The proper isolation distance for maintenance breeding of male sterile line (A×B) in hybrid rice is:

Correct option is A

✅ (a) 100 m: • For hybrid rice seed production, 100 meters of isolation is maintained for A (male sterile) × B (maintainer) lines. • Prevents contamination from other pollen sources. • Critical for genetic purity in hybrid seed production.
❌ (b), (c), (d): • These are higher than necessary for this purpose and used for different crops or stages.