Assessing gene action, combining ability and heterotic efficacy for grain yield and associated traits in maize (Zea mays L.) across heterogeneous environments

Breeding hybrid maize requires a thorough understanding of gene action, combining ability effects and heterosis across different germplasms of maize. Therefore, the present study aimed to assess the gene action, combining ability and heterotic efficacy for grain yield and its attributes in maize under heterogeneous environments. The study utilized 7 inbred lines, 21 hybrids produced through Griffing’s diallel mating scheme-II and a check variety, arranged in a randomized block design. The results revealed highly significant general combining ability (GCA) effects among parents and specific combining ability (SCA) effects among hybrids for all evaluated traits. This indicates the presence of variability due to both additive and non-additive gene effects. With the exception of days to 50 % anthesis, ear length and 1000-grain weight, the mean square (MS) values for GCA × environment interactions were greater than those of the corresponding SCA × environment interactions for all traits under study. This suggests that GCA was more impacted by environment than SCA. Among the parental lines, P1 exhibited highly significant positive GCA effects for ear diameter, grain rows per ear, grains per row and grain yield per plant, along with highly significant negative GCA effects for days to 50 % anthesis and days to 50 % silking. This demonstrates its potential for enhancing grain yield per plant with promoting early flowering. The best-performing experimental hybrid combination, P1 × P7, displayed high standard heterosis, superior parent heterosis, high SCA and strong GCA effects for both parents. Additionally, it showed a heterotic response for grain yield per plant, making it a promising candidate for commercial exploitation following further critical testing. Furthermore, standard heterosis exhibited a highly significant positive correlation between the 2 flowering traits (days to 50 % anthesis and days to 50 % silking), while its correlation with other traits was found to be insignificant.