Spraying sugarcane crop with a plant hormone increases length of plants and increases yield by as much as 20 tonnes/acre. The hormone is

Options

A. Gibberellin
B. Auxin
C. Cytokinin
D. ABA.

Answer

To solve the question regarding which plant hormone, when sprayed on sugarcane crops, increases the length of the plants and yields, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Plant Hormones Listed**: The options provided are gibberellin, auxin, cytokinin, and abscisic acid (ABA).

2. **Understand the Function of Each Hormone**:
- **Gibberellin**: This hormone is known for promoting stem elongation by increasing the length of the internodes. It plays a significant role in overall plant growth and can lead to increased yields in crops.
- **Auxin**: Primarily involved in apical dominance, auxins help in the elongation of cells but are not primarily responsible for increasing overall plant height or yield in the context of sugarcane.
- **Cytokinin**: This hormone mainly promotes cell division and is important for growth, but it does not specifically increase plant height or yield in the same way gibberellins do.
- **Abscisic Acid (ABA)**: This hormone is associated with stress responses in plants and does not promote growth or yield.

3. **Evaluate the Impact of Each Hormone on Sugarcane**:
- Given that the question specifies an increase in plant length and yield, gibberellin is the most suitable option as it directly promotes stem elongation and has been shown to increase crop yields significantly.

4. **Conclusion**: Based on the functions of the hormones and their impact on plant growth, the hormone responsible for the increase in length and yield of sugarcane when sprayed is **gibberellin**.

### Final Answer:
The hormone is **gibberellin**.

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