A combined pathway of organogenesis and somatic embryogenesis for an efficient large-scale propagation in date palm (Phoenix dactylifera L.) cv. Mejhoul

An efficient regeneration system via a combined pathway of organogenesis and somatic embryogenesis was developed for date palm (Phoenix dactylifera L.) cv. Mejhoul. Adventitious buds were obtained from shoot-tip explants with a frequency of 53.3% after 9 months of culture: 6 months on half-strength Murashige and Skoog (MS/2) medium containing 14.2 µM indole-3-acetic acid (IAA), 13.4 µM 1-naphthaleneacetic acid (NAA) and 0.5 µM 6-(dimethylallylamino) purine (2iP), and 3 months on MS/2 medium supplemented with 1.1 µM IAA, 1.1 µM NAA, 0.5 µM 2iP, 2.2 µM 6-benzyladenine (BA) and 0.4 µM kinetin. Adventitious bud segments were used as explants to induce somatic embryogenesis, and the effects of different concentrations (22.5, 45, 90, 225 or 450 µM) of 3,6-dichloro-o-anisic acid (dicamba) and 4-amino-3,5,6-trichloropicolinic acid (picloram) were evaluated. The optimal medium for somatic embryogenesis induction was MS medium supplemented with 45 µM picloram and 5 µM 2iP, in which the somatic embryogenesis rate was 70%. For somatic embryo maturation, the effects of sorbitol, mannitol, polyethylene glycol (PEG) and abscisic acid (ABA) were tested. The highest maturation rate (88.6 mature somatic embryos per 100 mg fresh weight callus) was observed on liquid MS medium supplemented with 20 g L-1 PEG. Subsequent somatic embryo germination was achieved with up to 52.0% in MS medium containing 2.5 µM NAA and 2.5 µM BA. The regenerated plantlets were transferred to the glasshouse where 76.0% of them survived.