Chemical Composition and Phytotoxic and Antibiofilm Activity of the Essential Oils of Eucalyptus bicostata , E. gigantea , E. intertexta , E. obliqua , E. pauciflora and E. tereticornis .

species are characterized by their richness in essential oils (EOs) with a great diversity of biological activities. This study reports the chemical composition and the phytotoxic and antibiofilm activities of the EOs of six species growing in Tunisia: and . Four EOs were rich above all in oxygenated monoterpenes (25.3-91.4%), with eucalyptol as the main constituent. However, in the EOs of and sesquiterpene hydrocarbons (28.8-54.0%) were the main class of constituents; piperitone was the main constituent of both EOs. The phytotoxicity of the EOs was tested against germination and radicle elongation of the weeds and and the crop , resulting in the different inhibition of seed germination and radicle elongation depending on both chemical composition and the seed tested, with remarkable phytotoxicity towards and . Furthermore, almost all EOs showed antibacterial potential, resulting in significant inhibition of bacterial biofilm formation and the metabolism of Gram-positive ( subsp. and ) and Gram-negative (, and ) bacterial strains, in addition to acting on mature biofilms. The EOs were inhibitory against all bacterial strains tested and usually reluctant to undergo the action of conventional antibiotics. Therefore, these EOs may be considered for applications both as herbicides and in food and health fields.