Effects of salinity stress on some morpho-physiological characteristics, essential oil content, and ion relations of two oregano subspecies (Origanum vulgare ssp. vulgare & ssp. gracile)

Oregano (Origanum vulgare L.) is a perennial herbaceous plant belonging to the fam. lamiaceae that is used as a spice for flavoring foods and also for medicinal purposes as carminative, diaphoretic, expectorant, sedative, stomachic, diuretic, antitussive, and antirheumatic. To evaluate the effects of salinity stress on some growth and physiological parameters, essential oil content, and nutrients absorption in two oregano subspecies, a factorial pot experiment was conducted in a completely randomized design with three replications. The experimental factors included two subspecies of oregano (ssp. vulgare and ssp. gracile) and salinity stress at four levels (0, 25, 50, and 100 mM of NaCl). The results showed that the salinity stress had a significant effect on the measured parameters. With increasing the salinity level, the growth characteristics (plant height, stem diameter, number of leaves, and dry matter yield), leaf relative water content (RWC), chlorophyll index (SPAD), percentage and essential oil yield, N, P, and K content and K/Na ratio in leaves and roots decreased, while Na and Cl content in leaves and roots of both subspecies increased. The two subspecies response to the different levels of salinity stress was different. The higher Na accumulation in the roots and higher K/Na ratio in the leaves compared to the roots indicated the ability of oregano subspecies to limit the transfer and accumulation of Na+ ions in their shoots. Overall, the findings of this study showed that the ssp. vulgare had higher tolerance to the salinity stress than ssp. gracile due to the less accumulation of Na and Cl ions, higher K/Na ratio, and lower reduction in chlorophyll index and dry matter yield.