No Evidence for Epistasis in Hybrid and Per Se Performance of Elite European Flint Maize Inbreds from Generation Means and QTL Analyses
2005
Mihaljevic, Renata | Utz, H Friedrich | Melchinger, Albrecht E.
Favorable epistatic gene complexes may be important for hybrid performance of maize (Zea mays L.). This study was conducted to assess the importance of epistasis in per se and testcross performance for grain yield and grain moisture in four crosses among four elite European flint maize lines by generation means analyses as well as genome-wide tests for significant digenic epistatic effects between marker loci. For each cross, six generations (P1, P2, F₁, F₂, BC1, BC2) and testcrosses of these generations plus the F₂–Syn1, F₂–Syn2, and F₂–Syn3 generations in combination with an unrelated dent tester were evaluated in four environments. Testcross generation means of P, BC, F₁, F₂, F₂–Syn1, F₂–Syn2, and F₂–Syn3 did not significantly differ from each other for grain yield and grain moisture, indicating that epistasis between unlinked and moderately linked loci was negligible in its net effect. Depending on the cross, QTL mapping for per se and testcross performance with the dent tester was conducted with 71 to 344 lines (F₃ to F₆) grown in four environments. In genome-wide two-way ANOVAs, significant epistatic interactions were found with only a few marker pairs that did not improve the fit of the model after including main-effect QTLs previously detected by composite interval mapping. Poor correspondence of the results from per se and testcross analyses reflects dominance and epistatic interactions between parental and tester alleles. Our results suggest that epistasis is of minor importance for both traits with regard to the optimum type of population (F₂ vs. BC) in recycling breeding of elite maize inbreds. Estimates of digenic epistasis detected with genome-wide tests must be treated with caution because of the problems associated with model selection in QTL mapping with the sample sizes commonly used.
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