Plant growth promoting rhizobacteria enhance oil content and physiological status of Thymus daenensis Celak. under drought stress

Currently, the use of beneficial microorganisms with the hope to reduce the adverse effects of drought has been the focus of attention. In present study, the effects of plant growth promoting rhizobacteria (PGPR) and drought stress on essential oil (EO) and physiological status of Thymus daenensis Celak, were investigated.

The experiment was arranged as a factorial pattern in a randomized complete design with three replications. Factors were four irrigation regimes included: well-watered (A: absence of stress), irrigation after depletion of 20-25% of field capacity (L: low stress), irrigation after depletion of the 35-40% of field capacity (M: mild stress) and irrigation after depletion of the 55-60% of field capacity (S: severe stress). Also, two PGPR treatments, non-inoculation (C: control) and inoculation with PGPR were conducted.

The results showed that drought stress reduced root and shoot dry weight, relative water content, photosynthetic pigments and gas change parameters but PGPR inoculation improved all of them. Proline, malondialdehyde, electrolyte leakage and stomatal resistance increased with increasing water stress, but PGPR inoculation ameliorate these increases in corresponding treatments. PGPR inoculation increased essential oil production although this increase was not statistically significant but water stress decreased it.

The results suggest that PGPR inoculation could be an excellent strategy to alleviate adverse effects of water stress in Thymus daenensis cultivation in drought stress conditions. Therefore, farmers in semiarid regions could produce T. daenensis by using of PGPR at low water stress for the highest economic amount of extracted essential oil.