The Effect of Pre-Chilling and Gibberellic Acid on Breaking Seed Dormancy of Two Medicinal Plants Species Silybum Mrianum and Citrulus Colocynthis

The seeds of two species (Citrulus colocynthis) and (Silybum mrianum) gathered from natural habitat located in the Koohdasht city (Lorestan province) and transferred to Kermanshah Agricultural and Natural Resources Research and Education Center in the summer of 2014. For each species, separate experiments in a completely randomized design with 14 treatments and 4 replications were done. Treatments included moist-chilling time (control, 10, 20, 30, 40, 50, 70 and 90 days at 4 °C), gibberellic acid concentration (200, 400, 600 and 800 PPM) and integrated treatment of gibberellic acid 400 ppm with moist-chilling for 30 days and 70 days. The results showed that for both species increasing of moist-chilling duration and concentration of gibberellic acid significantly increased germination percentage, germination rate and seed vigor index. The best breaking seed dormancy treatment was moist-chilling of 90 days for seeds of (Citruluus colocynthis) and gibberellic acid 800 ppm for (Silybum mrianum). The result showed that seeds of two species had the combination of physiological (related to seed inside inhibitors) and physical dormancy (related to hard coat)