Multiple patterns of heterotic grouping in temperate and tropical maize hybrids

Heatmap cluster figures that use correlation as distance function provide a powerful tool to visualize biologically meaningful information. By the use of an optimized R heatmap script to detect heterotic groups in corn, mexican tropical maize germplasm was analyzed, particularly some novel varieties of purple corn with high nutraceutical value (Vitamaize). Different genetic combinations (F1 hybrids) were evaluated in trials using an agricultural phenomic approach, and heterotic patterns were compared in two sets of temperate maize entries. Biostatistical analysis of grain yield data revealed various branches of genetically complementary inbred lines (groups with similar heterosis at the phenotypic level). In the set of Vitamaize germplasm, up to four heterotic groups were detected, in contrast to only two heterotic groups reported earlier in temperate yellow maize from the USA. Analysis of mixed germplasm from Argentina and the USA revealed five heterotic groups which demonstrated that heterotic patterns in maize are not restricted to only two (e.g. dent-flint, northern-southern, stifstalk-nonstifft, A-B), but can rather involve many more groups (e.g. ABCDEF). The occurrence of many heterotic groups in tropical germplasm, may explain the fact that in Mexico three way F2 hybrids have been the predominant form of released commercial varieties, whereas in temperate regions, one way F1 hybrids are much more common.