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Genetic Variability Within U.S. Hybrid Maize: Multivariate Analysis of Isozyme Data¹

Electrophoresis of isozymes coded by 21 loci was carried out for 111 widely grown U.S. hybrid cultivars of maize (Zea mays L.). The objectives were to compare levels of genetic diversity among elite and exotic germplasm, to assess the potential of isozyme data in cultivar identification and in the quality control of hybrid seed production, and to reveal relationships among hybrids using multivariate analysis of these data. Allele frequencies among U.S. and Canadian hybrids did not differ greatly but elite materials showed a reduction in numbers of alleles and an increase in numbers of monomorphic loci when compared to exotic and wild germplasm. Residual segregation among those inbred lines that were available for analysis was generally uncommon and the level of occurrence of unexpected homozygosity and heterozygosity suggested that selfing and outcrossing, respectively, were factors contributing to polymorphism in at least 30% of all hybrids. Principal componenat nalysis revealed that approximately 90% of the hybrids had different allele frequencies. However, differences among many hybrids were due to minor deviations in allele frequencies at few loci. Isozyme data could be useful in characterizing inbred lines and hybrids, provided representative seed sources were used. These data could be used to select hybrids representing different germplasm, thereby increasing genetic variability across regions of cultivation. Isozyme variability appeared to be sufficient to allow for the rapid checking of purity of U.S. hybrid maize under laboratory conditions.

Key Words: Electrophoresis • Isoenzymes • Germplasm • Seed production • Cultival identification • Principal components analysis • Zea mays L.

² Department of Research Specialists, Pioneer Hi-Bred Int., Inc., 7301 NW 62nd Ave., Johnston, IA 50131.

Received for publication November 16, 1983.

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