Effects of Nano-silicon as seed priming and the inoculation of plants growth promoting rhizobacteria (PGPRs) on morphological and phytochemical traits of Lemon balm (Melissa officinalis) was investigated. So, the study was carry out as a factorial design in the form of randomized complete design at the Institute of Medicinal Plants, faculty of agricultural and natural resources university of arak with three replications. Treatments including Nano priming 3 levels of Nanosilicon (control, 0.1, 0.3, and 0.4 mM) in different times 12, 24, 48 and 72 h application with two strain of Rhizobacteria (Putida and florescence). The result of this experiment indicated that the interaction of these treatments could increase the weight of the fresh and dry shoots remarkably in a way that the highest weight of the fresh and dry shoots is related to interaction of Nano-silicon 0.4 mM during 12 h and with inoculation of rhizobactria putida. Also the number of main branches compare to control has increased so that the most number of main branches is gained from the interaction of Nano-silicon 0.4 mM during the 12 h priming with inoculation of rhizobactria putida too. Application of Nano-silicon 0.1 mM during 12 h priming with inoculation of rhizobactria putida, indicated the maximum relative content of water (RWC) than the other concentrations that shows significant difference statically in the level of one percent. Also theined essential oil composition was changed so that the amount of Thymol with the application of Nano-solicon 0.3 mM with inoculation of rhizobactria florescence increased till six folds, and with inoculation of rhizobactria putida increased till four folds. Thymol has antibacterial properties. In addition to, Isomentol composition had been twice with application of Nano-silicon 0.4 mM along with inoculation of rhizobactria putida as well as Nano-silicon 0.3 mM with inoculation of rhizobactria florescence.
