Nucleic acids and polypeptides were identified and isolated from Poncirus trifoliata, a sexually compatible close relative of Citrus. These sequences, when present in a plant genome, result in the expression of resistance to CTV infection. Several methods of transforming citrus plants to produce citrus plants that are resistant to the broad genetic diversity of CTV strains are described. Transformed CTV-resistant germplasm and breeding lines can be used in conventional breeding programs to create new cultivars that carry and express the resistance genes.