They feed on living hosts. As parasites , fungi live in or on other organisms and get their nutrients from their host. Parasitic fungi use enzymes to break down living tissue, which may causes illness in the host. Disease-causing fungi are parasitic. Recall that parasitism is a type of symbiotic relationship between organisms of different species in which one, the parasite, benefits from a close association with the other, the host, which is harmed.
The American chestnut tree once covered  a large area of eastern North America. Until the the fungus that causes chestnut blight was accidentally imported from Asia. Since then the disease has killed virtually all the native American chestnuts in the United States and Canada.
What does the fungi get nutrients from?