Effect of Water Stress on Seed Germination of Thymus serpyllum L. from Tessala mount

Thymus serpyllum L. is a xerophytic perennial herb belongs to the Lamiaceae family commonly used for medicinal purposes. The aim of this study is to determine the effects of water potential on germination. Seeds were germinated under stress of aqueous polyethylene glycol (PEG) solutions mixed to create water stress of -0.03, -0.07, -0.2, -0.5, -1, -1.4 and -1.6 MPa. Distilled water was used as the control (0.0 MPa). A preliminary experiment showed 20C as the optimum germination temperature for seeds of this species. The decrease of water potential progressively declined Initial Germination Percentage (IGP) and Final Germination Percentage (FGP). The highest germination percentages (90%) were obtained under control conditions (without PEG) and increasing moisture stress progressively inhibited seed germination. Although, germination started to regress significantly at -0.5 MPa and decline completely at -1.6 MPa. However, the Initial Germination Day (IGD) and Mean Time of Germination (MTG) increased with decrease in water potential. We conclude that T. serpyllum is able to act as pioneer plant due to the ability of seeds to germinate under lowest water potential.