Effect of Thermal Period on Seed Dormancy of Damask Rose (Rosa damascena Mill.)

Damask rose (Rosa damascena Mill.) has high economic importance and commercial value. The plant essential oil is used for perfumery, food and medicinal industries. It is necessary to know much about seed germination for study of genetic variation and breeding improved varieties of R. damascena. In this study seed germination of R. damascena were evaluated, using thermal period treatments. The data were analyzed based on the Randomized Completely Design with 3 replications. Seeds were sterilized for elimination with NaOCl. Seeds of R. damascena were subjected to five different temperature regimes. For control, the seeds were placed at 4°C continuously. The seeds of all other treatments initially were placed at 25°C for the first warm stratification. Then they were placed at 4°C for 2, 4, 6 and 8 weeks for cold stratification as 2w/2w, 2w/4w, 2w/6w and 2w/8w, respectively. For the second cycle, seeds were placed at 20 °C for warm stratification followed by 2, 4, 6 and 8 weeks for cold stratification. The treatments were repeated for 3 cycles. Then the all of treatments were applied 30 weeks of continuously cold stratification at 4°C. The results of this study showed that the thermal period treatments had significantly promoted the germination percentage. The highest germination percentage and speed of germination were obtained for the 6w/2w treatment as (92%) and (1.17 seeds per day), respectively. The lowest germination percentage was found in the control and 8w/2w treatments (50%). In conclusion, it was observed that with application of thermal period (particularly 6w/2w) and 30 weeks of cold stratification to Damask rose seeds, dormancy was broken and germination was also highly improved.