Cryostorage of Germplasm of Tropical Recalcitrant-Seeded Species: Approaches and Problems

Premise of research. Storage of hydrated recalcitrant seeds is possible only in the short (and, occasionally, medium) term, as these metabolically active, desiccation-sensitive propagules either germinate and/or are overrun by proliferating fungi. However, cryostorage of the germplasm of recalcitrant-seeded species—generally as embryonic axes excised from the seeds—in or over liquid nitrogen (LN) affords the means of long-term conservation. Axis cryopreservation protocols all incorporate a series of common steps, but often these need fine-tuning per species. This notwithstanding, successful cryopreservation—ultimately assessed by seedling development—is generally more easily achieved for temperate recalcitrant-seeded species than for tropical/subtropical types.Methodology. Cryopreservation protocols involve axis excision, elimination of microfloral inoculum, rapid (flash) drying alone or preceded by cryoprotectant treatment, and immersion in LN. After cryostorage, warming and rehydration are pivotal steps...