Heterotic patterns among Latin America highland tropical maize cultivars
Ten tropical highland maize (Zea mays L.) cultivars (Cacahuazintle, Chalqueno, Conico 7, INIAP 153, Morocho Ecuatoriano, Cacao, Cabuya, Blanco Urubamba, Umutu, and Morocho Ayacuchano) and their 45 diallel crosses were evaluated at seven locations in three Andean countries, Bolivia, Ecuador, and Peru. The objectives of this study were to evaluate heterosis and to determine heterotic patterns among the ten tropical highland maize cultivars. The total variability among entries was partitioned following the analysis II and III of Gardner and Eberhart (1966). A mixed model was used with locations as random effects and cultivars as fixed effects;Additive gene effects seemed important in the expression of all traits as indicated by the statistical significance of cultivar effects and general combining ability effects. For yield, heterosis effects accounted for 75% of the total variability among entries suggesting that nonadditive gene effects also were important in the expression of heterosis. High-parent heterosis for yield ranged from -10.9% to 111.2%. Only four crosses had negative high parent heterosis for yield. Negative mid-parent heterosis was expressed in most crosses for female flowering, grain moisture content, and stalk lodging. Specific combining ability effects were significant for grain moisture content, plant height, ear height, and stalk lodging. Positive high parent heterosis was expressed in nearly 50% of the crosses for ear volume, kernel depth, and kernels per row;The earlier maturity cultivars, Cacahuazintle, Chalqueno, and Conico 7, had a similar heterotic pattern and could form a single population for recurrent selection. Another population could be formed by INIAP 153, Blanco Urubamba, and Umutu. These cultivars had the highest yields per se and had similar flowering dates. These two groups of cultivars have good heterosis response but differences in flowering time would limit their practical use as heterotic partners. The Cabuya and Blanco Urubamba cultivars had similar number of days to flowering and their F[subscript]1 cross yielded 7.37 t/ha with 28% HP heterosis. The cultivar Cacao performed well in crosses though it was very late flowering.