Interrelationships of Performance, Heterosis and Combining Ability of Corn (Zea mays L.) Crop under Elevated Plant Density Combined with Water Deficit

The objective of the present investigation was to test the validity of predictions of GCA and SCA effects from mean performance and/or heterobeltiosis for agronomic and yield traits under elevated plant density (D) combined with water deficit. Six maize inbreds varying in high-D tolerance were intercrossed in a diallel fashion and evaluated along with their F1 crosses in six environments representing combinations of 3 plant densities and two irrigation regimes in two seasons. Both GCA and SCA variances were significant for all studied traits under all environments. The magnitude of GCA was higher than SCA variance for 45.8% of cases, but the magnitude of SCA was higher than GCA variance for the rest of cases. The best general combiners were the inbreds L53 and L20 for all studied traits and the best SCA effects for grain yield were exhibited by the crosses Sk5 × L18, L20 × L53 and L28 × Sd7 under the 6 environments. The results indicate that the highest performing inbred lines are also the highest general combiners and vice versa for 9 out of 12 traits and the highest performing crosses are also the highest specific combiners and vice versa for all 12 studied traits. Yield traits did not exhibit any correlation between heterobeltiosis and mean performance of crosses, and between SCA effects and heterobeltiosis under all six environments. For agronomic traits, the useful heterosis of a cross could be used as an indicator of its SCA effects under all environments.