Quercus suber L. is the main woody tree species in the Mediterranean basin. The in vitro regeneration from adult material, through primary somatic embryogenesis, is a well-known process, but the use of secondary somatic embryos for plant regeneration remains a very sparsely studied process. The main objective of this work is to explore the cork oak regeneration potential by using the secondary somatic embryogenesis process. Mainly, in this work, we report the polyamine effect. Explants used consisted on primary mature embryos, derived from leaves rejuvenated by epicormic shoot of the Moroccan Quercus suber. Three different polyamines were added to the basal medium, which was composed by macronutrients of N30K, 30 g/l glucose, and 7 g/l agar. Three polyamines, Putrescine, Spermine, and Spermidine, were added to the basal medium at 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 mg/l. Explants were tested after 8 weeks. Morphological analysis showed that the medium with 0.4 mg/l Spermidine provided the best result for secondary embryos, which corresponds to a very significant (p < 0.05) increase of 375%. The number of secondary embryos directly formed was 2.70 ± 0.51. Similarly, the optimum concentrations for high number of clusters (0.50 ± 0.11) and embryo clusters (1.43 ± 0.35) were increased by 145% and 158%. The addition of the polyamine also acted on the quality of embryos formed. A very significant (p < 0.05) increase in the size of secondary embryos was observed compared to the medium without polyamines. Spermidine showed the greatest increase (about 38%).
Keywords: Cork oak; Putrescine; Spermidine; Spermine; secondary embryos; somatic embryos.