Journal of Chemical Ecology, Vol. 26, No. 9, 2000 0098-0331 / 00 / 0900-2035$18.00 / 0  2000 Plenum Publishing Corporation 2035 BACTERIAL COLONIZATION OF PHYLLOSPHERE OF MEDITERRANEAN AROMATIC PLANTS K. KARAMANOLI, 1 D. VOKOU, 2 U. MENKISSOGLU, 3 and H.-I. CONSTANTINIDOU 1, * 1 Laboratory of Agricultural Chemistry, School of Agriculture 2 Department of Ecology, School of Biology 3 Laboratory of Pesticides, School of Agriculture Aristotle University GR-54 006 Thessaloniki, Greece (Received November 8, 1999; accepted May 5, 2000) Abstract—The influence of secondary metabolites on the bacterial coloniza- tion of the phyllosphere of four aromatic species of the Mediterranean region was studied for the determination of total bacterial populations (TBP) and populations of ice nucleation active bacteria (INA). The aromatic plants used were lavender (Lavandula angustifolia), rosemary (Rosmarinus officinalis), Greek sage (Salvia fruticosa), and Greek oregano (Origanum vulgare subsp. hirtum), all growing in neighboring sites. Lavender was heavily colonized by bacteria, whereas rosemary, sage, and oregano were poorly colonized. The differences in bacterial colonization were related to the plants’ content of secondary metabolites and their antimicrobial activity, as recorded in the in vitro bioassays. Lavender had the lowest amount of surface phenolics, the lowest concentration of essential oil, and the overall weakest antibacterial activity. Among the epiphytic bacteria, ice nucleation active ones were not detected on oregano and sage leaves but were found in extremely low numbers on those of rosemary and lavender. For this reason, these aromatic plants were further studied regarding their effect against two INA bacteria, Pseudomonas syringae and Erwinia herbicola. Minimum inhibitory concentrations and minimum bactericidal concentrations were estimated for the essential oils and for their main constituents under different bacterial populations. The antibacterial effect of Labiatae aromatic plants against INA bacteria not only explains the scarce presence of the latter on their leaves but may have applications in agriculture as a frost-control method for sensitive crops. Key Words—Epiphytic bacterial colonization, antibacterial activity, essential oils, leaf surface phenolics, oxygenated constituents, INA bacteria. *To whom correspondence should be addressed.