Karin van der Walt

Conservation and Science Advisor

Otari Native Botanic Garden, Wellington City Council


General Arb Stream

Thurs 3 Nov

2:15 – 2:45

Freezing for survival – The use of cryogenics to store seed of native trees


Karin van der Walt is the Conservation and Science Advisor at Ōtari Native Botanic Garden in Wellington where most of her time is dedicated to conservation of threatened plants. By combining her ecological background with scientific research, she determines optimal ex situ conservation methods through tissue culture, seed banking and cryopreservation. Since the arrival of Myrtle Rust (Austropuccinia psidii) in New Zealand, much of her work is focussed on cryopreservation of Syzygium maire (swamp maire). As New Zealand’s only native Syzygium species, the conservation of this endemic, critically endangered species is a high priority.


Globally more than 15 000 tree species are threatened with extinction. The spread of invasive plant pathogens is also increasing, with pandemic invasions such as Chestnut Blight, Dutch Elm Disease and Sudden Oak Death responsible for killing millions of trees in America and Europe. Within New Zealand, our iconic Kauri (Agathis australis) is threatened by Kauri dieback, while the future for many native myrtles is unclear due to myrtle rust which arrived in 2017. Although control of these pathogens is challenging, the long-term storage of seed provides an opportunity to secure species and genetic diversity, thereby providing options for future restoration, resistance breeding or research. Once seed viability is quantified and germination protocols understood, the likely storage behaviour of the seeds is investigated. For rātā species, this means a simple orthodox method will suffice while things become a bit trickier for Kauri and swamp maire which require cryopreservation.