Which statement best describes the primary mode of spread for Dutch elm disease?

Which statement best describes the primary mode of spread for Dutch elm disease?

• A. Through wind-dispersed spores
• B. By elm bark beetle feeding and natural root grafts
• C. By soil-borne nematodes
• D. By seed transmission

Answer: (B)

Dutch elm disease spreads most effectively through bark beetle activity and underground root connections. The beetles feed beneath the bark of elms and, in the process, carry fungal spores on their bodies. When they move from an infected tree to a healthy one, they deposit those spores into the tree’s vascular system, where the fungus grows and blocks water transport, leading to wilting and death. In addition, many elm trees develop natural root grafts with neighboring elms; through these underground connections, the fungus can move from an infected tree into adjacent trees even without beetle involvement. This combination makes beetle feeding and root grafts the primary routes of spread. Wind-dispersed spores, soil-borne nematodes, and seed transmission do not account for the main transmission path in Dutch elm disease.

Dutch elm disease spreads most effectively through bark beetle activity and underground root connections. The beetles feed beneath the bark of elms and, in the process, carry fungal spores on their bodies. When they move from an infected tree to a healthy one, they deposit those spores into the tree’s vascular system, where the fungus grows and blocks water transport, leading to wilting and death. In addition, many elm trees develop natural root grafts with neighboring elms; through these underground connections, the fungus can move from an infected tree into adjacent trees even without beetle involvement. This combination makes beetle feeding and root grafts the primary routes of spread. Wind-dispersed spores, soil-borne nematodes, and seed transmission do not account for the main transmission path in Dutch elm disease.