Date of Award
Doctor of Philosophy
Kendall R. Lamkey
Associations between genotypes of molecular marker loci and phenotypic performance can be used to identify QTL. Phenotypic performance is subject to the choice of progeny for evaluation and environmental conditions where evaluation occurs. The objectives of this study were to compare the effectiveness of F[subscript]3 and testcross (TC) progeny evaluation in detecting QTL on the basis of empirical results and theoretical considerations and to determine the stability of QTL detection across environments;One hundred eighty-two F[subscript]2 individuals derived from a B52 x B73 cross were genotyped at 87 segregating RFLP loci. Field performance of F[subscript]3 lines and TC progenies, generated by crossing F[subscript]3 lines with the testers, Mo17 and Oh43, was determined for several agronomic traits, including grain yield and resistance to second generation European corn borer. Based on QTL positions estimated by interval mapping using means over environments (two to six environments, depending on trait), Mo17 TCs and Oh43 TCs identified QTL in common with one another more often than with F[subscript]3 lines. Mo17 TC evaluation was more effective in detecting QTL for grain yield than Oh43 TC evaluation, suggesting that specific combining ability is important for this trait;Based on theoretical considerations, F[subscript]3 lines are expected to be more effective than TC progenies at detecting a QTL when gene action at the locus is additive, regardless of tester choice. Variance expressed in TC evaluation will be maximized when the tester allele expresses a high level of dominance with the favorable population allele. Apparent overdominance was observed in 52% of F[subscript]3-identified QTL when using single-QTL analysis. This frequency was reduced to 38% when using multiple-QTL analysis. Deviation effects associated with heterozygous-derived TC families were often high although their expectation is zero;Marker genotype x environment interaction was extremely low for most traits. Significant interactions were more frequent for root lodging and stalk lodging although they rarely occurred at loci with significant marker main effects. QTL identified by interval mapping were generally stable across environments for grain yield and several other traits judging by the positions of log-likelihood peaks.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Thomas Lane Gocken
Gocken, Thomas Lane, "Identification of quantitative trait loci (QTL) in maize on the basis of F3 and testcross progeny performance " (1993). Retrospective Theses and Dissertations. 10433.