Step 1: Understanding the Question:
Apical dominance is a condition where the growth of the central stem is favored over lateral branches. The question asks which plant growth regulator controls this.
Step 2: Detailed Explanation:
Auxins (such as Indole-3-acetic acid or IAA) are synthesized primarily at the shoot apex (growing tip).
The high concentration of auxin at the tip promotes vertical growth but inhibits the growth of axillary (lateral) buds.
This ensures the plant grows taller to reach sunlight.
If the apical bud is removed (decapitation), the auxin concentration drops, allowing cytokinins to promote lateral bud growth, making the plant bushy.
Step 3: Final Answer:
Auxin is the hormone responsible for maintaining apical dominance in plants.