The antibacterial and the structure-activity relationship of ten natural monoterpenes against four plant pathogenic bacteria Erwinia carotovora, Ralstonia solanacearum, Rhodococcus fascians, and Rhizobium radiobacter was investigated. The antibacterial activity was evaluated in vitro by broth microdilution and agar dilution techniques as a minimum inhibitory concentration (MIC). The quantitative structure-activity relationships (QSARs) with some physicochemical descriptors of the tested monoterpenes were performed in order to investigate and predict the antibacterial activity. The results showed that the MICs depended on the bioassay test and the bacterial reduction rate increased with the increase of the concentration. Geraniol and thymol showed the highest potent activity among the tested monoterpenes against four plant pathogenic bacteria. The QSAR models showed excellent agreement between estimated and experimentally measured toxicity parameter (MIC) for the tested monoterpenes. The results of the current study could be used to identify or predict the best model for describing the antibacterial activity of new monoterpenes, the main constituents of plant essential oils, in the search for new biologically active agents against plant pathogenic bacteria.
