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Selection Among S₁ Families Vs. Selfed Half-Sib or Full-Sib Families in Autogamous Crops

USDA-ARS, North Carolina State Univ., Raleigh, NC 27695
Dep. of Agronomy, Oklahoma State Univ., Stillwater, OK 74078.

^* Corresponding author.

In autogamous craps, half- and full-sib families are rautinely generated in various systems of intermating. Usually, these families have not been used as units of selection, due to low expected gains relative to other selection units (e.g., S₁ families). The use of selfed half- (SHS) or full-sib (SFS) families, and differences in phenotypic variance between these and S₁ families, might reduce the difference in expected gains between the selection methods. Our primary objective was to predict the expected gain fram selection on each family unit, based on a genetic model with additive and homozygous dominance effects. A second objective was to empirically estimate phenotypic variances among SHS, SFS, and S₁ families derived fram random-mating populations of wheat (Triticum aestirum L.) and soybean [Glycine max (L.) Merr.], and use those estimates to compare expected gains. Estimates of phenotypic variance for yield of SFS wheat families (O²_SFS) were small compared with estimates for S₁ families (O²_S1) due to smaller error variances. Phenotypic variances of SHS soybean families (O²_SHS) tended to be smaller than those of S₁ families for seed yield and size but not for seed pratein and oil concentrations. As with the wheat populations, error variances tended to be smaller for SHS families. The expected relative efficiencies of S₁ family selection vs. SFS or SHS family selection are 1.14 (_SFS/_S1) in wheat and 2.29 (_SHS/_S1) soybean. Substituting phenotypic standard deviations into each formula resulted in no consistent advantage to using S₁ family selection with the exception of seed pratein and oil in soybean. In conclusion, election among SHS or SFS families should be of greatest benefit for productivity traits that require larger seed quantifies for testing. These selection units allow larger plot sizes and/or increased replications, thereby impraving the precision of entry-mcan estimates and reducing phenotypic variance.

Received for publication December 23, 1991.