One of the objectives of plant breeding is the development of high-yielding varieties under stress and optimum environments using different methods of plant breeding. The study was conducted to estimate combining ability and maternal effects of quality protein maize (QPM) for grain yield and other agronomic traits under low and optimum soil nitrogen environments. Crosses of 11 QPM inbred lines with five hybrid checks were evaluated both under low and optimum soil nitrogen environments at three locations. The results indicated that inbred lines TL156579, TL156583, TL148288 and TL156612 had significant positive GCA effects for grain yield. Significant positive maternal effects (MAT effects) were found in TL156612 and VL05128 inbred lines for grain yield under a low N environment. Inbred lines TL156579, TL148288, TL147078 and TL156612 had significant positive GCA effects for grain yield. Inbred lines TL156583 and TL155976 had both significant positive GCA and MAT effects for grain yield under optimum N environment. Both GCA and MAT effects were found significantly positive in VL05128 inbred line for ear height. However, significant negative GCA and MAT effects were found in TL155932 inbred line for ear height. Significant positive GCA and MAT effects were observed in TL156579 inbred line for ear length while significant negative GCA and MAT effects in TL156591 inbred line for ear length. Inbred lines TL156579, TL155976 and VL05128 had significant positive GCA effects for ear diameter.

Keywords: combining ability, low soil nitrogen, optimum soil nitrogen, maternal effect, quality protein maize