 200g of fresh leaves in 1L of distilled water, diluted in six treatments. The experiment followed a completely randomized design (CRD), with four repetitions of 25 seeds, and paper towel moistened with extract as substrate. The number of germinated seeds was counted daily. At the end of the experiment, radicle length (RL), germination percentage (GP), germination speed index (GSI), and average germination time (AGT) were evaluated. P. stipulacea’s GP and GSI averages and A. urundeuva’s AGT  decreased as extract concentration increased. As far as RL is concerned, in intermediate concentrations the extract hindered P. moniliformis and L. ferrea’s growth but favored C. pyramidale and A. urundeuva’s. Results allow us to infer that A. indica has an allelopathic effect on native species and might interfere with their rooting in the field, which in turn would affect the succession and balance of the forest over time, since the community structure and the ecosystemic processes would be impacted.