Response of transgenic Royal Gala apple (Malus x domestica Borkh.) shoots carrying a modified cecropin MB39 gene, to Erwinia amylovora

Transgenic Royal Gala apple (Malus x dometica Borkh.) shoots were obtained by Agrobacterium-mediated gene transfer using a binary plasmid vector pGV with T-DNA encoding MB39, a modified cecropin SB37 gene, joined to a secretory coding sequence from barley a-amylase and placed under the control of wound-inducible osmotin promoter from tobacco. Th integration of the cecropin MB39 gene. into apple wa confirmed by Southern blot analysis. Seven independent transgenic lines were, recovered from a total of 402 inoculated explants, with a transformation efficiency of 1.7%. Both non-transgenic and transgenic tetraploid plants were produced by treating leaf explants with colchicine at 25 mg l(-1). Polyploidy was confirmed by flow cytometry. Three of the seven diploid transgenics were significantly more resistant to Erwinia amylovora than the non-transformed Royal Gala control and, in one case a tetraploid transgenic line was significantly more resistant than the diploid shoot from which it was derived.