Cryopreservation of somatic embryos and shoot tips towards development of a cryo-bank for avocado germplasm (AV11025)

This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

At the time avocado germplasm was conserved ex situ in the form of field repositories across the globe including Australia. The maintenance of germplasm in the field was costly, labor and land intensive, exposed to natural disasters and always at the risk of abiotic and biotic stresses. The aim of this project was to overcome these problems using cryopreservation (storage at -196°C) to store avocado somatic embryos and shoot tips.

In the laboratory an optimised system for generation of avocado somatic embryos (SE) of ‘Reed’, ‘A10’, ‘Velvick’, ‘Hass’ and ‘Duke 7’ was used, which were routinely subcultured every 4-5 weeks to fresh maintenance medium. We had more than 100,000 SE of these cultivars in our repository.

Two methodologies (cyro-vial and droplet vitrification) were established for cryopreservation of SE of four avocado cultivars (‘Reed’, ‘A10’, ‘Velvick’ and ‘Duke 7’). SE was successfully multiplied on maintenance medium after 1 week, 3, 6 and 12 months of liquid nitrogen storage with >60% viability.

The efficiency of regeneration of the SE was also imporved from 5% to 58% for the cultivar ‘Reed’ and work was underway to apply this system to other avocado cultivars.

Shoot tips were initiated in vitro for shoot tip cryopreservation. Shoot tip re-growth was optimized from a small size of 2-3mm. These excised shoot tips have also been optimized for survival after different sucrose and vitrification treatments. The researcher was still investigating the best combinations for successful recovery of shoot tips post liquid nitrogen storage at the time.

The outcome from this work offered avocado growers an unlimited source of disease-free, genetic material that could be supplied upon demand for the establishment of orchards in Australia. The generation of a cryo-bank for avocado and other horticultural crops was a valuable source for growers and industry worldwide. Hort Innovation (which was then Horticulture Australia Limited) aimed to start a global initiative to establish the cryo-bank for germplasm conservation with international collaboration and funding at national, international, industry and government level.