Cryopreservation protocol development for Syzigium maire, a recalcitrant myrtaceae species

Nadarajan J1, van der Walt K2 and Pathirana R1

  1. The New Zealand Institute for Plant & Food Research Ltd, Private Bag 11-600, Palmerston North 4442, New Zealand.
  2. Otari Native Botanic Garden & Wiltons Bush Reserve, 160 Wilton Road, Wilton, Wellington, 6012, New Zealand.

The current threat of myrtle rust to Myrtaceae species including a number indigenous and socio-economically important plants of New Zealand, requires that ex-situ conservation is used to complement in-situ collections. To mitigate the effects of biotic and abiotic threats, ex-situ germplasm conservation is widely applied in many species using protocols for conservation of pollen, seed and clonal germplasm, complemented by in vitro propagation and cryopreservation. The New Zealand Myrtaceae have received little attention in terms of long-term ex-situ conservation. Seed of some Myrtaceae species are considered orthodox and can be stored relatively easily in conventional seed banks. However, some Myrtaceae species exhibit recalcitrant seed storage behaviour, e.g. Syzigium maire, and therefore require cryopreservation of isolated embryos. In this study, desiccation sensitivity profiles of S. maire seeds and excised embryos collected from various natural populations in New Zealand were investigated. S. maire was cryopreserved using excised embryos, encapsulation-dehydration and PVS2 vitrification techniques. Seeds and embryos of S. maire showed extreme sensitivity to desiccation and lost viability completely following desiccation to a moisture content below 20%, confirming its recalcitrant behaviour. No survival was recorded following excised embryo and PVS2 vitrification cryopreservation. Cryopreservation using the encapsulation-dehydration technique resulted in embryo survival and root formation (30%) though complete regeneration was not recorded. Further experiments are underway to refine the cryopreservation protocol for this species including optimisation of the seed harvesting period as seed development stage is a critical factor in the success of a cryopreservation strategy in recalcitrant species.