Somatic embryogenesis, secondary somatic embryogenesis, and shoot organogenesis in Rosa

The influence of various 2,4-D concentrations (11.3-181 μmol/L) on induction of callus from leaf tissues of Rosa hybrida cvs. Carefree Beauty and Grand Gala and R. chinensis minima cv. Red Sunblaze was evaluated. Following transfer of callus to a regeneration medium containing different concentrations of thidiazuron (TDZ) (0-90.8 μmol/L), 6-benzyladenine (BA) (0-44.4 μmol/L), or 2.9 μmol/L gibberellic acid (GA3), alone or in various combinations, the highest frequency of embryogenic (32 %) and organogenic (55.3 %) callus was induced on ‘Carefree Beauty’. Secondary somatic embryos were also induced on somatic embryos of ‘Carefree Beauty’. The effects of different concentrations of TDZ (2.3 μmol/L), BA (2.2 or 4.4 μmol/L), and abscisic acid (ABA) (3.8 or 7.6 μmol/L), alone or in combinations, on proliferation and germination of secondary somatic embryos were also evaluated. ABA was found to be the most effective in promoting proliferation and germination of somatic embryos. The growth rate of secondary embryogenic callus grown on ABA increased by 36-fold, while germination rate of somatic embryos was more than five times higher than those derived from embryogenic callus grown on BA and TDZ. For R. chinensis minima cv. Red Sunblaze, only somatic embryogenesis (6.6 %) was observed; while, for R. hybrida cv. Grand Gala, only shoot organogenesis (3.3 %) was observed.