Growth and oxidative damage effects of Sicyos deppei weed on tomato

We performed a greenhouse experiment to study the phytotoxic effects of Sicyos deppei (Cucurbitaceae)weed on tomato [Lycopersicon esculentum (Solanaceae)] growth. Tomato seedlings were grown for one month in pots with perlite and amended with either fresh or dry aerial plant material (20 and 2 percent, respectively)of S. deppei. We analyzed (i)the morphological (specific leaf area-SLA, leaf area ratio-LAR and leaf weight ratio-LWR)and (ii)physiological (net assimilation rate-NAR)parameters which contribute to relative growth rate (RGR). We correlated the effects of S. deppei material on growth of tomato by evaluating the oxidative damage in roots, stems and leaves and by measuring: the enzymes (cytosolic catalase, ascorbate peroxidase, superoxide dismutase, glutathione reductase)activity, levels of hydrogen peroxide (H 2O2)and superoxide (O2 -), membrane lipid peroxidation and activity of plasma membrane NADPH oxidase. Results showed that application of either fresh or dry material of S. deppei decreased the RGR, leaf area and dry weight of tomato seedlings. Regression coefficients analysis for RGR and its components showed that variation in growth was caused by the decreased net assimilation rate (NAR)and the physiological traits. These results were linked with an imbalance of antioxidant enzyme activity; increase in hydrogen peroxide and NADPH oxidase avtivity and an increase in lipid peroxidation in leaves of tomato plants.