The method of producing thousands of plants through tissue culture is called as:

Micro-propagation

Tissue culture is a remarkable technique that allows the regeneration of whole plants from small plant parts, known as explants. These explants can be taken from any part of a plant and grown in a controlled environment, typically in test tubes, under sterile conditions using specialized nutrient media. The unique ability of plant cells to develop into complete plants from these explants is referred to as totipotency.

It's important to note that the nutrient medium used in tissue culture must contain essential components such as a carbon source (usually sucrose), inorganic salts, vitamins, amino acids, and growth regulators like auxins and cytokinins. By employing these methods, it becomes possible to rapidly propagate a large number of plants within a short period. This specific technique of producing numerous plants through tissue culture is commonly referred to as micro-propagation.

One significant advantage of micro-propagation is that each of the resulting plants is genetically identical to the original plant from which the explant was derived. These genetically identical plants are known as somaclones. Many essential food plants, including tomato, banana, apple, and others, have been successfully mass-produced using this method on a commercial scale.

In summary, tissue culture is a powerful tool for the mass production of plants. It leverages the remarkable totipotency of plant cells to generate numerous genetically identical plants through micro-propagation, and it has found widespread application in the cultivation of various important food crops.

Isolated protoplasts from two different varieties of plants – each having a desirable character – can be fused to get hybrid protoplasts, which can be further grown to form a new plant. These hybrids are called somatic hybrids while the process is called somatic hybridisation.