Which of the following is NOT a source of infection mentioned in the material?

• A. Vegetative propagation
• B. Elm bark beetle feeding
• C. Natural root grafts
• D. Wind dispersal of spores

Answer: (D)

Infection sources for this disease are described as pathways that move the pathogen from sick plants to healthy ones through three main routes: infected material spread during vegetative propagation, transmission by elm bark beetle feeding, and spread via natural root grafts between trees. Wind dispersal of spores is not listed as a source of infection in the material for this particular disease, so airborne spores aren’t considered a route of infection here. That’s why the option describing wind dispersal of spores is the one that isn’t mentioned as an infection source.