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Establishment of the best combination among heterotic groups, heterotic patterns, is crucial to the development of successful maize (Zea Mays L.) hybrids. The use of molecular markers in maizebreeding programs might or might not increase the efficiency of heterosis prediction by classifying diverse inbred lines into heterotic groups. The objectives of present research were to classify elite North Dakota (ND) maize inbred lines into heterotic groups and evaluate the consistency between simple sequence repeat (SSR) grouping and testcross data. Thirteen ND inbred lines representing diverse genetic background were crossed in a diallel mating design in 2000. The crosses and 12 checks were evaluated across four ND environments in 2001 and 2002. In addition, these lines were crossed to commercial inbred testers representing known heterotic groups in 2002. Hybrids between public and private lines were evaluated across three ND environments in 2003. Inbred lines representing Lancaster Sure Crop, Iowa Stiff Stalk Synthetic (BSSS), Minnesota #13, Northwestern Dent, Golden Glow pedigrees and ND inbred lines were screened with 49 SSR markers.the Lancaster Sure Crop heterotic group. Inbred lines ND257 and ND288 grouped within Minnesota #13. Data from ND278 and ND290 testcrosses showed good combining ability with testers representing more than one heterotic group. Our research shows that groups of genetically similar germplasm could not be identified accurately and reliably with molecular markers even when the available germplasm was diverse contrary what has been suggested. Therefore, extensive field evaluation is recommended to classify unrelated inbred lines of maize.

Improved maize (Zea mays L.) populations and population hybrids can both be profitable alternatives to commercial single-cross hybrids as well as good elite sources of diverse inbred lines. The objective of this research was to compare grain yield and agronomic performance between early maturing maize population hybrids and current early maturing commercial single-cross hybrids. This is a consequence of our research program targeted at identifying alternative heterotic patterns for the northern Corn Belt. Improved maize populations and population hybrids (S 0 generations) were evaluated in experiments arranged in randomized complete block and partially balanced lattice designs across 29 environments. Grain yield potential of population hybrids was optimally expressed under irrigated conditions. Data across environments showed that 20% of the population hybrids evaluated were not different (P ≤ 0.05) from at least one of the commercial single-cross hybrids for grain yield performance, root lodging, and stalk lodging percentages. The average mid-parent heterosis value across population hybrids from different geographic regions was 20.4% with negative estimates observed in only two population hybrids. Breeding efforts toward elite populations and population hybrids have demonstrated that germplasm improvement is extremely valuable and deserves public funding. These efforts should be supported in order to enable the development of elite sources of diverse inbred lines and the development of improved population hybrids for specific markets (e.g., organic) to increase producer options. Public maize breeding programs utilizing recurrent selection methods for germplasm improvement could address the need. These programs, however, should incorporate extensive testing of population hybrids.

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corn leaf blight (caused by Bipolaris maydis [Nisik. & Miyake] Shoem.) outbreak on hybrids carrying the T-cyto-Development of maize (Zea mays L.) inbred lines is based on plasm for male sterility in the USA in the 1970s (Duvick, the identification and utilization of heterotic groups and patterns. The objective of this research was to identify alternative heterotic pat-1981; Hallauer and Miranda, 1988). Improved openterns for the northern Corn Belt. Ten maize populations [BS5, BS21 pollinated populations are valuable for the development (R)C7, BS22(R)C7, CGL(S 1 -S 2 )C5, CGSS(S 1 -S 2 )C5, LEAMING(S)C4, of inbred lines, especially when considering the impor-NDSAB(MER)C12, NDSCD(M)C10, NDSG(M)C15, and NDSM(M) tance of having genetic diversity in the germplasm pool. C7] were crossed in a diallel mating design. The 45 F 1 crosses along Differences in background, origin, and level of heterozywith nine checks were evaluated in experiments with two replicates gosity within and among populations are the basis of at each of four North Dakota and three Iowa locations in 2002. Data that diversity. were collected for grain yield, harvest grain moisture, and root and The identification of populations as sources of inbred stalk lodging. Analyses of variance were performed following the lines is based on their agronomic performance, presence Gardner and Eberhart Analysis III model. Differences among genoof useful genetic variance, high population mean, and types existed for all of the traits, and the general combining ability (GCA) sums of squares were larger than the specific combining abil-the heterosis observed from using them in crosses. Midity (SCA) sums of squares, indicating the predominance of additive ge-parent heterosis values provide the basis for the identifinetic effects. Alternative heterotic patterns to 'Iowa Stiff Stalk Syncation of heterotic patterns among a fixed set of populathetic' (BSSS) ϫ 'Lancaster Sure Crop' (LSC) were found for grain tions, and average heterosis and specific heterosis are yield among early-maturing populations. The most promising crosses the components in the expression of midparent heterowere those in which BS21(R)C7 was combined with CGL(S 1 -S 2 )C5, sis. Average heterosis is indicative of the superiority BS22(R)C7, NDSG(M)C15, LEAMING(S)C4, CGSS(S 1 -S 2 )C5, and of population crosses over the midparent values, while NDSAB(MER)C12, and the heterotic pattern formed by BS22(R)C7 specific heterosis indicates the heterosis observed in and LEAMING(S)C4. A strong association was found between the certain crosses (Hallauer and Miranda, 1988). Theregrain yield of populations per se and their GCA for harvest grainfore, the utilization of midparent heterosis values is both moisture. The population CGSS(S 1 -S 2 )C5 was the earliest among the 10 populations studied and had the best GCA value for grain moisture.