Dutch elm disease is a disease of elm trees caused by a fungus. The fungus lives off water and nutrients from the tree. It spreads through water-conducting vessels in the tree. Gum forms within these vessels in response to the fungus, and the tree weakens and dies. Beetles spread the fungus from infected trees. What is the relationship
between the fungus and the elm tree?
A. predator-prey
O
B. mutualism
C. commensalism
D. parasite-host