RNA interference (RNAi) was used to protect tobacco plants from infes…

The correct answer is Option (3) → Meloidogyne incognita, a nematode

RNA interference (RNAi) is a natural way in which a cell silences a specific mRNA: a complementary double-stranded RNA binds the mRNA and stops its translation. The nematode Meloidogyne incognita (printed in the book as ‘Meloidegyne incognitia’) infects the roots of tobacco plants and lowers the yield. Using Agrobacterium vectors, nematode genes were put into tobacco so that the plant made dsRNA against them. The parasite could not survive in the transgenic plant.

Option (1) Tobacco budworm — Incorrect. The tobacco budworm is an insect (a lepidopteran). It is controlled by Bt toxin proteins, not by RNAi.

Option (2) Armyworm — Incorrect. The armyworm is also a lepidopteran insect that Bt toxins kill. The book does not link it with RNAi.

Option (3) Meloidogyne incognita, a nematode — Correct. RNAi was used to protect tobacco from this root-infecting nematode.

Option (4) Cotton bollworm — Incorrect. Cotton bollworms are controlled by the Bt toxin genes cryIAc and cryIIAb in Bt cotton, not by RNAi.

NCERT Extract:
Pest Resistant Plants – “Several nematodes parasitise a wide variety of plants and animals including human beings. A nematode Meloidegyne incognitia infects the roots of tobacco plants and causes a great reduction in yield. A novel strategy was adopted to prevent this infestation which was based on the process of RNA interference (RNAi).”
Bt Cotton – “Some strains of Bacillus thuringiensis produce proteins that kill certain insects such as lepidopterans (tobacco budworm, armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes).”