Synthetic seed propagation of the therapeutic-honey plants Leptospermum polygalifolium and L. scoparium (Myrtaceae)
Ian D. Darby A , Aaron Wiegand A , Shahla Hosseini Bai B , Helen M. Wallace B and Stephen J. Trueman B *A Centre for Bioinnovation, University of the Sunshine Coast, Maroochydore DC, Qld 4558, Australia.
B Centre for Planetary Health and Food Security, School of Environment and Science, Griffith University, Nathan, Brisbane, Qld 4111, Australia.
Australian Journal of Botany 70(6) 447-454 https://doi.org/10.1071/BT22025
Submitted: 8 March 2022 Accepted: 11 September 2022 Published: 10 October 2022
© 2022 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)
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.
Keywords: adventitious rooting, alginate encapsulation, callus, cytokinin, mānuka honey, methylglyoxal, propagation, tissue culture.
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