Ex situ conservation techniques for Australian rainforest species

Seedbanking is an effective ex situ conservation technique for species with seeds that tolerate drying to 3-7% moisture content and long term storage at -20°C. However, it has been estimated that as many as 50% of rainforest species may produce seeds that do not tolerate desiccation; the remainder may tolerate desiccation but may not tolerate freezing or may be comparatively short-lived in storage at -20°C. We investigated freezing tolerance and comparative longevity in storage for 5 Australian rainforest trees with desiccation-tolerant seeds. Seeds stored at -20°C for 2 to 7 years were removed from storage, thawed and germinated on 0.7% agar at 20 or 25°C with a 12 h photoperiod. Seeds that had retained their viability following freezing (germination ≥84%) were rehydrated for two weeks at 20°C and 47% relative humidity then artificially aged at 43±2°C and 60% relative humidity. Seeds were withdrawn from the aging environment at intervals of 1, 2, 5, 9, 20 and 30 days and tested for their ability to germinate. The number of days in the aging environment required to reduce germination by 50% was estimated by Probit analysis in GenStat v11. Species found to be comparatively short-lived were further tested for their ability to tolerate cryopreservation (storage in LN vapour at -192°C) with no pre-treatment. Of the five species tested, only Archirhodomyrtus beckleri failed to germinate following freezing. Abrophyllum ornans tolerated freezing but storage for 7 years at -20°C reduced its germinability from 100 to 41%. The remaining three species NDASH Caldcluvia paniculosa, Cuttsia viburnea and Quintinia verdonii NDASH had retained viability following storage at -20°C for 2-3 years but proved to be comparatively short-lived under artificial aging conditions (p₅₀KLEINERDAN5 days) and therefore also likely to be short-lived in storage at the standard seedbanking temperature of -20°C. All three species tolerated storage for 1 week at -192°C with no significant reduction in germination percentage. Cryopreservation is likely to be the best option for long-term storage of both desiccation-sensitive and desiccation-tolerant seeds from rainforest regions.