TRANSFORMATION OF APPLE ROOTSTOCK M26 WITH AGROBACTERIUM-TUMEFACIENS

Different tissues of the apple (Malus X domestica Borkh.) rootstock M26 were inoculated with various wild-type strains of Agrobacterium tumefaciens. Galls formed on leaf but not on stem or petiole explants. Wild-type strain A281 was more effective than C58 and A348. Disarmed A. tumefaciens strains with the binary vectors pCGP257 and pBI121, which contain the npt II and gus genes, were used to transform leaf explants. The appropriate transformation protocol included an initial dark incubation period and the use of Gelrite-gelled medium. Transformation was confirmed by histochemical localization and fluorometric assays for GUS, by NPT II dot blot assay, and by Southern blot analysis for both gus and npt II. The extent to which transformed shoots initiated roots in the presence of kanamycin was quantified and related to the expression of the incorporated npt II gene.