SELECTION AMONG S3 YELLOW MAIZE LINES USING COMBINING ABILITY

Twenty-seven yellow maize inbred lines (S₃) derived from different wide genetic base populations were topcrossed to each of two inbred line testers, i.e., Gz-649 and Gm-1004 at Sids Agric. Res. Station during 2006 season. In 2007 season, the 54 topcrosses along with the two checks; SC-155 and SC-3084 were evaluated for grain yield plot^-1, days to 50% silking, plant and ear height and number of ears 100 plants^-1 at Sakha and Sids Agric. Res. Stations, ARC. Mean squares due to crosses, lines, testers and lines x testers was significant for all studied traits. These results indicated wide genetic diversity among each of lines and testers in their contribution to the performance of top crosses. The interaction of crosses x Loc was significant for ear height and grain yield plot^-1, lines x Loc and testers x Loc were significant for plant height, ear height and grain yield plot^-1. Whereas the L x T x Loc interaction was significant for grain yield plot^-1. These interactions with locations are mainly attributed to the different ranking of genotypes from location to another. Seven crosses, i.e. L-1, 5, 6, 10 and 16 x GZ-649, L-3 and L-5 x Gm-1004 significantly outyielded the checks SC-155 and SC-3084. Inbred lines L-3, L-4, L-5, L-6, L-7, L-10, and L-16 possessed the best GCA effects for grain yield. The best general combiners of parental lines were, L-4 for high yielding ability, earliness, short plants and low ear placement, L-3 for high yield and short plants, L-5 and L-16 for high yielding ability, number of ears 100 plants^-1 and earliness. For grain yield, positive and significant SCA effects were detected for crosses L-1 x Gz-649, L-2 x Gz-649, L-3 x Gm-1004, L-8 x Gm-1004, and L-11 x Gz-649. The topcrosses L-23 x Gz-649, L-24 x Gz-649and L-12 x Gm-1004 exhibited significant negative SCA effects toward earliness. The two crosses, L-6 x Gm-1004 and L-10 x Gm-1004 had favorable SCA effects toward short plants and low ear placement. L-16 x Gm-1004 was the only topcross that possessed favorable SCA effect toward producing more than one ear/plant. Variance magnitude due to SCA was higher than that due to GCA for all studied traits, except number of ears plant^-1. This indicates that non-additive genetic variance was the major source of genetic variation for the inheritance of grain yield and other traits. Also, the interaction of SCA with locations was higher than that of GCA for silking date, ears plant^-1 and grain yield. Generally, the seven crosses produced the highest grain yield and significantly outyielded both check hybrids and should be used in hybrid maize breeding program for further studies.