Storage Stability Using Cryopreservation: a Case study in Papaya

Abstract

Ex situ conservation of Carica papaya and its crop wild relatives has been the subject of ten years of research in our laboratory. This paper summarises the achievements and key findings of this work. Both clonal and seed materials have been investigated to allow storage of elite clonal material as well as maximum genetic diversity. Clonal material from several genotypes has been successfully stored using micropropagation followed by shoot tip cryopreservation, with >70% regeneration after 12 months storage in LN. The regeneration and acclimatisation of cryopreserved plants has been achieved for field testing and observations of morphological characteristics, including flowering and fruiting, have not detected any changes associated with cryopreservation. Genetic stability following shoot tip cryopreservation has also been monitored using both RAF (Random Amplified DNA Fingerprinting) and AMP (Amplified DNA Methylation Polymorphism) techniques. Whilst both RAF and AMP changes were observed following cryopreservation, these were not associated with cryopreservation per se and did not correlate with any modification in plant morphology. Investigations of papaya seed storage indicate that seed is essentially orthodox, but dormancy breaking treatments were required for germination. However, germination post storage for 12 months was >68% at ultra-low temperatures (LN), but <5% at conventional seed storage temperatures (-20é. This is in line with recent evidence that cryopreservation enhances storage stability and longevity, even in orthodox seeds, when compared with standard seed bank approaches. This highlights the importance of cryopreservation for the longterm management of genetic resources of both clonal and seed genetic resources of papaya.