Regeneration of transgenic plants from cell suspensions of transformed apple (Malus X domestica Borkh. cv. Gala)

Shoot regeneration in most apple cultivars is sensitive to antibiotic selection, thus Agrobacterium-mediated transformation is of low efficiency. Our experiments confirmed that, with a moderate selection pressure (10 or 20 mg l(-1) kanannycin), a high percentage of callus formation (67.0% or 54.8%, respectively) was observed. Over 80.0% or 95.6% of these calli were transgenic, although the efficiency of transgenic shoot regeneration was low. Modifying the kanamycin selection pressure, or shortening the time of kanamycin selection to 2 weeks, did not increase the efficiency of transformation. Multiplying suspension cultures could be produced from transgenic calli using single cells or small cell aggregates to initiate such cultures. When these transgenic cell aggregates were placed on regeneration medium without kanamycin selection, 17.3% of them regenerated shoots after 8 weeks, and at least 86 transgenic plants were obtained from one suspension culture line. This level of success makes it possible to obtain large numbers of transgenic apple plants from a single experiment for genetic breeding, and to study the mechanisms of integration of target genes.