Development of a reliable method for Agrobacterium tumefaciens-mediated transformation of mulberry callus

Plant transformation technology has become an indispensable tool for studying gene function in plant and for cultivar improvement (BIRCH, 1997; HANSEN and WRIGHT,1999). Many successful transf ormants of fruit trees have been reported (MATSUTA et al., 1993 and references therein). However, there are few reports on gene transfer systems for mulberry (Morus alba L.) trees by Agrobacterium (MACHII, 1990), by particle bombardment (MACHII et al., 1996; SUGIMURA et al., 2000) and by electroporation (SUGIMURA et al., 1999b). These authors showed that each transformation system was available for gene delivery into mulberry plant. However, whole plants developed from these transformed cells have not yet been obtained except for the case of development of the transformed plantlets from A. tumefaciens-inoculated leaf discs (MACHII, 1990). The limiting factors to practical transformation of mulberry plant may be a difficulty of regeneration and a low frequency of transformation. Many trials have shown that the mulberry is one of the species recalcitrant in regeneration. However, successful regeneration and organogenesis of mulberry plant from immature leaf cultures * Corresponding author 4 Present address: Horticulture Department , Southwest Agricultural University, Chongqing 400716, China