Vertical resistance can be exploited through

Vertical resistance refers to resistance that is usually governed by one or a few major genes and is often race-specific.

Option A: Development of varieties with individual major gene is a method to exploit vertical resistance because it involves using specific genes that provide resistance to certain races of a pathogen.

Option B: Gene pyramiding and gene developing enhances durability by combining multiple resistance genes, thereby increasing the effectiveness of vertical resistance.

Option C: Development of multiline involves creating a mixture of lines, each with different major resistance genes, which can reduce the likelihood of pathogen adaptation.

Hence, all these approaches can be used to exploit vertical resistance effectively.