Synthetic seed propagation of the therapeutic-honey plants Leptospermum polygalifolium and L. scoparium (Myrtaceae)

Abstract

Context: Increasing demand for therapeutic honey has driven establishment of Leptospermum nectar plantations. Methods for propagation involving synthetic seeds (artificially encapsulated miniature cuttings) may speed production of Leptospermum polygalifolium Salisb. and L. scoparium J.R.Forst. & G.Forst. Aims: The study aimed to determine how nutrient strength of the encapsulation solution and the presence of benzyladenine (BA) in the emergence medium affect shoot and root emergence from synthetic seeds of L. polygalifolium and L. scoparium. Methods: Nodes from in vitro shoots of three L. polygalifolium clones (P1, P6, P11) and two L. scoparium clones (S6, S12) were encapsulated in 3% sodium alginate with half- or full-strength Murashige and Skoog (MS) medium, and the synthetic seeds were placed on full-strength MS emergence medium containing 0 or 2.2 μM BA. Key results: Full-strength MS in the encapsulation solution was effective for shoot emergence of both species. BA increased the percentage of synthetic seeds with shoot emergence in clone P6 but decreased the percentage in clone S12. BA stimulated shoot emergence through callus in clones P1, P6, S6 and S12, and increased the number of shoots per emergent synthetic seed in clones S6 and S12. Surprisingly, the simple use of full-strength MS medium without hormones was highly effective for adventitious rooting, stimulating root emergence and plantlet formation in 26-57% of L. polygalifolium and 100% of L. scoparium synthetic seeds. Conclusions: These two Leptospermum species are highly amenable to propagation via synthetic seeds. A simple formulation of hormone-free, full-strength MS medium in the encapsulation solution and emergence medium provides high frequencies of plantlet conversion. Implications: Synthetic seeds have potential to assist in mass production of Leptospermum plants for nectar plantations to meet demand for therapeutic honey.