Testing the Effects of Putative QTL in F3 Maize Populations.

A number of candidate yield QTL were identified in an elite maize inbred pedigree using an identity by descent based approach.  To test the effects of these QTL, we developed single-cross populations in which one parent was derived from the targeted pedigree and the other parent was genetically dissimilar.  F3 populations were obtained by genotyping large F2 populations at loci linked to the putative QTL and individually self-pollinating those plants that had desirable genotypes.  Multiple individuals homozygous for the targeted allele at one or more of the candidate QTL as well as individuals homozygous for the non-targeted allele at the same loci were identified.  To reduce the impact of genetic background, individuals with the same genotype at a given set of loci were pooled by creating uniform bulks.  These bulks were then test-crossed to two testers.  The testers were orthogonal in the sense that one tester was known to combine well with the parent from the targeted pedigree while combining relatively poorly with the other parent.  Conversely, the other tester was known to combine well with the non-targeted parent and poorly with the targeted parent.  The resulting test-crosses were evaluated at multiple locations in 2005 using an experimental design that incorporated the sets of loci as a blocking factor.  Statistically significant differences in yield were associated with several of the sets of loci.  There were also significant interactions between some of the sets of loci and the testers.