Effect of Plant Growth-Promoting Rhizobacteria (PGPR) on the Quality and Yield of Essential Oil in Spearmint “Mentha viridis”

The essential oil of spearmint ( Mentha viridis L .) is widely utilized in the agriculture, food, traditional medicine, and cosmetics industries. This study reports the effect of a compatible bacterial consortium composed of the four PGPR strains, on plant growth and essential oil content. Application of this consortium significantly increased plant growth and nutrition as well as essential oil yield and improved its chemical composition. GC–MS analysis revealed that D-carvone and D-limonene were the major constituents of the oil, with higher relative abundance in inoculated plants than in the control. D-carvone increased from 57.57% in controls to 61.39%, 68.94%, and 65.80% in inoculated plants across the first, second, and third harvests. Furthermore, scanning electron microscopy (MEB) observations confirmed a remarkable increase in both the number and size of essential oil secretory glands in treated plants, demonstrating the beneficial impact of PGPR inoculation on essential oil biosynthesis.