Fitotoxicidade do extrato de Conyza bonariensis (L.) Cronquist no desempenho fisiológico de sementes e plântulas de alface

This study evaluated the infl uence of C. bonariensis extract concentrations on the physiological performance of seeds and the antioxidative metabolism of lettuce seedlings. The treatments were concentrations of 0; 2; 4; 6 and 8 % of the aqueous extract of leaves. The germination, speed index, electrical conductivity, seedling emergence, total dry mass of seedlings, hydrogen peroxide content, lipid peroxidation, enzyme activity, superoxide dismutase, catalase and ascorbate peroxidase were evaluated. C. bonariensis extract has toxic eff ects on seeds and lettuce seedlings. The higher extract concentrations (6 and 8 %) inhibited the germination and early growth of seedlings more. Increasing the concentration of the extract resulted in an increase of electrical conductivity in seeds and increased the levels of hydrogen peroxide, lipid peroxidation, superoxide dismutase, catalase and ascorbate peroxidase.