Somatic embryogenesis in elm

Abstract

Elm is a Nothern hemiphere tree that is greatly valued for its landscape, amenity and timber qualities. Elm populations have been devasted by Dutch elm disease (Brasier, 1991) caused, initially, by the vascular wilt fungus Ophiostoma ulmi and, later on, by the distinctly different and highly aggressive o. novo-ulmi (Brasier, 1994). There have been various attempts to control the disease through international research programs (Burdekin, 1982; Sticklen and Sherald, 1993), none of which have yet succeeded in significantly halting its spread or reducing its impact (Fenning et al., 1996). Genetic engineering might provide an use fui aid in the control ofthe disease. However, suitable in vitro regeneration systems need to be available for genetic transformation of elms. Micropropagation and regeneration of different elm species through axillary branching has been achieved not only from juvenile material (Fenning et al., 1993) but also from mature trees (Dorion et al., 1987; Corchete et al., 1993). Adventitious buds were achieved from protoplast culture (Dorion et al., 1994), leaf explants (Boylard et al., 1991; George and Tripepi, 1994) and from strips of stem (Ben Jouira el al., 1998). Elm internodes have been demonstrated to be suitable explants for genetic modification via Agrobacterium tumefaciens (Boylard et al., 1991; Dorion el al., 1995). Somatic embryogenesis could represent, not only a way of clonally propagating valuable genotypes, but an important tool for genetic engineering. In spite of the great number of papers reporting plantlet regeneration from axillary branching ami/or adventitious shoot induction, there are no reports, to our knowledge, on the capacity of elm tissue to form somatic embryos. In this report, we describe the induction of somatic embryogenesis from zygotic embryo tissues of Ulmus minor and U glabra.