Expression of SB-37 gene in transgenic pears enhanced resistance to fire blight

Preliminary in vitro experiments showed activity of Cecropin B from Hyalophora cecropia and its synthetic derivative SB-37 against E. amylovora. With the aim of increasing pear resistance to E. amylovora, we transformed cv. Passe Crassane using Agrobacterium strains EHA101 with plasmids containing the SE-37 gene under the control of the CaMV35S promoter. Leaves excised from in vitro shoots were transformed with a mean leaf transformation rate of 1%. DNA from 21 putative transgenic clones exhibited PCR amplification of a fragment of the SE-37 gene. Transcription was observed in all clones by RT-PCR. We were not able to detect SE-37 antigen by ECL western blotting. Partial degradation in the intercellular spaces could explain the lack of detection of the peptide. Fire blight susceptibility was quantified 10 days after leaf inoculation of in vitro shoots. Inoculations led to the onset of severe necrosis in cv. Passe Crassane after 3 days. Transgenic clones with reduced symptoms could be distinguished after 10 days.