Morphogenesis of Cotyledon Explants and Plantlet Regeneration of Tomato (Lycopersicon esculentum Mill.) Under Salt Stress

This study was aimed to determine the responses of salt stress on cotyledon callus of tomato cv. KC-1 for plant regeneration. Cotyledon explants from in vitro raised seedlings were placed on MS medium containing 1.0 mg/L BAP and 0.2 mg/L NAA or 1.0 mg/L NAA to select a suitable medium for callus formation. After 6 days of culture, green calli were initiated on the cut surfaces of cotyledon explants. Callus formation was observed in 81.2% of the explants on the medium with 1.0 mg/L BAP and 1.0 mg/L NAA. After 2 weeks of culture, cotyledon produced calli were transferred to the medium containing 1.0 mg/L BAP plus 1.0 mg/L NAA without (control) or with NaCl concentrations (20, 40, and 60 mM). Callus was evaluated after 4 weeks of subculture (i.e., after 6 weeks of initial culture) under salt stress based on callus colour, fresh and dry weights of callus and chlorophyll content of callus. Results showed that the effects of tomato KC-1 cultivar on the tested parameters had a significant effect on different salinity levels. The calli that were placed on 60 mM NaCl level were highly affected when compared with control. Calli were then transferred to the medium with 2.0 mg/L BAP and 0.2 mg/L NAA for plant regeneration. Within 4 weeks, plantlets were formed on the control treatment and 20 mM salt stressed calli and they were acclimatized under ex vitro conditions.