Relationship between seed yield heterosis and molecular marker heterozygosity in soybean
In soybean [Glycine max (L.) Merr.] heterosis has been reported for seed yield. Molecular markers may be useful to select diverse parents for the expression of heterosis and yield improvement. The objective of this study was to determine if molecular markers could be used to predict yield heterosis in soybean. From each Maturity Group (MG) II and III, 21 genotypes were selected on the basis of high yield (HY), different 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 F1 hybrids per group. The 21 parents and the 24 F1 hybrids of each MG were evaluated for yield in replicated tests at two locations in 2 years, and midparent 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 (GDM) for pairs of the 12 genotypes were calculated with this RFLP information and correlated with MPH and HPH estimates. Significant MPH averages for seed yield were observed in the combined analysis of variance 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 F1 hybrids 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 value; the RFLP group had generally the smallest. The observations indicated that the expression of heterosis in seed yield might be associated with diversity in the isozyme loci present in the parents. For the genotypes included in the second RFLP analysis, correlations of GDMs with MPH and HPH values on an entry-mean basis were low and not significant, indicating that heterosis in yield may not be associated with genetic diversity at the molecular level as determined by RFLPs. The results suggest that in soybean, parent selection on the basis of RFLPs and isozyme loci to exploit heterosis in seed yield may not be feasible. There was no association between genetic distance estimated by the RFLP analysis and seed yield heterosis, and in spite of the observed relationship between isozyme loci and heterosis for yield, the practicality of using the isozyme markers to select parents may be limited because of the reduced number of assayable isozyme loci in soybean.
Unable to display preview. Download preview PDF.