DIVERSITY OF UNITED-STATES HYBRID MAIZE GERMPLASM AS REVEALED BY RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISMS

One hundred six commercial hybrids of current importance in U.S. maize, Zea mays L., production were profiled for 46 restriction fragment length polymorphism (RFLP) probes. Objectives were to (i) compare diversity among hybrids with that found among public lines; (ii) reveal associations among hybrids; (iii) measure the correlation between RFLP and pedigree distances; and (iv) determine the impact on diversity from the usage of similar genotypes. Of RFLP variants found among 150 public lines 82% were found among the hybrids. Only three variants found among the hybrids were not also found among public lines. The RFLPs, therefore, showed little evidence of exotic germplasm usage. Fifty-three hybrids fell into 10 groups within which members shared 90% of their profiles; groupings based on higher levels of similarity were also evident. Inter-hybrid distances for RFLP vs. pedigree data for 36 hybrids with known pedigrees showed a correlation of r = 0.87. Collective use of hybrids with similar RFLP profiles had an impact on diversity at least equivalent to that of some widely used hybrids. Multivariate techniques and diversity indices failed to show a reduction of diversity due to the high intensity of individual hybrid usage because extremely disproportionate usage among maize varieties was not evident. Restriction fragment length polymorphisms could provide assessments of the amount of diversity among commercially available hybrids.