Phytotoxic potential of Eucalyptus leaf essential oil to control Parthenium hysterophorus L.

Herbicidal effects of leaf oil from 3-Eucalyptus species (Eucalyptus citriodora, Eucalyptus camaldulensis and Eucalyptus tereticornis) were evaluated on germination and seedlings growth of Parthenium hysterophorus L. In laboratory bioassay the different concentrations of eucalyptus essential oils significantly reduced the seed germination. Based on the germination, a dose-response curve was made and LC25 values were calculated as 0.35, 0.8 and 1.8 mg/L for E. citriodora, E. camaldulensis and E. tereticornis, respectively. The E. citriodora proved most inhibitory to seedling growth and biomass of P. hysterophorous, even at 0.25 mg/L. Spraying of E. citriodora on P. hysterophorous 4-wk-old plants decreased the plants height, membrane integrity and cellular defense i.e. showed the adverse effects of eucalyptus leaf essential oil on growth, photosynthesis and energy metabolism of target plants. Exposure of P. hysterophorus to E. citriodora leaf essential oil also enhanced the electrolyte leakage, indicating membrane disintegration. An increased level of H2O2 in spray treatment indicates the induction of oxidative stress. Thus the essential oil from E. citriodora inhibited the P. hysterophorus growth through oxidative damage, hence, could be used as directed spray to control P. hysterophorus.