An efficient buds culture method for the regeneration via somatic embryogenesis of table grapes 'Red Globe' and 'Flame Seedless'

Introduction: Chile is the leading table grape exporter from the Southern Hemisphere and this industry is mainly based on 'Thompson Seedless', 'Red Globe' and 'Flame Seedless' ('Flame'), covering more than 75 % of the table grape planted area in the country. With the aim of improving the productivity and quality of these and other cultivars, a genetic transformation program was initiated by 1999, mainly focused in the introduction of genes related to biotic stress tolerance (HINRICHSEN et al., 2005). With this goal in mind, somatic embryogenesis (SE) was settled for these cultivars, as this has become the most efficient procedure for the generation of in vitro cultures prone to genetic transformation (STAMP and MEREDITH 1988, SCORZA et al. 1996, MARTINELLI et al. 2001, IOCCO et al. 2001, TORREGROSA et al. 2002). However, grapevine SE is not a routine procedure that can be easily and efficiently reproduced in different cultivars (MARTINELLI et al. 2001). There exists a genotype-specific response even when using the same culture medium in the induction process (SRINIVASAN and MULLINS 1980, STAMP and MEREDITH 1988, TORREGROSA et al. 2002). In this regard, most of the advances published on SE has been focused on wine cultivars (STAMP and MEREDITH 1988, IOCCO et al. 2001) as well as in 'Thompson Seedless' (SCORZA et al. 1996). Very few additional work has been directed to optimize SE in other table grape cultivars such as 'Red Globe' (PERL et al. 1996) and 'Flame Seedless'. In the case of 'Flame', there are no reports specifically related to the optimization of the production of somatic embryos. Taking these antecedents into consideration, the purpose of this note is to describe the best combination of growth regulators for these two table grape cultivars, in order to optimize the induction of somatic embryos. Material and Methods: Apical and axial buds with 2 to 4 leaves were cut from in vitro grown plants of 'Red Globe' and 'Flame'. Plants were grown in C2D medium (CHEE and POOL 1987) supplemented with 4 μM 6-benzyladenine (BA) to induce multiple budding, in a period of about 30 d. Buds were excised using a stereoscopic lens and later incubated for callus induction in a modified basal medium [NB® (PhytoTechnology Labs., Shawnee Mission, KS) plus 3 % sucrose, 1 g·l-1 myoinositol and 0.7 % (p/v) TC-agar® (PhytoTechnology) and 5 μM 2,4-dichlorphenoxyacetic acid (2,4-D)] plus a range of concentrations of α-naphthalene acetic acid (NAA) and BA (see Table for specific conditions). Media were adjusted to pH 5.8 and sterilized by autoclaving at 121°C for 20 min before pouring in 90 x 15 mm Petri dishes. Five explants per plate were incubated for 30 d in darkness at 24 ± 2 °C. After this time, calli formed were kept at 16 h light/8 h darkness, at the same temperature for 150 d.