A plant disease which is not caused by a fungus is

Options

A. Red rot of Sugarcane
B. lete blight of Potato
C. Black rot of crucifers
D. Brown rust of wheat.

Explanation

To answer the question "A plant disease which is not caused by a fungus is," we need to analyze the options provided and identify the causative agents of each disease mentioned.

### Step-by-Step Solution:

1. **Identify the diseases and their causative agents**:
- **Red rot of sugarcane**: This disease is caused by a fungus known as *Colletotrichum falcatum*, which belongs to the group of imperfect fungi (Deuteromycetes).
- **Late blight of potato**: This disease is caused by *Phytophthora infestans*, which is a member of the oomycetes, a group of organisms that are often classified with fungi due to similar characteristics but are not true fungi.
- **Black rot of cruciferous plants**: This disease is caused by the bacterium *Xanthomonas campestris*. This is a key point since it indicates that this disease is not fungal.
- **Brown rust of wheat**: This disease is caused by the fungus *Puccinia triticina*, which is a well-known fungal pathogen affecting wheat.

2. **Determine which disease is not caused by a fungus**:
- From the analysis, we see that the black rot of cruciferous plants is the only disease among the options that is caused by a bacterium (*Xanthomonas campestris*), while the other three diseases are caused by fungi.

3. **Conclude the correct answer**:
- Therefore, the plant disease that is not caused by a fungus is the **black rot of cruciferous plants**.

### Final Answer:
The plant disease which is not caused by a fungus is **black rot of cruciferous plants**.