Transformation of apple cultivars with T4-lysozyme-gene to increase fire blight resistance

Because of the susceptibility to diseases of many of the most commercially important apple cultivars and rootstocks grown in Europe, genetic transformation is emphasizing the development of improved forms of varieties with disease resistance. Genes encoding lytic proteins are a potential source of antibacterial resistance genes for use in plants. Transgenic potato plants expressing a bacteriophage T4 lysozyme gene have increased resistance to the bacterial pathogen Erwinia carotovora subsp. atroseptica (During et al., 1993) and T4 lysozyme has in vitro activity against E. amylovora. A transformation system was developed for several apple cultivars: 'Pinova', 'Pirol', 'Pilot', 'Pingo', 'Remo', 'Elstar' and 'Liberty'. Leaf pieces of in vitro grown microshoots were inoculated with Agrobacterium tumefaciens strain EHA 105 containing the plasmid binary vector pSR 8-36 bearing a chimeric lysozyme gene naturally occurring in bacteriophage T4 and previously used for transformation of potato for increased resistance to Erwinia carotovora atroseptica (Porsch et al., 1998). 8 weeks after inoculation, regenerants were produced on leaf explants cultivated on a selective medium containing kanamycin and cefotaxime. Regenerants were placed on several media amended with 0, 50 or 100 mg/l paromomycin. Transformation was confirmed by an ELISA for the NPT II protein and by PCR tests to confirm the presence of the lysozyme gene.