Cryopreservation of Papaya (Carica papaya L.) Seed: Overcoming Dormancy and Optimizing Seed Desiccation and Storage Conditions

Abstract

Protocols for efficient storage and germination of fresh and desiccated seeds of Carica papaya are needed for improved management of seed stocks by the industry. Two genotypes of papaya of importance to Australia were investigated: the tropical cultivar 'Solo' and a Queensland line '007'. Germination of fresh seed was close to zero, but high proportions of the seeds were found to be viable by tetrazolium staining: 93% for 'Solo' and 94% for '007'. We aimed to overcome the dormancy blocking by pre-soaking seeds in gibberellic acid (for up to 60 min) or potassium nitrate (for up to 24h). The most effective treatments were: 2 mM GA3 for 30 min; and 2 or 3h in 0.25 M KNO3. All treatments resulted in 61-65% germination. Seeds of both cultivars tolerated drying to low moisture contents, but required GA3 pre-treatment to stimulate 30-60% germination; KNO3 pre-treatment was much less effective in stimulating germination in desiccated seeds. Desiccated seeds (5, 15 and 30% RH) germinated (>70%) after storage in liquid nitrogen(-196°C) for 3 months if GA3 pre-treatment was applied. Recovery from storage at the standard genebank storage temperature of -20°C was very low (1-36%). These results provide valuable information for improved seed handling practices in the papaya industry.