Organisms in this phylum are largely responsible for food spoilage and are usually weak pathogens of plants. They exist primarily as saprophytes in dung, plant debris, and soil. However, some members of the Zygomycota are important pathogens of amoebae, humans, insects, and nematodes. The human pathogens are usually associated with diseases of immunocompro-mised individuals (zygomycosis), while other species can also cause tropical subcutaneous mycoses in noncompromised individuals. Many species in the Zygomycota (e.g., Gigospora, Glomus, and Scutellospora, etc.) are involved in mutualistic associations within the roots (i.e., endomycorrhizal) of more than 70% of the species of herbaceous plants.2 Depending on structures formed within the roots of plants, endomycorrhizae are classified as being vesicular arbuscular mycorrhizal (VAM), or arbuscular mycorrhizal (AM) fungi.
Members of the Zygomycota exhibit filamentous growth, and hyphal cells that comprise the mycelium are not delimited by cross-walls (e.g., aseptate, coenocytic mycelium). The hyphal cell walls are composed predominantly of chitosan and polyglucuronic acid, but chitin is also present. Unlike the chytrids, members of the Zygomycota produce nonmotile, asexual (sporan-giospore), and sexual (zygospore) spores. Recent evidence suggests that the Zygomycota are evolutionarily divergent, and that this phylum may not represent a monophyletic group of fungi derived from a single common
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