Allelopathic potential from leaves of weeds by sandwich method

Abstract

Allelopathic studies investigate the positive and negative effects of secondary metabolites from plants, microorganisms and fungi on the development of neighbouring individuals. The aim of this work was to evaluate the allelopathic effect from leaves of Amaranthus viridis, Acanthospermum hispidum, Bidens pilosa, Conyza canadensis, Galinsoga parviflora, Parthenium hysterophorus, Commelina benghalensis, Euphorbia heterophylla, Leonurus sibiricus, Digitaria insularis, Eleusine indica and Nicandra physaloides on germination and growth of lettuce, applying the sandwich method. In the bioassays, dried leaves (10, 25 and 50 mg) of the weeds were placed between two layers of agar and 25 lettuce seeds (Lactuca sativa) were sown. All the evaluated species, except C. canadensis, presented allelopathic effect on lettuce. The more significant effects were verified on A. viridis and L. sibiricus, which inhibited the germination percentage (> 40%), the growth of root (≥ 70%) and hypocotyls (> 50%) of lettuce. The results indicate that A. viridis and L. sibiricus present chemical compounds with phototoxic activity. Further studies are necessary for isolation and identification of metabolites playing a role in allelopathy.