In vitro selection for NaCl tolerance in Thymus vulgaris L.

Thyme (Thymus vulgaris L.) is an aromatic and medicinal plant which is very important for the herbal industry. In this research, in vitro selection for NaCl tolerance was investigated in this plant. Hypocotyl and shoot explants (apical meristem and cotyledonary leaves) of sterilized seedlings were cultured in MS medium supplemented with different combinations of 2, 4-dichlorophenoxyacetic acid (2, 4-D), napthaleneacetic acid (NAA), kinetin (KIN) and N6-benzyladenine (BA) for callus induction. Results showed that the maximum frequency of callus induction was obtained on MS medium containing 1:0.5 ratio of 2, 4-D:Kin (mgl-1), while optimal callus induction with the best quality and regeneration potential was achieved in 1:1 ratio of NAA:BA (mgl-1). The calli grown in 1:1 ratio of NAA:BA (mgl-1) were transferred to NaCl supplemented medium at 50, 75 and 100 mM concentrations. Fresh and dry weights, percentage of necrosis and regeneration of calli were determined after 4 weeks. There were significant differences between fresh and dry weights of calli in different concentrations of NaCl. The highest and the lowest of fresh and dry weights of calli from hypocotyl explants were observed in 0 (control) and 100 mM NaCl concentrations, respectively. But fresh weight of shoot-derived calli induced from shoots reduced only in 100 mM NaCl and the dry weight of them was not significantly different. The necrosis percentage increased by increasing the salt concentration. Callus regeneration just occurred at the concentration of 50 mM of NaCl and all regenerated shoots well rooted on half strength MS medium, with 0.8% (w/v) sucrose and without growth regulators.