Key message Encapsulation of cotyledonary stage somatic embryos combined with high in vitro germination rates provides a feasible tool for interim storage and exchange of A. lebbeck germplasm. Embryogenic synseeds were prepared in Albizia lebbeck by encapsulating cotyledon stage somatic embryos derived from in vitro maintained embryogenic cultures in different types of Ca-alginate beads. The germination rate of somatic embryos was affected significantly by the bead type, matrix composition and germination substrate. A matrix made of 3% Na-2-alginate complexed with 100 mM CaCl2 center dot 2H(2)O for a hardening period of 20 min provided uniform encapsulation of somatic embryo. Among different types of synseeds, type IIA, wherein somatic embryos encapsulated in a single layer of Ca-alginate matrix composed of MS medium supplemented with 2 g L-1 activated charcoal and 1.0 mu M gibberellic acid (GA(3)) as reconstituted endosperm, was found to be the most efficient type having maximum germination rates (88.6 +/- 0.51%). Incorporation of GA(3) in the alginate beads stimulated greater germination of somatic embryos as against GA(3) supplementation in the germination substrate. Further, viability studies on short term cold (4 degrees C) storage of different types of embryogenic synseeds revealed that double layered synseeds (DLS) were found comparatively more robust to withstand longer storage durations than single layered synseeds as evident by greater germination rates of the former after 4-8 weeks of refrigerated storage. Also, the elevated levels of antioxidative enzymes (superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase) and leaf proline content in the plantlets derived from DLS reveals the possible role of alginate coatings in conferring alleviation to low temperature stress generated during different storage durations. Similar Inter simple sequence repeat profiles of embryogenic synseeds derived plantlets and mother tree nullifies the possible occurrence of somaclones, thereby establishing the efficacy of synseed technology for clonal propagation of A. lebbeck germplasm.
