A CLASSIFICATION OF 148 US MAIZE INBREDS .1. CLUSTER-ANALYSIS BASED ON RFLPS

Knowledge of relationships among lines is essential to the maize (Zea mays L.) breeder because it directs the exploitation of germplasm in h ybrid production. Restriction fragment length polymorphism (RFLP) data should be useful for estimating relationships among inbreds because t hey reflect differences in the DNA sequence. Cluster analysis, based o n RFLPs resulting from 46 probe-enzyme combinations, was used to revea l associations among 148 U.S. maize inbreds and assign inbreds to hete rotic groups. Estimates of genetic relationship between all pairs of i nbreds were computed by Cower's Coefficient of Similarity and expresse d as Euclidean distances. Then, these estimates were used to assign in breds to groups by the average linkage method (UPGMA). Differences in the hybridization fragments exhibited by lines within and between grou ps were evaluated to explore the basis for partitioning the lines. In the cluster analysis, inbreds were ordered into two major groups gener ally coinciding with distinctions between breeding groups derived from 'Lancaster Sure Crop' open pollinated variety and from Iowa Stiff Sta lk Synthetic. Within these two groups, 11 subgroups were formed, each containing lines associated with an elite inbred (WF9, MO17, C103, PA9 1, OH43, T8, B14, B73, N28, B37, or OH07). The classification generall y agreed with pedigree information and was supported by principal comp onent analysis. Groups differed markedly in the proportions of lines e xhibiting particular fragments. However, differences between groups re flected differences in frequencies rather than distinctions between th e presence or absence of fragments by the vast majority of the lines i n the respective groups.