Agrobacterium tumefaciens– mediated transformation of embryogenic avocado cultures and regeneration of somatic embryos

Embryogenic avocado cultures were genetically transformed with the uidA (GUS) and nptII genes, and transformed somatic embryos were recovered from these cultures. Embryogenic avocado cultures derived from zygotic embryos of `Thomas' and consisting of proembryonic masses were gently separated and co-cultivated with disarmed, acetosyringone-activated Agrobacterium tumefaciens strain A208, which contained the cointegrative vector pTiT37-ASE::pMON9749 (9749 ASE). Kanamycin-resistant embryogenic suspension cultures were selected in two steps: (1) initial selection in maintenance medium, consisting of MS basal medium, supplemented with 0.1 mg l–1 picloram and 50 mg l–1 kanamycin sulfate for 2–4 months and (2) subsequent selection in maintenance medium with 100 mg/ml kanamycin sulfate for 2 months in order to eliminate chimeras. Somatic embryo maturation was initiated by subculture onto semisolid maturation medium (without picloram) followed by transfer to maturation medium with 100 mg l–1 kanamycin sulfate. Genetic transformation of embryogenic cultures and somatic embryos was confirmed by the X-gluc reaction, and integration of nptII and uidA into the avocado genome was confirmed by PCR and Southern hybridization, respectively.