Advances and Challenges in Cryopreservation of Oil Palm Germplasm: A Complementary Approach to In Vitro Conservation

In vitro germplasm conservation provides an alternative method for preserving plant species that are vulnerable to natural hazards or for which in situ conservation is costly and challenging to manage. This conservation approach includes two strategies: medium-term conservation, where plants are maintained through the slow growth of explants, facilitated by the gradual release of nutrients and low-temperature storage. The second approach involves long-term preservation, achieved through cryopreservation in liquid nitrogen. Cryopreservation allows for the storage of pollen, calli, somatic, and zygotic embryos. Significant progress has been made in cryopreservation, which was initially limited to cold-tolerant species. New techniques focus on conserving sensitive species, such as oil palm, through rapid dehydration and vitrification procedures using various plant materials, particularly polyembryoids and zygotic embryos. Initial incubation of somatic embryoids in high sucrose concentrations (0.3–0.5 M) enhances their viability, while further dehydration of propagules extends their shelf life. Various loading materials, including 10% (w/v) DMSO and 0.7 M sucrose, along with vitrification solutions like PSV2, have been evaluated with minimal adverse effects on propagule viability. Molecular analyses of the cryopreserved embryos indicate that conservation induces the expression of genes related to reactive oxygen species in somatic embryoids compared to zygotic embryos, likely due to their sensitivity to osmotic stress. This review aims to analyze the importance and challenges associated with various in vitro and cryopreservation methods. It provides an overview of the current advances in cryopreservation technology for oil palm. Moreover, the review offers an outlook on optimizing cryopreservation protocols and addressing challenges to overcome genotype specificity by understanding the mechanisms of stress tolerance in cryopreserved species.