The effects of Plant Growth Regulators on Breaking Seed Dormancy in Silybum marianum L.

Milk thistle (Silybum marianum L.)، belonging to Asteraceae as an Iranian native-landscape plant، has a well-known position in traditional medicine. But، its seeds are dormant. The current study investigated the most efficient hormonal treatment to break the species dormancy. The seeds were treated using gibberellic acid، kinetin and auxin (100، 250، 500 and 1000 ppm) –and 24-epibrassinolid (0. 5 and 1 ppm) for 24 and 48 h. Also، a combined treatment of gibberellic acid (500 ppm) and pre-chilling (for 5، 10 and 15 d) was accomplished. All treatments significantly increased seed germination in milk thistle; though the most effective treatment was gibberellic acid (500 ppm) which caused 70% increasing in seed germination. Kinetin and auxin (100 ppm) and 24-epibrassinolid (0. 5 ppm)، in 24 h respectively increased seed germination about، 40%، 38% and 60%. Also combination of gibberellic acid (500 ppm) and chilling (5d) treatment increased seed germinating 60%. Results showed gibberellic acid (500 ppm) is the best treatment for breaking of Silybum marianum seed dormancy.