Improving Maize Breeding Effectiveness Via Three Heterotic Group Classification Methods.

Maize (Zea mays L.) heterotic group classification impacts maize breeding efficiency. Two (DiHG), three (TriHG), and even more heterotic groups have been postulated for classifying maize germplasm. However, no direct comparison exists between DiHG and TriHG in relation to breeding efficiency. Objectives of this study were: 1) to investigate if TriHG has any advantage over DiHG for improving maize-breeding efficiency evaluated via three different measurements, viz., Ceccarelli breeding efficiency (CBE), general breeding efficiency (GBE), and specific breeding efficiency (SBE); and 2) to determine the impact of different maize heterotic groups on breeding efficiency. Using six testers from three heterotic groups (Reid, non-Reid, and Suwan1), 25 exotic inbred lines were classified into heterotic groups on the basis of specific combining ability (SCA) for grain yield. The results showed that the TriHG method increased SBE and GBE by 29.3% and 77.8%, respectively, over DiHG method, without loss of significant CBE. Since SBE and GBE measure how efficiency for detecting high-yield crosses among potential resulted high-yield crosses with selected germplasms, TriHG should be preferred over DiHG for developing high-yielding hybrids. Most of the crosses with lines from Suwan1 heterotic group showed significantly higher yield than the crosses made between lines from Reid and nonReid heterotic groups, suggesting the importance of Suwan1 heterotic group in improving breeding efficiency. Testers with high GCA effects generally increased breeding efficiency. Thus, we concluded that TriHG method would be better than DiHG for improving breeding efficiency. The germplasm from Suwan1 heterotic groups is highly valuable in hybrid development programs.