Sour orange fruits were collected from Ramsar Citrus Research Center, Ramsar, Iran. Seeds were extracted from mature sour orange and air dried at room temperature for 24 hours. Following removal of integuments, the seeds were sterilized in 2.5% sodium hypochlorite solution for 15 minutes by shaking and followed by three times rinsing in sterilized distilled water. Subsequently, seeds were soaked in 75% ethanol for 1 min and rinsed by sterilized distilled water three times under aseptic conditions. Epicotyl segment-derived explants (0.8 - 1.0 cm) were extracted from seedlings (12 to 15 cm in height) and a 1 mm longitudinal incision was made at each end.