Effects of temperature, provenance, drought stress and salinity on seed germination response and early seedling stage of Thymus atlanticus (Ball) Roussine

Thymus atlanticus (Ball) Roussine is a valuable aromatic and medicinal species endemic to Morocco. Climate change and anthropogenic threats are factors driving this species to vulnerability and extinction. Therefore, the current study aims to examine the effects of provenance, temperature, drought stress, and salinity on the germination parameters of T. atlanticus seeds and seedling vigor. Seeds are collected from two provenances (Saghro and Tizi n’Telghemt). Treatments included six alternating temperature regimes (10/0, 15/05, 20/10, 25/15, 30/20, and 40/25 °C), five osmotic potentials of aqueous solutions of polyethylene glycol (PEG-6000) (0, −0.1, −0.3, −0.6, and −0.9 MPa), and five concentrations of sodium chloride (NaCl) (0, 1, 2.5, 5, and 7 g/l). The two-way ANOVA test reveals that alternating temperatures, drought, salinity, and their interactions with provenance almost all have a significant impact on germination parameters. However, no significant effect is registered for the interaction between provenance and alternating temperatures on the final germination percentage (FGP). The highest FGP is recorded at several alternating temperatures (15/05, 20/10, 25/15, and 30/20 °C), and the maximum one is at 20/10 °C for both populations (Saghro and Tizi n’Telghemt, respectively 93% and 89%). This temperature regime is also the best in terms of germination time and speed. The most vigorous seedlings are obtained at 20/10 and 30/20 °C for Tizi n’Telghemt and Saghro populations, respectively. Concerning salinity and moisture stress, the results show that the increase in NaCl and PEG-6000 concentrations leads to a significant reduction in the germination capacity (FGP) and seedling vigor index as well as an increase in the mean germination time (MGT) of the two populations studied. The Saghro population tolerates the studied stresses better than the Tizi n’Telghemt population. These results may serve as guidelines for the domestication and rehabilitation of this medicinal plant. •Thymus atlanticus is an aromatic and medicinal plant endemic to Morocco.•Temperature has a significant effect on the final germination percentage, time and speed of germination.•The best germination capacity is registered at several alternating temperatures (15/05, 20/10, 25/15, and 30/20 °C).•The increases in NaCl and PEG-6000 concentrations significantly decrease the germination capacity and seedling vigor index of T. atlanticus.•The population of Saghro withstands better the stu