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Expected Genetic Advances from Three Simulated Selection Schemes¹

In an eight-replicate oat experiment with 78 F₂-derived and 234 F₃-derived lines (3 from each F₂), I measured grain yield, heading date and plant height, and in a four-replicate barley experiment with 90 F₂-derived and 270 F₃-derived lines (3 from each F₂), I measured grain yield, plant height and weight per volume. I conducted three simulated selection experiments using portions of these data.

The resource input for each selection experiment was sufficient to evaluate 78 oat lines in eight replicates and 90 barley lines in four replicates. In one case (random F₃ system), random F₃-derived lines were chosen without regard to the F₂'s from which they were progenies. In a second case (stratified F, system), stratified F₃-derived lines (one F₃-derived line from each F₂) were chosen, and in the third case (tandem system), group of derived lines were evaluated and the best 2056 for the trait under selection, were saved. Families of F₃-derived lines (three per family) were tested for each selected F₂. Expected genetic gatns were calculated from the three selection systems for the six trait-species combinations.

In five of six trait-species combinations, the tandem system produced greater expected genetic gains than either the random or stratified F₃ systems. The latter two produced about equal selection gains. The degree of superiority of the tandem system was related to the heritability percentage of the trait in question. With low heritability percentage, the expected genetic gain from the tandem method was more superior than when the heritability percentage was high.

With barley, 40 to 50% of the expected genetic gain from the tandem system resulted from the F₃-derlved line test, but most of this gain was due to exploiting genotypic variance among selected F₂ families. With oats much of the expected genetic gain from the second phase of the tandem system was due to exploiting genotypic variances among F₃-derived lines within F₂ families.

² Professor of Plant Breeding.

Received for publication October 11, 1967.