Factors influencing secondary somatic embryogenesis inMalus x domestica Borkh. (cv 'Gloster 69')

A procedure for regeneration of apple plants through secondary somatic embryogenesis (SSE) was developed in apple 'Gloster 69'. Primary somatic embryos were produced from cotyledon-derived cultures of immature zygotic embryos. These somatic embryos were multiplied by secondary somatic embryogenesis (SSE) on media with different Plant Growth Regulator (PGR) combinations. The highest SSE rate (55.5%) was obtained with a combination of NAA (5.3 μM), BAP (0.9 μM) and KIN (0.9 μM) or with TDZ alone (10 μM). In addition, effects of explant source, somatic embryo size, type and concentrations of carbohydrates and gelling agents on SSE were investigated. The optimum SSE (>73%) was obtained by the culture of large size somatic embryos or cotyledon-like structures on medium containing a combination of NAA/BAP/KIN or TDZ (10 μM) alone, maltose (175 mM) and Phytagel (2.8 g/1).