Estimates of selection parameters associated with harvest index in oat lines derived from a bulk population

Summary Harvest index of grain crops is defined as grain yield divided by total plant yield. We estimated the heritability percentages of harvest index and its components, grain yield and plant weight, the genotypic and phenotypic correlations among these three traits, and the genotypic correlations of harvest index with plant height, 100-seed weight, grain number, and heading date by using a population of 1200 F₉-derived oat lines tested in six environments. Furthermore, we examined the relative selection efficiencies of indirect selection for yield through harvest index and of index selection for yield through yield plus harvest index.Heritability percentages were computed by use of variance-component, standard-unit, and realizedheritability methods. The heritability percentages for harvest index, grain yield, and plant weight were similar, and averaged between 50 and 65 precent across environments. Standard-unit and realized heritability percentages agreed closely and generally were lower than those computed via the variance-component method. Expected heritability percentages for harvest index calculated by using grain and plant yield data agreed almost exactly with actual values. Genotypic correlations were 0.88 between grain yield and plant weight, 0.42 between harvest index and grain yield, and –0.07 between harvest index and plant weight. Genotypic and phenotipic correlations were similar in magnitude. Theoretical and actual genotypic and phenotypic correlations of harvest index with grain yield and plant weight agreed closely. Genotypic correlations, computed via parent-offspring relationships, between harvest index and plant height, 100-seed weight, grain number, and heading date averaged –0.41, 0.43, 0.00, and –0.33 respectively.Indirect selection for grain yield through harvest index was 43 percent as efficient as direct selection, and a selection index that combined harvest index and grain yield was no more efficient than direct selection for yield. Harvest index had little value as a selection criterion for grain yield improvement when unrestricted selection was used. Indirect selection for grain yield through harvest index, however, would be expected to retain lines with a more favorable combination of yield, plant height and heading date than would unrestricted direct selection for yield.Journal Paper No. J-7914 of the Iowa Agriculture and Home Economic Experiment Station, Ames, Iowa 50010, Project No. 1752.