Germination response of Ajowan, Fennel and Dill to osmotic potential of sodium chloride and polyethylene glycol 6000 in different temperature regimes

In order to study the germination response of three medicinal plants’ seeds, Ajowan (Trachyspermum ammi), Fennel (Foeniculum vulgare) and Dill (Anethum graveolens) to osmotic potential of sodium chloride and polyethylene glycol 6000 under different temperature regimes, two separate experiments were carried out in a factorial arrangement based on completely randomized design with three replications. Levels of temperatures were 5, 10, 15, 20, 25, 30 and 35ºC and osmotic potential with four levels of (0, -5, -10 and -15 bars). Results indicated that the effects of species, temperature and osmotic potential and also interactions of species and temperature with stress were significant. Germination rate and percentage and also length of radicle and plumule were decreased as stress intensity increased. Optimum temperature for germination percentage was 15ºC and for germination rate, length of radicle and plumule was 20ºC. Ajowan and dill seeds showed the highest and lowest resistance to temperature change and osmotic potential. Water deficit had more inhibitory effects on germination rate and percentage and -15 bar caused complete failure in germination. Effect of salinity was more pronounced on length of radicle and plumule compared with the effects of water deficit. In both drought and salinity percentage reduction for plumule length was higher which indicate the higher sensitivity of this trait to stress in comparison with radicle length.