Rust of wheat caused by...........in wheat.

Options

A. Algae
B. Virus
C. Bacteria
D. Fungi

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the cause of rust in wheat. Rust is a plant disease that affects various crops, including wheat.

2. **Identifying the Options**: The options provided are:
- A) Algae
- B) Virus
- C) Bacteria
- D) Fungi

3. **Analyzing Each Option**:
- **Algae**: These are primarily aquatic organisms and do not cause rust in plants.
- **Virus**: While viruses can affect plants, they are not responsible for rust diseases.
- **Bacteria**: Bacterial infections can occur in plants, but they do not cause rust.
- **Fungi**: Fungi are known to be responsible for many plant diseases, including rust.

4. **Conclusion**: Based on the analysis, the correct answer is D) Fungi. Specifically, the rust of wheat is caused by the fungus *Puccinia triticina*, which is an obligate parasite that infects wheat plants.

5. **Final Answer**: Rust of wheat is caused by fungi.

---