This group of infectious disease-causing organisms consists of microscopic roundworms living on plant roots or other plant parts (examples soybean cyst nematode, pine wilt).

• A. Bacteria
• B. Viruses
• C. Nematodes
• D. Mites

Answer: (C)

Nematodes are microscopic roundworms that live on plant roots or other parts of the plant, feeding on tissue and disrupting the plant’s ability to take up water and nutrients. This group includes notable pests like the soybean cyst nematode and the pine wilt nematode, which are classic examples of nematodes harming plants.

Bacteria are single-celled microorganisms, not worm-like and not multicellular parasites of this root-nematode type. Viruses are tiny infectious particles that require living cells to reproduce and are not organisms with a body like worms. Mites are very small arachnids, not roundworms, and they belong to a different group of pests.

So, the group described is nematodes.