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Comparison of Gains Predicted by Several Selection Methods for Cold Tolerance Traits of Two Maize Populations¹

Index selection was developed to help breeders practice simultaneous selection for several traits. Our objective was to compare selection differentials, expected gains, and relative index efficiencies of several indexes constructed to improve cold tolerance of two maize (Zea mays L.) populations. Cold tolerance traits were percentage emergence, emergence index (i.e., rate of emergence), and seedling dry weight.

Best predicted results for all traits were given by a rank summation index, a multiplicative, weight-free index, and a base index (index weights were reciprocals of phenotypic standard deviations). These indexes were not seriously affected by unequal variances among traits and combined 1) simplicity of use, 2) freedom from need to estimate genetic parameters, and 3) good selection differentials and predicted gains in each trait and in the aggregate genotype. Our results also showed that selection for dry weight/plot identified lines with excellent percentage emergence and seedling dry weight.

Key Words: Zea mays L. • Selection index • Selection advance

² Assistant professor, Dep. of Agronomy, Iowa State Univ., Ames, IA; director of corn research, Northrup King Co., Stanton, MN 55081; and research geneticist, USDA, SEA, AR, Ames, IA 50011.

Received for publication February 4, 1980.