Which of the following is NOT listed as a group that can cause plant disease?

• A. Fungi
• B. Bacteria
• C. Nematodes
• D. Algae

Answer: (D)

Plant diseases are typically caused by certain groups of organisms that actively attack and damage plant tissues. Fungi and bacteria are classic culprits; they invade leaves, stems, and roots, producing toxins or enzymes that disrupt plant functions. Nematodes are another well-known group, living in the soil and feeding on roots, which stunts growth and reduces nutrient and water uptake.

Algae, while can appear on plant surfaces in very moist environments, do not usually cause the kinds of infections or systemic diseases that fungi, bacteria, and nematodes do. In forestry and agricultural practice, algae aren’t considered a primary disease-causing group, so they aren’t listed among the organisms that commonly cause plant disease. That’s why algae is the correct choice here.