To generate a fire blight (fb) resistant ‘Gala’ line, the fb-resistance gene FB_MR5, from wild apple Malus × robusta 5, was transferred to the highly fb susceptible cultivar ‘Gala’ by mean of Agrobacterium tumefaciens mediated transformation. The vector used to insert FB_MR5 into ‘Gala’ in vitro plant’s explants was designed to allow production of cisgenic lines by elimination of a cassette containing all transgenes supporting transformation and excision steps (e.g., recombinase, antibiotic resistance), after a heat induction step. 13 different transgenic ‘Gala’ lines were regenerated. A heating treatment, to activate the recombination and generate cisgenic genotypes, was then applied. So far one single cisgenic line was regenerated. Plants of this line were considered cisgenic as, after recombination, only the apple endogenous FB_MR5 gene, in normal-sense orientation and under control of its native regulatory elements, was present. We focused on molecular characterization of this single line and determined a single insertion. Resistance of the cisgenic line against Erwinia amylovora was assessed performing pathogen inoculations by scissors in the greenhouse. The cisgenic line showed less disease symptoms on inoculated shoots compared to untransformed ‘Gala‘ plants. To our knowledge this is the first prototype of a cisgenic fb-resistant ‘Gala’ apple line.
