Integrated ex situ conservation strategies for endangered New Zealand Myrtaceae species

ABSTRACT

The current threat of myrtle rust (Austropuccinia psidii) to New Zealand Myrtaceae, including a number of indigenous and socio-economically important species, requires that ex situ conservation is used to complement in situ populations. New Zealand’s Myrtaceae have received little attention in terms of ex situ conservation. In this study, we assessed the integrated ex situ conservation strategies for selected New Zealand Myrtaceae. We particularly investigated seed banking options by assessing seed desiccation tolerance, in vitro culture, pollen cryopreservation and zygotic embryo cryopreservation of the recalcitrant Syzygium maire. A desiccation trial was conducted on six Myrtaceae species: Lophomyrtus bullata, L. obcordata, Metrosideros diffusa, M. umbellata, M. bartlettii and Syzygium maire. S. maire seeds and embryos showed extreme sensitivity to desiccation confirming its recalcitrant behaviour. The seeds of the other species were desiccation tolerant i.e. orthodox. Zygotic embryos of S. maire were successfully cryopreserved using an encapsulation-dehydration technique. Pollen cryopreservation was successful for M. excelsa following desiccation to about 5% moisture content, rapid freezing and rapid thawing. For M. bartlettii, one of the most endangered and a nationally critical Myrtaceae species in New Zealand, we tested the efficacy of hand pollination in producing viable seeds. Our assessment confirmed that one of the M. bartlettii trees at Otari is self-incompatible, and successful hand pollination using pollen obtained from different genotypes growing in the gardens at the University of Auckland resulted in seed production with c. 20% germination. Tissue culture protocols were successfully developed for selected Myrtaceae. In addition, photoautotrophic micropropagation techniques were developed for the first time for L. scoparium. This paper highlights the importance of holistic conservation strategies to ensure future access to New Zealand’s unique Myrtaceae germplasm as a key component of long-term management response to the threat posed by A. psidii.

KEYWORDS:

• Myrtle rust
• seed storage
• zygotic embryo
• cryopreservation
• pollen conservation
• in vitro culture
• artificial pollination
• photoautotrophic micropropagation‌

Acknowledgements

We gratefully acknowledge Otari Native Botanic Garden, Wellington City Council (WCC) for contributions to this project; Department of Conservation (DOC), New Zealand for supplying seeds and plant materials. Funding for this project by the Ministry of Primary Industries (MPI), New Zealand (Project 18608) is greatly appreciated.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Ministry of Primary Industries (MPI), New Zealand [Project 18608].