Concept:Root-knot disease is a plant disease caused by a specific group of microscopic worm-like pests that attack plant roots, especially in tomatoes.
Explanation:Root-knot disease in tomato plants is caused by root-knot nematodes, which are scientifically known as
Meloidogyne spp.
These nematodes are soil-dwelling parasitic worms, not viruses, bacteria, or fungi.
They enter the tomato root system and cause the formation of swollen galls or "knots" on the roots.
Infected plants show stunted growth, wilting, and reduced fruit yield because the damaged roots cannot absorb water and nutrients properly.
Therefore, the causal organism is a nematode, making option B the correct choice.
Answer:B. Nematode