Study on physiological traits, percentage and essential oil components of two oregano subspecies (Origanum vulgare subsp. gracile (K.Koch) letsw. and O. vulgare subsp. hirtum (Link) letsw.) under salinity stress

Abstract

To investigate the effects of different salinity levels on the essential oil content, and some morphological and physiological characteristics of two oregano subspecies (Origanum vulgare subsp. gracile (K.Koch) letsw. and O. vulgare subsp. hirtum (Link) letsw.), a factorial greenhouse experiment was conducted in a completely randomized design with four treatments and three replications. The salinity stress treatment was applied using sodium chloride in Hoagland nutrient solution at four levels of control (no stress), and mild (salinity 30 mM), moderate (salinity 60 mM), and severe (salinity 90 mM) stresses. According to the results, under salinity stress the growth indices, total carotenoids, and chlorophyll index decreased, but the activity of antioxidant enzymes and concentration of malondialdehyde and hydrogen peroxide increased in both subspecies. The wet and dry weight, carotenoids, hydrogen peroxide, and guaiacol peroxidase activity were obtained higher in subsp. hirtum than subsp. gracile. The percentage and essential oil composition were also affected by salinity. With increasing the salinity levels, the essential oil percentage was significantly increased compared to the control and its highest amount (0.8%) was observed under mild stress. Thirty five compounds were identified in both oregano subspecies essential oil. Carvacrol (30-72%: subsp. hirtum crarvacrol more than the other subsp.), γ-terpinene, carvacrol methyl ether, and p-cymene were the main components of both subspecies. The results of this study demonstrated the superiority of subsp. hirtum to the other oregano subspecies in terms of the tolerance to salinity stress and also quantitative and qualitative yields.