Assessment of allelopathic effects of <em>Phalaris aquatica</em> on <em>Chloris truncata, Trifolium subterraneum, Medicago trunculata</em>, and <em>P. aquatica</em>


  • A. A. Adams
  • A. Raman
  • H. I. Nicol


We examined the effect of Phalaris aquatica L. cv. Sardinia on populations of Chloris truncata R. Br. (Poaceae) and Trifolium subterraneum L. (Fabaceae) under laboratory conditions to assess interspecific allelopathy and, on P. aquatica, to assess intraspecific allelopathy (autotoxicity). A population-ecological pilot study measured the abundance and morphometrics of Medicago trunculata that occurred in association with populations of P. aquatica. We found the abundance of M. trunculata was reduced in the presence of P. aquatica litter; lengths of shoots of M. trunculata were enhanced, but those of roots remained unaffected. Previous laboratory-based studies on P. aquatica allelopathy utilized >10% extracts in bioassays on different leguminous taxa; therefore in the present study we attempted to assess the allelopathic potential of P. aquatica with <10% extracts (0-2.5% in 0.5% increments), to determine the optimal rate of concentration at which the allelochemicals became either inhibitory or stimulatory. Six concentrations (0.25, 0.5, 1, 1.5, 2, 2.5%) of aqueous extracts of P. aquatica were applied to seeds of C. truncata, T. subterraneum, and P. aquatica. Germination of C. truncata, T. subterraneum, and P. aquatica was observed for eight days and lengths of radicles were measured as an indicator of growth. Assessment of the allelopathic potential tested with aqueous extracts of P. aquatica on seeds of C. truncata and T. subterraneum neither inhibited germination nor impacted on radicle lengths. However, P. aquatica exhibited autotoxicity by inhibiting radicle growth, although not that of germination. Phalaris aquatica water extracts were subjected to high-performance-liquid-chromatographie analysis revealing gramine. Gramine, known to be allelopathic in other grasses, could be a potential allelopathic agent in this taxon.