Apple (Malus domestica) transgenic T1 was obtained by Agrobacterium tumefaciens-mediated transformation of Malling 26 rootstock using the plasmid binary vector pLDB 15. pLDB 15 contains within its T -DNA a gene encoding the lytic protein attacin E. The integration of the attacin E gene into the apple genome was confirmed by Southern analysis. Northern analysis indicated the presence of an attacin E mRNA in plants inoculated with Erwinia amylovora. After inoculation of in vitro grown plants of T1, Malling 26, and Malling 7 (resistant control) with E. amylovora, the loglo of the inoculum concentration lethal to 50% of the plants was 5.4, 4.4, and 5.6, respectively. In greenhouse trials for resistance to fire blight, T1 was significantly more resistant than 'Mailing 26'. © 1994 Kluwer Academic Publishers.