How has mutation breeding helped in improving crop varieties? Give one example where this technique has helped.

Mutation breeding sometimes referred to as "variation breeding", is the process of exposing seeds to chemicals or radiation in order to generate mutants with desirable traits to be bred with other cultivars.  It helps in the crop variety in the following ways:-
    ? Mutation breeding can be used for both oligogenic and polygenic traits in plants.
    ? It improves morphological and physiological characters of cultivated crops.
    ? Mutation breeding can improve the disease resistance of crop plants.
    ? Induced mutations can induce desirable mutant alleles in crop plants.
    ? Mutation breeding can be used to improve the specific characters of a well-adapted high yielding variety.
For example-  Jiahezazhan and Jiafuzhan rice.