Pollination is stimulus necessary for the fruit development. It can be replaced mainly by

Options

A. ethylene
B. 2, 4-D
C. cytokinin
D. auxins

Answer

### Step-by-Step Solution:

1. **Understanding Pollination**: Pollination is the process of transferring pollen grains from the anther (male part) to the stigma (female part) of a flower. This can occur within the same flower or between different flowers.

2. **Role of Pollination in Fruit Development**: In horticulture and agriculture, pollination is crucial for fruit development. It leads to fertilization, which is essential for the formation of seeds and subsequent fruit.

3. **Hormonal Influence on Fruit Development**: The development of fruit is initiated by growth-regulating hormones produced by the developing seeds. One key hormone involved in this process is auxin.

4. **Identifying Alternatives to Pollination**: The question asks what can replace the stimulus of pollination for fruit development. We need to evaluate the given options to find the correct answer.

5. **Evaluating Options**:
- **Option A: Ethylene**: This hormone is primarily involved in the production of flowers and the ripening of fruits, but it does not replace pollination.
- **Option B: 2,4-D**: This is a synthetic auxin used as a herbicide and does not serve as a substitute for pollination.
- **Option C: Cytokinin**: This hormone promotes cell division in roots and shoots but does not replace the need for pollination in fruit development.
- **Option D: Auxin**: This is a growth-regulating hormone that plays a significant role in fruit development and can replace the need for pollination.

6. **Conclusion**: Based on the evaluation, the correct answer is **Auxin** (Option D), as it can replace the stimulus necessary for fruit development that is typically provided by pollination.