Format: ORAL

Karen Sommerville, Cathy Offord

Botanic Gardens of Sydney, Mount Annan, Australia

The preservation of Macadamia diversity is important to conservation of species in the wild and the future of the world-wide macadamia industry. We aimed to determine whether standard seed banking or cryopreservation of whole seeds would be suitable for preserving these taxa. We first investigated the response of seeds of fiva taxa to desiccation and storage for 1 month at -20 and -192C. All taxa tolerated drying but responded poorly to storage at both temperatures. Thermal analysis of dry seeds was then used to investigate energy transitions during freezing and thawing that might explain the observed response. Samples of cotyledonary tissue were sealed in aluminium pans then lowered from 20 to -150C, and raised from -150 to 50C, in a differential scanning calorimeter. The resulting thermograms showed a crystallisation transition between -10 and -20C, and a broad melting transition from around -20 to 0C, for all taxa. Based on these results, we compared the effect of storage at 4 and -5C (avoiding the crystallisation transition zone) against storage at -20 and -192C for seeds of M. integrifolia x tetraphylla Beaumont and M. jansenii. Both taxa responded significantly better to storage at the higher temperatures than at -20 or -192C. However, we expect the large seeds of some Macadamia taxa may still be short-lived under those conditions so have commenced research on cryopreservation of the much smaller embryonic axes. Preliminary experiments have shown that normal seedlings can be produced from fresh embryonic axes providing they have a small amount of cotyledon attached, are sterilised in 2% bleach for no more than 15 minutes, and are sown on MS medium containing 2% activated charcoal and 250 ppm gibberellic acid. Experiments testing survival following drying and immersion in liquid nitrogen will be undertaken in the next fruiting season.