Which of the following statements are correct regarding the process of RNA interference ?
(i) RNAi has been used to prevent nematode infestation of tobacco plants .
(ii) RNAi takes place in all eukaryotic organisms as a method of cellular defense.
(iii) The method involves silencing of specific mRNA using a complementary dsDNA molecule that binds and prevents the translation of mRNA.
(iv) using retrovirus vectors , nematode–specific genes were introduced into the host plant .

Options

A. (i) and (ii)
B. (i) and ( ii)
C. (i) and (iii)
D. (ii) and (iv)

Answer

To determine which statements regarding RNA interference (RNAi) are correct, let's analyze each statement step by step.

### Step-by-Step Solution:

1. **Statement (i): RNAi has been used to prevent nematode infestation of tobacco plants.**
- This statement is **correct**. RNA interference has been successfully utilized in tobacco plants to combat nematode infestations, specifically targeting the nematode Meloidogyne incognita, which affects the roots of these plants.

2. **Statement (ii): RNAi takes place in all eukaryotic organisms as a method of cellular defense.**
- This statement is **incorrect**. While RNAi is a cellular defense mechanism found in many eukaryotic organisms, it does not occur in all eukaryotes. Some organisms may not have the RNAi machinery, and in those cases, RNAi needs to be introduced artificially through genetic engineering.

3. **Statement (iii): The method involves silencing of specific mRNA using a complementary dsDNA molecule that binds and prevents the translation of mRNA.**
- This statement is **incorrect**. RNA interference involves the use of double-stranded RNA (dsRNA) that is complementary to the target mRNA, not dsDNA. The dsRNA binds to the specific mRNA, leading to its degradation and preventing translation.

4. **Statement (iv): Using retrovirus vectors, nematode-specific genes were introduced into the host plant.**
- This statement is **incorrect**. The introduction of RNAi into tobacco plants to combat nematodes was achieved using Agrobacterium vectors, not retrovirus vectors. Retroviruses are not typically used for this purpose in plant genetic engineering.

### Conclusion:
Based on the analysis:
- **Correct Statements**: (i)
- **Incorrect Statements**: (ii), (iii), (iv)

Thus, the correct answer is that only statement (i) is correct regarding RNA interference.