Date of Award
Doctor of Philosophy
Kendall R. Lamkey
Evaluating of Recurrent Selection (RS) programs can lead to increase knowledge of methods, populations, and traits and give support for better management of breeding programs. The objective herein was to evaluate the effects of seven cycles of half-sib selection followed by seven cycles of S2 selection on the genetic structure of BSSS maize population. Individuals from BSSSP (progenitor lines), BS13(S)C0 (original S2 selection), and BS13(S)C7 (7th S2 cycle) cycles were genotyped based on a sample of 105 RFLP loci.;Measures of genetic variation within (expected heterozygosity, number of alleles, average frequency of the most common allele, and proportion of polymorphic loci) and among (Principal Component Analysis and Nei's genetic distance, NGD) cycles of selection indicated: BSSSP has a considerable genetic variability, substantial loss of variation and increase of divergence over the cycles of selection, greatest loss of diversity occurred during the HS selection program, future cycles of RS are predicted to have narrow genetic variation, and low average effective population size was an important factor in loss of genetic variation.;Changes in allele frequencies for about 30% of the loci cannot be explained by genetic drift alone, suggesting that selection also was an important factor of variation. The majority of loci in C0 and C7 were in H-W equilibrium. Progenitor line Illinois Hy had a lower NGD to C0 and C7 and five of its unique alleles had frequencies significantly increased in later generations, indicating a selective advantage over the cycles of RS. Hybrid Hy x LE 23 showed the lowest NGD to C0 and C7 populations. NGD among parental lines was not a good predictor of single-crosses yield performance. A founder effect observed herein may explain partially reduced genetic gains during the S2-selection period reported in other studies. Limited RFLP diversity in BS13(S)C7 suggests this population may not have enough genetic variability to sustain significant long-term genetic gains per se for grain yield. RFLP data were useful tools to evaluate this RS program. However, much more information could be obtained about recurrent selection programs by integrating of molecular (a standard set of marker loci) and phenotypic data.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu
Paulo Evaristo de Oliveira Guimarães
de Oliveira Guimarães, Paulo Evaristo, "Effects of a long-term recurrent selection program on the genetic structure of the BSSS maize population " (2001). Retrospective Theses and Dissertations. 643.