The selection response of a complex maize population improved primarily for quantitative disease resistance to northern leaf blight (NLB) and secondarily for common rust resistance and agronomic phenotypes

The selection response of a complex maize population improved primarily for quantitative disease resistance to northern leaf blight (NLB) and secondarily for common rust resistance and agronomic phenotypes was investigated at the molecular genetic level. A tiered marker analysis with 151 simple sequence repeat (SSR) markers in 90 individuals of the population indicated that on average six alleles per locus were available for selection. An improved test statistic for selection mapping was developed, in which quantitative trait loci (QTL) are identified through the analysis of allele frequency shifts at mapped multi-allelic loci over generations of selection. After correcting for the multiple tests performed, 25 SSR loci showed evidence of selection. Many of the putatively selected loci were unlinked and dispersed across the genome, which was consistent with the diffuse distribution of previously published QTL for NLB resistance. Compelling evidence for selection was found on maize chromosome 8, where several putatively selected loci co-localized with published NLB QTL and a race-specific resistance gene. Analysis of F 2 populations derived from the selection mapping population suggested that multiple linked loci in this chromosomal segment were, in part, responsible for the selection response for quantitative resistance to NLB. 4 ITRODUCTIO Selection mapping (SM) refers to a range of approaches that identifies alleles, loci and epistatic interactions using populations that have been subjected to iterative cycles of recombination and selection. The effects of selection can be seen as differences in allele frequency, diversity, and/or patterns of recombination, through comparisons of temporally or spatially-defined subpopulations. Several studies have been conducted on the principle that significant phenotypic change can be explained by significant changes in allele frequencies (e. differentiate the effects of selection from those of genetic drift. Information on patterns of recombination and sequence variation can be useful for SM in populations that are highly diverged, when genetic drift confounds the identification of significant changes in allele frequency combination of allelic frequency data and functional evidence was used as an alternative to population-genetic evidence in the study of LAURIE et al. (2004). In the present study, we use temporal shifts in allele frequency to identify putatively selected quantitative trait loci (QTL) for resistance to northern leaf blight (NLB) of maize. Putatively selected QTL are identified with a simulation-based test statistic that compares observed allele frequency shifts to those expected under genetic drift for the specific maize breeding population under study. We also genetically tested one …