APPLICATION OF SCAR MARKERS LINKED TO A PUTATIVE PRSV-P RESISTANCE LOCUS FOR ASSISTED BREEDING OF RESISTANT C. PAPAYA CULTIVARS

Papaya ringspot virus type P (PRSV-P) is a serious disease of Carica papaya. Several wild relatives of the papaya, belonging to the genus Vasconcellea, exhibit complete resistance to PRSV-P, namely V. cundinamarcensis, V. cauliflora and V. quercifolia. Molecular genetic analysis of interspecific hybrids of V. cundinamarcensis and V. parviflora using Randomly Amplified DNA Fingerprinting (RAF) permitted the construction of genetic maps of these species. Identification and mapping of several DNA markers linked to a PRSV-P resistance gene locus in V. cundinamarcensis was possible, two of which (OPK41R and OPA115R), resulted from a Single Nucleotide Polymorphism (SNP), in close proximity to the PRSV-P resistance gene locus. The Sequence Characterised Amplified Regions (SCAR’s), were shown to be present in both parents, and produced codominant markers, which were applied as reliable diagnostic markers for resistant and susceptible genotypes. The OPK41R SCAR was identified in 4 additional Vasconcellea species made available, including V. cauliflora and V. quercifolia, but not in C. papaya. The indel identified may be useful for the selection of PRSV-P resistant individuals in breeding programs with Vasconcellea and C. papaya to assist introgression of putative resistance genes. The markers were subsequently applied to an intergeneric hybrid population from C. papaya and V. quercifolia. Genetic characterisation of the hybrid population using RAF markers confirmed hybridity of the F1 and reduced V. quercifolia DNA content of back cross generations. The OPK41R and OPA115R SCARs were tested in the quercifolia hybrids, and did not identify linkage to PRSV-P resistance. From the results it can be inferred that Vasconcellea may contain multiple sources of resistance to PRSV-P. Overall these studies indicate that there is significant potential for the continued application of DNA markers in molecular breeding for PRSV-P resistant papaya genotypes.