High-efficiency Agrobacterium tumefaciens-mediated transformation of cucumber (Cucumis sativus L.) using stem nodes as explants

An efficient Agrobacterium-mediated transformation system was developed for cucumber (Cucumis sativus L. 'Jinyan') using stem nodes as explants. Stem nodes were isolated from cucumber seedlings 10 d after germination, wounded four-to-five-times with a knife, infected for 30 min with Agrobacterium tumefaciens strain EHA105 harbouring the binary vector pCAMBIA 1303, then co-cultured for 5 d. Adding a washing step after co-culturing, and using 25 mg l(-1) meropenem to suppress bacterial growth in the regeneration medium, eliminated any overgrowth of Agrobacterium and significantly improved the efficiency of transformation when 15 mg 1(-1) hygromycin was applied as a selection agent. Finally, a transformation efficiency of 7.1% was achieved with a high frequency (50%) of single-copy T-DNA integration 2 months after co-culture. On average, two-to-three independent transformation events occurred from each original explant.