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.