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driven by the CaMV 35S promoter was used. Transformation parameters were optimized including bacterial concentration, pre-culture period, co-cultivation period, immersion time, acetosyringone (AS)
concentration and mannitol treated time. Results were obtained based on the percentage of GUS expression. Agrobacterium tumefaciens strain EHA105 at concentration OD600 nm = 0.8 showed the highest virulence on sweet potato embryogenic callus. Four days of pre-culture, four days of
co-cultivation, 10 min of immersion, 200 M acetosyringone and 60 min of mannitol-treated embryogenic callus gave the highest percentage of GUS positive transformants.