Effect of water stress on growth indices, chlorophyll fluorescence and essential oil ‎compositions of American oregano (Origanum vulgare subsp. vulgare)‎

In the arid and semiarid regions, water stress mainly affects the growth, yield and secondary metabolit production of oregano. In order to determine the effect water stress on growth, physiological and phytochemicals characteristic of American oregano (Origanum vulgare L.), a greenhouse study based on a completely randomized design (CRD) with four treatments and three replications was performed. The plants, were subjected to four water stress conditions, including no water stress (field moisture capacity), mild (75 % FMC), moderate (55 % FMC) and sever water stress (35 % FMC). The results showed that the plant height, dry matter yield, the ratio of inflorescence weight/stem, chlorophyll index and relative water content were reduced under water stress. The highest essential oil content (1.15 %) was observed under mild water stress. Also, mild water stress significantly decreased the chlorophyll fluorescence parameters (Y(NO) and Fv) in compared with moderate and severe water stress. Analysis of the essential oil components demonstrated that in all treatements, sabinene, (Z)-β-ocimene, (E)-β-ocimene, (E)-caryophyllene, germacrene D and γ-terpinene were the major components. The highest amount of γ-terpinene (16.79 %) and (E)-caryophyllene (9.92 %) were observed in mild water stress which increased by 344.1 % and 14.28 % compared with control, respectively. Based on the obtained results, mild water stress significantly ameliorate the quality and quantity of oregano.