Insights into the chemical composition of Ocimum forskaolii and O. americanum essential oils and their phytotoxicity

The essential oils (EOs) of numerous Ocimum species are well-known. The EOs of O. forskaolii and O. americanum growing naturally in Saudi Arabia are compared chemically in the current study. The GC-MS and GC-FID analysis was used for identification and quantitation of EOs` chemical components, and the chemometric analysis was used to determine the differences between the two species. Additionally, against the weeds Dactyloctenium aegyptium and Chenopodium murale, the allelopathic potentiality of the two EOs was assessed. Fifty-one compounds were assigned as overall O. forskaolii EO' components, with abundance of mono- and sesquit-terpenes (40.49 and 55.15%, respectively). endo-Fenchol (18.15%), tau-cadinol (11.42%), beta-atlantol (10.54%), alpha-eudesmol (7.29%), and alpha-terpineol (6.94%) were the major components. Sixty-one components were identified via the GC-MS analysis of O. americanum EO, with sesquiterpenes (81.24%) serving as the major class. alpha-Bulnesene (10.17%), germacrene B (7.72%), endo-borneol (5.51%), isoshyobunone (5.37%), and gamma-eudesmol (5.31%) represented the main compounds. Chemometric study showed a distinct difference between the two species' chemical make-up of the EOs, which might be attributed to genetic changes. The extracted EOs of O. forskaolii and O. americanum demonstrated a significant allelopathic effect against the weeds D. aegyptium and C. murale. Compared to O. americanum, O. forskaolii EO demonstrated greater allelopathic activity. The main components of each species may be a candidate for the observed allelopathic activity, which may act singularly or in combination.