F2 X F2 and BC1 X BC1 Interpopulation Crosses as Sources of Improved Maize Hybrids

109 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.Introgression of broadbase germplasm to improve the elite maize (Zea mays L.) single cross B73 x Mo17H was considered. Genetic parameters in a (B73 x B Composite) F2 x (Mo17H x A Composite) F2 Design II and a (B73(B73 x B Composite)) BC1 x (Mo17H(Mo17H x A Composite)) BC1 Design II were investigated theoretically and empirically.The order of mean performance (most favorable to least favorable) for all traits studied was B73 x Mo17H, BC1 x BC1, F2 x F2, and A Composite x B Composite. This result was expected for a one-locus, two-allele genetic model with the + allele fixed in one or both parental inbreds, partial to complete dominance, and intermediate frequencies of the + allele in the composites. Half sib covariances (Cov HS) and specific combining ability variance (Var SCA) were expected to be two to seven times greater and two to three times greater, respectively, in the F2 than in the BC1. Empirical estimates of Cov HS and Var SCA for grain moisture and plant and ear heights were consistent with these expectations. Contrary to expectations, the estimates for grain yield of Cov HS of families related to B73 and Var SCA were two and four times greater, respectively, in the BC1 than in the F2.The large estimates of Cov HS and Var SCA for grain yield in the BC1 were consistent with expectations for a model involving a quantitative trait locus and a dominance-modifying locus. This model implied superior performance of elite single crosses due to fixation of alleles that increase dominance at a quantitative trait locus in both parental inbreds. These results suggested the use of backcross populations for selection procedures that exploit specific combining ability effects. Together with higher frequencies of crosses superior to B73 x Mo17H for most traits, they indicated a higher probability for immediate derivation of superior single crosses from the BC1.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD