Virulence assay on apple rootstock MM106. Bacteria were inoculated by prick technique in the shoot tips with an inoculum of 5 × 106 CFU/shoot. Establishment of a population of E. amylovora Ea1189 wild type (○), mdtUVW-deficient mutant (●) and mdtABC-deficient mutant (◊) was determined 1, 3 and 7 days post inoculation (dpi), respectively. A minimum of 5 plant shoot tips were inoculated. Data points represent the CFU/cm stem per shoot tip. The horizontal line through the points of a dataset indicates the mean value of the replicates. Average values and standard deviations are listed in Additional file 7.