SOYBEAN PEDIGREE ANALYSIS USING MAP-BASED MOLECULAR MARKERS .1. TRACKING RFLP MARKERS IN CULTIVARS

The history of soybean [Glycine max (L.) Merr.] cultivar development i s relatively short. Approximately 80% of the germplasm present in mode rn cultivars can be traced back to just 12 ancestral lines which were introduced into the USA in the early 1900s. This limited number of anc estral contributors and short history make soybean a promising system for marker-facilitated, pedigree-based, genetic analysis, The overall objectives of this project were to (i) identify a core set of markers that would be useful for pedigree-based analyses of elite soybean cult ivars, (ii) trace markers and chromosomal regions from ancestral to de scendent cultivars, (iii) determine if the observed and theoretical co ntribution of parental genomes to cultivar progeny were comparable, an d (iv) demonstrate the utility of pedigree-based or codescent mapping in the detection of putative linkages between molecular markers and ph enotypic traits. Sixty-four soybean lines including ancestral and mile stone cultivars were analyzed at 217 RFLP loci to identify a core set of markers to use in evaluating these, and other elite breeding lines. A core set of 97 polymorphic loci were identified for genetic: analys is. Results demonstrated that genomic regions contributed by a parent can be traced, often for more than a generation. Six generations of cu ltivar development were included in this analysis, and one RFLP allele , R013-1-b, could be traced through all six generations. Results also revealed that two pedigrees, that of Lincoln and Ogden, could not be s upported by RFLP analysis, although it is possible that the pedigrees reported are correct and the incorrect accessions are maintained in th e USDA collection. Comparison of the predicted amount of germplasm con tributed by a parent, and the amount observed by RFLP analysis reveale d that in only four out of 26 instances did one parent provide more ge netic information than expected, Codescent analysis of markers and phe notypes demonstrated putative linkages with B and Dt1. The ability to follow regions of chromosomes from parent to offspring through multipl e generations should provide an understanding of what transpired at th e molecular level during the breeding of cultivars over the last 55 yr , Graphical genotypes of the cultivars analyzed in this study, and the raw RFLP data, are available for electronic transfer.