Which of the following crop diseases is caused by a fungus?

Step 1: Analyze the question We need to find the disease whose causal agent (pathogen) is a fungus, not a virus or bacterium.

Step 2: Concept Plant diseases are caused by different pathogens:

• Viruses: usually show "mosaic," "rosette," "streak," or "leaf curl" symptoms.
• Bacteria: blight, wilt, and soft rot (e.g., cassava bacterial blight).
• Fungi: black pod, rusts, smuts, mildews, and anthracnose.

Step 3: Check each option

• A. Cassava blight: This is commonly cassava bacterial blight, caused by Xanthomonas (a bacterium). Not fungal.
• B. Cocoa black pod: Caused by the fungus-like organism Phytophthora palmivora, which is traditionally classified and taught in Nigerian syllabi as a fungus. ✔
• C. Groundnut rosette: Caused by a virus (Groundnut rosette virus), spread by aphids.
• D. Lettuce mosaic: Caused by Lettuce mosaic virus.
• E. Yam mosaic: Caused by Yam mosaic virus.

Step 4: Answer Cocoa black pod is the fungal disease, so the answer is B.

Tip: Remember "mosaic" and "rosette" point to viruses. "Black pod," "rust," "smut," and "mildew" point to fungi. Blight in cassava is bacterial.