Recovery of plants from leaf protoplasts of hybrid-poplar and aspen clones.

Leaf protoplasts were isolated from shoot cultures of two hybrid poplar clones (Populus alba × P. grandidentata 'Crandon', NC-5339 and P. nigra 'Betulifolia' × P. trichocarpa, NC-5331) and the Upright European Aspen (P. tremula 'Erecta') and were cultured in contact with screen discs floated in liquid medium. Protoplast culture was influenced by the growth medium of the source shoot cultures, the protoplast purification procedure, the plating density, and the presence or absence of a coconut water and casein hydrolysate supplement added to the culture medium. The protoplast-derived cells divided more quickly and with higher incidence than previously reported for hybrid poplars. Shoots were regenerated from the protoplast-derived calli and were maintained as shoot cultures. Plants were developed from microcuttings rooted ex vitro and were grown-on in the greenhouse and field.