Investigation of the drought stress tolerance of Origanum sipyleum L. under in vitro conditions

Drought is one of the major abiotic stress factors that negatively impacts plant growth, development, and yield. This study aims to observe the responses of Origanum sipyleum L., an endemic species of significant ecological and genetic value, to in vitro drought stress. In vitro, plant explants were subjected to six polyethylene glycol (PEG) doses (0.5%, 1.0%, 3.0%, 5.0%, 10.0%, and control), and 12 plant growth parameters were examined. It was observed that PEG application negatively affected all plant growth parameters up to a certain dose, while the 5.0% PEG dose resulted in an increase in parameters such as shoot number, leaf number, and root length compared to the control group. Additionally, the highest rooting rates observed at the 5.0% PEG dose suggest that this concentration may represent a critical adaptation threshold for plant growth. The 5.0% PEG dose was identified as the optimal dose for plant growth performance, whereas higher doses exhibited inhibitory effects on growth and development.