The effect of dormancy breaking treatments on seed germination of Licorice medicinal plant (Glycyrrhiza glabra L.)

In order to evaluate the effect of different mechanical treatments (application of sulphuric acid, boiling water and flooding) on seed dormancy breaking of Licorice, an experiment was carried out in randomized complete block design in 2012. Moreover, a factorial scheme in RCBD was performed to assess the application of giberalic acid and potassium nitrate treatment as well as stratification and rotational temperature/light treatment. Treatments included different levels of giberalic acid (0, 100, 250 and 500 mg) at two time levels of 2 and 24 hour (along with scarification pre-treatment), concentrations of potassium nitrate (0, 50, 100 and 150 mM) in 10 and 30 minutes (along with scarification pre-treatment), stratification temperatures treatment of -5, 0 and 5 °C for one, two and three weeks of treatment, treatment of rotational temperature (5-15 and 10-20 °C), in full light, dark and rotational light periods (8 h light and 16 h dark) and mechanical treatments of dormancy breaking. Treatment duration of two minutes in boiling water and two days water-logging treatment were the most effective treatments on germination percentage of Licorice (81.33% and 53.33% increase in germination percentage compared to control, respectively). Application of giberalic acid and potassium nitrate treatments and stratification had no effect on Licorice dormancy. According to the Licorice seed dormancy breaking in mechanical treatments and the effect of rotational temperature and light, it can be concluded that the dormancy of Licorice seeds is intermittent.