Technical Abstract: Plant, ear and kernel traits directly or indirectly associated with grain yield in corn (Zea mays) were suggested as "secondary" traits to select for larger grain yield, especially in open-pollinated corn varieties (OPVs) and their hybrids (OPVhs). Thirty-four secondary traits, besides grain yield, were measured or estimated on 46 OPVhs in eight maternal heterotic groups (HGs) grown under four environments. For each trait, components of total phenotypic variance, polymorphic diversity index, and population differentiation were estimated and used to identify HGs with combinations of desired variants of secondary traits. Maternal heterotic groups were identified as potential sources of desirable variants of single or multiple traits appropriate for adaptation to short-growing seasons, low-input farming, and adverse environmental condition.