Phytotoxic effects of Cerbera manghas L. leaf extracts on seedling elongation of four monocot and four dicot test species

Exploration of allelochemicals with phytotoxic effects is intended to minimize a current dependency on synthetic herbicides in weed management. Several allelochemicals from the tropical tree Cerbera manghas (sea mango) have been reported as termiticides and bactericides. The present study investigated possible phytotoxic effects of C. manghas leaf extracts under laboratory conditions. Four monocots: barnyard grass (Echinochloa crus-galli), foxtail fescue (Vulpia myuros), Italian ryegrass (Lolium multiflorum), and timothy (Phleum pratense) and four dicots: alfalfa (Medicago sativa), garden cress (Lepidium sativum), lettuce (Lactuca sativa), and rapeseed (Brassica napus) were used as test species. Elongation of both shoots and roots of seedlings was measured to assess any phytotoxic effects. The results showed that the sensitivities of shoots and roots were different between the test species, and the inhibition of seedling elongation significantly increased with increasing concentration of leaf extracts of C. manghas for all the test species. The IC50 (50% inhibitory concentration) values showed that 8.50–32.30 and 4.26–34.67 mg dry weight equivalent extract mL−1 of C. manghas inhibited seedling elongation by 50%, for shoots and roots respectively. Isolation and identification of the phytotoxic substances from C. manghas are suggested for future investigation.