AGROBACTER1UM-MED1ATED TRANSFORMATION OF APPLE

Two strains of Agrobacterium tumefaciens carrying a disarmed Ti-binary vector, pZA-7, were used as vectors for transformation of apple leaf segments, EHA101:pZA-7 carries a helper plasmid derived from pTiB0542, and C58Z707:pZA-7 carries a helper plasmid derived from pTiC58. The binary vector provides two selection markers, neomycin phosphotransferase (nptII) and hygromycin resistance genes, and a screening marker, β-glucuronidase (GUS) gene. Preliminary experiments were conducted to determine the effect of different concentrations of kanamycin, carbenicillin, and cefotaxime on regeneration of apple leaf sections and inhibition of A. tumefaciens strains. In vitro-derived leaf sections of `Royal Gala' apple were grown on a regeneration medium containing thidiazuron and NAA; these were then dipped into a suspension culture of A. tumefaciens and transferred to a fresh regeneration medium. Callus lines exhibiting kanamycin and hygromycin resistance were obtained mostly with agrobacterium strain EHA101:pZA-7. Expression of GUS activity was also determined in putative transformed calli. Southern blot analysis was used for confirming integrative transformation in transgenic lines.