Which of the following growth regulator helps to prevent fruit and leaf drop at early stage but promote the abscission of older mature leaves and fruits ?

Options

A. Auxin
B. GA
C. ABA
D. Ethylene

Answer

To solve the question regarding which growth regulator prevents early fruit and leaf drop while promoting the abscission of older mature leaves and fruits, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Functions of Growth Regulators**:
- Growth regulators (or plant hormones) play various roles in plant growth and development, including influencing abscission (the process of shedding leaves, flowers, or fruits).

2. **Analyze the Options Provided**:
- **Auxin**: Known to prevent the premature drop of leaves and fruits, especially in their early stages.
- **Gibberellins (GA)**: Primarily involved in promoting growth and elongation; not directly related to abscission.
- **Abscisic Acid (ABA)**: Generally promotes abscission and stress responses but does not prevent early drop.
- **Ethylene**: A gas that promotes ripening and can lead to the abscission of mature fruits and leaves.

3. **Identify the Correct Function**:
- We are looking for a growth regulator that prevents early drop (which points towards Auxin) but also promotes the shedding of older leaves and fruits (which could relate to Ethylene).

4. **Conclude with the Correct Answer**:
- **Auxin** is the growth regulator that fits the criteria of preventing early drop of young leaves and fruits while promoting the abscission of older, mature leaves and fruits.

### Final Answer:
The growth regulator that helps to prevent fruit and leaf drop at an early stage but promotes the abscission of older mature leaves and fruits is **Auxin**.