Effect of Drought Stress and its Interaction with Salicylic Acid on Fennel (Foeniculum vulgare Mill.) Germination and Early Seedling Growth

Environmental stress, particularly drought stress can play an important role in reducing plant growth especially during the germination stage in arid and semi-arid regions in Iran. For cultivation of medicinal plants in arid and semi-arid areas, the assessment of their tolerance is very important. In this research, in order to evaluate the effects of salicylic acid pretreatment on enhancement of seed germination and early seedling growth of Foeniculum vulgare Mill.  under drought stress, a factorial experiment based on completely randomized design was employed. The factors were the combination of five levels of drought stress induced by poly ethylene glycol (0, -0.1, -0.2, -0.3 and -0.4 MPa) and five concentrations of salicylic acid (0, 0.25, 0.5, 0.75 and 1 mM) with three replicates. The results indicated that an increase in drought stress reduced germination components such as  germination percentage and rate, total biomass, seed vigor index, root length, root fresh and dry weight, shoot length, shoot fresh and dry weight and relative water content and increased electrolyte leakage and proline content. Salicylic acid improved germination; therefore, the average time necessary for germination decreased under drought conditions. The seeds treated by salicylic acid, produced a higher root and shoot length, root and shoot fresh and dry weight, total biomass and seed vigor index.  Salicylic acid ameliorated the negative effects of drought stress on fennel germination and seedling's growth. Higher concentrations of salicylic acid were more effective than the lower ones. It seems that salicylic acid can enhance the tolerant ability of the seeds to germination under drought stress.