Effects of drought stress and alternating temperature on seed quality parameters of Thymus munbyanus Boiss & Reut

Thymus munbyanus Boiss & Reut, is an aromatic and medicinal plant, negatively affected by anthropogenic pressure and climate change. The objective of this research is to examine the effect of alternating temperature and PEG-induced drought stress on seed germination parameters and seedling vigor of T. munbyanus. Treatments included five alternating temperature regimes (10/0, 15/05, 20/10, 30/20, and 40/25°C), and five PolyEtylenGlycol6000–(PEG-6000) induced osmotic potentials (0, -0.1, -0.3, -0.6, and − 0.9 MPa). The Final germination percentage (FGP), the mean germination time (MGT) and Seedling vigor index I and II were assessed to examine the effect of alternating temperature, and drought stress. Our findings showed that temperature and PEG-induced drought stress significantly influence germination parameters and seedling vigor. In fact, the temperature 15/05°C registered the highest final germination percentage of 96%, the fast germination speed with a MGT of 4.3 ± 0.1 days and the best seedling vigor index I and II with values of 137.8 + 12.5 and 28.2 + 6.0 respectively. Germination parameters and seedling vigor are highest for low temperatures regimes; a very signification decrease is registered from 20/10°C to inhibition at alternating temperature 40/25°C. Drought stress results shows that the increase in PEG-6000 concentration affect negatively germination parameters and seedling vigor. In fact, germination is suppressed at the highest concentration (-0.9 MPa). These results are important for the restoration or rehabilitation of the species studied in degraded rangelands.