A Retrospective Analysis of Selection in the University of Nebraska-Lincoln Replicated Recurrent Selection Program.

Dissecting the genetic basis of adaptation and heterosis in maize is an overarching goal of maize breeders and quantitative geneticists. Many approaches and tools to help illuminate the complex underlying mechanisms exist. One such methodology involves the genetic dissection of populations that have been improved for specific traits, especially economically important, complex traits. Populations derived from the replicated recurrent selection program carried out at the University of Nebraska-Lincoln are potentially a valuable genetic resource for studying the genetic architecture of heterosis and adaptation. The primary objective of this preliminary analysis was to examine the extent that selection and genetic drift genetically differentiated the replicate populations. Reciprocal full-sib selection (RFS) and S1 selection were each replicated three times from the base populations Nebraska B Synthetic (NBS) and Nebraska Stiff Stalk Synthetic (NSS). Each replicate was maintained independently throughout the selection program. Thus six RFS populations, six S1 populations, and the two base populations were evaluated. Individuals from each population were genotyped with 768 biallelic SNP markers by Pioneer Hi-Bred. To differentiate random allele frequency shifts due to genetic drift from directed allele frequency shifts due to selection, null distributions were developed from 10 000 simulations derived from a binomial sampling scheme of a recurrent selection program. In the NSS populations undergoing RFS selection three loci were found significant across all replicates, while the NBS populations undergoing RFS selection revealed no loci. After eight cycles of S1 and RFS recurrent selection the NSS derived populations revealed a stronger response to selection than the NBS derived populations.