Somaclones are obtained by

In tissue culture, whole plants are regenerated from explants (any part of a plant) grown in a nutrient medium under sterile conditions; this capacity is called totipotency.
By micropropagation thousands of plants can be produced in a short time.
Each of these plants is genetically identical to the original plant from which they were grown; they are called somaclones.
Hence somaclones are obtained by tissue culture.