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Effect of Planting Density on Correlations among Yield and Its Components in Two Corn Populations¹

Forty-eight S₁ lines of corn (Zea mays L.) from each of two synthetic populations were grown at three planting densities at two Minnesota locations to estimate genotypic and phenotypic correlations between yield and its components (ears per plant, ear length, and kernel depth). A second objective was to assess predicted genetic gain for yield under S₁ testing assuming direct selection for yield compared to progress for yield from selection for the components individually. A split-plot arrangement in a randomized complete block design with two replications per location was used. Planting densities formed whole plots and split plots were S₁ lines (arranged as blocks-in-replicates within whole plots).

Phenotypic and genotypic correlations were, in general, of the same magnitude and tended to increase with increased planting density although there were exceptions to this trend. All genetic variance estimates were significantly different from zero. Only the variances for ears per plant were different from each other at the high and the low density. Predicted genetic gains from direct yield selection were greater than correlated responses. The correlated responses for yield with ears per plant as the selection criterion were important in both populations at the high planting densities. Ear length appeared to be a satisfactory selection criterion for yield progress at the high density in one population.

Key Words: Genotypic correlations • Phenotypic correlations • Genetic variances • Predicted genetic gains • Zea mays L.

² Former research assistant (presently Colaborador Cientifico, Mision Biologica de Galicia, Pontevedra, Spain) and professor, Dep. of Agronomy and Plant Genetics, Univ. of Minnesota, St. Paul, MN 55108.

Received for publication October 16, 1976.