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Relative Efficiencies of Population Improvement Methods in Corn: A Simulation Study¹

The relative selection gains per year of three breeding methods (mass, modified ear-to-row, and S₁ selection) for corn (Zea mays L.) population improvement were simulated for additive and complete dominance genetic models. The character was assumed to be controlled by 20 major (genotypic value of A = 2) and 20 minor (A = 1) genes with half of the genes of each type at an initial frequency of 0.5 and half at a frequency of 0.1. Genes were independently assorted. Selection intensities of 0.05 and 0.25 (or equivalent), and heritabilities of 0.2 and 0.6 were used~ The population size was 400. The half-sib families in modified ear-to-row selection were evaluated in a four-replication trial, and the S₁ progenies were tested in a 10-plant plot with four-replications.

Our studies indicated that S₁ selection would be more efficient than the other two methods, provided that a winter nursery is used to shorten the cycle to 2 years. At the high heritability (0.6), mass selection was more effective than modified ear-to-row selection, but the latter was more effective under the low heritability. Genotypic variances decreased in all cases as selection proceeded, but the decrease was most rapid under S₁ selection. About 14 cycles of S₁ selection exhausted the genotypic variance at the high heritability and high selection intensity. The results also suggested that an S₁ progeny evaluation trial with 10-plant plots and four replications is adequate for improving population performance.

Key Words: Mass selection • Modified ear-to-row selection • S₁ selection

² Former research associate (now research scientist, Res. Stn., Agriculture Canada, P. O. Box 1210, Charlottetown, P. E. I. CIA 7M8) and professor, Crop Sci. Dep., Univ. of Guelph, Guelph, Ontario N1G 2W1.

Received for publication November 4, 1977.