Gamma irradiation induces neo-organogenesis in a Rosmarinus officinalis callus line selected for secondary metabolites production

Rosmarinus officinalis is a Mediterranean plant well known for its antioxidant and antibacterial properties due to the phenolic and terpenoidic compounds commonly extracted from leaves. A selected line (R. Officinalis 'Bianco', ROB) has been recently chosen for its ornamental value and carnosic acid content. Leaves of this genotype were cut in 0.5 cm2 fragments and then cultured in vitro on Murashige and Skoog micro-, macro-elements and vitamins supplemented with 1 mg/L of NAA to obtain callus. Callus was sub-cultured every 30 days giving good proliferation; the use of a regeneration medium containing 1 mg/L BA or 0.5 mg/L TDZ or an embryogenic-one containing 2 mg/L 2,4-D + 0.8 mg/L 2-iP, never induced shoot and/or embryo neoformation. All the cultures were grown at 23±1°C under a 16 h d-1 photoperiod. Undifferentiated callus fragments were exposed to γ-ray at Low Dose Rate (LDR, total dose 25 Gy, delivered at 0.33 Gy min-1 by a 60Co source) and were compared to untreated samples. After three subcultures callus proliferation and the presence of the novo organogenesis were evaluated. Regenerated shoots were isolated only from γ-ray exposed material then further transferred onto elongation and proliferation media; the addition of IAA and activated charcoal improved the shape and the multiplication rate of these shoots