Allelopathic Effect of Root Extract of Prosopis juliflora (Mesquite) on Seed Germination and Seedling Growth of Native Dry Forest Plant Species

Abstract

Prosopis juliflora is an alien exotic plant in many arid and semi-arid areas in the tropics such as Saudai Arabia, India and Sri Lanka. This species was introduced to Hambanthota district in the Southern Province of Sri Lanka in early 1950s to improve saline soils in the area. P. juliflora produces water soluble alleloapathic chemicals in their leaves, roots, pods and flowers such as L-tryptophan, syringin and laricriesinol. This study was conducted to determine effects of allelopathic compounds present in P. juliflora on seed germination and initial seedling growth of Bauhinia racemosa (Maila), Cassia occidentalis (pinithora), Drypetissepiaria (weera), Dichrostachya cinerea (andara), Flueggea leucopyrus (katupila) and Salvodora persica (mallithan) by keeping seeds in concentration series of root extract of P. juliflora in five replicates. The effect on seed germination and initial seedling growth were evaluated by measuring percentage seed germination and root and shoot lengths. Percentage seed germination of B. racemosa, C. occidentalis, D. sepiaria D. cinerea and F. leucopyrus were significantly (p<0.05) reduced in the aqueous root extract. However, the seed germination was delayed only in C. occidentalis. Both root and shoot growth of all selected plant species were significantly (p<0.05) reduced by the root extract with an exception of F. leucopyrus in which the shoot growth was not significantly (p>0.05) affected. These results confirm the presence of allelopathic compounds in root extracts of P. juliflora, and these allelopathic compounds may adversely affect on seed germination and initial seedling growth of some native dry forest plant species. However, there may be a variation in the sensitivity to allelopathic compounds among native dry forest plant species.