Heterotic Relationships among Nine Temperate and Subtropical Maize Populations
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The introgression of exotic germplasm could increase the heterosis among maize (Zea mays L.) populations. Our objective was to assess heterotic relationships among BSSS (R) ('Reid' germplasm) and BS 26 ('Lancaster' germplasm) from the temperate USA; the southern African cultivars Salisbury White, Southern Cross, and Natal Potchefstroom Pearl Elite Selection (NPP ES); and the subtropical CIMMYT Populations 34, 42, 44, and 47. The nine cultivars and their diallel crosses were evaluated at five Mexico, Zimbabwe, and U.S. locations. Populations 34, 42, 44, and 47 and NPP ES demonstrated the highest per se grain yield with Population 44 ranking first (8.42 Mg ha(-1)). Low to moderate levels of high parent heterosis was observed for their crosses; nonetheless, they occurred frequently as parents of superior crosses at Mexico where Population 42 X Population 47 ranked first (8.42 Mg ha(-1)). BSSS (R) demonstrated the best general combining ability with variety heterosis effects averaging 1.34 Mg ha(-1). Diversity among varieties was determined on the basis of "dominance-associated" gene effects. When the diversity was resolved by principle coordinate analysis, BSSS (R) was separated from BS 26, and Salisbury White from Southern Cross along different dimensional axes, suggesting that the two pairs are sources of different genes for heterosis. The highest yielding cross (9.28 Mg ha(-1)) and best heterotic combination involved Population 44 and BSSS (R). BSSS (R), NPP ES, and Populations 44 and 42 performed well outside their target ecologic zones, indicating their potential benefit to breeding programs in new geographic areas.
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