Choose the mechanism that is used in the tobacco plants that are introduced with nematode - specific using certain vectors.

Options

A. RNAi
B. Insecticidal protein
C. DNAi
D. Cry gene

Answer

### Step-by-Step Solution:

1. **Understanding the Problem**: The question asks for the mechanism used in tobacco plants to combat nematode infestation, specifically through the introduction of nematode-specific genes using vectors.

2. **Identifying the Nematode**: The nematode that affects tobacco plants is identified as *Meloidogyne incognitia*. This nematode attacks the roots of tobacco plants, leading to reduced yield.

3. **Mechanism of Action**: The mechanism employed to combat this nematode is RNA interference (RNAi). This is a biological process where RNA molecules inhibit gene expression or translation, effectively silencing specific genes.

4. **Introduction of RNAi**: In this case, a double-stranded RNA (dsRNA) that is complementary to the RNA of the nematode is introduced into the tobacco plants. This dsRNA binds to the mRNA of the nematode, preventing its expression.

5. **Outcome**: By silencing the mRNA of the nematode, the introduced RNAi mechanism ensures that the nematodes cannot survive in the tobacco plants, thus protecting the plants from damage.

6. **Conclusion**: The correct answer to the question is the use of RNA interference technology to introduce nematode-specific genes into tobacco plants, utilizing vectors for this purpose.