Intergeneric Hybridisation between Carica papaya and Wild Vasconcellea Species and Identification of a PRSV-P resistance Gene

Abstract

Intergeneric hybridisations between Carica papaya and related Vasconcellea species have been conducted for 15 years, despite limitations due to postzygotic barriers. Successful crosses have been achieved between C. papaya and PRSV-P resistant Vasconcellea species cauliflora and pubescens, however the infertility of these hybrids has prevented further backcrossing. A few hybrids with low fertility have been present in large populations of C. papaya × V. quercifolia. An extensive backcrossing program between these hybrids and papaya is currently underway in both Australia and the Philippines. A single dominant gene for PRSV-P resistance in V. pubescens has been mapped by use of dominant, polymorphic randomly amplified DNA fingerprint (RAF) markers in an F2 interspecific population of V. parviflora (PRSV-P susceptible) and V. pubescens (PRSV-P resistant). Using a bulked segregant analysis strategy, a RAF marker was identified as being linked to the resistant phenotype and was shown to be present in other PRSV-P resistant Vasconcellea species. It mapped to within 6.3 cM of the predicted PRSV-P resistance locus. The RAF marker was converted into a co-dominant CAPS marker, diagnostic for resistance based on digestion with the restriction endonuclease Psi I. This marker may provide a useful tool for future marker-assisted breeding programs aimed at introgressing PRSV-P resistance genes from wild Vasconcellea species into the commercially important papaya.