To observe the effect of plant growth-promoting rhizobacteria (PGPR) and salicylic acid under drought stress conditions on yarrow, an experiment was arranged as split-plot factorial based on a randomized complete block design with three replications in a research farm in Basht, Kohgiluyeh and Boyer-ahmad provice, during two years (2018 and 2019). Drought stress as the main factor in two levels (drought and non-drought stress), and secondary factors include foliar spraying with salicylic acid in two levels: control (no foliar spraying) and foliar spraying with salicylic acid (400 mg/L), and PGPR at four levels: control (no inoculation with bacteria), inoculation with Pseudomonas, inoculation with Azotobacterial and inoculation with both bacteria were assigned to the main and sub-plots, respectively. The results of a two-year combined variance analysis showed that effects of year, drought stress, bacteria, salicylic acid and drought stress × salicylic acid × bacteria on plant height, thousand seed weight, flower yield, biological yield, essential oil content, and essential oil yield were significant. The average flower yield in the first year was 731.45 kg/ha, which had a significant difference compared to the second year. The highest plant height (65.94 cm) was obtained from azotobacterial and salicylic acid treatment under non-drought stress conditions. Meanwhile, in both conditions (non-drought stress and drought stress), the maximum thousand seed weight (0.29 and 0.23 g), flower yield (1389 and 492 kg/ha), biological yield (8634 and 4106 kg/ha), harvest index (16.09 and 11.99 %), essential oil content (1.41 and 0.80 %) and essential oil yield (1.77 and 19.54 kg/ha) were obtained for bacteria and salicylic acid treatment. Although drought stress caused a significant decrease in all traits, especially flower yield, essential oil content and yield, the use of growth-promoting bacteria or salicylic acid, especially in the treatment of simultaneous application of two bacteria and salicylic acid, significantly reduced the damage of drought stress on flower yield, essential oil content and yield compared to the control.
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