Cryopreservation of tropical recalcitrant-seeded species – perspectives

Abstract

Cryopreservation is an alternative strategy for the long-term conservation of tropical recalcitrant-seeded species. Embryonic axes/embryos or shoot tips are possible explants for this purpose as the seeds are sensitive to cold temperature and they are not tolerant to desiccation to a low moisture content required for seed banking. Shoot tips are used for species with large axes or those without clear differentiated embryonic axes in their seeds. Though not strictly, desiccation and vitrification are usually used for embryonic axes and shoot tips, respectively. Several species under study provide examples, including species in the genus Garcinia. Cryopreservation of shoot tips of tropical recalcitrant species faces many challenges. Amongst these are the lack of tolerance to ultra-low temperature; osmotic stress and chemical toxicity (to the vitrification chemicals used) and the availability of experimental materials throughout the year. With a systematic approach in addressing each problem/challenge, a successful cryopreservation protocol could possibly be obtained. Differential scanning calorimetry and ultrastructural changes observed during each step of the protocol are helpful in understanding successes or failures of the cryopreservation technique used.