Associations among 150 publicly available inbred lines as revealed by cluster analysis of RFLP data
--J.S.C. Smith, S. Wright, M. Walton, O.S. Smith, and S. Wall
One hundred fifty publicly available inbred lines, including those most widely used in U.S. maize breeding and agriculture from 1930-1990, were profiled for 46 well dispersed RFLP probes. Distances between lines were calculated according to Nei and Li (1979) and associations among lines were revealed by cluster analysis. There was a major split between lines at a distance of and below 70% dissimilarity. Iowa Stiff Stalk Synthetic lines such as B14, B37, B73 and lines with a Krug background partitioned into one side of the total cluster with Oh43, C103 (both non-Stiff Stalk) and Wf9 derived lines falling into the other side of the cluster. Lines were associated broadly in agreement with family assignments made on the basis of known pedigree. Of the 8 families into which public lines are usually classified (Seedsman's Handbook, Mike Brayton Seeds, Ames, IA, 1978), 4 (Wf9, C103, Oh43, and SSS) were represented by many lines and were further split into 2 subclusters for C103, Oh43, and Wf9; SSS split into 3 subclusters. Four families were either virtually extinct as clusters of lines (CMV3, CO109 x Early Butler, and W153R) or were represented by a few dissimilar lines (Hy). RFLP data revealed 3 additional small and diverse families. These were Krug, Clarage, and Illinois Synthetic. B14 and B73 appeared more similar to each other than was either to B37. Fourteen of the 16 original members of the Iowa Stiff Stalk Synthetic constituent lines were included in the study. They were spread throughout the cluster showing that collectively they represent a broad diversity of germplasm. Conspicuously, none of the Iowa Stiff Stalk Synthetic progenitors that were studied clustered within or between the Oh43 and C103 related lines. Approximately 33% of all lines clustered with one or more lines at or below a dissimilarity level of 25% (lines >=75% similar). Only 15 lines clustered at or below a dissimilarity level of 10% (lines >=90% similar). Most pairs of lines were more than 75% different with regard to their RFLP profiles. Most lines with more than 75% RFLP similarity were related through backcrossing in their pedigrees.
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