Combining Ability of Tropical Maize Accessions with U.S. Germplasm

Abstract

To supplement minimal information regarding the utility of tropical maize (Zea mays L.) germplasm to temperate maize breeding programs, agronomic evaluations of typical accessions of the Latin American races were made. Based on data from previous evaluation stages, 40 accessions exhibiting superior agronomic performance in tropical environments were chosen for photoperiod conversion and combining ability evaluations with U.S. germplasm in temperate environments. Accessions were converted to photoperiod insensitive semiexotic populations by crossing each to Mo44, a temperate‐adapted inbred unrelated to either of two major U.S. heterotic groups. Four families from each semiexotic population were crossed to two U.S. testers. Testcrosses were evaluated in three North Carolina locations for 2 yr. Based on these results, 29 agronomically superior semiexotic testcrosses were tested a third year. The variation for combining ability for yield was estimated to be two times greater among vs. within accessions, suggesting that sampling among accessions be given priority compared with sampling within to maximize genetic diversity for combining ability. Family yields were highly correlated across testers (r = 0.78), suggesting that a single temperate tester would be sufficient for evaluating large samples of Latin American accessions. Grain yields, resistance to gray leaf spot disease (incited by Cercospora zeae‐maydis Tehon & E.Y. Daniels), and other agronomic traits of superior semiexotic testcrosses were competitive with the public U.S. hybrid Mo17 × B73. The best accessions should be a promising source of useful genes for commercial U.S. maize breeding programs.