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Variation among Full-sib Families of Corn for Different Generations of Inbreeding

Pioneer Hi-Bred Intl., Inc., Maracay Aragua, Venezuela

A. R. Hallauer^*

USDA-ARS, Dep. Agronomy, Iowa State Univ., Ames, IA 50011

*Corresponding author.

Recurrent selection for improvement of yield of corn (Zea mays L.) germplasm emphasizes early testing of either S₀ or S₁ progeny testcrosses. On the basis of early testing information, progenies are selected and intermated to form populations for continued selection. This study was conducted to determine if early testing was effective in identifying superior full-sib families of S₀ plants in reciprocal fullsib selection. The effectiveness of early testing was investigated by comparing the relative genetic variability and genetic correlations of 136 full-sib families for the S₀ S₁, S₂, S₃, and S₄ generations of in breeding. Full-sib families and six hybrid checks were evaluated in three environments for each generation for grain yield and five other agronomic traits. The among full-sib component of variance for grain yield tended to increase with inbreeding of the parents, and there was evidence that variability among full-sib families was reduced in stress environments. Genetic correlations for yield between generations of inbreeding ranged from 0.87 for S₀-S₁ generations to 0.31 for S₀-S₄ generations. Genetic correlations decreased as the number of intervening generations increased. Selection of the 20 highest and lowest-yielding S4 full-sib families included only three and four, respectively, of the 20 highest- and lowest-yielding S₀ full-sib families. None of the 20 lowest-yielding S₁ full-sib families, however, was included in the 20 highest-yield S₄ full-sib progenies. The objective of early testing in reciprocal full-sib selection was achieved because none of the poorer performing families was included for intermating.

Received for publication December 26, 1989.

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