The colour of high yielding Mexican wheats were not liked by the indians. It was originally red grained. Their cultivation was adopted in India on large scale only when exposure to gamma radiations converted them to amber grained. Which of following methods of plant-breeding has been put into practice in the given case ?

Options

A. Polyploid breeding
B. Interspecific hybridisation
C. Tissue culture
D. Mutation breeding

Answer

To solve the question regarding the method of plant breeding used for the high-yielding Mexican wheat, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Problem**: The question states that high-yielding Mexican wheat was originally red-grained and was not favored by Indian farmers. However, after exposure to gamma radiation, the wheat changed to an amber color, which was accepted and cultivated on a large scale in India.

2. **Identifying the Process**: The key aspect here is the exposure of the wheat to gamma radiation. This process is known to induce mutations in the genetic material of the plant.

3. **Defining Mutation Breeding**: Mutation breeding is a technique where plants are exposed to physical (like radiation) or chemical agents to induce mutations. These mutations can lead to desirable traits, such as a change in grain color, which in this case made the wheat more acceptable to Indian farmers.

4. **Evaluating Other Options**:
- **Polyploid Breeding**: This method involves increasing the number of chromosome sets in plants, typically used for sterile plants. This does not apply here.
- **Interspecific Hybridization**: This involves crossing different species within the same genus, which is not the case here.
- **Tissue Culture**: This is a laboratory technique for growing plants from cells or tissues, which is also not applicable in this scenario.

5. **Conclusion**: Since the method used involved inducing mutations through gamma radiation, the correct answer is **mutation breeding**.

### Final Answer:
The method of plant breeding put into practice in the given case is **mutation breeding**.