DETERMINING THE LINKAGE OF QUANTITATIVE TRAIT LOCI TO RFLP MARKERS USING EXTREME PHENOTYPES OF RECOMBINANT INBREDS OF SOYBEAN (GLYCINE-MAX L MERR)

An experimental test is described for linkages between RFLP markers an d quantitative trait loci (QTL). Two hundred and eighty-four F7-derive d recombinant inbred lines (RIL) obtained from crossing the soybean cu ltivars (Glycine max L. Merr.) 'Minsoy' and 'Noir 1' were evaluated fo r maturity, plant height, lodging, and seed yield. RIL exhibiting an e xtreme phenotype for each trait (earliest and latest plants for maturi ty, etc.) were selected, and two bulked DNA samples were prepared for each trait. A Southern transfer of the digested bulked DNA was hybridi zed with restriction fragement length polymorphism (RFLP) probes, and linkages with QTL were established by quantitating the amount of radio active probe that bound to fragments defining alternative parental RFL P alleles. When an RFLP marker was linked to a QTL, one parental allel e predominated in the bulked DNA from a particular phenotype; the othe r allele was associated with the opposite phenotype. When linkage was absent, radioactivity was associated equally with both alleles for a g iven phenotype (or with both phenotypes for a given allele). These res ults confirmed RFLP-QTL associations previously discovered by interval mapping on a smaller segregating population from the same cross. New linkages to QTL were also verified.