Cryopreservation of avocado (Persea Americana Mill.) using somatic embryos

Avocado genetic resources are currently maintained in the form of field repositories at great cost and risk of natural disasters, pest and diseases. Cryopreservation offers a necessary, complimentary method that is safe, cost-effective and long-term. However, long-term maintenance and regeneration of plantlets from avocado somatic embryos has been a major barrier in the development of new avocado cultivars. In this study, two protocols for vitrification-based cryopreservation of avocado somatic embryos were investigated. Globular somatic embryos of two avocado cultivars were tested, revealing cultivar-dependent differences in desiccation tolerance and subsequent freezing resistance, possibly attributed to their size and culture age. A two-step regeneration system, involving an intermediate liquid phase step between subcultures in solid medium, significantly enhanced shoot development from somatic embryo tissue. This work will add considerable value towards cryopreservation of avocado somatic embryos for germplasm conservation and the generation of new and improved avocado cultivars.

Cryopreservation of somatic embryos for avocado germplasm conservation

Presently avocado germplasm is conserved ex situ in the form of field repositories across the globe including Australia. The maintenance of germplasm in the field is costly, labour and land intensive, exposed to natural disasters and always at the risk of abiotic and biotic stresses. The aim of this study was to overcome these problems using cryopreservation to store avocado (Persea americana Mill.) somatic embryos (SE). Two vitrification-based methods of cryopreservation were optimised (cryovial and droplet-vitrification) using four avocado cultivars (‘A10′, ‘Reed’, ‘Velvick’ and ‘Duke-7′). SE of the four cultivars were stored for short-term (one hour) in liquid nitrogen using the cryovial-vitrification method and showed a viability of 91%, 73%, 86% and 80% respectively. While when using the droplet vitrification method viabilities of 100%, 85% and 93% were recorded for ‘A10′, ‘Reed’ and ‘Velvick’. For long-term storage, SE of cultivars ‘A10′, ‘Reed’ and ‘Velvick’ were successfully recovered with viability of 65–100% after 3 months of LN storage. For cultivar ‘Reed’ and ‘Velvick’ SE were recovered after 12 months of LN storage with viability of 67% and 59%, respectively. The outcome of this work contributes towards the establishment of a cryopreservation protocol that is applicable across multiple avocado cultivars.