Transformation in apple for increased disease resistance

An apple genetic engineering program focused on increasing of disease resistance was started at the Institute for Fruit Breeding Dresden-Pillnitz in 1997. Because of the susceptibility to diseases of many of the most important commercially apple cultivars and rootstocks grown in Europe, genetic transformation is emphasizing the development of improved forms of varieties with disease resistance. The experiments were conducted on apple scion and rootstock genotypes: 'Pinova', 'Pilot', 'Pirol', 'Pingo', 'Elstar', 'Liberty', 'Remo', 'Reka' and Pi-AU 56-83. A transformation protocol was developed based on coculture of leaf explants from in vitro grown apple cultures with Agrobacterium tumefaciens strain EHA 105. To increase fire blight resistance, caused by the bacterium Erwinia amylovora, the following genes encoding lytic proteins were used: the attacin E gene originated from Hyalophora cecropia and previously reported to be active in apple and pear and the lysozyme gene originated from bacteriophage T4 and previously used in potato for increased resistance to Erwinia carotovora. Transgenic lines for fungal resistance to apple scab, caused by the pathogen Venturia inaequalis, and to apple mildew, caused by Podosphaera leucotricha, were produced by introduction of chitinolytic protein genes originated from Trichoderma harzianum. The integration of the transgenes was checked by PCR analysis, the expression of the nptII marker gene was analyzed by an ELISA test for the NPTII protein. The transgenic lines bearing a lysozyme gene from bacteriophage T4 and/or the attacin E gene were transferred to the greenhouse in 1999 and evaluated for their fire blight resistance by artificial inoculation.