National Geographic : 2000 Aug
SHAMELESS EXPLOITERS, members of the huge category of parasitic fungi infest other life-forms. Each year agricultural pests such as smuts and plant rusts do untold mil lions of dollars in damage to crops world wide. One species has the unappetizing name corn smut (below), yet it is a delicacy in Mexico and is gaining popularity in the United States marketed as "Mexican truffles." Trichaptum (below right) and other mush rooms that rot wood are sometimes hosts themselves for smaller species such as various ascomycetes, a group of fungi that includes truffles, yeasts, morels, and some molds. Curiously, some rusts require more than one host plant to live out their life cycle. In tem perate climes Puccinia spar ganioidesspends winter on cordgrass. Come spring, it pro duces small, delicate spores that are blown to nearby ash trees where they germinate on new leaves (above right). Their spores then infect the cord grass, completing the cycle. Fungal pests can cause social turmoil. Some scholars suspect that the physical symp toms and erratic behavior that Ustilago maydis, led to the Salem witch trials up to 5 in across were caused by a toxic fungus consumed with cereal grains, especially rye. In the mid 1800s a fungus turned Ireland's potato crops into black gooey masses. About one million people died, and more than a million emi grated to North America and other lands. Piggyback riders: Bulbous growths of smut commandeer an ear of corn (above left). Rust envelops the base of a green ash leaf (top right). Tiny mushrooms stick out like straight pins from a host mushroom stained by algae.