Mycorrhizal association controls root affecting pathogens in plants because

Options

A. Mycorrhizal fungi colonize the roots and act as a barrier during infection
B. Mycorrhizal fungi help phosphorus uptake
C. Mycorrhizal fungi help during stress and shock
D. Mycorrhizal fungi produce toxins against pathogens

Answer

### Step-by-Step Solution:

1. **Understanding Mycorrhizal Association**:
- Mycorrhizal association is a symbiotic relationship between fungi and the roots of higher plants. In this relationship, both organisms benefit from each other.

2. **Role of Plants in Mycorrhizal Association**:
- Plants, through the process of photosynthesis, produce food and nutrients. They provide these essential resources to the fungi, which helps sustain the fungi's growth and function.

3. **Role of Fungi in Mycorrhizal Association**:
- The fungi, in turn, attach to the plant roots and absorb minerals and nutrients from the soil. They transfer these nutrients to the plant, enhancing its growth and health.

4. **Protection Against Pathogens**:
- Mycorrhizal fungi also play a protective role. They can produce certain toxins that help defend the plant against root-affecting pathogens. This is a crucial aspect of their symbiotic relationship, as it helps the plant resist diseases.

5. **Conclusion**:
- Therefore, the mycorrhizal association controls root-affecting pathogens in plants primarily because the mycorrhizal fungi produce toxins that protect the plant from these pathogens.

### Final Answer:
Mycorrhizal fungi produce toxins that protect the plant from root-affecting pathogens.

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