Apical dominance is stimulated by auxin whereas it is inhibited by

Options

A. Ethylene
B. ABA
C. Gibberellic acid
D. Cytokinin

Answer

### Step-by-Step Solution

1. **Understanding Apical Dominance**:
- Apical dominance is a phenomenon where the growth of lateral buds is inhibited by the presence of the apical bud. This means that the main shoot grows more vigorously than the lateral shoots.

2. **Role of Auxin**:
- Auxin is a plant hormone that stimulates apical dominance. It promotes the growth of the apical bud while inhibiting the growth of lateral buds.

3. **Identifying Inhibitors of Apical Dominance**:
- To answer the question, we need to identify which substance inhibits apical dominance. The options provided are:
- Ethylene
- Abscisic Acid (ABA)
- Gibberellic Acid
- Cytokinin

4. **Analyzing Each Option**:
- **Ethylene**: This is a plant growth inhibitor but it promotes apical dominance and increases dormancy of lateral branches, so it does not inhibit apical dominance.
- **Abscisic Acid (ABA)**: This is also a growth inhibitor, but it does not have a significant effect on apical dominance.
- **Gibberellic Acid**: This hormone primarily promotes growth in terms of stem elongation and does not significantly affect apical dominance.
- **Cytokinin**: This is an adenine derivative that inhibits apical dominance and promotes the growth of lateral branches. It acts as an antagonist to auxin.

5. **Conclusion**:
- The correct answer to the question "Apical dominance is stimulated by auxin whereas it is inhibited by" is **Cytokinin**.

### Final Answer
Apical dominance is stimulated by auxin whereas it is inhibited by **Cytokinin**.