Abstract
We attempted to backcross Carica papaya as a pollen donor to previously developed intergeneric hybrid plants (C. papaya × Vasconcellea cundinamarcensis) showing Papaya leaf distortion mosaic virus (PLDMV) resistance (Tarora et al. 2016). By employing embryo culture technique, 45 seeds with embryos were obtained from 5,762 seeds in the matured fruits (180 to 210 days after pollination) of backcrossed plants. Finally, 32 independent plants were regenerated from these embryos. Of these regenerated plants, 19 individuals were confirmed to have the Y chromosome from the pollen donor (papaya), indicating that backcross was succeeded. All the backcrossed plants also had both sex chromosomes of C. papaya and V. cundinamarcensis, derived from the intergeneric hybrids as female parents, suggesting that unreduced gametes might be produced in the intergenic hybrid plants. By inoculation of PLDMV to leaves, 66% of the backcrossed plants showed no symptoms and the remaining plants showed necrotic lesions on the upper leaves, which prevented virus proliferation. Therefore, all the infected backcrossed plants were resistant to PLDMV. These results showed that the developed backcrossed plants are valuable materials for developing PLDMV-resistant cultivars in papaya.
