Genetic Variability within U.S. Maize Germplasm. II. Widely‐Used Inbred Lines 1970 to 19791

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Abstract
Isozyme data for 21 loci from lines previously found to be of major importance in the production of U.S. hybrid maize (Zea mays L.) between 1970 and 1979 were analyzed by principal component analysis. The objectives were to provide an objective appraisal of the extent of genetic diversity among lines, to reveal evidence of genetic diversity in time, and to compare genetic diversity among public lines with theft found among commercial hybrids. Overall genetic variability among public lines increased gradually from 1970 to 1979. Although there was a reduction in the use of genetically diverse ‘Reid Yellow Dent’ lines, continued selections from ‘Iowa Stiff Stalk Synthetic’ produced genotypically different lines. Although there was a decline in variation among widely used ‘Lancaster Sure Crop’ lines, changes in the usage of genotypically different Lancaster Sure Crop and related lines provided genetic diversity in time. No major differences were seen in allelic frequencies between public lines and commercial hybrids. Continued use of genetically different elite lines contributes to genetic conservation by maximizing the use of currently deployed genetic res.ources. However, the longterm goal should be to increase the genetic base available to breeders and producers.