Inter-Population Maize Improvement in the F(2) and in the Bc(1) Following Elite Line by Broadbase Population Crosses (Linkage, Intra-Population Parameters)
Meghji, Moezali Rajabali
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https://hdl.handle.net/2142/71605
Description
Title
Inter-Population Maize Improvement in the F(2) and in the Bc(1) Following Elite Line by Broadbase Population Crosses (Linkage, Intra-Population Parameters)
Author(s)
Meghji, Moezali Rajabali
Issue Date
1984
Department of Study
Agronomy
Discipline
Agronomy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Genetics
Abstract
Estimates of genetic parameters from 3 x 3 Design II analyses, pooled over 32 sets and evaluated at two locations, of crosses among random F(,2)S(,1) lines of B73 x B Comp. with random F(,2)S(,1) lines of Mo17H x A Comp. and among random BC(,1)S(,1) lines (backcrossed to the inbreds) of the two backgrounds were used to compare expected inter-population cross improvement from reciprocal recurrent selection (S(,1)RRS) and from fullsib RRS (S(,1)FSRRS) based on S(,1) testcross performance initiated in the F(,2)'s and in the BC(,1)'s for agronomically important traits. Because the F(,2)'s and the BC(,1)'s were not random mated, expectations of the estimated genetic parameters were derived algebraically. Effects of linkage in the inbreds, initial disequilibrium in the composites, and epistasis on these parameters were investigated using a two-locus model.
The advantage of backcrossing to the inbreds compared to the F(,2) for improvement in performance prior to initiating selection and for the immediate derivation of inbred lines with superior combining abilities, if any, was only slight for most of the traits. Estimates of halfsib family covariances were expected to be and were approximately twice as large for the F(,2)S(,1) crosses as for the BC(,1)S(,1) crosses for both parental backgrounds and for most of the traits. Epistatic variance, if present, will contribute more to the halfsib covariances for the F(,2)S(,1) crosses than to those for the BC(,1)S(,1) crosses. Linkage effects in the halfsib covariances, if any, will be substantially greater in the F(,2) than in the BC(,1) and will be positive if the respective inbred or the majority of the gametic output of the respective composite is in coupling phase linkage and will be negative if the inbred or the composite produces a predominance of repulsion phase gametes.
Inter-population cross improvement is expected to be greater if selection is initiated in the F(,2) than in the BC(,1) and is expected to offset any initial performance advantage of the BC(,1) in one cycle of selection. A practical comparison suggests that at low selection intensities S(,1)FSRRS will be superior and at high selection intensities inferior to S(,1)RRS for inter-population cross improvement.
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