RELATIONSHIP BETWEEN SEED YIELD HETEROSIS AND MOLECULAR MARKER HETEROZYGOSITY IN SOYBEAN

In soybean [Glycine max (L.) Merr.] heterosis has been reported for se ed yield, Molecular markers may be useful to select diverse parents fo r the expression of heterosis and yield improvement. The objective of this study was to determine; if molecular markers could be used to pre dict yield heterosis in soybean. From each Maturity Group (MG) II and III, 21 genotypes were selected on the basis of high yield (HY), diffe rent geographic origin (GO), and isozyme loci (ISO) and for diversity in restriction fragment length polymorphisms (RFLP), and crosses were made within MGs and selection criteria groups to obtain 6 F-1 hybrids per group. The 21 parents and the 24 F-1 hybrids of each MG were evalu ated for yield in replicated tests at two locations in 2 years, and mi dparent heterosis (MPH) and high-parent heterosis (HPH) estimates were calculated. On the basis of hybrid performance during the first year, 12 parents (3 per selection criteria group) were chosen in each MG to conduct a second RFLP analysis using 129 probes. Genetic distances (G D(M)) for pairs of the 12 genotypes were calculated with this RFLP inf ormation and correlated with MPH and HPH estimates. Significant MPH av erages for seed yield were observed in the combined analysis of varian ce in each of the four selection criteria groups of MG II, and in the HY, ISO, and GO of MG III. Significant HPH averages were observed only in the ISO and GO groups of MG II. The greatest frequency of F-1 hybr ids with significant MPH was observed in the ISO and GO groups of both MGs. For HPH, the greatest frequency was observed in the ISO group of both MGs. In both MGs, the ISO group had the largest absolute MPH val ue; the RFLP group had generally the smallest. The observations indica ted that the expression of heterosis in seed yield might be associated with diversity in the isozyme loci present in the parents. For the ge notypes included in the second RFLP analysis, correlations of GD(M)s w ith MPH and HPH values on an entry-mean basis were low and not signifi cant, indicating that heterosis in yield may not be associated with ge netic diversity at the molecular level as determined by RFLPs. The res ults suggest that in soybean, parent selection on the basis of RFLPs a nd isozyme loci to exploit heterosis in seed yield may not be feasible . There was no association between genetic distance estimated by the R FLP analysis and seed yield heterosis, and in spite of the observed re lationship between isozyme loci and heterosis for yield, the practical ity of using the isozyme markers to select parents may be limited beca use of the reduced number of assayable isozyme loci in soybean.