Sexual and asexual propagation of Syzygium maire, a critically endangered Myrtaceae species of New Zealand

Abstract

ABSTRACT Syzygium maire (swamp maire) is an endemic New Zealand Myrtaceae tree species. Current threats to this species include habitat destruction, myrtle rust, declining remnant populations and low capacity for natural regeneration. Large-scale replanting for conservation/restoration initiatives would mitigate against these threats. However, there is limited information available on propagation of this species. In this study, we looked at sexual propagation using seed germination and asexual propagation using softwood cuttings. For seed germination, we examined the effect of seed pretreatments (intact fruit or de-pulped seed) and temperature settings (15/25°C or 20/30°C) to optimise germination. For softwood cutting propagation, we investigated the diameter of the cuttings (1–2 mm or 3–5 mm) and application of exogenous indole-3-butyric acid (IBA) (0, 1.5, 3.0, or 4.5 g L−1) on their efficacy of producing adventitious rooting. The most critical factor for seed germination was the removal of seed pulp. De-pulping the seeds shortened the mean time to germination and positively affected the germination percentage, regardless of the incubation temperature. Germination percentage of ≥94.5% was achieved in seeds sown without pulp. Propagation by softwood cutting of 1–2 mm in diameter was possible without IBA treatment (63.3% of cuttings rooted), but the application of 1.5 g L−1 IBA increased the rooting percentage (to 75%), thereby inducing the production of a higher number of roots. Seed germination and softwood cutting were effective strategies to propagate S. maire. The findings of this research contribute to the knowledge of propagation and restoration of S. maire populations.