Allelopathy Journal

Methanolic extracts of 39 aquatic plants were screened for herbicidal, fungicidal and insecticidal activities. The responses to aquatic plant extracts greatly varied depending on the types of bioactivity assays. All extracts at 1% concentration remarkably suppressed the germination and seedling growth of E. crus-galli. Seven plant spp. reduced the germination rate of E. crus-galli >80%. The highest inhibitory activity on germination and germination rate was 62 and 87% from S. pygmaea and P. pubescens, respectively. The inhibition in total seedling dry weight of E. crus-galli varied from 0.3 to 58.9%. Five aquatic plants, S. pygmaea, P. pubescens, M. pumilus,

E. prostrate and T. orientalis inhibited the germination and seedling growth of E. crus-galli. In fungicidal test, E. robustius, S. pygmaea and J. leschenaultii showed highest fungicidal activity against fungal crop diseases, with rice blast (75%), tomato late blight (94%) and wheat leaf rust (53%) pathogens, respectively. In insecticidal activity, T. japonica, R. mexicana and A. sinicus caused 80 and 97% mortality of spotted spider. To further evaluate the relationship between the herbicidal activity and the concentration of P. pubescens, Lemna bioassay was conducted. After 7 days of exposure, growth inhibition rate of Lemna gibba with IC₅₀ value of 125 mg l⁻¹ was increased linearly similar to P. pubescens.