Phytotoxic Effects of Senna garrettiana and Identification of Phytotoxic Substances for the Development of Bioherbicides

Phytotoxic substances in plants that may serve as alternative natural herbicides for controlling weeds are required for sustainable agriculture. We explored the phytotoxic activities of aqueous methanol extracts of Senna garrettiana (Craib) Irwin & Barneby leaves and the active substances they contain. The results revealed that the S. garrettiana leaf extracts had significant phytotoxic effects on three dicotyledons (Lepidium sativum L., Lactuca sativa L., and Medicago sativa L.) and two monocotyledons (Phleum pratense L. and Lolium multiflorum Lam.). An bioassay-guided isolation process yielded three active substances; caffeic acid, methyl caffeate, and (S)-6-hydroxymellein inhibited the seed germination, seedling growth, and biomass accumulation of L. sativum in a concentration-dependent manner. Based on the concentration required for 50% growth inhibition (IC50), (S)-6-hydroxymellein had the highest inhibitory effects on L. sativum in all test parameters, followed by methyl caffeate and caffeic acid. The L. sativum roots were the most susceptible to (S)-6-hydroxymellein (IC50 = 383 mu M) and caffeic acid (IC50 = 2627 mu M), whereas methyl caffeate (IC50 = 1361 mu M) had the greatest effect on the L. sativum shoots. Thus, three isolated compounds may explain the phytotoxic effects of the S. garrettiana extracts. Consequently, caffeic acid, methyl caffeate, and (S)-6-hydroxymellein could be potential candidates for the future production of bioherbicides.

Automated summary

This study explores the phytotoxic activities of Senna garrettiana leaf extracts and isolated three active substances. The isolated compounds, caffeic acid, methyl caffeate, and (S)-6-hydroxymellein, showed significant inhibitory effects on the germination and growth of weeds. These compounds have the potential to be used as bioherbicides.