Before discussing the fungi causing corn leaf diseases it may be helpful to address the confusing names given to the pathogens. International standards, allowing for research communication across languages, was established in 1753 by Carl Linnaeus. Every known organism is assigned a Latin-based name for genus and species. Species that are determined to be closely related are assigned a common genus name. Furthermore, there is an International Code of Botanical Nomenclature in which there is a traditional agreement on the name.
Most plant species have traditionally been designated names and relationships based upon structures of flowers, with the assumption that this sexual reproduction stage would be genetically stable. This standard has been more difficult to apply to many fungi, including those that attack corn plants. Many of those have two types of reproductions. The asexual reproduction is often dominant as the spores (conidia) are produced without sexual recombination and, in some cases, are the only reproduction form of the fungus that is known. Consequently, a name was created based on the conidia for the corn pathogen causing northern leaf blight as Helminthosporium turcicum in 1876. Because the conidia were long and dark, like a worm (Helminth) it and a similarly shaped fungus causing southern corn leaf blight (Helminthosporium maydis) were assumed to be in the same genus. In 1959, these two fungi were separated from other members of the genus Helminthosporium into a separate genus named Bipolaris. These names were still based upon conidia structure. Later, again based upon conidia structure, the genus was changed to Drechslera in 1966. In 1974, the northern leaf blight pathogen was given the name of Exserohilum turcicum, because of the microscopic structure of the conidia that is like a group of related fungi. Also in 1974, the rare sexual stage of this species was identified as being like others in the genus Setosphaeria. The sexual name generally takes precedence and thus the ‘official’ name should be Setosphaeria turcica.
Formal literature concerning the cause of northern leaf blight will list the most recently accepted name first as well as the authors of the research giving it the name. The formal name for this fungus is Setosphaeria turcica (Luttr.) K.J. Leonard& Suggs. (syns. Bipolaris turcica (Pass.) Shoemaker. Drechslera turcica (Pass.) Subram. &P. C. Jain. Helminthosporium turcicum Pass. Trichometasphaereia turcica Luttr.)
These name histories, and the taxonomy features involved are of interest to those who study fungi per se (I was one) but those who are interested in diseases of corn mostly want the cause to be identified and do not want to be confused by the names. On one hand, we appreciate that the name correctly identifies the genetic relationships with other fungi and that it could lead to further understanding of its control, but on the other hand we do not want to be confused by the name changes. I like Helminthosporium turcicum but do adapt to Exserohilum turcicum in my communications with others in the practical aspects of corn. I cannot escape my mycological past, however, so the Latin names for a species will be italicized.
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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.