Yield Manipulation from Selection on Allozyme Genotypes in a Composite of Elite Corn Lines1

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Abstract
The possibility that alleles at allozyme loci are markers of quantitative trait loci and that they may serve as selection criteria in population improvement programs was studied in a composite population. Thirty inbred corn (Zea mays L.) lines were intercrossed to generate the base population, which was expected to have strong linkage disequilibria, a primary prerequisite for effectively utilizing allozyme marker loci in selection. Prior to this study, one cycle of intensive topcross selection (with B73 as tester) among S2, lines from this population was conducted that provided yield data and seed from the C1 cycle to identify yield‐responsive allozyme alleles. Allozymes at 23 loci were assayed and 8 of them showed markedly higher frequencies in the high performing S, lines. These eight were defined as yield‐associated allozymes. Divergent selection for high (+) and low (−) multilocus frequencies of these yield‐associated allozyme alleles showed an upward trend for yield in the positive allozyme selections when evaluated at seven locations as B73 topcrosses, but a downward trend when evaluated as populations per se. Checks that were selected by a topcross procedure with B73 as tester showed the same yield trends, indicating that allozyme selection as well as phenotypic selection increased specific combining ability with B73 but decreased the population performance per se. Five allelic contrasts also were generated in which favorable allozymes at individual loci were fixed in the (+) populations and unfavorable allozymes were fixed in the (−) populations. Yields of these contrasting populations showed consistent trends with increases in the (+) groups and decreases in the (−) groups. Differences for yield (and plant height) were significant, however, only when all contrasts were subjected to a combined analysis. It was concluded that allozyme associations with yield existed, but the magnitudes of their effects on yield in the allozyme selection experiment were small in the specific population used for the study.