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 F2 populations of elite line crosses. Objectives of our study were to determine the mean and genetic variability (σ2G) of yield and other traits within three F2 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 S1 progenies for each of the nine populations were evaluated at three locations for 2 yr. Differences among S1 progenies within each population were significant for most traits. Estimates of σ2G were determined from the S1 component of variance, and average estimates of σ2G for grain yield were similar for F2 and BBS populations, whereas the average estimate of σ2G for NBS populations was 40% smaller. Within population types, the related line cross (B73 × B84)F2 had 50% less σ2G for grain yield than the other two F2 populations. BS14, H73‐Syn., and BSCBI(R)C9 had smaller estimates of σ2G for grain yield than the other synthetic populations. Estimates of σ2G suggest selected F2 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 σ2G, 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.