Assessment of expression and inheritance patterns of three transgenes with the aid of techniques for promoting rapid flowering of transgenic apple trees

Rapid flowering of transgenic Royal Gala apple (Malus×domestica) trees was achieved by growing trees under controlled greenhouse conditions. The expression and inheritance of three transgenes were confirmed in the seedling progeny. Grown as single stems on their own roots, the transgenic apple trees produced 80–110 nodes and were 2 m high on average at the end of the 1st year's growth. In the 2nd year, approximately 20% of these trees flowered around node 80. However, when scions collected from the top of 1-year-old trees were grafted onto the dwarfing rootstock Malling 9, 85% produced flowers and fruit within the next year. The grafted trees continued to produce fruit in the following years. Expression of the transgene uidA was monitored by assaying β-glucuronidase (GUS) activity in leaves, flowers and fruit. Inheritance of three transgenes, uidA, neomycin phototransferase II and acetolactate synthase, were demonstrated through the recovery of GUS-positive, kanamycin-resistant and chlorsulfuron-resistant progeny. Segregation patterns fitted a 1:1 ratio in most lines. However, a detailed analysis in one progeny line revealed a complex T-DNA integration pattern. Received: 8 June 1998 / Revision received: 19 November 1998 / Accepted: 26 November 1998