A growth-inhibitory substance exuded from freeze-dried mesquite (Prosopis juliflora (Sw.) DC.) leaves

Abstract

When lettuce seeds were incubated in a concentric circle aroundfreeze-dried mesquite leaves in a dish containing agar culture medium, thegrowth, especially radicle growth, of the seedlings was inhibited, the morestrongly the closer they were to the leaves. This result indicates thatallelopathic substance(s) inhibiting the lettuce growth are exuded from themesquite leaves. A potent substance was isolated from the exudates of thefreeze-dried mesquite leaves and identified as L-tryptophan by spectralanalyses. L-Tryptophan inhibited the radicle growth of lettuce and barnyardgrass at concentrations greater than1.5 × 10⁻³ . The content ofL-tryptophan in the exudates of freeze-dried mesquite leaves (1 eq.) was 4.8 × 10⁻³ . Theseresults suggest that L-tryptophan may play an important role in the allelopathyof mesquite leaves.