GENETIC ENGINEERING OF APPLE FOR INCREASED RESISTANCE TO FIREBLIGHT

The goal of this research is to transform apple rootstock and scion cultivars with genes encoding proteins that lyse bacterial cells, and to select transgenic lines that have increased resistance to Erwinia amylovora. Using an Agrobacterim tumefaciens mediated leaf piece transformation system, over 250 transgenic lines of the rootstock M7 and the scion ‘Royal Gala’ have been selected that contain genes encoding the lytic proteins attacin E, cecropin SB-37, cecropin Shiva-1, and hen egg white lysozyme. In addition, lines transformed with pBI121 vector plasmid not containing lytic protein genes were selected. Transformation of ‘Royal Gala’ and M7 with the gene encoding attacin E has resulted in a significant increase in resistance to fireblight. In greenhouse and field tests, resistance was evaluated by recording the final percentage of the shoot length that became necrotic following inoculation of vigorously growing shoots with E. amylovora. In previous published reports on this project, the parent cultivar of T1 and other transgenic rootstocks was thought to be M26. Recent RAPD and isozyme testing indicated that the parent cultivar is M7, and not M26. In addition, plant material referred to as M26 in previous reports was in fact M7. These M7 transgenics will still be used to evaluate the effect of the lytic protein genes on fireblight resistance, but will likely be of little commercial value. Currently, we are working on producing lytic protein transgenics of M26 and M9 rootstocks.