Identify the incorrect pair.

Options

A. Puccinia - Causative organism of wheat rust.
B. Aspergillus - Production of citric acid.
C. Ustilago - it is also known as rust fungi.
D. Neurospora - Extensively used in genetics.

Answer

To solve the question of identifying the incorrect pair, we will analyze each option provided in the question step by step.

### Step 1: Analyze the first pair - Paxinia and wheat rust
- **Paxinia** is known to be the causative organism of **wheat rust**.
- Paxinia belongs to the group of fungi known as **Basidiomycetes**.
- This pair is **correct**.

### Step 2: Analyze the second pair - Aspergillus and citric acid production
- **Aspergillus** is a genus of fungi that is indeed used for the **production of citric acid**.
- Aspergillus belongs to the group of fungi known as **Ascomycetes**.
- This pair is **correct**.

### Step 3: Analyze the third pair - Ustilago and rust fungi
- **Ustilago** is a genus of fungi, but it is known as **smut fungi**, not rust fungi.
- The correct genus associated with rust fungi is **Paxinia**.
- Therefore, this pair is **incorrect**.

### Step 4: Analyze the fourth pair - Neurospora and genetics
- **Neurospora** is a genus of fungi that is extensively used in **genetics** and biochemical studies.
- Neurospora also belongs to the group of fungi known as **Ascomycetes**.
- This pair is **correct**.

### Conclusion
After analyzing all the pairs, we find that the incorrect pair is the third one: **Ustilago and rust fungi**. Ustilago is actually known as smut fungi, not rust fungi.

### Final Answer
The incorrect pair is: **Ustilago (smut fungi) - rust fungi**.

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