The phenomenon of apical dominance can be overcome by exogenous application of

Options

A. ABA
B. gibberellins
C. cytokinins
D. ethylene

Answer

### Step-by-Step Solution:

1. **Understanding Apical Dominance**:
- Apical dominance is a phenomenon in plants where the main (apical) shoot grows more vigorously than the lateral shoots (buds). This is primarily regulated by the plant hormone auxin, which is produced at the tips of the shoots.

2. **Role of Auxin**:
- Auxin promotes the growth of the apical bud and inhibits the growth of lateral buds. This means that when auxin is present, it suppresses the lateral buds, allowing the plant to grow taller rather than bushier.

3. **Identifying the Need to Overcome Apical Dominance**:
- In some cases, it is desirable to encourage the growth of lateral buds to create a bushier plant. To achieve this, we need to apply a substance that can counteract the effects of auxin.

4. **Exogenous Application of Substances**:
- The question asks for an exogenous application that can overcome apical dominance. The options provided are:
- ABA (Abscisic Acid)
- Gibberellin
- Cytokinins
- Ethylene

5. **Analyzing the Options**:
- **ABA**: Generally inhibits growth and promotes dormancy.
- **Gibberellin**: Promotes stem elongation and can stimulate growth but does not specifically target lateral bud growth.
- **Cytokinins**: Promote cell division and can stimulate lateral bud growth, effectively overcoming the suppression caused by auxin.
- **Ethylene**: Primarily involved in fruit ripening and does not directly influence apical dominance.

6. **Conclusion**:
- The correct answer is **Cytokinins**. They work antagonistically to auxin, promoting the growth of lateral buds and thus overcoming apical dominance.

### Final Answer:
The phenomenon of apical dominance can be overcome by exogenous application of **Cytokinins**.

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