Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2007
Publication Date: 1/16/2008
Citation: Mian, R.M., Missaoui, A.M., Walker, D.R., Phillips, D.V., Boerma, H.R. 2008. Frogeye Leaf Spot of Soybean: A Review and Proposed Race Designations for Isolates of Cercospora Sojina Hara. Crop Science. 48:14-24. Interpretive Summary: Frogeye leaf spot (FLS), caused by Cercospora sojina, is a common leaf disease of soybean which can significantly lower yields. Many genetic variants or races of C. sojina have been described, and there is evidence for at least 90 different races just in the US. This research was designed to determine the relationships among these many races by testing them on 10 soybean varieties that are known to vary in their resistance to FLS. Based on the reactions to these varieties, we were able to identify 15 genetic groups among a set of 93 isolates of Cercospora sojina. This set of differential soybean varieties and the resulting classifications of the fungus will be useful for soybean pathologists who are interested in the diversity of the fungus, and to soybean breeders who are developing FLS resistant varieties.
Technical Abstract: Frogeye leaf spot (FLS), caused by Cercospora sojina, is a common disease of soybean which lowers yields by reducing photosynthesis and causing premature defoliation. At least five physiologhical races of C. sojina have been described, but interactions between C. sojina isolates and sets of differential hosts suggest that there were over 90 different races just in the US. Resistance genes with varying levels of effectiveness against different races have also been identified, but additional sources of resistance genes are needed to develop soybean cultivars with broad and durable resistance. Molecular mapping has been useful for studying the genetics of resistance and facilitates efforts to pyramid resistance genes, but breeding efforts are hampered by the lack of a publication that clearly summarizes what is currently known about FLS biology and resistance genetics. A major objective of the current project was to group a collection of 93 FLS isolates using a set of ten differentials and cluster analysis methods. The differentials themselves were selected from an initial group of 38 by using the 93 isolates to group them into clusters of similarity, from which representative differentials were chosen. The resulting representative sets of ten differentials and 15 FLS isolates are intended to serve as a foundation that soybean breeders and pathologists can use immediately and also build on in the future.