Which of the following growth regulator is not used to break dormancy?

Options

A. Ethylene
B. Gibberellins
C. Cytokinins
D. Abscisic acid

Answer

To determine which growth regulator is not used to break dormancy, we can analyze each of the given options: Ethylene, Gibberellins, Cytokinins, and Abscisic acid.

### Step-by-Step Solution:

1. **Understanding Dormancy**:
- Dormancy refers to a state of inactivity in seeds or buds where growth and development are temporarily halted. This is often a survival mechanism in response to unfavorable conditions.

2. **Analyzing Ethylene**:
- Ethylene is a plant hormone primarily known for its role in fruit ripening. However, it also plays a role in breaking seed and bud dormancy. Therefore, Ethylene is **not** the correct answer.

3. **Analyzing Gibberellins**:
- Gibberellins (often misspelled as Zyberlin) are hormones that promote growth and are particularly known for breaking dormancy in seeds. They help in the germination process by promoting the elongation of stems and the growth of leaves. Thus, Gibberellins are also **not** the correct answer.

4. **Analyzing Cytokinins**:
- Cytokinins are hormones that promote cell division and can also help in the mobilization of nutrients, which aids in germination. They delay senescence (aging) in plants and can assist in breaking dormancy. Hence, Cytokinins are **not** the correct answer.

5. **Analyzing Abscisic Acid**:
- Abscisic acid (ABA) is known as a stress hormone. Its primary role is to promote dormancy and inhibit germination. It is responsible for closing stomata and is crucial in response to stress conditions. Therefore, Abscisic acid is the hormone that **does not** break dormancy.

6. **Conclusion**:
- The growth regulator that is **not** used to break dormancy is **Abscisic acid**.

### Final Answer:
The correct option is **Abscisic acid**.

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