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Theory of Selection for Yield of Plants in Disease-Stress Environments. M. L. Carson, Associate professor, Plant Science Department, South Dakota State University, Brookings 57007; Z. W. Wicks, III, associate professor, Plant Science Department, South Dakota State University, Brookings 57007. Phytopathology 79:70-76. Accepted for publication 21 July 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-70.

The effects of selection for yield in disease stress environments (Y_DS) on yield performance in nonstress environments (Y_NS) and disease resistance (X) were examined where disease losses (bX) are a linear function of disease resistance: Y_NS = Y_DS = bX. Genetic correlations between Y_DS and Y_NS and between Y_DS and bX were calculated in terms of the genetic correlation between Y_NS and bX and the ratio between genetic variances for bX and Y_NS. Correlated responses in Y_NS and bX to selection for Y_DS were compared to those predicted from optimum index selection for high Y_NS and low bX, with both traits having equal economic weight. Simulated selection for Y_DS resulted in favorable correlated responses in Y_NS and bX except in certain situations where the genetic correlation between bX and Y_NS is highly positive. Predicted responses in Y_NS and bX from selection for Y_DS compared favorably to those predicted from index selection.