Among the following, under which condition for maize hybrid seed production, the modification of isolation distance by planting border rows is not permitted?

Correct option is A

✅ (a) Contaminating field with sweetcorn/popcorn/teosinte [High Crossability Risk] • Sweetcorn, popcorn, and teosinte easily cross with maize, posing a high contamination risk. • Hence, no modification of isolation distance is allowed, even with border rows. • This ensures genetic purity of hybrid seed.
❌ (b) Border rows planted with male parent • A standard practice to reduce isolation distance by buffering contamination. • Permitted under specific guidelines.
❌ (c) Seed field with diagonal exposure • Border rows can still be effective in this layout, although effectiveness may reduce.
❌ (d) Different hybrid fields within isolation distance • Can be allowed with permission and temporal isolation (staggered planting) or border rows.