In the plant disease pyramid, what happens if one factor is missing?

• A. No disease will occur
• B. Disease will occur
• C. Disease severity increases
• D. Pathogen dies

Answer: (A)

The plant disease pyramid shows that disease only develops when three elements are present at once: a susceptible host, a virulent pathogen, and environmental conditions that favor disease. If any one of these is missing, the chain is broken and disease does not occur. So, even with a pathogen and a susceptible plant, unfavorable weather or insufficient moisture can prevent disease symptoms from appearing. Likewise, a conducive environment won’t cause disease if the host isn’t susceptible or the pathogen isn’t present. That’s why the correct idea is that no disease will occur when one factor is missing. The other ideas—disease occurring, severity increasing, or the pathogen dying—don’t fit the basic requirement that all three factors must align for disease to manifest.