seed corn vs seed stock

seed corn and seed stock both are nouns.

Word	Noun	Adjective	Verb	Adverb
seed corn	Yes	No	No	No
seed stock	Yes	No	No	No

As nouns, seed stock is a hypernym of seed corn; that is, seed stock is a word with a broader meaning than seed corn:

seed corn: good quality seeds (as kernels of corn) that are reserved for planting
seed stock: a supply of seeds (or tubers) reserved for planting

seed corn (noun)	seed stock (noun)
good quality seeds (as kernels of corn) that are reserved for planting	a supply of seeds (or tubers) reserved for planting