The technique of obtaining large number of plantlets by tissue culture method is called –

In plant tissue culture, a small piece of plant tissue (explant) is grown on a sterile nutrient medium. Because of totipotency, each cell can regenerate a whole plant.
The method of producing a large number of plants in a short time by tissue culture is called micropropagation.
The plants produced are genetically identical to the original plant (somaclones). It is widely used for tomato, banana, apple and ornamental plants.
So the technique is micropropagation.