Recurrent Selection in Soybeans. III. Selection for Increased Percent Oil in Seeds1

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Abstract
Three cycles of recurrent selection to increase seed oil percentage were conducted in a soybean [Glycine max (L.) Merr.] population segregating for male sterility (ms1ms1). The base population was planted single plant hills to allow for natural cross pollination of male‐sterile plants by male‐fertile plants. At maturity, male‐sterile plants with the highest seed oil percentages were selected from this crossing block. The halfsib families from the selected plants w.ere grown to maturity in the greenhouse, and the individual within each half‐sib family with the highest seed oil percentage was selected. A new cycle was begun by a natural intermating of the progeny of theselected individuals in the field.The selected progenies from each cycle of selection were evaluated in composite populations and singly as lines. The combined composite and lines tests showed cycles of selection, at an average rate of 0.35 ± 0.03/cycle. There was a nonsignificant increase in total oil from 444 to 460 kg/ha. Protein percentage decreased at a rate of −0.52 ± 0.08/cycle. Changes in yield and total protein were not statistically significant.An investigation of variation within the selection populations showed that genotypic variation among the mass selected lines did not change through three cycles of selection. Variation among the within half‐sib family selected lines was greater than the variation among mass selected lines in cycle one and two but not three. Realized heritability estimated from the observed response to mass selection was 0.28 ± 0.03, and the heritability estimated from the within family selection response was 0.20 ± 0.04. The difference between the two was attributed, in part, to differences in phenotypic variance.The results showed that both mass and within family selection contributed to the overall progress. The segregation of genetic male sterility in the population proved to be a convenient and inexpensive way to allow natural random mating of selected individuals and to provide half‐sib families.

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