Meloidogyne incognita: The Nematode That Infects Tobacco Roots
Biology · Biotechnology and Its Applications · NEET
Meloidogyne incognita is a nematode (round worm) that infects the ROOTS of tobacco plants and lowers the yield. To protect the plant, scientists use RNA interference (RNAi): a double-stranded RNA (dsRNA) silences the nematode's own mRNA, so the parasite cannot survive. Memory hook: "Melo attacks the ROOT, RNAi is the boot" - the nematode goes for roots, RNAi kicks it out.
Flow of the RNAi strategy: transgenic tobacco makes dsRNA in its roots; when Meloidogyne incognita feeds and takes up this dsRNA, its specific mRNA is silenced (translation blocked), so the parasite cannot survive and the plant is protected.
Your doubts, answered
Which exact part of the tobacco plant does Meloidogyne incognita infect?
The ROOT. NCERT is very clear: Meloidogyne incognita infects the roots of tobacco plants and causes a great reduction in yield. NEET 2016 asked exactly this, and the answer is Root (not leaf, stem or flower). Remember it as a soil-living worm that attacks the underground part.
Is Meloidogyne incognita a nematode, a fungus, or a bacterium?
It is a nematode - a round worm. NCERT says several nematodes parasitise a wide variety of plants and animals. Do not confuse it with Bacillus thuringiensis (a bacterium giving Bt toxin) or Agrobacterium (a bacterium used as a vector). Meloidogyne is the pest, not a tool.
What strategy is used to make tobacco resistant to this nematode?
RNA interference (RNAi). This is a novel strategy where a specific mRNA of the nematode is silenced by a complementary double-stranded RNA (dsRNA). The transgenic plant is engineered to produce this dsRNA, so the nematode's key gene is switched off and the parasite cannot survive.
Why must the silencing molecule be double-stranded RNA (dsRNA) and not single-stranded?
RNAi works only with dsRNA. The double-stranded RNA is complementary to the target mRNA; it binds that mRNA and prevents its translation (this blocking is called silencing). NEET 2019 (Odisha) directly asked this - the answer is ds-RNA, not ss-RNA, ss-DNA or ds-DNA.
How does the nematode's own gene get silenced inside a plant?
The transgenic tobacco carries a gene that makes both the sense and anti-sense RNA of a chosen nematode gene. These two strands pair to form dsRNA. When the nematode feeds on the root and takes up this dsRNA, the RNAi machinery silences that nematode mRNA. So the plant makes the weapon, the parasite takes it in and is disarmed.
Does RNAi harm the tobacco plant itself?
No. RNAi naturally takes place in all eukaryotic organisms as a method of cellular defence. It is used here to target only the nematode's specific mRNA. The plant is protected, and only the parasite that feeds on it is affected.
⚠️ The NEET trap ✗ Meloidogyne incognita infects the LEAVES of tobacco, and genes are silenced using single-stranded RNA (ssRNA). ✓ It infects the ROOTS of tobacco, and RNAi silences genes using double-stranded RNA (dsRNA). Both facts are direct NEET answers - lock them in exactly. 🧠 NTA loves swapping the infected plant PART and the type of molecule used.
Real NEET questions
NEET 2016
Which part of the tobacco plant is infected by Meloidogyne incognita?
A · Flower
B · Leaf
C · Stem
D · Root ✓
Solution: The nematode Meloidogyne incognita parasitises tobacco plants by infecting their ROOTS, causing a great reduction in yield. NCERT (Ch 10) states this directly. Resistance is later engineered using RNAi. So the answer is Root.
NEET 2019 (Odisha)
In RNAi, the genes are silenced using:
A · ds-RNA ✓
B · ss-DNA
C · ss-RNA
D · ds-DNA
Solution: RNA interference silences a specific mRNA through a complementary double-stranded RNA (dsRNA) that binds the target mRNA and prevents its translation. In the nematode-resistance strategy, sense and anti-sense RNAs pair to form this dsRNA. Hence genes are silenced using ds-RNA.
Solved Biotechnology and Its Applications NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
What is Meloidogyne incognita in one line for NEET?
A nematode (round worm) that infects tobacco ROOTS and reduces yield; it is controlled using RNAi.
What does RNAi stand for?
RNA interference - a natural cellular defence in all eukaryotes where dsRNA silences a specific mRNA by blocking its translation.
Why is Meloidogyne incognita important in the Biotechnology chapter?
It is the classic example of making a pest-resistant transgenic plant using RNA interference, so NEET often pairs the nematode with dsRNA and root infection.
What is the difference between the Bt cotton strategy and the RNAi strategy?
Bt cotton uses a Bt toxin (Cry protein) to physically damage the insect gut, while the RNAi strategy silences a specific gene of the pest using dsRNA. Bt uses a protein; RNAi uses RNA.
