Genetic Variation within Maize Breeding Populations

Abstract

Proper choice of germplasm determines the ultimate success of selection for genetic improvement. Germplasm included in maize (Zea mays L.) breeding has evolved from the original landrace cultivars to F 2 populations of elite line crosses. Objectives of our study were to determine the mean and genetic variability (σ 2 G) of yield and other traits within three F 2 populations (B73 × B84, B90 × Mo17, and B73 × Mo17), within three genetically narrow‐base synthetics (NBS) [BS14, Mol7‐Syn., and H73‐Syn.], and within three genetically broadbase synthetics (BBS) [BSll(FR)C9, BSCBI(R)C9, and BSSS(R)C9]. Fifty S 1 progenies for each of the nine populations were evaluated at three locations for 2 yr. Differences among S 1 progenies within each population were significant for most traits. Estimates of σ 2 G were determined from the S 1 component of variance, and average estimates of σ 2 G for grain yield were similar for F 2 and BBS populations, whereas the average estimate of σ 2 G for NBS populations was 40% smaller. Within population types, the related line cross (B73 × B84)F2 had 50% less σ 2 G for grain yield than the other two F 2 populations. BS14, H73‐Syn., and BSCBI(R)C9 had smaller estimates of σ 2 G for grain yield than the other synthetic populations. Estimates of σ 2 G suggest selected F 2 and BBS populations have greater potential for improved gains than the NBS populations. The related line (B73 × B84)F2 had 50% less 62G than either (B90 × Mo17)F2 or (B73 × Mo17)F2. (B90× Mo17)F2 and (B73 × Mo17)F2 had similar estimates of σ 2 G, although B90 and Mo17 are in the same heterotic group, whereas B73 and Mo17 are in different heterotic groups [Reid Yellow Dent (B73) and Lancaster Sure Crop (Mo17)]. Selection for improvement of yield would be more effective within the (B90 × Mo17)F2 than within (B73 × B84)F2 and more useful than within (B73 × Mo17)F2.