Bacterial colonization of phyllosphere of mediterranean aromatic plants

The influence of secondary metabolites on the bacterial colonization of the phyllosphere of four aromatic species of the Mediterranean region was stud ied for the determination of total bacterial populations (TBP) and populati ons 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 bact eria, whereas rosemary, sage, and oregano were poorly colonized. The differ ences in bacterial colonization were related to the plants' content of seco ndary metabolites and their antimicrobial activity, as recorded in the in v itro bioassays. Lavender had the lowest amount of surface phenolics, the lo west 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 number s on those of rosemary and lavender. For this reason, these aromatic plants were further studied regarding their effect against two INA bacteria, Pseu domonas syringae and Envinia herbicola. Minimum inhibitory concentrations a nd minimum bactericidal concentrations were estimated for the essential oil s and for their main constituents under different bacterial populations. Th e antibacterial effect of Labiatae aromatic plants against INA bacteria not only explains the scarce presence of the latter on their leaves but may ha ve applications in agriculture as a frost-control method for sensitive crop s.