PAPAYA AS A MODEL TROPICAL FRUIT SPECIES FOR THE DEVELOPMENT OF CONSERVATION AND BREEDING TECHNOLOGIES

Abstract

Papaya (Carica papaya) has been used in our laboratory with a range of technologies for ex situ conservation of germplasm. It represents a good model species, as it has been the subject of major research efforts in tissue culture and biotechnology. We have investigated seed storage behaviour via desiccation curves based on accurate water activity measurements and a range of storage environments from liquid nitrogen to 15°C/15% RH. Treatments have been optimised to break dormancy and to ensure germination after seed storage. Twenty years of accumulated experience in papaya cell and tissue culture has facilitated our investigation of cryopreservation protocols, including vitrification based techniques, encapsulation and slow freezing, on a range of in vitro tissues from shoot tips to somatic embryos. This research has led to the development of optimum protocols for ex situ conservation of papaya germplasm, both as seed and vegetative tissue which have application to other tropical fruit species. Plants that were recovered post-cryopreservation have been screened for changes in genomic DNA and DNA methylation using the Polymerase Chain Reaction (PCR) based Randomly Amplified DNA Fingerprinting (RAF) and Amplified DNA Methylation Polymorphism (AMP) techniques, and are being evaluated in field plantings. Similarly, work on embryo culture techniques in our lab have contributed to the success of intergeneric breeding programs. Efficient molecular markers have been employed to assess genetic diversity within and between papaya genotypes and related Vasconcella species.