If male sterility of a line in hybrid seed production is maintained by altering the temperature it is known as:

Correct option is B

✔️ (b) Two line breeding: In two-line breeding, male sterility is controlled by environmental conditions, especially temperature or photoperiod. This involves:
· A TGMS (Thermo-sensitive Genetic Male Sterile) or PGMS (Photo-sensitive Genetic Male Sterile) line
· Male sterility under specific environmental conditions and fertility under others
· Eliminates the need for a maintainer line, simplifying hybrid seed production This method is extensively used in crops like rice.
❌ (a) One line breeding: Not a recognized system in hybrid seed production.
❌ (c) Three line breeding: Involves a cytoplasmic-genetic male sterility (CMS) system with three lines — A (sterile), B (maintainer), and R (restorer). It is not dependent on environment.
❌ (d) Mutation breeding: Refers to artificially induced mutations using radiation/chemicals, not related to male sterility or hybrid breeding systems.