An efficient interspecific hybridisation protocol for Carica papaya L. × C. cauliflora Jacq.

Abstract

Summary. A protocol for interspecific hybridisation between Carica papaya and C. cauliflora is necessary for gene introgression between these 2 incompatible species. Carica papaya × C. cauliflora hybrids were successfully created using a new, efficient hybridisation protocol. This protocol includes the use of highly viable pollen of C. cauliflora produced during summer, autumn and/or spring, the use of an isolation time ranging from 90 to 120 days post-pollination of hybrid embryos, and the use of the most compatible C. papaya cultivar 2001 for crossing with C. cauliflora. Two types of interspecific hybrid embryos, namely single and multiple, were isolated in all resulting fruit. The application of gibberellic acid (0.6 or 0.8 mol/L) or 2,4- dichlorophenoxyacetic acid (1.5 or 2.0 mol/L) to freshly cross-pollinated flowers and pollination by mentor pollen did not promote either the rate of successful crosses or the production of hybrid embryos. Using this efficient protocol, hybridisation between C. papaya and C. cauliflora conducted in 3 locations in south-east Queensland produced 338 crosses which generated 43 736 seed. From these seed, 2100 hybrid embryos were recovered resulting in the production of 485 morphologically normal interspecific hybrid plants. Studies reported elsewhere show that these hybrids are resistant to papaya ringspot virus type P.