Essential oil variations and physiological responses of rosemary (Rosmarinus officinalis L.) to growth elicitors under drought stress condition

To investigate effects of some plant growth elicitors on rosemary under drought stress, a CRD factorial experiment was conducted at Shahrekord University, Iran. Full irrigation and drought stress (50 % full irrigation) as first factor, and varying concentrations of salicylic acid (SA) (100, 200, and 400 mg/L), L -phenylalanine (80, 160, and 320 mg/L), and lovastatin (40, 80, and 160 mg/L), along with a control as second factor were examined. Drought increased antioxidant activity (5 %), but decreased chlorophyll b (40 %), essential oil yield (12.6 %), and shoot dry weight (16.6 %), while foliar spraying with optimal concentrations of 200 mg/L SA and 320 mg/L L -phenylalanine under these conditions increased chlorophyll a , carotenoids, essential oil content, PAL enzyme activity, phenolic and flavonoid compounds. Main components of rosemary essential oil were α-pinene (11.9 %), camphor (12.9 %), 1,8-cineole (7.6 %), camphene (3.8 %), borneol (10.4 %), verbenone (4.9 %), and bornyl acetate (12.9 %) which reduced under drought, except for borneol and bornyl acetate. SA (100 mg/L) increased α-pinene (116 %), camphene (94 %) and 1,8-cineole (50.6 %), while 200 mg/L SA increased verbenone (58 %) and 320 mg/L L -phenylalanine increased borneol (20.6 %) and bornyl acetate (33.7 %). Higher concentrations of SA and L -phenylalanine decreased hydrocarbon monoterpenes while increased oxygenated monoterpenes and sesquiterpenes. However, lovastatin likely redirected the energy towards other pathways, such as carotenoids, which prevent hydrocarbon monoterpenes conversion to oxygenated ones. Overall, it can be stated that SA, L -phenylalanine, and lovastatin improve plant performance especially under drought condition by enhancing specific pathways, thereby alleviating adverse effects of stress might be offers potential for special purposes. • Salicylic acid improved growth and tolerance against drought stress. • L-Phenylalanine increased essential oil and stimulated phenol and flavonoid biosynthesis. • Lovastatin enhanced carotenoids and isoprenoid pigments.