or pathogenic fungi, fungi that use as a source of food live tissues of various organisms. Parasitic fungi cause diseases in plants, animals, and humans.
Many parasitic fungi are members of the class Fungi imperfecti, since they reproduce only asexually. The body of a parasitic fungus consists of branching multicellular filaments (hyphae) of the mycelium. Parasitic fungi form spores of various sizes and shapes. Obligate parasitic fungi feed only at the expense of live tissues, and, as a rule, do not grow in artificial nutritional media. Among the facultative parasitic fungi, some feed predominantly on organic substances of decaying tissues (saprophytes) but can also parasitize live tissues; other saprophytes are usually parasitic but can also grow on dead tissue.
There are parasitic fungi that live on animals and are called zoopathogenic fungi, which include entomopathogenic fungi, which live on insects. Parasitic fungi that live on plants are called phytopathogenic fungi and include mycophthorous fungi—that is, those that live on mushrooms. Phytopathogenic fungi are the most common. They act by means of toxic secretions or enzymes, which damage plant tissue, and then use these tissues as food. Many of the phytopathogenic fungi attack economically valuable plants. For example, various rust fungi cause stem rust and brown rust of grasses (Puccinia graminis, P. triticina), sunflower rust (P. helianthi), and flax rust (Melampsora lini); smut fungi cause durum and powdery wheat smut (Tilletia tritici, Ustilago tritici); and powdery mildew fungi cause powdery mildew of grasses (Erysiphe graminis). Parasitic fungi cause apple scab (Venturia inaequales), grape mildew (Plasmopara vitícola), and many other diseases. There is a large well-known group of wood-destroying fungi that grows on living trees (various species of Polyporaceae and honey fungus), as well as on commercial wood and wooden parts of buildings (house fungi). Fungous plant parasites are combated by means of special agricultural techniques, the production of hardy varieties, and the application of chemical substances (disinfection of seeds, spraying of plants, etc.). Mycophthorous fungi parasitize the fruit bodies and mycelia of many other fungi.
Zoopathogenic fungi include those that cause ringworm, favus, and other diseases of the skin of mammals and humans. Malassezia furfur causes furfur, and fungi from the genus Epidermophyton cause epidermophytosis of the feet and groin. Parasitic fungi from the genera Candida and Geo-trichum cause mycoses of the mucous membranes, skin, nails, and other areas. Parasitic fungi from the genera Blastomyces, Sporotrichum, and Aspergillus attack not only the skin but also subcutaneous cell tissues, muscles, bones, and the internal organs of animals and humans. Under certain conditions (for example, when the natural bacterial flora in the human organism are suppressed by excessive use of antibiotics) some parasitic fungi can cause a systemic disease in the organism, for instance, candidiasis.
Entomopathogenic fungi are used for exterminating harmful insects. The best known are Empusa muscae, a parasite of house flies; E. grilly, a parasite of locusts; and Beauveria bassiana, which parasitizes many insect species.
M. V. GORLENKO