Which of the following is false regarding plant disease?

• A. Abiotic factors and biotic pathogenic microorganisms cause diseases in plants.
• B. Sometimes both pathogens and disorders can cause symptoms that have an identical appearance
• C. Symptoms are an indication of disease by reaction of the host plant
• D. Spots, blight, galls, wilts, rots, and slow growth are examples of disease signs

Answer: (D)

Understanding the difference between signs and symptoms is key here. Signs are direct evidence of the pathogen itself—visible parts of the disease organism, such as fungal spores, hyphae, fruiting bodies, or bacterial ooze. Symptoms are the plant’s responses to the problem—visible changes in the plant like spots on leaves, leaf blight, galls formed by growth responses, wilting, rots, or reduced growth.

The statement that spots, blight, galls, wilts, rots, and slow growth are examples of disease signs is incorrect because those are manifestations of the plant’s response—the symptoms—rather than the actual presence of the pathogen itself. The other statements are correct: diseases can be caused by both abiotic factors and biotic pathogens; sometimes symptoms caused by pathogens and by disorders look the same; and symptoms indicate disease through the host plant’s reaction.