Diversity of United States Hybrid Maize Germplasm; Isozymic and Chromatographic Evidence

Abstract

One‐hundred and thirty‐eight hybrids currently used in U.S. maize (Zea mays L.) production were genotyped for 21 isozymic loci. Sixtysix of these hybrids could be classified into 10 groups on the basis of their isozymic similarities and were additionally analyzed for their zein constitution by reversed‐phase high‐performance liquid chromatography. Objectives were to: (i) obtain isozymic genotypes widely used maize hybrids; (ii) to reveal any trends toward eithernarrowing or a broadening of the genetic base; and (iii) to reveal associations among hybrids on the basis of isozymic and chromatographic data. Compared to an earlier survey, isozymic data revealed no trend toward either an increased or decreased level of diversity over all hybrids during the prior 5‐yr period. Fifty‐six percent of proprietary brand hybrids and 88% of foundation seed company hybrids examined were judged to represent different genetic entities when both isozymic and chromatographic data were considered. Over all hybrids examined, 42% were unique and were released by private companies; 25% were unique and were released by foundation seed companies. Nonunique hybrids fell into seven groups with similar or identical isozymic and chromatographic profiles. From biochemical data, U.S. maize cultivation and breeding appear to remain heavily dependent upon usage of B73, A632, Oh43, and Mo17 or closely related derivatives thereof. ‘Iowa Stiff Stalk Synthetic’ lines crossed to ‘Lancaster Sure Crop’ derived lines still appear to be the predominant heterotic pattern.