Plant growth regulators affecting the agro-physiological and phytochemical traits of Damask rose (Rosa damascena Mill.)

• PGPR affecting growth, phenolics, nutrient uptake and essential oils of damask rose • Higher flower yield due to higher nutrient uptake, pigments and antioxidants by PGR • Alcoholic monoterpenoid were the main constituents of plant essential oil • Geraniol and citronellol, two important compounds of rose essence affected by PGR This research (2019 and 2020) investigated the effects of plant growth regulators (PGR) on growth and physiology of Rosa damascena in a randomized complete block design with three replications. Foliar spraying of humic acid (HA, 0, 1, 2, and 3 mL L -1 ), methyl jasmonate (MJ, 0, 0.5, 1 and 2 mM) and titanium dioxide nanoparticles (TDN, 0, 100, 200 mg L -1 ) were separately applied three times before flower blossoming (early May). PGR improved flower yield by increasing photosynthesis pigments, nutrient uptake and antioxidant capacity. HA (3 mL L -1 ), MJ (1 mM) and TDN (100 mg L -1 ) significantly enhanced antioxidant activity by 62.06, 65.44 and 61.99%, respectively. Essential oil content of treated plants with HA (3 mL L -1 ), MJ (1 mM) and TDN (200 mg L -1 ) at 13.82, 34.32 and 17.40%, was significantly higher than untreated plants. Alcoholic monoterpenoid represented by β-citronellol, trans -geraniol, and long-chain hydrocarbons represented by nonadecane and heneicosane were main constituents of plant essential oil. Application of HA (3 mL L -1 ) and MJ (1 mM) significantly enhanced flower yield and essential oil production of R. damascena . The highest amounts of geraniol and citronellol as two important compounds determining quality and commercial value of rose essence were resulted.