Abstract
Demand for therapeutic honey is driving establishment of Leptospermum plantations. This study developed micropropagation methods for two species – Leptospermum polygalifolium Salisb. and L. scoparium J.R.Forst. & G.Forst. The study determined how shoot proliferation and adventitious rooting were influenced by the original explant position on the seedling and the concentration of benzyladenine (BA) in the proliferation medium. Hormone-free node culture was highly effective for both species. Nodal explants often formed roots in the absence of BA and developed elongated axillary shoots. Median shoot numbers of 584 and 659 were formed in 31–32 weeks from a single L. polygalifolium or L. scoparium seed, respectively. A low BA dose was effective for callogenesis and shoot proliferation of L. polygalifolium, but not L. scoparium. The median number of shoots produced from a single L. polygalifolium seed was 630 using 2.22-μM BA. This dose induced extremely high shoot numbers in some clones because explants often produced extensive callus and multiple short shoots. Shoots formed adventitious roots without indole-3-butyric acid and plantlets were acclimatised to nursery conditions. The original explant position did not influence shoot proliferation or adventitious rooting. Leptospermum polygalifolium and L. scoparium proved amenable to micropropagation, facilitating rapid establishment of nectar plantations.
Highlights
Manuka honey has been harvested traditionally in New Zealand from hives of honeybees that forage on the manuka tree, Leptospermum scoparium (Morgan et al 2019; Bong et al 2021; Schmidt et al 2021)
The highest production of both L. polygalifolium and L. scoparium shoots during the first proliferation passage occurred in hormone-free medium (Fig. 2a, b)
Seedling shoots of L. polygalifolium and L. scoparium proved highly susceptible to shoot death in the presence of BA doses, 4.44–17.78 and 2.22–17.78 mM respectively that are commonly used for proliferation of eucalypt shoots
Summary
Manuka honey has been harvested traditionally in New Zealand from hives of honeybees that forage on the manuka tree, Leptospermum scoparium (Morgan et al 2019; Bong et al 2021; Schmidt et al 2021). Clonal propagation has been used to propagate limited numbers of elite clones in clonal plantation programs (Trueman 2006; Xavier et al 2013; Trueman et al 2018) These programs have the advantage that individual clones have been selected for desirable mature-age characteristics such as trunk straightness, wood volume or fruit yield (Aimers-Halliday and Burdon 2003; Mitchell et al 2004; Wendling et al 2014a, 2014b). Clonal propagation is used instead to propagate multiple clones that are the progeny of selected mother trees in ‘vegetative family plantation programs’ (Lee 2007; Trueman et al 2018) These programs have the disadvantage that not all clones share the full suite of desirable characteristics of the selected mother tree
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