Effect of cooling pre-treatment on germination criteria and drought stress resistance in Dorema ammoniacum

Water deficiency is one of the important problems in arid and semi-arid regions. Thus, in germination and growing stages selection of resistant medicinal plant species is very important. In this investigation in order to seed dormancy breakage of Dorema ammoniacum seeds, wet cooling treatment was assessed first. After selection of the best cooling treatment (5 °C), treated seeds were placed in germinating medium with drought stress; at a period of 20 days at 15 and 20 °C. Drought stress trial was conducted at 5 levels as factorial layout based on a completely randomized design including control, -4, -8, -12, and -16 bar treatments. PEG was used to make drought stress. Results showed germination rate and percentage, radicle length, and stem length were significantly (P<0/01) decreased by increasing drought stress. The best range for germination in conditions of without stress was to -12 bar water potential. It appears that stem length was more vulnerable than other characters. In addition, 20 °C was the most appropriate temperature for germination under drought treatment.