Cryopreservation of zygotic embryos for New Zealand’s critically endangered tree, Syzygium maire

Karin Van Der Walt, Jayanthi Nadarajan, David J Burritt, Peter Kemp, Otari Native Botanic Garden – Wellington City Council & Massey University New Zealand, The New Zealand Institute for Plant and Food Research Limited, University of Otago, Massey University

The pandemic pathogen, Myrtle Rust(Austropuccinia psidii) was discovered in New Zealand in 2017 and has now become established through most of the climatically suitable areas. Of the approximately 30 native Myrtaceae species, three genera representing four species are of particular concern due to unknown seed storage behaviour. One of these, Syzygium maire (swamp maire) – New Zealand’s only Syzygium species, was found to be highly sensitive to desiccation with complete embryo viability loss following dehydration to 20% moisture content. Comparison of desiccation sensitivity profiles across populations and seasons is
being conducted to understand the role of genotype and environmental conditions on chilling sensitivity and desiccation tolerance. Preliminary studies investigated cryopreservation of zygotic
embryos using naked embryo desiccation, encapsulation-dehydration and Plant Vitrification Solution 2 (PVS2) techniques. No survival was recorded following naked embryo and PVS2 vitrification cryopreservation. Limited root formation, but no regeneration following encapsulation-dehydration was also
found. Optimization of cryopreservation steps are being investigated by using oxidative damage and antioxidant metabolism as biomarkers of stress, as well as embryo/seedling germination to build a better understanding of how stress caused by embryo excision, decontamination, desiccation rate (rapid vs slow) and rehydration are impacting embryo survival. In addition, embryo survival following exposure to PVS2 is studied to optimize duration (30-90minutes), temperature (0oC and 20oC) and method (conventional vitrification and vacuum infiltration vitrification). Further research is underway to refine cryopreservation protocols further through preculture and acclimatization and comparing embryo desiccation tolerance at three seed developmental stages.