Through mutation breeding maximum varieties have been released for the character:

Correct option is D

What is Mutation Breeding?
Mutation breeding is the process of inducing heritable mutations in plants using physical (e.g., gamma rays, X-rays) or chemical mutagens (e.g., EMS) to develop new and improved varieties.
It enables the development of traits not easily accessible through conventional breeding.
�� Why Is Reduction in Height a Key Target?
Reduction in plant height is one of the most successfully achieved traits through mutation breeding.
Shorter plants are:
Lodging resistant (don’t fall over easily)
More responsive to fertilizers
Often have better harvest index
This trait was crucial during the Green Revolution, particularly in crops like wheat and rice.
�� Examples:
Wheat (e.g., Sharbati Sonora) and Rice (e.g., Jaya) varieties were developed with reduced height genes (like Rht and sd1) via mutation breeding.
Many dwarf and semi-dwarf lines were induced and used globally to improve crop yields.
�� Explanation of Other Options:
(a) Salt tolerance – ❌ Mutation breeding for abiotic stress tolerance is possible but less successful and less frequent.
(b) Improved grain quality – ❌ A complex trait involving multiple genes; fewer varieties are developed solely through mutations.
(c) Increase in height – ❌ Opposite of breeding goals for modern cereals.
(d) Reduction in height – ✅ Correct, most varieties released via mutation breeding focus on this trait.