Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: May 21, 2008
Publication Date: February 19, 2010
Citation: Goodwin, S.B., Dunkle, L.D. 2010. Cercosporin production in Cercospora and Related Anamorphs. In: Lartey, R.T., Weiland, J.J., Panella, L., Crous, P.W., and Windels, C.E. editors. Cercospora Leaf Spot of Sugar Beet and Related Species. St. Paul, MN:APS Press. p. 97-108. Technical Abstract: Cercosporin is a phytotoxin produced by members of the genus Cercospora. However, its evolutionary history and whether it is required for pathogenicity are not known. Analysis of gene knockouts showed that it probably is required for full pathogenicity. Phylogenetic analyses of the internal transcribed spacer region (ITS1, 5.8S gene, ITS2) of species of Mycosphaerella and related fungi identified a large cluster of Cercospora species separated by short branches, with most species from cereal crops forming a separate subgroup. The short branch lengths separating species of Cercospora could indicate recent speciation, possibly triggered by acquisition of a new trait. Ability to produce cercosporin was placed on the tree to test the hypothesis that this could have initiated speciation. Only species closely related to the Cercospora cluster produced cercosporin, suggesting that the ability to produce the toxin had a single evolutionary origin. Within the maize gray leaf spot pathogen, C. zeae-maydis, analysis of amplified fragment length polymorphisms (AFLP) clearly delimited two groups. Group I produces cercosporin and occurs throughout the maize belt of the United States and South America, while Group II does not produce cercosporin in culture. Group II was sympatric with Group I in the eastern U.S. and South America and was the sole representative of the pathogen in Africa. ITS sequences of Groups I and II differed by seven bases, confirming the AFLP data that they represent different species. Thus, ability to produce cercosporin may have stimulated the speciation process and could help to explain the large number of closely related Cercospora species from different hosts.