M. A. R.
Department of Crop and Soil Sciences, University of Georgia, Athens 30602-7272
Department of Plant Pathology, Georgia Experiment Station, Griffin 30223
American Cyanamid Co., Collierville, TN 38017
Delta and Pine Land Co., Scott, MS 38772
Department of Crop and Soil Science, Clemson University, Clemson, SC 29634-0359
A. R. Soffes
NFREC, Quincy, FL 32351
Department of Agronomy, Auburn University, Auburn, AL 36849
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Accepted for publication 8 June 1998.
Frogeye leaf spot (FLS) caused by Cercospora sojina Hara is a disease of soybean (Glycine max (L.) Merr.) that causes significant seed yield losses in warm, humid environments of southeastern United States. The Rcs3 gene in soybean has been reported to condition resistance to all known races of C. sojina. The objectives of this study were to determine the effectiveness of Rcs3 in limiting seed yield loss due to FLS and to compare the seed yield of the resistant and susceptible near-isolines (NILs) in the absence of significant FLS disease. Four pairs of NILs—Colquitt/Colquitt-Rcs3, Gordon/Gordon-Rcs3, Thomas/Thomas-Rcs3, and Wright/Wright-Rcs 3—were evaluated in 23 field experiments in Alabama, Florida, Georgia, Louisiana, Mississippi, and South Carolina during 1992 to 1994. The amount of damage to susceptible soybean caused by FLS was dependent on the specific environment. All four of the Rcs3 NILs were resistant to the prevalent races of FLS in all environments. In the absence of significant FLS disease, each of the Rcs3 NILs was at least equal to the respective susceptible line in its seed yield. In the presence of FLS infestation, the susceptible lines suffered significant seed yield loss (up to 31%) compared to their Rcs3 NILs. The effect of FLS on seed yield was dependent on cumulative disease severity over the growing season. Thus, the area under disease progress curve was more useful than percent of leaf area infected at the end of the growing season (R7 stage of development) in explaining the seed yield loss due to FLS.
© 1998 The American Phytopathological Society