Plant Growth Regulators

Answer (c) Acidic

Gibberellins induce stem elongation in "rosette??plants. Cabbage is a good example of such a plant in which leaf development is profuse, whereas intemodal growth is retarded. Just prior to the reproductive phase, the intemodes elongate enormously causing a marked increase in stem height. This is called bolting. Bolting requires either long days or cold nights. If a cabbage head is kept under warm nights, it retains its rosette habit. Bolting in cabbage can be induced artificially by the application of gibberellins under conditions that would normally maintain the rosette form.

Step 1: Understanding the Concept: Plant Growth Regulators (PGRs) have distinct physiological effects and commercial agricultural applications.
Step 2: Key Formula or Approach: Match the specific agricultural function ("synchronising fruit set in pineapples") to the correct plant hormone.
Step 3: Detailed Explanation: While auxins are known to promote flowering in pineapples, ethylene is distinctly and specifically known for both initiating flowering and synchronizing fruit set.
Ethylene application ensures that the entire crop flowers and fruits at the same time, which is highly beneficial for the mass harvesting of pineapples.
This dual function of initiating and synchronizing fruit-set in pineapples is a textbook application of the gaseous hormone ethylene (often applied as Ethephon).
Step 4: Final Answer: The correct option is (1).