Allelopathic effects of sunflower on seed germination and seedling growth of Trianthema portulacastrum

Herbicidal resistance in Horse purslane (Trianthema portulacastrum) threatens the quality and yield of Kharif crops in India, prompting research to discover novel natural plant compounds with herbicidal properties. Due to its novel nature and potentially interesting chemistry, the American native, Sunflower (Helianthus annuus), was tested for its ability to suppress Horse purslane growth and its feasibility for use in weed control strategies. Aqueous extract of sunflower significantly inhibited seed germination, seedling growth and dry matter accumulation of T. portulacastrum in laboratory bioassays at concentrations of 5, 10 and 15% (w/v). In pot trials, sunflower rhizosphere soil (SRSS), at the stage of 60 days after sunflower sowing (DAS), inhibited above 50% of growth and yield attributes of T. portulacastrum. Extract fractionation showed the highest phytotoxicity against shoot and root growth of test weeds at 100 ppm. Several phenolic acids were identified in stem and leaf extracts through paper chromatography. Their identity was confirmed through spraying with diazotized-p-nitro aniline, sufanilic acid, ferric chloride-potassium ferricyanide and also tested with Hoepfner'scoplin reaction. These results suggest that sunflower is an important potential source of compounds for control of horse purslane in kharif crops.