Which of the following methods can be used to produce 'disease-free plants’?

Disease-free plants can be produced by tissue culture. In this technique, we can take few healthy cells and selectively multiply them to form new plants under sterile and aseptic conditions. But, in grafting or layering or cutting, the chances of having diseased plants are there because the cells cannot be selectively chosen in these and at any time, the pathogens may attack them.