Plant growth promoting rhizobacteria (PGPR) improve plant growth, antioxidant capacity, and essential oil properties of lemongrass (Cymbopogon citratus) under water stress

Among abiotic stresses, drought is considered as the most important growth limiting factor, especially in arid and semiarid regions. Drought impacts can be adjusted by soil microorganisms. Accordingly, the present study was organized in order to the increase the tolerance of lemongrass (Cymbopogon citratus) to drought using plant growth promoting rhizobacteria (PGPR). Treatments were water stress in four levels (100% field capacity (FC), 75% FC, 50% FC, and 25% FC) and inoculation by PGPR in three levels (uninoculated, inoculated with pseudomonas sp., and inoculated with Azotobacter sp.). Water stress significantly decreased chlorophyll content.Compared to control, severe stress decreased Chlorophylle a+b by 36%. The maximum proline content was accumulated in plants under severe stress and PGPR application. Catalase (CAT) and super oxide dismutase (SOD) activities were increased by 77% and 71%, respectively under severe stress compared to the well-watered condition. The highest total phenol content (TPC) was obtained in the interaction of 50% FC and PGPR application. Moreover, 50% FC induced the maximum total flavonoid content (TFC) by 42% compared to 100% FC. Pseudomonas and Azotobacter increased the TFC by 6% and 18%, respectively in comparison with uninoculated plants. Essential oil (EO) content and yield were increased under 75% FC, and decreased under 50% and 25% FC. EO percentage in 75% FC and PGPR application was higher than other treatments. Under 75% FC, 14% increase in EO yield was reported for both Pseudomonas and Azotobacter application. To sum up, PGPR can improve the plant growth and EO properties by increasing antioxidant capacity of lemongrass.