Genetic mapping of a PRSV-P resistance gene in "highland papaya" based on inheritance of RAF markers
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Papaya ringspot virus type P (PRSV-P) is a significant disease of Carica papaya. A major gene for PRSV-P resistance has been mapped in Vasconcellea cundinamarcensis, a distant relative of C. papaya. This was achieved by genetic mapping of the resistance phenotype and inherited, dominant, polymorphic randomly amplified DNA fingerprint (RAF) markers in F2 progenies of V. parviflora and V. cundinamarcensis. The parents of this cross confer resistance to several major diseases that affect C. papaya including PRSV-P in V. cundinamarcensis. Heredity of DNA markers and PRSV-P resistance was studied in the intrageneric population presented due to intergeneric fertility barriers between Carica and Vasconcellea. Genetic polymorphism between parents, based on RAF markers, was 75% with more than 70% of markers generated showing mendelian segregation for the expected ratios 1:3 or 1:1 (p < 0.05). Preferential inheritance of markers from either parent was not detected in the F2, indicating stable transfer of the genetic material. Discrete V. parviflora and V. cundinamarcensis linkage maps were compiled from 79 and 83 framework markers, delineating to 10 and 11 groups respectively. F1 and F2 progeny were screened for resistance to PRSV-P under controlled conditions. The resistant phenotype segregated 3:1 in the F2 and mapped to V. cundinamarcensis linkage group 7 with adjacent RAF markers within 4 cM. The framework maps of V. parviflora and V. cundinamarcensis presented cover 630.2 and 745.4 cM respectively, accounting for between 47-52 and 49-55 percent of the predicted genome lengths. These maps provide a platform for further genetic study of disease resistance characteristics identified in these species and the development of DNA markers tightly linked to these traits, which could be applied to the breeding of resistant C. papaya cultivars.