Which of the following pairs of organisms shows heterothallism?

Options

A. Agaricus and Colletotrichum
B. Alternaria and Saccharomyces
C. Rhizopus and Saccharomyces
D. Trichoderma and Agaricus

Answer

To determine which pair of organisms shows heterothallism, we need to understand the concept of heterothallism and how it differs from homothallism.

### Step-by-Step Solution:

1. **Define Heterothallism**:
- Heterothallism refers to a reproductive strategy where male and female reproductive structures are found in separate individuals. This means that two different organisms are required for reproduction.

2. **Define Homothallism**:
- Homothallism is the opposite of heterothallism, where both male and female reproductive structures are found within the same individual organism. This allows for self-fertilization.

3. **Analyze the Options**:
- We need to evaluate the given pairs of organisms to see which ones exhibit heterothallism.

4. **Evaluate Each Pair**:
- **Option 1: Agaricus and Polytrichum**:
- Both are homothalic. They possess both male and female reproductive structures within the same organism.
- **Option 2: Rhizopus and Saccharomycetes**:
- Rhizopus exhibits heterothallism, as it has distinct male and female strains. Saccharomycetes also shows heterothallism.
- **Option 3: Trichoderma and Agaricus**:
- Both are homothalic, as they have both reproductive structures in the same organism.

5. **Conclusion**:
- The correct answer is the pair of organisms that shows heterothallism, which is **Rhizopus and Saccharomycetes**.

### Final Answer:
- The pair of organisms that shows heterothallism is **Rhizopus and Saccharomycetes**.