Abstract: O₂(Opaque No.2)corn generally yields 7-15% less than common corn of the same type,due to reduced kernel volume weight caused by starch endosperm.The way to solve this problem in breeding is to use the hard endosperm modifier(gene)and to select hard or semi-hard O₂ inbred lines with higher kernel volume weight.Since different types of corn carry different amount of hard endosperm modifiers,only by screen-ing and utilizing parent materials rich in hard endosperm modifiers,through the breeding method of self-cross or a combination of selfing and sib-mating with the selection objective of showing"corny cap"and"corny ring",can hard endosperm or semi-hard endosperm O₂ corn inbred lines be effectively bred.

Key words: Hard endosperm, O₂ corn, Breeding