The smallest organisms which cause diseases among plants are

Options

A. Viruses
B. Fungi
C. Bacteria
D. Mycoplasma.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the smallest organisms that cause diseases in plants. We need to identify the correct organism from the given options.

2. **Analyzing the Options**:
- **Option 1: Virus** - Viruses cause diseases in plants but are not considered living organisms as they are acellular and require a host to survive.
- **Option 2: Fungi** - Fungi can cause diseases in plants, but they are larger than the smallest organisms.
- **Option 3: Bacteria** - Bacteria can also cause diseases in plants, but they are generally larger than mycoplasmas.
- **Option 4: Mycoplasma** - Mycoplasmas are the smallest known prokaryotes and can cause diseases in plants.

3. **Identifying the Smallest Organism**: Mycoplasmas are known to be the smallest organisms, with a diameter of approximately 0.0001 mm. They lack a cell wall, which contributes to their small size and irregular shape.

4. **Understanding Mycoplasma's Role in Plant Diseases**: Mycoplasmas can cause various diseases in plants, including yellow disease and white leaf disease. They are also referred to as "TTLO" or "jokers of the plant kingdom" due to their unique characteristics.

5. **Conclusion**: Based on the analysis of the options and the characteristics of mycoplasmas, the correct answer to the question is **Option 4: Mycoplasma**.

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