For biological control, which fungus is used in the treatment of plant diseases?

Explanation

### Step-by-Step Solution:

1. **Understanding Biological Control**: Biological control refers to the use of living organisms to control pests and diseases in agriculture. This method is environmentally friendly and sustainable compared to chemical pesticides.

2. **Identifying Biocontrol Agents**: Biocontrol agents are organisms that help in controlling harmful pests or pathogens. These can include bacteria, fungi, and other microorganisms.

3. **Fungi as Biocontrol Agents**: Among the various biocontrol agents, certain fungi are particularly effective in combating plant diseases. These fungi can inhibit the growth of pathogens and promote plant health.

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