More on CMS and pathogen toxins
Race T of Bipolaris maydis is not the only fungus that produced toxins affecting corn tCMS. Phyllosticta maydis was not known to be an aggressive pathogen of corn until 1967 when first reported in Wisconsin. It later became apparent that it was notable pathogen of tCMS only. The disease was called yellow leaf blight. There was confusion about the species identification for a few years as another Phyllosticta species (P. zeae-maydis) was a common saprophyte on corn and was mainly differentiated by the size of conidia. The toxin produced by P. maydis affected the mitochondrial membranes of tCMS about the same as the Bipolaris maydis, causing swelling and loss of the respiration function during energy transfer in the corn. The switch away from the tCMS also essentially caused the disappearance of this pathogen.
At least two other cytoplasmic sterile sources have become useful to the corn seed industry. Both apparently involve some of the same mutation in mitochondrial DNA as tCMS. These are designated as c cytoplasm (cCMS) and s cytoplasm (sCMS). The DNA mutations apparently are slightly different in that they don’t appear to have the same vulnerability to the toxins produced by the fungi affecting tCMS. There were reports from China that a race of Bipolaris maydis affected cCMS but I am unsure if that concern remains.
It is probably significant also that neither cCMS or sCMS are as effective as tCMS in controlling pollen production in all corn genotypes or even in all environments. This makes them both slightly less desirable to seed corn producers as most do at least some detasseling in the seed fields when using female parents with either of these cytoplasms.
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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.