Callusing, Cell Suspension Culture and Secondary Metabolites Production in Persian Oregano (Origanum vulgare L. ) and Arabian Oregano (O. syriacum L.)

In vitro cultures of Persian oregano (Origanum vulgare L.) and Arabian oregano (O. syriacum L.) were initiated from seeds on Murashige and Skoog (MS) medium containing 2.0 mg/l Gibberellic Acid (GA3) and 15 g/l sucrose. Callus induction was experimented by culturing leaf discs at different levels (0.0, 0.1, 0.5, 1.0, 1.5 or 2.0 mg/l) of 2,4-dichlorophenoxyacetic acid (2,4-D). Best callus induction and fresh weight were obtained at lower levels (0.1 or 0.5 mg/l) of 2,4-D. Callus maintenance was tested on different levels (0.5, 1.0, 1.5, 2.0, or 2.5 mg/l) of N6-Benzyladenine (BA) or Thidiazuron (TDZ) (with or without 0.5 mg/l 2,4-D). The largest callus diameter (12.5 mm) of O. vulgare L. was obtained when TDZ was at 1.0 mg/l without using 2,4-D. Adding 2,4- D at 0.5 mg/l was inhibitory on callus growth and diameter during 30 days of incubation when used in combination with TDZ or BA. BA gave less callus growth and smaller diameter than TDZ for the two species. O. syriacum L. callus was best grown when TDZ was 1.5 mg/l (with or without 0.5 mg/l 2,4-D). Callus from the third generation was friable and able to release cells in cell suspension culture. Cells were successfully subcultured every 17 days on liquid MS media supplemented with 1.0 mg/l TDZ for both Origanum spp. O. syriacum L. grown under greenhouse conditions, produced higher oil yield (1.76 %) than in vitro grown plants (1.17 %), whereas O. vulgare L. was a poor oil producing plant in this study. Callus and cells produced very low oil percentage compared to intact plants. Thymol was identified by gas chromatography analysis in O. syriacum L. intact plants. Ex vitro plants gave 13.1 % thymol while in vitro cultures gave 5.9 %. No thymol was identified in O. vulgare L. intact plants or in oil produced from callus and cells in both species