Influence of drought stress on seed germination and physiological characteristics of Origanum vulgare

In this study, we examined the effects of drought stress induced by different concentrations of PEG-6000 (5%, 10%, 15%, 20%, and 25%) on the germination and seedling growth of Origanum vulgare seeds, and assessed the drought resistance of O. vulgare seeds and seedlings. The results revealed that with an increase in PEG-6000 concentration, there were gradual reductions in the rate of germination, germination potential, germination index, and vitality index of O. vulgare seeds. Whereas low concentrations of PEG-6000 (< 10%) had no significant effects on the germination of seeds, whereas high concentrations (> 20%) inhibited germination. The root length, stem length, and fresh weight of O. vulgare seedling showed a trend of initial increase and subsequent decline, with the biomass of seedlings reaching a maximum value of 37.05 mg in response to the 10% PEG-6000 treatment. In addition, we observed increases in the contents of malondialdehyde, proline, and soluble proteins, and the activity of catalase with an increase in PEG-6000 concentration. In contrast, the contents of soluble sugars, and the activities of superoxide dismutase and peroxidase showed a trend of initial increase and subsequent decline with an increase in PEG-6000 concentrations. In summary, we found that although the seeds and seedlings of O. vulgare have a certain degree of drought resistance (PEG-6000 concentrations < 15%), moderate and severe drought stress (PEG-6000 concentrations ≥ 20%) can adversely affect seed and seedling growth.