Objective P. deltoides cl. ‘Danhong’ × P. nigra cl. ‘44’ was used to establish an efficient and stable regeneration tissue culture system and genetic transformation system for black poplars (P. deltoids × P. nigra), based on the roots as explants.

Method The 0.5～1.0 cm root segments from clone ‘44’ seedlings were used to induce adventitious buds. The effects of different hormone ratios on the induction and rooting of adventitious buds were investigated and the critical screening concentration of phosphine oxalate for genetic transformation of the root segments was explored. Agrobacterium-mediated method was employed to introduce foreign genes into the clone ‘44’ root cells, and the transformed seedlings were identified by β-glucuronidase staining.

Result The optimal medium for bud differentiation of clone ‘44’ was WPM + 20 g·L⁻¹ sucrose + 7.8 g·L⁻¹ agar + 0.25 mg·L⁻¹ 6-BA + 0.05 mg·L⁻¹ NAA, and the differentiation rate was 86.67%. The optimal medium for seedling rooting was WPM + 0.075 mg·L⁻¹ NAA + 7 g·L⁻¹ agar + 0.1 g·L⁻¹ AC, and the rooting rate was 75.00%. The optimal genetic transformation screening concentration for glyphosate resistance in roots was determined to be 0.8 mg·L⁻¹ through a gradient test. Exogenous genes were introduced into roots by Agrobacterium-mediated method, and the specific PCR primers were designed for identification of the transgenic lines. Nine transgenic plants were obtained from 31 explants, with a transformation efficiency of 29.0%.

Conclusion The efficient regeneration and genetic transformation system for clone ‘44’ has been established, which provides a technical support for transformation of black poplar species and adding excellent traits through genetic transformation to clone ‘44’ in particular.