Isolation and identification of plant growth inhibitors as candidate(s) for allelopathic substance(s), from aqueous leachate from mesquite (Prosopis juliflora (Sw.) DC.) leaves

As candidate(s) for allelopathic substance(s), two plant growth inhibitors were isolated from aqueous leachate of leaves of mesquite, which show a strong allelopathy, and which were identified as syringin and (-)-lariciresinol by their spectral analyses. Syringin inhibited root and shoot growth of lettuce seedlings at concentrations greater than 0.8 μM, and root and shoot growth of barnyard grass seedlings at concentrations greater than 2.7 and 26.9 μM, respectively. On the other hand, (-)-lariciresinol inhibited root and shoot growth of lettuce seedlings at concentrations greater than 2.8 and 0.8 μM, and root and shoot growth of barnyard grass seedling at concentrations greater than 0.8 and 2.8 μM, respectively. The contents of syringin and (-)-lariciresinol in the rhizosphere soil of mesquite were 0.34 and 0.38 μg/g soil, respectively. These results indicate that syringin and (-)-lariciresinol are allelopathic substance(s), and may play roles in the allelopathy of mesquite.