Agrobacterium-mediated transformation of strawberry

Traditional breeding for improvement of strawberry (Fragaria x ananassa) is difficult because strawberry is an octoploid, hybrid species. Genetic modification of strawberry would though be a promising alternative for obtaining the desired improvements in existing elite strawberry cultivars (Schaart et al., 2011). The availability of suitable genes for trait improvements in strawberry has however been a rate-limiting step until recently, but with the completion of the sequencing of the genome of woodland strawberry (F. vesca) (Shualev et al., 2011), we now have access to a treasure chest with valuable candidate genes. For strawberry, methods for genetic transformation have originally been described by Nehra et al. (1990) and James et al. (1990) and success of transformation was shown to be highly cultivar dependent. The latest progress in strawberry transformation is reviewed by Husaini et al. (2011). In our lab transformation of strawberry is based on the method for shoot regeneration described by Passey et al. (2003) and the use of the supervirulent Agrobacterium strain AGL0 (Lazo et al., 1991). We mainly make use of the strawberry transformation as a tool for functional analysis of candidate genes. For this the cultivar Calypso is a very suitable genotype because of its high transformation efficiencies (up to 100%) and ever-bearing fruiting characteristic, which provides a continuous supply of strawberry fruits once the plants start flowering.