Breaking the intergeneric hybridization barrier in Carica papaya and Vasconcellea cauliflora

The present investigation was undertaken to develop PRSV (Papaya ringspot virus) resistant hybrids through intergeneric hybridization. Intergeneric hybridization was done involving nine Carica papaya cultivars as female and Vasconcellea cauliflora as male. To break the intergeneric hybridization barrier, various nutrient combinations were used. Among the combinations used, sucrose 5%, sucrose 5% + boron 0.5% and sucrose 5% + CaCl₂ 0.5% improved the fruit set and seed set percentage. A total number of 1197 flowers were pollinated and 308 fruits were obtained. On extraction, 721 seeds were obtained from CO 7, Pusa Nanha and CP 50. Out of 721 F₀ seeds (crossed seeds) sown, 419 seeds germinated and artificial screening for PRSV was carried out 27 days after sap inoculation. Out of 29 F₁ hybrid plants from CO 7 x V. cauliflora cross, only six plants namely CO 7V1 to CO 7V6 were found free from PRSV symptoms. Similarly, out of 55 F₁ hybrids from cross involving Pusa Nanha x V. cauliflora only 23 plants namely PNV1 to PNV23 were found free from the symptoms and 70 plants namely CPV1 to CPV70 out of 335 plants of CP50 x V. cauliflora cross were found free from PRSV symptoms. Among the crosses, Pusa Nanha x V. cauliflora had higher yield under PRSV infected conditions, however, total soluble solids and total sugars were found lesser than the CO 7 x V. cauliflora cross. The hybridity of the progenies were confirmed by using ISSR (Inter Simple Sequence Repeats) primers by the amplification of DNA from progenies and their parents. ISSR primers UBC 856, UBC807 and ISSR primer combinations UBC 856-817, UBC 810-817, UBC 861-817, UBC 856-810, UBC 861-810 and UBC 856-817 clearly amplified specific bands of the male parent, which were present in F₁ progenies, but it was absent in female parents.