Seventeen yellow maize (Zea mays, L) inbred lines were top crossed into each of two line testers, i.e Gm 2 and Gm 9. All inbred lines and testers were developed at Gemmeiza Res. Station.The 34 topcrosses were evaluated at Gemmeiza and Nubaria Research Stations during 1999 summer season. General (GCA) and specific (SCA) combining ability as well as genetic parameters for days to 50 % silking, plant height, ear height, ear length, ear diameter, number of rows/ear, number of grains/row, 100-grain weight, grain yield (ard/fad) and grain yield/plant (g) were calculated.
Test of homogeneity of the experimental error for the two locations was found to be insignificant for all studied traits. Therefore the combined data were presented herein. Highly significant differences were found among the 34 top-crosses for all studied traits across the two locations. Differences among testers and inbreds due to partitioning crosses sums of squares were highly significant for all traits except lines and testers for number of grains/row and testers for 100-grain weight. The interaction of inbreds with environments was significant in case of ear length and grain yield per fad and per plant. Also, significant interaction of testers with environments was also detected for number of days to 50% silking, plant height, ear height and ear diameter.
For plant height, ear height, 100-grain weight and grain yield, the variance magnitude due to GCA (lines) was higher than that due to SCA. This indicates that additive genetic variance was the major source of variation responsible for the inheritance of theses traits. Also, the interaction of GCA by locations was markedly higher and positive for grain yield and other traits, except silking date, ear length and number of grains/row. General and specific combining ability effects for inbred lines, testers and their topcrosses were also estimated.