Which of the following is not typically considered a plant pathogen?

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

Answer: (D)

Plant pathogens are organisms that cause disease in plants. Viruses invade plant cells and disrupt normal cellular function, leading to symptoms and reduced growth. Bacteria infect plant tissues, causing cankers, blights, or wilts and spreading through plant water or tissue. Nematodes live in or on roots, feeding on plant tissues and impairing water and nutrient uptake, which stunts or harms the plant.

Algae, while they are photoautotrophic organisms found mainly in water or on surfaces, do not typically cause disease in terrestrial crops. They may form surface films or grow on plant surfaces, but they are not standard agents that induce the kind of systemic diseases associated with plant pathogens. Therefore, algae are not typically considered plant pathogens.