Genetic variation within populations used in maize (Zea mays L.) breeding
Maize (Zea mays L.) breeders utilize F[subscript]2, backcross, and synthetic populations for inbred line development. Although F[subscript]2 and backcross populations have been extensively used in pedigree breeding programs, breeders have increased their use of synthetic populations for inbred line development. Genetic variation for traits of interest must exist within the populations for successful development of improved inbred lines. The objective of this study was to identify the superior source population for inbred line development by comparison of the means, genetic variability, predicted selection responses, and usefulness for traits within nine maize populations; three F[subscript]2 (B73 x B84, B90 x Mo17, B73 x Mo17), three genetically narrow-base synthetic (BS14, Mo17-Syn, H73-Syn), and three genetically broad-base synthetic (BS11(FR)C9, BSCB1(R)C9, BSSS(R)C9) populations;An ideal source population for selection of improved inbred lines would have a high mean and adequate genetic variation for the trait of interest. Fifty unselected S[subscript]1 entries within each population were evaluated for trait means and genetic parameters. The BSSS(R)C9 population had a high mean and the highest estimate of genetic variance for yield in comparison with the other eight populations. The genetically narrow-base synthetic populations had less genetic variation than the F[subscript]2 and the genetically broad-base synthetic populations. Estimates of heritabilities for yield on a progeny mean basis ranged from 0.44 for the BS14 population to 0.84 for the (B90 x Mo17) F[subscript]2 population;The usefulness criterion combines the mean and the predicted selection response of the population and can be used to identify the superior source population for inbred line development. Based upon the values of usefulness, the BSSS(R)C9 population would be the superior source population for development of lines with improved yield, kernel-row number, ear diameter, and kernel depth in comparison with the other eight populations. The (B73 x B84) F[subscript]2, (B73 x Mo17) F[subscript]2, and BS11(FR)C9 populations also have high values of usefulness as source populations for development of lines with improved yield, kernel-row number, ear diameter, cob diameter, kernel depth, and ears plant[superscript]-1.