The correct option is A protoplast fusion
Somatic hybridization is a technique which allows the manipulation of cellular genomes by protoplast fusion.
In grafting, the upper part (scion) of one plant grows on the root system (rootstock) of another plant.
Conjugation is the transfer of genetic material between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells.
Recombinant DNA technology is the joining of DNA molecules from two different species that are inserted into a host organism.