After Agrobacterium inoculation, the explants were blotted onto sterilized filter paper for 30 min to remove excessive bacte-ria. Then, the explants were plated onto co-cultivation medium with a layer of sterile filter paper for co-cultivation. After 3 days,the explants were washed thoroughly with 500 mg l−1 cefotaxime. After brief dry out on sterilized filter paper, the explants were transferred to callus induction and maintenance medium