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Genetic Variation within Maize Breeding Populations

Northrup King Co., Napoleon, OH

A. R. Hallauer^*

Dep. of Agronomy, Iowa State Univ., Ames, IA 50011.

^* Corresponding author.

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 (²G) of yield and other traits within three F₂ populations (B73 x B84, B90 x Mo17, and B73 x 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 ²G were determined from the S₁ component of variance, and average estimates of ²G for grain yield were similar for F2 and BBS populations, whereas the average estimate of ²G for NBS populations was 40% smaller. Within population types, the related line cross (B73 x B84)F2 had 50% less ²G for grain yield than the other two F2 populations. BS14, H73-Syn., and BSCBI(R)C9 had smaller estimates of ²G for grain yield than the other synthetic populations. Estimates of ²G suggest selected F2 and BBS populations have greater potential for improved gains than the NBS populations. The related line (B73 x B84)F2 had 50% less 62G than either (B90 x Mo17)F2 or (B73 x Mo17)F2. (B90x Mo17)F2 and (B73 x Mo17)F2 had similar estimates of ²G, 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 x Mo17)F2 than within (B73 x B84)F2 and more useful than within (B73 x Mo17)F2.

Received for publication August 17, 1994.

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