Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 6/12/2006
Publication Date: 7/24/2007
Citation: Dugan, F.M. 2007. Agonomycetes. In: McGraw-Hill Encyclopedia of Science & Technology, 10th edition. p.214-215
Interpretive Summary: Certain fungi are very important as plant pathogens or mutualistic symbionts of plants in spite of the lack of ability of these fungi to reproduce by means of spores. These fungi are called Agonomycetes (or Mycelia Sterilia). They do not comprise a separate evolutionary group, but are closely related to other fungi that make true spores, such as basidiomycetes (a class of fungi including the meadow mushroom and cereal rusts), or ascomycetes (a class of fungi including the morel mushroom and brewer's yeast). Several members of the Agonomycetes make structures that differ from true spores in their genesis and morphology, but which function effectively in spread and survival, just as do true spores. Other members make no spores at all. Notable species are Rhizoctonia solani (a pathogen of many kinds of plants), R. cerealis (a pathogen of small grains), and species of Sclerotium (pathogens of vegetables). Because their spore production is difficult or infrequent under laboratory conditions, Sclerotinia species are sometimes included in this group. Both Sclerotinia and Sclerotium, as their names imply, make structures called sclerotia. Sclerotia are effective in survival and dispersal, and are very persistent once established in the soil, thus presenting a big problem in control of the plant diseases they cause. Some species of Rhizoctonia establish a beneficial symbiosis with orchid roots, and the species Cenococcum geophilum is a widely distributed fungus mycorrhizal with many host plants.
Technical Abstract: Agonomycetes are fungi which usually produce neither sexual (meiotic) nor asexual (mitotic) spores. Some members of this artificial (non-phylogenetic) group are related to ascomycetes, while others are related to basidiomycetes. Many members form spore-like propagules called chlamydospores, papulospores, microsclerotia or other analogous structures, none of which are produced in the same manner as true spores. Larger structures called sclerotia are commonly produced by several members of the Agonomycetes. Several species are important plant pathogens. Sketches are provided for identification, biology, host range and/or economic impact of several important species.