Final answer:
Dutch elm disease, caused by the fungus Ophiostoma ulmi, is transmitted by the elm bark beetle and triggers a harmful overreaction in elm trees, leading to their death. Other fungi cause plant galls, disrupting growth by affecting hormone levels and causing disease cycles across different host species.
Step-by-step explanation:
Dutch Elm Disease and Plant Pathology
Dutch elm disease is an ailment caused by the ascomycete fungus Ophiostoma ulmi, with the elm bark beetle serving as a vector for its transmission. The interaction between this fungus and its transporter has devastating effects on elm trees, leading to their widespread death. The fungus benefits from the beetle by being transported to new trees and deposited into nutrients-rich tissue it can consume. However, its presence incites the tree to produce gums, which while meant to combat the infection, end up excessively blocking water transport, effectively starving the tree of nutrients and water.
Galls are abnormal growths on plants caused by various pathogens, including insects and fungi, that modify growth patterns by influencing plant hormones. One such pathogen is rust fungus, which causes galls that release spores to infect alternate host plants, leading to a cycle of infection.
Fungi not only affect plants like the elm or other trees susceptible to galls, but can also cause diseases in animals, and even humans. While not all interactions with fungi are harmful—some, like the corn smut in Mexico, are even welcomed—the majority are unwanted due to the damage and economic losses they can cause.