Combining Ability and Heterosis in Corn (Zea mays L.) Grain Quality and Yield Traits under Different Plant Densities

The objective of this study was to assess mean performance, heterosis and combining ability and their interrelationships in six maize inbreds and their 15 diallel F1 crosses under elevated plant density (D). Three experiments were carried out in each season of 2013 and 2014, using RCBD with 3 replicates; each experiment was assigned to either low-D, medium-D or high-D (47,000, 71,200 and 95,200 plants/ha, respectively). Specific combining ability (SCA) were higher than general combining ability (GCA) mean squares for GYPP, GYPH, PYPH OYPH and SYPH) under elevated plant density, suggesting the existence of a greater portion of non-additive than additive and variance in controlling the inheritance of these traits, but the opposite was true for grain protein (GPC), grain oil (GOC) and grain starch (GSC). Out of 8 studied traits, significant correlations between means of the parents and their GCA effects existed for 6 traits, namely GPC, GYPP, GYPH, PYPF, OYPF and SYPF under all environments and GOC under high-D. These results indicate that the mean performance of a given parent for these traits is an indication of its general combining ability. Moreover, significant correlations existed between the means of crosses and their SCA effects in 20 out of 24 cases, suggesting that the mean performance of a cross could be used as an indicator of its SCA effects. For GOC under low-D and medium-D, GSC under low-D and high-D and GPC under low-D, the mean performance of a cross could be used as an indicator of its useful heterosis under the corresponding environments. The useful heterosis of a cross could be used as an indicator of its SCA effects for GOC under low-D and high-D and GPC under medium-D and high-D.