Evaluation of phytotoxic potential and identification of phytotoxic substances in Cassia alata Linn. leaves

Cassia alata (Caesalpiniaceae) is a large perennial shrub native to tropical America. It is an important medicinal and ornamental plant and has been reported to possess several pharmacological properties. However, phytotoxic substances from C. alata have not yet been documented in the literature. Therefore, this study seeks to evaluate the phytotoxic potential of C. alata leaves and to identify inhibitory substances for the purpose of eco-friendly weed management. The effect of aqueous methanol extracts of C. alata on the seedling growth of alfalfa, cress, lettuce, rapeseed, barnyard grass, foxtail fescue, Italian ryegrass, and timothy was examined. The level of inhibition of the extracts corresponded to concentration. Several chromatographic steps were performed to separate the extracts, and through spectroscopic analysis, two active substances were isolated and characterised as rutin and syringone. These two active substances significantly inhibited the seedling growth of cress and foxtail fescue. The range of I ₅₀ values (required concentration for 50% growth inhibition) of rutin and syringone for the seedling growth of cress and foxtail fescue were 129.5–417.8 and 160.1–466.5 µM, respectively. These results indicate that the two identified active phytotoxic substances from C. alata may be responsible for its growth inhibitory properties.