There are probably more fungal species than of plants. They occupy nearly all space where some sort of carbohydrate is available. Most fungi produce enzymes to digest complex carbohydrate molecules such as cellulose, lignins and pectins, the main components of cell walls. Most fungi produce filaments called hyphae. The term for a mass of hyphae is mycelium. Competition among fungi for any dead plant material must be fierce and thus evolution has favored mechanisms for fight off competitors with production of antibiotics. Those of us who attempt to culture fungi in a petri dish often witness this when two species develop a neutral zone between them, not penetrated by either. The other tactic favored is to produce large numbers of propagules (spores) that can spread the species to other locations and new sources of food. Spore numbers are huge, as is probably necessary for survival because distribution is mostly random. Most fungi produce small light spores that are easily carried by wind, some for great distances. Spores of corn and wheat rust fungi have been collected in high altitude wind currents. Puccinia sorghi, cause of common rust on corn, overwinters in Mexico but its spores are carried to the US Midwest by those winds in the summer. Spores of the gray leaf spot fungus, Cercospora zeae-maydis, easily are moved between corn fields whereas those of the northern leaf blight (Exserohilum turcicum) appear to be heavier and less mobile.
A few fungal species produce only swimming spores. The fungus causing crazy top, Sclerophthora macrospora, produces such spores (zoospores) when in water that literally swim towards corn (and many other grass species) roots, germinate and infect. The hyphae formed from the germinated spore grow within the plant towards the growing points, causing deformities that favor the fungus. Then it has sex and produces thick-walled spores (oospores) that can remain in dry conditions for several years until conditions favor the swimming spores and infection of a new host. This is one of the many strategies that fungi have for survival and success in their complex, competitive world.
Spores of fungi not only allow them success biologically but also, are used by mycologists as among the few structures available to identify many species. That is the topic for next week’s blogs.
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.