Combining ability and heterosis for earliness, grain yield and quality characters of white and yellow maize, Zea mays L. across eight environments

Mean squares due to environments, genotypes and genotypes x environments showed highly significant differences for days to 50% silking, protein%, oil%, total carbohydrate% and grain yield/ha in both white and yellow maize. Variances due to top crosses and their components i.e., line effect, tester effect and line x tester effect were highly significant across eight environments indicating the existence of genetic variability in both white and yellow maize except oil and protein% for line effect and tester effect in yellow maize. White inbred line L3 had the best combination of general combining ability effects for protein and oil % across environments (0.89** and 0.10**, respectively). Also, white lines Ls and L4 had positive and significant GCA effects for total carbohydrates, while white inbred line L7 and tester T10 had the best desirable significant GCA effects for days to 50% tasseling and grain yield/ha. Yellow inbred L1 had the best combination of GCA effects for all traits across environments except protein %. White top cross (L2 X T10) had the most favorable significant SCA effects for protein and oil % and one hybrid (L2 x T8) for carbohydrate % over eight environments. The ratio of ó2 GCA/ó2 SCA was more than unity for days to 50% silking but less than unity for all quality characters and grain yield in both white and yellow maize, indicating that non additive genetic variance was predominant and played the major role in the gene expression of these traits. . Heterosis for grain yield/ha ranged from 40.50 to 68.33% for mid parent; 10.08 to 60.99% for high parent and from - 39.30 to 3.90 for standard heterosis (S.C. 10) of white maize, and varied from 42.62 to 64.75% for mid parent; 29.98 to 63.93% for high parent and from -34.81 to 0.63% for standard heterosis (S.C. 155) of yellow maize. The white hybrid (L6 x T8) was superior to its commercial control (S.C. 10) for grain yield and quality characters.