Genetic Variability Estimates in Improved ans Nonimproved ‘Iowa Stiff Stalk Synthetic’ Maize Populations

Progress from selection is dependent on the additive variance within the population. Selection and genetic drift are two biological processes that can change gene frequencies and thus change the magnitude of the genetic variance of a breeding population over cycles of a recurrent selection program. Our objective was to determine if changes in genetic variance had occurred after recurrent selection primarily for grain yield in two maize ( Zea mays L.) selection programs originating from ‘lowa Stiff Stalk Synthetic’ (BSSSCO). One program consisted of reciprocal recurrent selection and the second program consisted of seven cycles of half‐sib followed sequentially by three cycles of S 2 per se recurrent selection. Nonselected S 2 progenies from each of five populations [BSSSCO, BSSS(R)CS, BSSS(R)C9, BSI3(S)C0=BSSS(HT)C7, and BSI3(S)C3] were evaluated in a replications‐within‐sets experiment conducted in six environments. Average grain yield of the nonselected S 2 progenies relative to the original BSSSCO population increased 62% after nine cycles of reciprocal recurrent selection and 81% after seven cycles of half‐sib followed by three cycles of S 2 recurrent selection. Evidence suggests that genetic variance decreased in the population improved using reciprocal recurrent selection but not in the population improved by using the sequential half‐sib and S 2 recurrent selection methods. Estimates of genetic variance among random S 2 progenies decreased in the BSSS(R)C9 population, when compared to the BSSSCO, for stalk lodging; dropped ears; grain yield; and grain moisture at harvest, and increased for root lodging. Genetic variance estimates among random S 2 progenies increased for root and stalk lodging, and grain yield, but decreased for dropped ears and moisture at harvest for BSI3(S)C3 relative to BSSSCO.